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2019 Volume 47 Issue 4
2019, 47(4): 479-487
doi: 10.19756/j.issn.0253-3820.181632
Abstract:
The combination of multivariate calibration model and spectroscopic analysis technology can complete the rapid analysis of substances. However, when the external environmental conditions such as instrument or accessories are replaced or temperature changes, the existing master calibration can be "invalidated", and the reconstruction of the calibration usually takes a lot of time and financial resources. The development of calibration transfer technology solves this problem well, and the adaptability and robustness of the model are enhanced by correcting the spectra or selecting variables, therefore it is very important for popularizing and using the calibration. This paper reviews some of new calibration transfer methods and their applications in recent years, and introduces them according to traditional model transfer methods, new methods and new strategies. The application of each algorithm as well as both its advantages and disadvantages are evaluated.
The combination of multivariate calibration model and spectroscopic analysis technology can complete the rapid analysis of substances. However, when the external environmental conditions such as instrument or accessories are replaced or temperature changes, the existing master calibration can be "invalidated", and the reconstruction of the calibration usually takes a lot of time and financial resources. The development of calibration transfer technology solves this problem well, and the adaptability and robustness of the model are enhanced by correcting the spectra or selecting variables, therefore it is very important for popularizing and using the calibration. This paper reviews some of new calibration transfer methods and their applications in recent years, and introduces them according to traditional model transfer methods, new methods and new strategies. The application of each algorithm as well as both its advantages and disadvantages are evaluated.
2019, 47(4): 488-499
doi: 10.19756/j.issn.0253-3820.171539
Abstract:
Aptamers are single stranded short deoxyribonucleic acid or ribonucleic acid sequences screened from a random oligonucleotide library that has high affinity and specific recognition for specific target molecules. Since the advent of the systematic evolution of ligands by exponential enrichment (SELEX), there have been various improved screening processes based on SELEX and SELEX or non SELEX selection processes based on capillary electrophoresis separation method. As a molecular recognition element similar to antibody, aptamers have been applied to the detection of residues of pesticide and veterinary drugs closely related to food and environmental safety. In these applications, aptamers usually form composite probes with other materials that can produce signals, such as gold nanoparticles, quantum dots, or constitute sensors with electrochemical electrode. In this paper, the screening methods and the applications of aptamers in the detection of pesticide and veterinary drug residues are summarized, in order to provide a reference for the screening of aptamers and the application in the detection of pesticide and veterinary drug residues.
Aptamers are single stranded short deoxyribonucleic acid or ribonucleic acid sequences screened from a random oligonucleotide library that has high affinity and specific recognition for specific target molecules. Since the advent of the systematic evolution of ligands by exponential enrichment (SELEX), there have been various improved screening processes based on SELEX and SELEX or non SELEX selection processes based on capillary electrophoresis separation method. As a molecular recognition element similar to antibody, aptamers have been applied to the detection of residues of pesticide and veterinary drugs closely related to food and environmental safety. In these applications, aptamers usually form composite probes with other materials that can produce signals, such as gold nanoparticles, quantum dots, or constitute sensors with electrochemical electrode. In this paper, the screening methods and the applications of aptamers in the detection of pesticide and veterinary drug residues are summarized, in order to provide a reference for the screening of aptamers and the application in the detection of pesticide and veterinary drug residues.
2019, 47(4): 500-507
doi: 10.19756/j.issn.0253-3820.181764
Abstract:
Miniaturization of separation techniques can minimize consumption of solvent and requirement of sample size and leads to high efficiency, high speed, high resolution and high throughput analysis. In this study, a microfluidic chip-based array liquid chromatographic platform enabling multicolumn separation and detection was developed. The platform was based on the combination of glass, poly(methyl methacrylate) (PMMA) and polydimethylsiloxane (PDMS) chips and up to 8 packed chromatographic channels were manufactured on such a microfluidic device. Pressurization experiments showed that the array chip could be reliably used under pressure-driven liquid chromatographic mode. A nanoflow of 300 nL/min per column was realized through multi-stage flow splitting. We investigated feasibility and effectiveness of the 8 column array chip and obtained a high efficiency of 80000 plates per meter and a good reproducibility of RSD=1.1% for the retention time. Using a protein digest as the sample, we also explored the chip's potential applicability in high throughput separations of complex biological samples.
