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2019 Volume 47 Issue 9
2019, 47(9): 1283-1292
doi: 10.19756/j.issn.0253-3820.191270
Abstract:
Glycoprotein is a binding protein whose structure is mainly determined by the content of sugars and proteins and the peptide bonds to which it binds. The glycoproteins can be mainly classified into lectin, hormone, enzyme and immunoglobulin according to the clinical role in the medical field. Glycoproteins have a variety of biological functions and are of great significance in the medical and biological fields. To study the biological information related to glycoproteins, it is necessary to establish a highly sensitive and efficient analytical detection method for glycoproteins. The assay of glycoproteins includes separation and purification method, structural analysis, and content determination. The commonly used methods for determination of glycoproteins are mass spectrometry, chromatography-mass spectrometry, surface excimer resonance, enzyme-linked immunosorbent assay, etc. In recent years, in the detection of glycoproteins, the research and application of sensors have gradually increased. This paper briefly summarized the analysis methods of glycoproteins and reviewed the research and application of glycoprotein biosensors based on glycosyl recognition. The glycoprotein biosensors including electrochemical sensors, optical sensors and mass sensors were introduced in detail. The future development direction of glycoprotein sensors was prospected.
Glycoprotein is a binding protein whose structure is mainly determined by the content of sugars and proteins and the peptide bonds to which it binds. The glycoproteins can be mainly classified into lectin, hormone, enzyme and immunoglobulin according to the clinical role in the medical field. Glycoproteins have a variety of biological functions and are of great significance in the medical and biological fields. To study the biological information related to glycoproteins, it is necessary to establish a highly sensitive and efficient analytical detection method for glycoproteins. The assay of glycoproteins includes separation and purification method, structural analysis, and content determination. The commonly used methods for determination of glycoproteins are mass spectrometry, chromatography-mass spectrometry, surface excimer resonance, enzyme-linked immunosorbent assay, etc. In recent years, in the detection of glycoproteins, the research and application of sensors have gradually increased. This paper briefly summarized the analysis methods of glycoproteins and reviewed the research and application of glycoprotein biosensors based on glycosyl recognition. The glycoprotein biosensors including electrochemical sensors, optical sensors and mass sensors were introduced in detail. The future development direction of glycoprotein sensors was prospected.
2019, 47(9): 1293-1301
doi: 10.19756/j.issn.0253-3820.191225
Abstract:
Cell cycle is a basic process during the cell life. Analyzing cell cycles can better understand the nature of diseases. Currently, cell cycles are mainly analyzed by flow cytometry, which investigate cell cycles by measuring intracellular DNA contents and cell cycle specific proteins. With the development of technology, several new methods have emerged for cell cycle analysis in recent years to improve and enhance image analysis, single-cell analysis, sample reduction, and high throughput. These new methods including image flow cytometry, mass flow cytometry, microfluidic technology and Raman spectroscopy greatly expand the methods for cell cycle analysis and increase the accuracy of cell cycle measurements. Here we briefly introduced these new methods for cell cycle analysis.
Cell cycle is a basic process during the cell life. Analyzing cell cycles can better understand the nature of diseases. Currently, cell cycles are mainly analyzed by flow cytometry, which investigate cell cycles by measuring intracellular DNA contents and cell cycle specific proteins. With the development of technology, several new methods have emerged for cell cycle analysis in recent years to improve and enhance image analysis, single-cell analysis, sample reduction, and high throughput. These new methods including image flow cytometry, mass flow cytometry, microfluidic technology and Raman spectroscopy greatly expand the methods for cell cycle analysis and increase the accuracy of cell cycle measurements. Here we briefly introduced these new methods for cell cycle analysis.
2019, 47(9): 1302-1308
doi: 10.19756/j.issn.0253-3820.191249
Abstract:
Tungstotellurate(Ⅵ)-coated magnetic nanoparticles(MNP) were prepared by immobilization of tungstotellurate (Ⅵ) salt onto the surface of branched polyethyleneimine (PEI)-modified magnetic nanoparticles via electrostatic interaction. The structure and composition of TeW@MNP were confirmed by characterization with FT-IR, EDS and SEM. The obtained TeW@MNP composite had proven to be a promising adsorbent for the adsorption of ovalbumin in egg whites. Approximately 0.5 mg of TeW@MNP composite gave rise to a maximum adsorption efficiency of 91.6% for 100 μg/mL ovalbumin in 200 μL of sample solution at pH 4.0 (BR buffer). The retained ovalbumin was readily recovered by using 0.1% SDS as a stripping reagent, providing a recovery of 98.1%. The adsorption behavior of ovalbumin fitted Langmuir model, corresponding to a theoretical adsorption capacity of 373.4 mg/g. The TeW@MNP composite was practically applied to the selective isolation of ovalbumin from egg whites, and SDS-PAGE assay results clearly indicated that the ovalbumin with high purity was obtained. The above experimental results illustrated the great application potentials of polyoxometalates for protein isolation and purification and extended the application scope of polyoxometalates in life science field.
Tungstotellurate(Ⅵ)-coated magnetic nanoparticles(MNP) were prepared by immobilization of tungstotellurate (Ⅵ) salt onto the surface of branched polyethyleneimine (PEI)-modified magnetic nanoparticles via electrostatic interaction. The structure and composition of TeW@MNP were confirmed by characterization with FT-IR, EDS and SEM. The obtained TeW@MNP composite had proven to be a promising adsorbent for the adsorption of ovalbumin in egg whites. Approximately 0.5 mg of TeW@MNP composite gave rise to a maximum adsorption efficiency of 91.6% for 100 μg/mL ovalbumin in 200 μL of sample solution at pH 4.0 (BR buffer). The retained ovalbumin was readily recovered by using 0.1% SDS as a stripping reagent, providing a recovery of 98.1%. The adsorption behavior of ovalbumin fitted Langmuir model, corresponding to a theoretical adsorption capacity of 373.4 mg/g. The TeW@MNP composite was practically applied to the selective isolation of ovalbumin from egg whites, and SDS-PAGE assay results clearly indicated that the ovalbumin with high purity was obtained. The above experimental results illustrated the great application potentials of polyoxometalates for protein isolation and purification and extended the application scope of polyoxometalates in life science field.