Miniaturization of separation techniques can minimize consumption of solvent and requirement of sample size and leads to high efficiency, high speed, high resolution and high throughput analysis. In this study, a microfluidic chip-based array liquid chromatographic platform enabling multicolumn separation and detection was developed. The platform was based on the combination of glass, poly(methyl methacrylate) (PMMA) and polydimethylsiloxane (PDMS) chips and up to 8 packed chromatographic channels were manufactured on such a microfluidic device. Pressurization experiments showed that the array chip could be reliably used under pressure-driven liquid chromatographic mode. A nanoflow of 300 nL/min per column was realized through multi-stage flow splitting. We investigated feasibility and effectiveness of the 8 column array chip and obtained a high efficiency of 80000 plates per meter and a good reproducibility of RSD=1.1% for the retention time. Using a protein digest as the sample, we also explored the chip's potential applicability in high throughput separations of complex biological samples.
2019, 47(4): 508-518
doi: 10.19756/j.issn.0253-3820.181806
Abstract:
A disulfide bond analysis method was presented in this study, which digested protein with pepsin, and combined post-column reduction with liquid chromatography-tandem mass spectrometry for peptide analysis. When protein was digested in an acidic environment, the original conformation of the disulfide bond could be maintained as much as possible; the method of post-column online reduction could make up for the poor specificity of pepsin and difficulty in data analysis. This method was used to analyze the disulfide bonds of recombinant human granulocyte-colony stimulating factor (rhG-CSF), and the results showed that disulfide bonds in NEM treated rhG-CSF were Cys36-Cys42 and Cys64-Cys74, leaving Cys17 alkylated by NEM, and no scrambling signal was detected. When analyzing the disulfide bond of rhG-CSF by this method without alkylating, the scrambling ratios were 9.1% (Cys36-Cys42), 0%(Cys64-Cys74) and 12.6% (Cys17), the results obtained from traditional method with chymotrypsin and Glu-C + trypsin were 73.4%, 58.1%, 97.5% and 40.3%, 5.2%, 22.3% correspondingly. Compared with the conventional method, this method showed a lower disulfide bond scrambling ratio, the measurement could more accurately represent the actual existence state of the disulfide bond in the protein.
A disulfide bond analysis method was presented in this study, which digested protein with pepsin, and combined post-column reduction with liquid chromatography-tandem mass spectrometry for peptide analysis. When protein was digested in an acidic environment, the original conformation of the disulfide bond could be maintained as much as possible; the method of post-column online reduction could make up for the poor specificity of pepsin and difficulty in data analysis. This method was used to analyze the disulfide bonds of recombinant human granulocyte-colony stimulating factor (rhG-CSF), and the results showed that disulfide bonds in NEM treated rhG-CSF were Cys36-Cys42 and Cys64-Cys74, leaving Cys17 alkylated by NEM, and no scrambling signal was detected. When analyzing the disulfide bond of rhG-CSF by this method without alkylating, the scrambling ratios were 9.1% (Cys36-Cys42), 0%(Cys64-Cys74) and 12.6% (Cys17), the results obtained from traditional method with chymotrypsin and Glu-C + trypsin were 73.4%, 58.1%, 97.5% and 40.3%, 5.2%, 22.3% correspondingly. Compared with the conventional method, this method showed a lower disulfide bond scrambling ratio, the measurement could more accurately represent the actual existence state of the disulfide bond in the protein.
2019, 47(4): 519-526
doi: 10.19756/j.issn.0253-3820.181646
Abstract:
A method of high performance liquid chromatography coupled with electron spray ionization quadrupole time-of-flight mass spectrometry was established for analysis of short chain chlorinated paraffins (SCCPs) in plastic. No chlorine solvent was added and SCCPs were quantified by their[M-H]- ions. For each congener group of SCCPs with carbon chain lengths in 10-13 and chlorine substituents in 5-13, the two most abundant m/z signals were extracted from the full-scan mass spectra as the quantitative and qualitative ions. The influence of medium chain chlorinated paraffins (MCCPs) was eliminated efficiently based on the high resolution of the mass spectrometry. Plastic samples were extracted by dichloride methane and purified by silica gel solid phase extraction column. SCCPs were eluted by hexane/dichloride methane (1:1, V/V). The instrumental detection limits (IDLs) were 0.01-0.05 mg/L for SCCPs with chlorine content from 51.5%-63%. Method detection limit (MDL) and quantitative limit were 1.4 μg/g and 4.6 μg/g, respectively. Recoveries of SCCPs were 118.0%±8.2%, 81.9%±6.9% and 77.8%±6.6%, at spiking concentrations of 5 μg/g, 20 μg/g and 50 μg/g, respectively. The intra- and inter-day variations were 5.7% and 8.1%, respectively. The quantitative results verified that SCCPs concentration in CPs were similar with the short chain alkane in the corresponding paraffin, which demonstrated the accuracy of this method. This method was applied in determination of four kinds of plastic samples. Cable and track presented to have a high concentration of SCCPs within the range of 555-1049 μg/g. Plastic toys had lower concentrations of SCCPs in the range of 1.86-6.56 μg/g.