2019, 47(9): 1309-1313
doi: 10.19756/j.issn.0253-3820.191333
Abstract:
Click reaction is a reliable, powerful and selective method in material science, medical science and biochemistry. Monitoring of click reaction at single particle scale contributes to revealing anisotropy and mechanism of click reaction. In this study, electrochemically confined glass nanopipette was acted as a sensor to monitor the click reaction on a single gold nanoparticle (Au NP). Driven by electroosmotic flow, Au NPs modified with alkynyl moved towards the inner channel of glass nanopipette. When Cu+ was presented in the inner channel, alkynyl on the surface of Au NPs would react with azide on the gold layer. Click reaction resulted in the cross-linking between Au NPs and gold layer, which hindering the movement of Au NPs. Hence, Au NPs were transitorily resided near the orifice of glass nanopipette, which was responded to a higher frequency of ionic blockage and a longer blockage time. The method proposed here paved a way for real-time monitoring of chemical reaction.
Click reaction is a reliable, powerful and selective method in material science, medical science and biochemistry. Monitoring of click reaction at single particle scale contributes to revealing anisotropy and mechanism of click reaction. In this study, electrochemically confined glass nanopipette was acted as a sensor to monitor the click reaction on a single gold nanoparticle (Au NP). Driven by electroosmotic flow, Au NPs modified with alkynyl moved towards the inner channel of glass nanopipette. When Cu+ was presented in the inner channel, alkynyl on the surface of Au NPs would react with azide on the gold layer. Click reaction resulted in the cross-linking between Au NPs and gold layer, which hindering the movement of Au NPs. Hence, Au NPs were transitorily resided near the orifice of glass nanopipette, which was responded to a higher frequency of ionic blockage and a longer blockage time. The method proposed here paved a way for real-time monitoring of chemical reaction.
2019, 47(9): 1314-1320
doi: 10.19756/j.issn.0253-3820.181818
Abstract:
A sensitive mercury ion (Hg2+) sensor was designed by using CdS QDs/TiO2 composite material as the photoelectric conversion unit. After the coupling of two inorganic semiconductors (CdS QDs and TiO2) with different band gaps, the performance of electrode has been improved. After excited by the specific wavelength of light, the electron in CdS QDs would be motivated from the valence band to the conduction band. Then the Excited state electron would move to TiO2 due to that the valence band of TiO2 was lower than CdS QDs. The spatial separation of the e--h+ pairs in the different semiconductors could retards their recombination, and thereby the photoelectric conversion efficiency would be improved. We constructed a sensitive sensor for Hg2+ by two complementary short-stranded DNAs. One of the DNA single strands (ONS1) was rich in T bases, and Hg2+ could specifically bind to the T base to form a T-Hg2+-T structure, thus ONS1 could not be paired with complementary single stranded DNA (ONS2) labeled by gold nanoparticles (AuNPs), inhibiting the decrease of photocurrent and achieving sensitive detection of Hg2+. The Hg2+ sensor displayed a linear range from 1.0×10-10 mol/L to 1.5×10-7 mol/L and a detection limit of 6.0×10-11 mol/L (S/N=3).
A sensitive mercury ion (Hg2+) sensor was designed by using CdS QDs/TiO2 composite material as the photoelectric conversion unit. After the coupling of two inorganic semiconductors (CdS QDs and TiO2) with different band gaps, the performance of electrode has been improved. After excited by the specific wavelength of light, the electron in CdS QDs would be motivated from the valence band to the conduction band. Then the Excited state electron would move to TiO2 due to that the valence band of TiO2 was lower than CdS QDs. The spatial separation of the e--h+ pairs in the different semiconductors could retards their recombination, and thereby the photoelectric conversion efficiency would be improved. We constructed a sensitive sensor for Hg2+ by two complementary short-stranded DNAs. One of the DNA single strands (ONS1) was rich in T bases, and Hg2+ could specifically bind to the T base to form a T-Hg2+-T structure, thus ONS1 could not be paired with complementary single stranded DNA (ONS2) labeled by gold nanoparticles (AuNPs), inhibiting the decrease of photocurrent and achieving sensitive detection of Hg2+. The Hg2+ sensor displayed a linear range from 1.0×10-10 mol/L to 1.5×10-7 mol/L and a detection limit of 6.0×10-11 mol/L (S/N=3).
2019, 47(9): 1321-1329
doi: 10.19756/j.issn.0253-3820.191275
Abstract:
As an important part of laboratory chip (LOC) and micro-total analysis system (μTAS), micro-mixer has been widely used in the fields of biological analysis and chemical synthesis, most of which are used in the pre-treatment part of the detection system to achieve sufficient mixing of detection samples and reagents and improve the detection accuracy and efficiency. In this work, a novel planar passive micro-mixer with narrow slits and obstacles arranged in a pentagonal mixing chamber was designed. The new micro-mixer made full use of the fluid jet characteristics and the vortex principle of the baffles to enhance the fluid disturbance and break the laminar state of fluid flow, which could effectively promote fluid mixing. The accuracy of numerical simulation was verified by the experimental method combining high-speed photography and Micro-PIV system, and the flow characteristics and mixing mechanism of the micro-mixer at different Reynolds Numbers (Re) were summarized. Under the premise of comprehensive consideration of the mixing index and pressure drop, the effects of the slit width, the gap width, the mixing chamber shape and the obstacle shape of the mixing performance and flow characteristics of the micro-mixer were analyzed. The results showed that the narrowing of the slit width could significantly improve the mixing index and achieve efficient mixing. When Re ≤ 5 and Re ≥ 20, the optimized pentagonal mixing chamber micro-mixer could increase the mixing index while reducing the pressure drop due to the introduction of the progressive expansion structure compared with the quadrilateral mixing chamber micro-mixer; When Re ≥ 20, the I-shaped baffle and the grooved baffle led to a higher mixing index than that the rectangular baffle. The results are helpful for the design and development of micro-mixers with efficient mixing function in microfluidic and micro-total analysis pre-processing parts.
As an important part of laboratory chip (LOC) and micro-total analysis system (μTAS), micro-mixer has been widely used in the fields of biological analysis and chemical synthesis, most of which are used in the pre-treatment part of the detection system to achieve sufficient mixing of detection samples and reagents and improve the detection accuracy and efficiency. In this work, a novel planar passive micro-mixer with narrow slits and obstacles arranged in a pentagonal mixing chamber was designed. The new micro-mixer made full use of the fluid jet characteristics and the vortex principle of the baffles to enhance the fluid disturbance and break the laminar state of fluid flow, which could effectively promote fluid mixing. The accuracy of numerical simulation was verified by the experimental method combining high-speed photography and Micro-PIV system, and the flow characteristics and mixing mechanism of the micro-mixer at different Reynolds Numbers (Re) were summarized. Under the premise of comprehensive consideration of the mixing index and pressure drop, the effects of the slit width, the gap width, the mixing chamber shape and the obstacle shape of the mixing performance and flow characteristics of the micro-mixer were analyzed. The results showed that the narrowing of the slit width could significantly improve the mixing index and achieve efficient mixing. When Re ≤ 5 and Re ≥ 20, the optimized pentagonal mixing chamber micro-mixer could increase the mixing index while reducing the pressure drop due to the introduction of the progressive expansion structure compared with the quadrilateral mixing chamber micro-mixer; When Re ≥ 20, the I-shaped baffle and the grooved baffle led to a higher mixing index than that the rectangular baffle. The results are helpful for the design and development of micro-mixers with efficient mixing function in microfluidic and micro-total analysis pre-processing parts.
2019, 47(9): 1330-1336
doi: 10.19756/j.issn.0253-3820.191087
Abstract:
Methylanthranilate (MA) is a kind of spice illegally added in the wine in China. The determination of MA in wine is an important quality control link. Therefore, it is of great significance to develop a rapid method for detection of prohibited spice in wine. In this work, an inverse opal structural molecularly imprinted photonic hydrogels (MIPHs) membrane was fabricated by using the photonic crystal techniques and molecular imprinting techniques. The MIPHs membrane was prepared by using methylanthranilate as template molecule, methacrylic acid as functional monomer, ethylene glycol dimethacrylate as cross linker, followed by a thermal polymerization at 60℃. Then the inverse opal structural MIPHs membrane was obtained after removing photonic crystal template and imprinted molecules. The results showed that the MIPHs membrane exhibited a good selectivity property to MA, and it responded to MA within 6 min. The Bragg diffraction peak shifted with increasing concentration of MA. A linear relationship was found between Δλ and the concentration of MA in the range from 0.1 mmol/L to 10 mmol/L. And the least detectable concentration was about 31 μmol/L. Furthermore, a color change of the MIPHs membrane couldbe observed by naked eyes. Therefore, the smart MIPHs membrane showed great potential in rapid and visual detection of MA in wine.
Methylanthranilate (MA) is a kind of spice illegally added in the wine in China. The determination of MA in wine is an important quality control link. Therefore, it is of great significance to develop a rapid method for detection of prohibited spice in wine. In this work, an inverse opal structural molecularly imprinted photonic hydrogels (MIPHs) membrane was fabricated by using the photonic crystal techniques and molecular imprinting techniques. The MIPHs membrane was prepared by using methylanthranilate as template molecule, methacrylic acid as functional monomer, ethylene glycol dimethacrylate as cross linker, followed by a thermal polymerization at 60℃. Then the inverse opal structural MIPHs membrane was obtained after removing photonic crystal template and imprinted molecules. The results showed that the MIPHs membrane exhibited a good selectivity property to MA, and it responded to MA within 6 min. The Bragg diffraction peak shifted with increasing concentration of MA. A linear relationship was found between Δλ and the concentration of MA in the range from 0.1 mmol/L to 10 mmol/L. And the least detectable concentration was about 31 μmol/L. Furthermore, a color change of the MIPHs membrane couldbe observed by naked eyes. Therefore, the smart MIPHs membrane showed great potential in rapid and visual detection of MA in wine.
2019, 47(9): 1337-1343
doi: 10.19756/j.issn.0253-3820.191311
Abstract:
Based on the specific recognition of T-Hg2+-T mismatched for mercury ions (Hg2+), a simple and sensitive method for detecting Hg2+ was developed by using Fe3O4 nano-magnetic beads (MB) as reaction platform and portable blood glucose meter (PGM) as detection means. Gold nanoparticles (AuNPs) were prepared by sodium citrate reduction. The surface of AuNPs was modified with sulfhydryl terminal-rich thymine (T) oligonucleotide probe (S1) and glucose oxidase (GOx). In the presence of Hg2+, functionalized AuNPs were captured by capture-probe (S2)-modified MB due to T-Hg2+-T coordination. The labeled GOx oxidized glucose (Glu) to gluconic acid and H2O2. Thus, the concentration of Glu in the reaction solution was reduced and could be detected quantitatively by PGM. The optimal conditions of the assay were as follows:the volume ratio of S2 and GOx was 1:3, the reaction time of Hg2+ was 2 h, and the hydrolysis time of Glu was 1 h. Under optimized conditions, the PGM response of the system had a good linear relationship with the logarithm of Hg2+ concentration. The linear range was 0.05-8.00 nmol/L, and the detection limit was 0.02 nmol/L (3σ). The recovery of Hg2+ in actual water samples was 97.8%-113.7%, and the relative standard deviation was 0.2%-1.3%, which met the detection requirements of Hg2+ in actual water samples.
Based on the specific recognition of T-Hg2+-T mismatched for mercury ions (Hg2+), a simple and sensitive method for detecting Hg2+ was developed by using Fe3O4 nano-magnetic beads (MB) as reaction platform and portable blood glucose meter (PGM) as detection means. Gold nanoparticles (AuNPs) were prepared by sodium citrate reduction. The surface of AuNPs was modified with sulfhydryl terminal-rich thymine (T) oligonucleotide probe (S1) and glucose oxidase (GOx). In the presence of Hg2+, functionalized AuNPs were captured by capture-probe (S2)-modified MB due to T-Hg2+-T coordination. The labeled GOx oxidized glucose (Glu) to gluconic acid and H2O2. Thus, the concentration of Glu in the reaction solution was reduced and could be detected quantitatively by PGM. The optimal conditions of the assay were as follows:the volume ratio of S2 and GOx was 1:3, the reaction time of Hg2+ was 2 h, and the hydrolysis time of Glu was 1 h. Under optimized conditions, the PGM response of the system had a good linear relationship with the logarithm of Hg2+ concentration. The linear range was 0.05-8.00 nmol/L, and the detection limit was 0.02 nmol/L (3σ). The recovery of Hg2+ in actual water samples was 97.8%-113.7%, and the relative standard deviation was 0.2%-1.3%, which met the detection requirements of Hg2+ in actual water samples.