A method of high performance liquid chromatography coupled with electron spray ionization quadrupole time-of-flight mass spectrometry was established for analysis of short chain chlorinated paraffins (SCCPs) in plastic. No chlorine solvent was added and SCCPs were quantified by their[M-H]- ions. For each congener group of SCCPs with carbon chain lengths in 10-13 and chlorine substituents in 5-13, the two most abundant m/z signals were extracted from the full-scan mass spectra as the quantitative and qualitative ions. The influence of medium chain chlorinated paraffins (MCCPs) was eliminated efficiently based on the high resolution of the mass spectrometry. Plastic samples were extracted by dichloride methane and purified by silica gel solid phase extraction column. SCCPs were eluted by hexane/dichloride methane (1:1, V/V). The instrumental detection limits (IDLs) were 0.01-0.05 mg/L for SCCPs with chlorine content from 51.5%-63%. Method detection limit (MDL) and quantitative limit were 1.4 μg/g and 4.6 μg/g, respectively. Recoveries of SCCPs were 118.0%±8.2%, 81.9%±6.9% and 77.8%±6.6%, at spiking concentrations of 5 μg/g, 20 μg/g and 50 μg/g, respectively. The intra- and inter-day variations were 5.7% and 8.1%, respectively. The quantitative results verified that SCCPs concentration in CPs were similar with the short chain alkane in the corresponding paraffin, which demonstrated the accuracy of this method. This method was applied in determination of four kinds of plastic samples. Cable and track presented to have a high concentration of SCCPs within the range of 555-1049 μg/g. Plastic toys had lower concentrations of SCCPs in the range of 1.86-6.56 μg/g.
2019, 47(4): 527-532
doi: 10.19756/j.issn.0253-3820.181275
Abstract:
A solid phase micro-extraction coupled with portable gas chromatography-tandem mass spectrometry method for field analysis was developed for the determination of 2-methylisoborneol(2-MIB)and geosmin(GSM)in water. The selective reaction monitoring(SRM)parameters were optimized. The SPME conditions such as stirring rate, extraction time and extraction temperature were investigated. Optimum SPME conditions were as follows:stirring rate of 1200 r/min, extraction time of 40 min, extraction temperature of 70℃. Limits of detection of 2-MIB and GSM were 1.1 ng/L and 0.5 ng/L respectively. Limits of quantification were 3.6 ng/L and 1.8 ng/L respectively. Linear detection range was 5-100 ng/L with correlation coefficients of 0.9922 and 0.9996, respectively. At the spiked level of 10-100 ng/L, the average recoveries of target compounds were 91.5%-107.9% with RSDs ≤ 10.1%(n=6). This method combines simplicity and rapidtity of SPME and high sensitivity and high selectivity of tandem mass spectrometry, and performance of the method is comparable to that of national standard method. It is especially suitable for the field determination of 2-MIB and geosmin GSM in real water samples.
A solid phase micro-extraction coupled with portable gas chromatography-tandem mass spectrometry method for field analysis was developed for the determination of 2-methylisoborneol(2-MIB)and geosmin(GSM)in water. The selective reaction monitoring(SRM)parameters were optimized. The SPME conditions such as stirring rate, extraction time and extraction temperature were investigated. Optimum SPME conditions were as follows:stirring rate of 1200 r/min, extraction time of 40 min, extraction temperature of 70℃. Limits of detection of 2-MIB and GSM were 1.1 ng/L and 0.5 ng/L respectively. Limits of quantification were 3.6 ng/L and 1.8 ng/L respectively. Linear detection range was 5-100 ng/L with correlation coefficients of 0.9922 and 0.9996, respectively. At the spiked level of 10-100 ng/L, the average recoveries of target compounds were 91.5%-107.9% with RSDs ≤ 10.1%(n=6). This method combines simplicity and rapidtity of SPME and high sensitivity and high selectivity of tandem mass spectrometry, and performance of the method is comparable to that of national standard method. It is especially suitable for the field determination of 2-MIB and geosmin GSM in real water samples.