2019, 47(9): 1344-1351
doi: 10.19756/j.issn.0253-3820.191202
Abstract:
Active bioaerosols suspended in the atmosphere can harm human health through the human respiratory system, so the detection of active bioaerosols is extremely important. In recent years, more and more research has attempted to apply single particle aerosol mass spectrometry (SPAMS) to monitor atmospheric bioaerosols. In this work, 13 known strains were analyzed by SPAMS and it was found that the single cell spectra of different active bioaerosols had high consistency, so it was difficult to identify the strains. However, the common peaks of active bioaerosols were quite different from the characteristic peaks of other fine particles in the atmosphere. For example, there were m/z 30, 70, 72, 74, 86, 88, 110, 120 and other amino acid fragments, m/z -26, -42, -79, -97, -159 and other cyanide and phosphate ion peaks in living bacterial aerosols. In the detection of external atmospheric aerosols, it was found that the above-mentioned negative ion peaks were relatively stable, which could be used as a characteristic peak for identifying bacterial aerosols in practical applications to achieve the purpose of identifying active bacterial aerosols online.
Active bioaerosols suspended in the atmosphere can harm human health through the human respiratory system, so the detection of active bioaerosols is extremely important. In recent years, more and more research has attempted to apply single particle aerosol mass spectrometry (SPAMS) to monitor atmospheric bioaerosols. In this work, 13 known strains were analyzed by SPAMS and it was found that the single cell spectra of different active bioaerosols had high consistency, so it was difficult to identify the strains. However, the common peaks of active bioaerosols were quite different from the characteristic peaks of other fine particles in the atmosphere. For example, there were m/z 30, 70, 72, 74, 86, 88, 110, 120 and other amino acid fragments, m/z -26, -42, -79, -97, -159 and other cyanide and phosphate ion peaks in living bacterial aerosols. In the detection of external atmospheric aerosols, it was found that the above-mentioned negative ion peaks were relatively stable, which could be used as a characteristic peak for identifying bacterial aerosols in practical applications to achieve the purpose of identifying active bacterial aerosols online.
2019, 47(9): 1352-1358
doi: 10.19756/j.issn.0253-3820.191347
Abstract:
A method was developed for producing double emulsion droplets based on a compositional microfluidic chip that was consisted of a T-micro connector, a cross-micro connector and a glass capillary. T-junction microfluidic chip could fabricate high throughput and uniform oil-in-water (O/W) and water-in-oil (W/O) droplets without hydrophobic or hydrophilic treatments. T-junction microfluidic chip was reusable and highly reliable. The process of generation droplet was simulated by COMSOL in 3D simulation model. The T-junction microfluidic chip was used to generate W/O droplets, and it was found that the high throughput and uniform W/O droplets could be obtained by adjusting the phase flow. Besides, the W/O droplets with different colors were obtained by a microfluidic chip comprised of cross-micro connector and glass capillary. Based on the above experiments, a combination microfluidic chip of T-micro connector, cross-micro connector and glass capillary was constructed. The constructed chip could produce W/O/W double emulsion droplets by adjusting the phase flows. This method offered a simple, low-cost way to produce double emulsion droplets in a short time without professional facilities.
A method was developed for producing double emulsion droplets based on a compositional microfluidic chip that was consisted of a T-micro connector, a cross-micro connector and a glass capillary. T-junction microfluidic chip could fabricate high throughput and uniform oil-in-water (O/W) and water-in-oil (W/O) droplets without hydrophobic or hydrophilic treatments. T-junction microfluidic chip was reusable and highly reliable. The process of generation droplet was simulated by COMSOL in 3D simulation model. The T-junction microfluidic chip was used to generate W/O droplets, and it was found that the high throughput and uniform W/O droplets could be obtained by adjusting the phase flow. Besides, the W/O droplets with different colors were obtained by a microfluidic chip comprised of cross-micro connector and glass capillary. Based on the above experiments, a combination microfluidic chip of T-micro connector, cross-micro connector and glass capillary was constructed. The constructed chip could produce W/O/W double emulsion droplets by adjusting the phase flows. This method offered a simple, low-cost way to produce double emulsion droplets in a short time without professional facilities.
2019, 47(9): 1359-1365
doi: 10.19756/j.issn.0253-3820.191221
Abstract:
The pure standards of 10 linear alkanes (C6-C15) were detected by proton-transfer-reaction mass spectrometry (PTR-MS) through a self-made liquid sampling device. The experimental results showed that the fragmentation of linear alkanes in PTR-MS underwent similar patterns in the electron impact ionization source (EI). It could be seen from the mass spectrum that the main products were a series of[CiH2i+1]+,[CiH2i-1]+ and[CiH2i-3]+ (i ≥ 3) ions. In the experiment, protonated molecular ions[M+H]+ were not detected, and the appearance of[M-H]+ ions and other fragment ions indicated that once the protonated product of the alkane was formed, dehydrogenation or direct cleavage occurred. Furthermore, it was found that the relative abundance of fragment ions was affected greatly by E/N (the ratio of electric field strength, E, and number density of particles in the drift tube, N). In the range of 80-170 Td, as the E/N value increased, the relative abundances of the fragment ions with high m/z would decrease first, until the signal was below the detection limit of the instrument and could not be detected. The relative abundance of the fragment ions with low m/z (such as[C4H9]+ (m/z 57),[C3H7]+ (m/z 43), etc.) first increased and then decreased, while the relative abundances of the fragment ions[C3H5]+ (m/z 41) always showed an upward trend. This indicated that the fragment ions with high m/z would undergo secondary cracking under high E/N conditions, and the fragment ions with low m/z were generated step by step.
The pure standards of 10 linear alkanes (C6-C15) were detected by proton-transfer-reaction mass spectrometry (PTR-MS) through a self-made liquid sampling device. The experimental results showed that the fragmentation of linear alkanes in PTR-MS underwent similar patterns in the electron impact ionization source (EI). It could be seen from the mass spectrum that the main products were a series of[CiH2i+1]+,[CiH2i-1]+ and[CiH2i-3]+ (i ≥ 3) ions. In the experiment, protonated molecular ions[M+H]+ were not detected, and the appearance of[M-H]+ ions and other fragment ions indicated that once the protonated product of the alkane was formed, dehydrogenation or direct cleavage occurred. Furthermore, it was found that the relative abundance of fragment ions was affected greatly by E/N (the ratio of electric field strength, E, and number density of particles in the drift tube, N). In the range of 80-170 Td, as the E/N value increased, the relative abundances of the fragment ions with high m/z would decrease first, until the signal was below the detection limit of the instrument and could not be detected. The relative abundance of the fragment ions with low m/z (such as[C4H9]+ (m/z 57),[C3H7]+ (m/z 43), etc.) first increased and then decreased, while the relative abundances of the fragment ions[C3H5]+ (m/z 41) always showed an upward trend. This indicated that the fragment ions with high m/z would undergo secondary cracking under high E/N conditions, and the fragment ions with low m/z were generated step by step.
2019, 47(9): 1366-1372
doi: 10.19756/j.issn.0253-3820.181654
Abstract:
An optical sensing system for specific detection of F- was developed on the basis of room-temperature phosphorescence of manganese-doped Zinc sulfide quantum dots (Mn-ZnS QDs). In this system, Eu3+ bonded with Mn-ZnS QDs to form nanocomposites, and the energy transfer due to the approach of QDs quenched the room-temperature phosphorescence. In the presence of F-, the stong coordinative competition between F- and Eu3+ collapsed the aggregation-state of QDs and thereby gradually recovered the phosphorescence, which contributed to the trace F- detection. This method based on phosphorescence sensing avoids the interference from background fluorescence and scattering light in complex environmental substrate and is featured with high convenience and sensitivity. This method had a detection limit of 0.05 mg/L, a linear range of 0.2-20.0 mg/L, and a relative standard deviation of 3.2% in determination of F-. The spiked recovery of F- in environmental water samples was 94%-106%. This study offers an efficient method for F- detection in environmental water bodies.
An optical sensing system for specific detection of F- was developed on the basis of room-temperature phosphorescence of manganese-doped Zinc sulfide quantum dots (Mn-ZnS QDs). In this system, Eu3+ bonded with Mn-ZnS QDs to form nanocomposites, and the energy transfer due to the approach of QDs quenched the room-temperature phosphorescence. In the presence of F-, the stong coordinative competition between F- and Eu3+ collapsed the aggregation-state of QDs and thereby gradually recovered the phosphorescence, which contributed to the trace F- detection. This method based on phosphorescence sensing avoids the interference from background fluorescence and scattering light in complex environmental substrate and is featured with high convenience and sensitivity. This method had a detection limit of 0.05 mg/L, a linear range of 0.2-20.0 mg/L, and a relative standard deviation of 3.2% in determination of F-. The spiked recovery of F- in environmental water samples was 94%-106%. This study offers an efficient method for F- detection in environmental water bodies.
2019, 47(9): 1373-1381
doi: 10.19756/j.issn.0253-3820.191306
Abstract:
A method was proposed for the effective and accurate colorimetric detection of ultra-trace trivalent chromium ions (Cr3+) in water based on citric acid-modified gold nanoparticles (CA-AuNPs). CA-AuNPs under different pH conditions were prepared by in-situ reduction at 273 K. After adding ultra-trace Cr3+, the color change of the system was visible to the naked eye, and the color changed from red to dark gray or colorless, other metal ions (Na+, Ca2+, Co2+, Zn2+, Cu2+, Fe2+, Mg2+, Al3+, Fe3+) showed no significant changes. The proposed sensing strategy coupled with spectroscopic detection method showed a low detection limit of 40.7 nmol/L(3σ) for detection of Cr3+ in drinking water, which was lower than that of the national standard method. And a minimum concentration of 1.0×10-5 mol/L for Cr3+ could be detected with naked eyes. This visual sensor based on CA-AuNPs had low detection limit and high selectivity, which would play an important role in drug analysis, clinical diagnosis and environmental monitoring.
A method was proposed for the effective and accurate colorimetric detection of ultra-trace trivalent chromium ions (Cr3+) in water based on citric acid-modified gold nanoparticles (CA-AuNPs). CA-AuNPs under different pH conditions were prepared by in-situ reduction at 273 K. After adding ultra-trace Cr3+, the color change of the system was visible to the naked eye, and the color changed from red to dark gray or colorless, other metal ions (Na+, Ca2+, Co2+, Zn2+, Cu2+, Fe2+, Mg2+, Al3+, Fe3+) showed no significant changes. The proposed sensing strategy coupled with spectroscopic detection method showed a low detection limit of 40.7 nmol/L(3σ) for detection of Cr3+ in drinking water, which was lower than that of the national standard method. And a minimum concentration of 1.0×10-5 mol/L for Cr3+ could be detected with naked eyes. This visual sensor based on CA-AuNPs had low detection limit and high selectivity, which would play an important role in drug analysis, clinical diagnosis and environmental monitoring.
2019, 47(9): 1382-1389
doi: 10.19756/j.issn.0253-3820.191232
Abstract:
A new strategy for eliminating mass spectral interference in analysis of soft magnetic ferrite powders by inductively coupled plasma tandem mass spectrometry (ICP-MS/MS) in the MS/MS mode using mixed reaction gases was proposed. The mixture of nitric acid and hydrochloric acid was used for digesting the samples by a microwave-based digestion system. The contents of harmful elements (Na and Mg) and doping elements (Al, K, Ti and Co) in the digestion solution were determined by ICP-MS/MS. For interferences of mass spectrum in the complex matrix composition of different soft magnetic ferrite powders, in the MS/MS mode, the interferences were eliminated using mixed reaction gases of NH3/He/H2 through mass shift and on-mass methods. The limits of detection for Na, Mg, Al, K, Ti and Co were 17, 3.1, 5.4, 11, 0.64 and 0.53 ng/L, respectively. The developed method was evaluated by sector field ICP-MS (SF-ICP-MS), and there was no significant difference between the two analytical methods at a 95% confidence level, indicating that the developed method was accurate and reliable. This method was demonstrated simple and quick, and could be used in interference-free determination of Na, Mg, Al, K, Ti and Co in soft magnetic ferrite powders, which provided a new technical means for quality control of harmful and doping elements in soft magnetic ferrite powders.