2019, 47(4): 533-540
doi: 10.19756/j.issn.0253-3820.181766
Abstract:
To evaluate PFASs (Per- and polyfluoroalkyl substances) in the environment comprehensively, two trace analytical methods were developed for the determination of 12 kinds of perfluoroalkyl acids (PFAAs) and 8 kinds of associated precursor substances. The first ultra-high-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) method was applied to analysis of 9 perfluorooalkyl carboxylates (PFCAs) and 3 perfluorooalkyl sulfonates (PFSAs). Two perfluoroalkane sulfonamidoethanols (FOSEs), 2 perfluoro-1-octanesulfonamides (FOSAs), and 4 fluorotelomer alcohols (FTOHs) were detected with the second UPLC-MS/MS method because these compounds have different physicochemical properties from those of previous ones. The wastewater samples were extracted and cleaned with WAX solid-phase extraction cartridges. The sludge samples were extracted with accelerated solvent extraction (ASE) with acetonitrile. With the use of UPLC-MS/MS, the limits of quantification were in the range of 0.24-4.32 ng/L in wastewater samples and 0.04-0.12 ng/g in sludge samples. The recoveries were in the range of 62%-130% in wastewater samples and 71%-126% in sludge samples, and the RSDs were 0.9%-12.7% and 0.4%-15.2%, respectively. The method was sensitive and accurate, and also suitable for simultaneous determination of 20 kinds of PFASs in wastewater and sludge samples.
To evaluate PFASs (Per- and polyfluoroalkyl substances) in the environment comprehensively, two trace analytical methods were developed for the determination of 12 kinds of perfluoroalkyl acids (PFAAs) and 8 kinds of associated precursor substances. The first ultra-high-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) method was applied to analysis of 9 perfluorooalkyl carboxylates (PFCAs) and 3 perfluorooalkyl sulfonates (PFSAs). Two perfluoroalkane sulfonamidoethanols (FOSEs), 2 perfluoro-1-octanesulfonamides (FOSAs), and 4 fluorotelomer alcohols (FTOHs) were detected with the second UPLC-MS/MS method because these compounds have different physicochemical properties from those of previous ones. The wastewater samples were extracted and cleaned with WAX solid-phase extraction cartridges. The sludge samples were extracted with accelerated solvent extraction (ASE) with acetonitrile. With the use of UPLC-MS/MS, the limits of quantification were in the range of 0.24-4.32 ng/L in wastewater samples and 0.04-0.12 ng/g in sludge samples. The recoveries were in the range of 62%-130% in wastewater samples and 71%-126% in sludge samples, and the RSDs were 0.9%-12.7% and 0.4%-15.2%, respectively. The method was sensitive and accurate, and also suitable for simultaneous determination of 20 kinds of PFASs in wastewater and sludge samples.
2019, 47(4): 541-549
doi: 10.19756/j.issn.0253-3820.181812
Abstract:
As the basic element of tea, aroma is one of the most important factors determining the quality of tea. In this paper, a novel and objective method for rapid discrimination and classification of green tea aromas was developed by coupling of dynamic headspace sampling high-pressure photoionization/chemical ionization-time-of-flight mass spectrometer (HPPI-TOFMS) and multivariate statistical analysis techniques, such as partial least squares discrimination analysis (PLS-DA) and layer cluster analysis (HCA). The classification efficiency was evaluated by analyzing the receiver operating characteristic (ROC) curve. The observations and the robustness were assessed using 200 permutation tests. The volatile fingerprint mass spectra of 31 green tea samples of 4 sub-types (tender chestnut-like, tender-like, chestnut-like and roasted chestnut-like aroma) collected from different production areas in Sichuan, Guizhou, Zhejiang, Anhui, etc, were obtained based on this method. In the HPPI/CI mass spectra of the aroma VOCs from different sub-types of green teas, the types and relative intensities of the characteristic mass peaks were obviously different. The results of multivariate statistical analysis showed that there were little differences among the aroma VOCs of the same sub-type, but significant differences were exhibited among different sub-types, which could achieve accurate classification and identification. The prediction ability of the model for unknown samples reaches 85.1%. This method provided a new idea and approach for the effective identification of green tea aromas, indicating that it had potential application value and broad development prospects in the fields of food quality and safety evaluation.