A new strategy for eliminating mass spectral interference in analysis of soft magnetic ferrite powders by inductively coupled plasma tandem mass spectrometry (ICP-MS/MS) in the MS/MS mode using mixed reaction gases was proposed. The mixture of nitric acid and hydrochloric acid was used for digesting the samples by a microwave-based digestion system. The contents of harmful elements (Na and Mg) and doping elements (Al, K, Ti and Co) in the digestion solution were determined by ICP-MS/MS. For interferences of mass spectrum in the complex matrix composition of different soft magnetic ferrite powders, in the MS/MS mode, the interferences were eliminated using mixed reaction gases of NH3/He/H2 through mass shift and on-mass methods. The limits of detection for Na, Mg, Al, K, Ti and Co were 17, 3.1, 5.4, 11, 0.64 and 0.53 ng/L, respectively. The developed method was evaluated by sector field ICP-MS (SF-ICP-MS), and there was no significant difference between the two analytical methods at a 95% confidence level, indicating that the developed method was accurate and reliable. This method was demonstrated simple and quick, and could be used in interference-free determination of Na, Mg, Al, K, Ti and Co in soft magnetic ferrite powders, which provided a new technical means for quality control of harmful and doping elements in soft magnetic ferrite powders.
2019, 47(9): 1390-1394
doi: 10.19756/j.issn.0253-3820.191283
Abstract:
In recent years, single cell analysis has become one of hot topics in analytical chemistry. In this work, a method was developed for quantitative analysis of silver nanoparticles (AgNP) in single cells by laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS). An inkjet printer was used to produce droplets of silver standards, which were similar to the matrixes of single cells. After exposed to AgNP, 95 single cells were quantitatively analyzed by LA-ICP-MS using the droplet standards. The contents of AgNP in single cells showed a lognormal distribution, ranging from 19.1 fg to 1682 fg Ag per cell with an average of (166±188) fg Ag per cell, which was in good agreement with the average from cell population ((175±2) fg Ag per cell). LA-ICP-MS had great potential in single cell analysis and provided a new tool for studying biological effects of metal nanoparticles at a single cell level.
In recent years, single cell analysis has become one of hot topics in analytical chemistry. In this work, a method was developed for quantitative analysis of silver nanoparticles (AgNP) in single cells by laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS). An inkjet printer was used to produce droplets of silver standards, which were similar to the matrixes of single cells. After exposed to AgNP, 95 single cells were quantitatively analyzed by LA-ICP-MS using the droplet standards. The contents of AgNP in single cells showed a lognormal distribution, ranging from 19.1 fg to 1682 fg Ag per cell with an average of (166±188) fg Ag per cell, which was in good agreement with the average from cell population ((175±2) fg Ag per cell). LA-ICP-MS had great potential in single cell analysis and provided a new tool for studying biological effects of metal nanoparticles at a single cell level.
2019, 47(9): 1395-1401
doi: 10.19756/j.issn.0253-3820.191277
Abstract:
Protonated chitosan (PCTS) modified gold nanoparticles (AuNPs) composites coating was fabricated using an etched stainless steel wire as a support on which AuNPs were first deposited, then after modified with CTS by self-assembly method and protonated. A method of stir bar sorptive extraction (SBSE) based on PCTS/AuNPs-ion chromatography (IC) was thus developed for measurement of nitrite and nitrate in dairy products. Experimental parameters including extraction temperature, pH, extraction time, desorption solvent and time were optimized. Under the optimized conditions, the dynamic linear ranges of the developed PCTS/AuNPs-SBSE method were 0.005-0.5 mg/L and 0.02-5.0 mg/L for the nitrite and nitrate with enrichment factors of 22-25 folds, the correlation coefficients were 0.9985 and 0.9988, the limits of detections were 0.0012 mg/L and 0.0067 mg/L (S/N=3), and RSDs were in the range of 2.6%-7.2% (n=5), respectively. In the case of real samples analyses, the recoveries of spiked nitrite and nitrate were 84.7%-100.4% with RSDs of 2.8%-8.5% (n=3). The developed method was simple, sensitive and selective, and could be used for the analysis of nitrite and nitrate in dairy products.
Protonated chitosan (PCTS) modified gold nanoparticles (AuNPs) composites coating was fabricated using an etched stainless steel wire as a support on which AuNPs were first deposited, then after modified with CTS by self-assembly method and protonated. A method of stir bar sorptive extraction (SBSE) based on PCTS/AuNPs-ion chromatography (IC) was thus developed for measurement of nitrite and nitrate in dairy products. Experimental parameters including extraction temperature, pH, extraction time, desorption solvent and time were optimized. Under the optimized conditions, the dynamic linear ranges of the developed PCTS/AuNPs-SBSE method were 0.005-0.5 mg/L and 0.02-5.0 mg/L for the nitrite and nitrate with enrichment factors of 22-25 folds, the correlation coefficients were 0.9985 and 0.9988, the limits of detections were 0.0012 mg/L and 0.0067 mg/L (S/N=3), and RSDs were in the range of 2.6%-7.2% (n=5), respectively. In the case of real samples analyses, the recoveries of spiked nitrite and nitrate were 84.7%-100.4% with RSDs of 2.8%-8.5% (n=3). The developed method was simple, sensitive and selective, and could be used for the analysis of nitrite and nitrate in dairy products.
2019, 47(9): 1402-1410
doi: 10.19756/j.issn.0253-3820.191172
Abstract:
A sample preparation method was developed to simulate the process of intracellular metabolites metabonomics analysis of Escherichia coli. The Escherichia coli cell was firstly quenched with cold sodium chloride solution (0.85%, precooled at -80℃ for 15 min). The quenched bacterial cell was treated by using the technique of vacuum freeze-drying and liquid nitrogen freezing combined with ultrasonic processing to increase cell membrane penetrability. Finally, a cold aqueous solution of methanol (MeOH:H2O, 1:1, V/V, 4℃) was used as extraction solvent to extract metabolites. In the present research, flow cytometry and OD value recovery were performed to evaluate the degree of cell damage caused by quenching at single cell level and at integral level respectively. The tested results indicated that the degree of damage to cells caused by cold sodium chloride solution was less than 5%. The peak quantity and the total ion intensity detected by LC-TOF in low collision energy were used to evaluate extraction effects. Three different cell membrane penetrability modes and 4 kinds of extraction solvents were investigated and compared. The results showed that the technique of liquid nitrogen freezing combined with ultrasonic processing for cell membrane penetrability and a cold aqueous solution of methanol (MeOH/H2O, 1:1, V/V, 4℃) for extraction of metabolites had the best extraction effect (peak quantity was greater than or equal to 105, and total ion intensity was in the range of 106-107). Therefore, in this work, the freeze drying, grinding with liquid nitrogen and ultrasonic extraction were combined to extract metabolites. In this way, it effectively promoted cell lysis and improved the efficiency of extraction. The result of synthetic analysis showed that the method proposed here could meet the requirements of the metabonomics analysis of Escherichia coli.
A sample preparation method was developed to simulate the process of intracellular metabolites metabonomics analysis of Escherichia coli. The Escherichia coli cell was firstly quenched with cold sodium chloride solution (0.85%, precooled at -80℃ for 15 min). The quenched bacterial cell was treated by using the technique of vacuum freeze-drying and liquid nitrogen freezing combined with ultrasonic processing to increase cell membrane penetrability. Finally, a cold aqueous solution of methanol (MeOH:H2O, 1:1, V/V, 4℃) was used as extraction solvent to extract metabolites. In the present research, flow cytometry and OD value recovery were performed to evaluate the degree of cell damage caused by quenching at single cell level and at integral level respectively. The tested results indicated that the degree of damage to cells caused by cold sodium chloride solution was less than 5%. The peak quantity and the total ion intensity detected by LC-TOF in low collision energy were used to evaluate extraction effects. Three different cell membrane penetrability modes and 4 kinds of extraction solvents were investigated and compared. The results showed that the technique of liquid nitrogen freezing combined with ultrasonic processing for cell membrane penetrability and a cold aqueous solution of methanol (MeOH/H2O, 1:1, V/V, 4℃) for extraction of metabolites had the best extraction effect (peak quantity was greater than or equal to 105, and total ion intensity was in the range of 106-107). Therefore, in this work, the freeze drying, grinding with liquid nitrogen and ultrasonic extraction were combined to extract metabolites. In this way, it effectively promoted cell lysis and improved the efficiency of extraction. The result of synthetic analysis showed that the method proposed here could meet the requirements of the metabonomics analysis of Escherichia coli.
2019, 47(9): 1411-1418
doi: 10.19756/j.issn.0253-3820.181712
Abstract:
A simple and economical type of electrospray ionization (ESI) technique was developed for loading and ionization of samples by use of disposable wooden tips of sunflower seed husk. Samples could be loaded by simply dipping the tip into sample solutions or normal pipetting onto the natural groove of sunflower seed husk. Instrument parameter settings were optimized to obtain highly sensitive determination of ion intensity of samples, and full MS mode was applied to obtain the mass spectra. The wooden tip of the sunflower seed husk was pointed to the mass spectrometer inlet for Q-Orbitrap mass spectrometer, and the angles were between 60° and 90° in wooden tip. The tip was positioned 2-3 mm away from the inlet of mass spectrometer. The applied voltage to wooden tip of sunflower seed husk was adjusted in the range of 3.5-4.0 kV until optimal ion signals were obtained and all desolvation gases were turned off. The experimental results showed that this new ionization technique was applicable for analysis of various samples, e.g. lignin, ginsenoside, amino acid, proteins, etc. Comparing ESI technique and wooden tip spray coupled toothpick technique, the wooden tip spray with sunflower seed husk (WTSSSH) technique had better efficient in determination of lignin, ginsenoside and proteins by mass spectrometry. Some special sample, e.g. powder, could not be directly analyzed by ESI and wooden tip spray with toothpick, but it was convenient for WTSSSH. In this study, we established a continuous injection device based on the single needle injection method of ESI. The ginseng powder was on-line extracted with the device and the extracts was ionized in wooden tip of sunflower seed husk for mass spectrometric analysis, and a continuous and stable total ion chromatogram and abundant information of mass spectra were obtained.
A simple and economical type of electrospray ionization (ESI) technique was developed for loading and ionization of samples by use of disposable wooden tips of sunflower seed husk. Samples could be loaded by simply dipping the tip into sample solutions or normal pipetting onto the natural groove of sunflower seed husk. Instrument parameter settings were optimized to obtain highly sensitive determination of ion intensity of samples, and full MS mode was applied to obtain the mass spectra. The wooden tip of the sunflower seed husk was pointed to the mass spectrometer inlet for Q-Orbitrap mass spectrometer, and the angles were between 60° and 90° in wooden tip. The tip was positioned 2-3 mm away from the inlet of mass spectrometer. The applied voltage to wooden tip of sunflower seed husk was adjusted in the range of 3.5-4.0 kV until optimal ion signals were obtained and all desolvation gases were turned off. The experimental results showed that this new ionization technique was applicable for analysis of various samples, e.g. lignin, ginsenoside, amino acid, proteins, etc. Comparing ESI technique and wooden tip spray coupled toothpick technique, the wooden tip spray with sunflower seed husk (WTSSSH) technique had better efficient in determination of lignin, ginsenoside and proteins by mass spectrometry. Some special sample, e.g. powder, could not be directly analyzed by ESI and wooden tip spray with toothpick, but it was convenient for WTSSSH. In this study, we established a continuous injection device based on the single needle injection method of ESI. The ginseng powder was on-line extracted with the device and the extracts was ionized in wooden tip of sunflower seed husk for mass spectrometric analysis, and a continuous and stable total ion chromatogram and abundant information of mass spectra were obtained.
2019, 47(9): 1419-1426
doi: 10.19756/j.issn.0253-3820.181772
Abstract:
The organophosphorus pesticides are widely used in agriculture and food in China. Parathion, which is highly toxic and persistent, is one of the most widely used organophosphorus pesticides. Variable domain of the H chain of heavy-chain antibodies (VHH) is a fragment derived from camelids antibody. Due to its small size (only 15 kDa), high stability, ease of expression, and intact antigen-binding activity, VHHs have recently emerged as attractive reagents for immunodetection of chemical contaminants in food. In this study, five VHHs namely VHH1, VHH6, VHH13, VHH21 and VHH24 were selected from phage display library. Among these VHHs, VHH1 with the highest binding ability to parathion was selected for further analysis. VHH1 and parathion recognition mechanism predicted by homology modeling and molecule docking revealed the H bond and hydrophobic force, indicating the key amino acids Ser60, Lys104, Phe105, Gly106 and Arg107, which provided insights into antibody modification and antigen design.
The organophosphorus pesticides are widely used in agriculture and food in China. Parathion, which is highly toxic and persistent, is one of the most widely used organophosphorus pesticides. Variable domain of the H chain of heavy-chain antibodies (VHH) is a fragment derived from camelids antibody. Due to its small size (only 15 kDa), high stability, ease of expression, and intact antigen-binding activity, VHHs have recently emerged as attractive reagents for immunodetection of chemical contaminants in food. In this study, five VHHs namely VHH1, VHH6, VHH13, VHH21 and VHH24 were selected from phage display library. Among these VHHs, VHH1 with the highest binding ability to parathion was selected for further analysis. VHH1 and parathion recognition mechanism predicted by homology modeling and molecule docking revealed the H bond and hydrophobic force, indicating the key amino acids Ser60, Lys104, Phe105, Gly106 and Arg107, which provided insights into antibody modification and antigen design.
2019, 47(9): 1427-1432
doi: 10.19756/j.issn.0253-3820.191217
Abstract:
A method for visual detection of Pb2+ in water based on lead ion (Pb2+) functional nucleic acid colorimetric biosensor was developed. The specific recognition and cleavage of Pb2+ by GR-5 deoxyribozyme was carried out, and the cleavage products of GR-5 deoxyribozyme were combined with the color templates to convert into a G-quadruplex by clever nucleic acid design, wherein the color templates mainly included a complementary region to the cleavage product nucleic acid sequences, a guanine-rich G quadruplet forming region, and a spacer arm. In the presence of Pb2+, the substrate chain of the GR-5 deoxyribozyme was recognized to be cleaved and released, and the cleavage product was converted into a G-quadruplex by binding to a chromogenic template, since the G-quadruplex was under specific conditions. The peroxidase-like activity catalyzed the color development of H2O2 and 3,3',5,5'-tetramethylbenzidine (TMB), thus completing the construction of the Pb2+ functional nucleic acid colorimetric biosensor. Through a series of conditions optimization, it was found that the optimal ratio of substrate chain and enzyme chain of GR-5 deoxyribozyme was 1:1, the cleavage time was 3 min, the color template concentration was 5 μmol/L, and the optimal TMB concentration was 50 μL. Under the optimal conditions, the detection range of Pb2+ was 25 nmol/L-2.5 μmol/L, the linear relationship was y=0.039x+0.3486 (R=0.9904), and the lowest detection concentration was 10.1 nmol/L (3σ). The recoveries were 98.2%-115.5%. The proposed method had a good application prospect due to its high sensitivity, strong specificity and simple operation.
A method for visual detection of Pb2+ in water based on lead ion (Pb2+) functional nucleic acid colorimetric biosensor was developed. The specific recognition and cleavage of Pb2+ by GR-5 deoxyribozyme was carried out, and the cleavage products of GR-5 deoxyribozyme were combined with the color templates to convert into a G-quadruplex by clever nucleic acid design, wherein the color templates mainly included a complementary region to the cleavage product nucleic acid sequences, a guanine-rich G quadruplet forming region, and a spacer arm. In the presence of Pb2+, the substrate chain of the GR-5 deoxyribozyme was recognized to be cleaved and released, and the cleavage product was converted into a G-quadruplex by binding to a chromogenic template, since the G-quadruplex was under specific conditions. The peroxidase-like activity catalyzed the color development of H2O2 and 3,3',5,5'-tetramethylbenzidine (TMB), thus completing the construction of the Pb2+ functional nucleic acid colorimetric biosensor. Through a series of conditions optimization, it was found that the optimal ratio of substrate chain and enzyme chain of GR-5 deoxyribozyme was 1:1, the cleavage time was 3 min, the color template concentration was 5 μmol/L, and the optimal TMB concentration was 50 μL. Under the optimal conditions, the detection range of Pb2+ was 25 nmol/L-2.5 μmol/L, the linear relationship was y=0.039x+0.3486 (R=0.9904), and the lowest detection concentration was 10.1 nmol/L (3σ). The recoveries were 98.2%-115.5%. The proposed method had a good application prospect due to its high sensitivity, strong specificity and simple operation.
2019, 47(9): 1433-1439
doi: 10.19756/j.issn.0253-3820.191113
Abstract:
When nature sediments (e.g. clay/carbonate sediments) are dissolved by hydrochloric acid, a large number of metallic ions such as Ca, Mg, Fe, Al and rare earth elements are released. These metal ions make large amount of water-insoluble hydroxide precipitate under alkaline condition which can easily absorb and affect the extraction of boron (B) along with boron isotope composition (δ11B) determination. In this work, it was proved that when the solution was adjusted to alkalescent, adding an appropriate EDTA-2Na could effectively avoid insoluble hydroxide precipitation. The interference of EDTA-2Na to boron isotope determination was effectively reduced by rinsing the resin with ammonia after the alkalescent solution passing through the boron specific resin and extending the ionization time of simples in the measurement process. After the entire process, the recovery rate of boron was more than 95%, and the boron isotopic ratio of NIST SRM 951 ranged from 4.05146 to 4.05628. The boron isotopic composition (δ11B) of sediment of Sanya, Dachaidan lacustrine and Dachaidan intercrystalline were +17.64‰, -5.74‰ and +1.8‰, respectively. This method could meet the need of the high-precision determination of boron isotope of sediments such as clay sediments, carbonate sediments, loess and paleosol. In addition, this study provided a simple and low interference pretreatment method for high-precision determination of boron isotope.
When nature sediments (e.g. clay/carbonate sediments) are dissolved by hydrochloric acid, a large number of metallic ions such as Ca, Mg, Fe, Al and rare earth elements are released. These metal ions make large amount of water-insoluble hydroxide precipitate under alkaline condition which can easily absorb and affect the extraction of boron (B) along with boron isotope composition (δ11B) determination. In this work, it was proved that when the solution was adjusted to alkalescent, adding an appropriate EDTA-2Na could effectively avoid insoluble hydroxide precipitation. The interference of EDTA-2Na to boron isotope determination was effectively reduced by rinsing the resin with ammonia after the alkalescent solution passing through the boron specific resin and extending the ionization time of simples in the measurement process. After the entire process, the recovery rate of boron was more than 95%, and the boron isotopic ratio of NIST SRM 951 ranged from 4.05146 to 4.05628. The boron isotopic composition (δ11B) of sediment of Sanya, Dachaidan lacustrine and Dachaidan intercrystalline were +17.64‰, -5.74‰ and +1.8‰, respectively. This method could meet the need of the high-precision determination of boron isotope of sediments such as clay sediments, carbonate sediments, loess and paleosol. In addition, this study provided a simple and low interference pretreatment method for high-precision determination of boron isotope.