As the basic element of tea, aroma is one of the most important factors determining the quality of tea. In this paper, a novel and objective method for rapid discrimination and classification of green tea aromas was developed by coupling of dynamic headspace sampling high-pressure photoionization/chemical ionization-time-of-flight mass spectrometer (HPPI-TOFMS) and multivariate statistical analysis techniques, such as partial least squares discrimination analysis (PLS-DA) and layer cluster analysis (HCA). The classification efficiency was evaluated by analyzing the receiver operating characteristic (ROC) curve. The observations and the robustness were assessed using 200 permutation tests. The volatile fingerprint mass spectra of 31 green tea samples of 4 sub-types (tender chestnut-like, tender-like, chestnut-like and roasted chestnut-like aroma) collected from different production areas in Sichuan, Guizhou, Zhejiang, Anhui, etc, were obtained based on this method. In the HPPI/CI mass spectra of the aroma VOCs from different sub-types of green teas, the types and relative intensities of the characteristic mass peaks were obviously different. The results of multivariate statistical analysis showed that there were little differences among the aroma VOCs of the same sub-type, but significant differences were exhibited among different sub-types, which could achieve accurate classification and identification. The prediction ability of the model for unknown samples reaches 85.1%. This method provided a new idea and approach for the effective identification of green tea aromas, indicating that it had potential application value and broad development prospects in the fields of food quality and safety evaluation.
2019, 47(4): 550-559
doi: 10.19756/j.issn.0253-3820.181722
Abstract:
The hybrid poly(GMA-EDMA-MFSNP) monolithic column was prepared by in-situ copolymerization of γ-(methylacryloyloxy)propyltrimethoxysilane modified fumed silica nanoparticles with glycidyl methacrylate (GMA) and ethylene glycol dimethacrylate (EDMA) as monomers, cyclohexanol and dodecanol as binary porogenic agent, and azobisisobutyronitrile (AIBN) as initiator. With the ring-opening reaction of glycidyl methacrylate (GMA), phenylalanine was chemically bonded on hybrid monolithic column. To obtain high efficiency, permeability and electroosmotic flow (EOF), the contents of the polymerization mixture and the chemical modification conditions of phenylalanine were optimized. The column prepared under the optimal conditions was a zwitterionic monolith with a mix-mode mechanism of reversed-phase and anion-exchange. By using the column prepared here, various analytes such as alkybenzenes, polycyclic aromatic hydrocarbons, benzoic acid analytes, phenol analytes and peptides were successfully separated in pressurized capillary electrochromatography. The column efficiency for toluene was up to 122592.
The hybrid poly(GMA-EDMA-MFSNP) monolithic column was prepared by in-situ copolymerization of γ-(methylacryloyloxy)propyltrimethoxysilane modified fumed silica nanoparticles with glycidyl methacrylate (GMA) and ethylene glycol dimethacrylate (EDMA) as monomers, cyclohexanol and dodecanol as binary porogenic agent, and azobisisobutyronitrile (AIBN) as initiator. With the ring-opening reaction of glycidyl methacrylate (GMA), phenylalanine was chemically bonded on hybrid monolithic column. To obtain high efficiency, permeability and electroosmotic flow (EOF), the contents of the polymerization mixture and the chemical modification conditions of phenylalanine were optimized. The column prepared under the optimal conditions was a zwitterionic monolith with a mix-mode mechanism of reversed-phase and anion-exchange. By using the column prepared here, various analytes such as alkybenzenes, polycyclic aromatic hydrocarbons, benzoic acid analytes, phenol analytes and peptides were successfully separated in pressurized capillary electrochromatography. The column efficiency for toluene was up to 122592.
2019, 47(4): 560-566
doi: 10.19756/j.issn.0253-3820.181787
Abstract:
Orange luminescent nitrogen doped carbon dots (N-CDs) were prepared via one-step hydrothermal treatment by using p-phenylenediamine and citric acid as precursors. The morphology and optical properties of the N-CDs were characterized by transmission electron microscopy, fourier transform infrared spectra, ultraviolet-visible absorption spectroscopy and fluorescence spectroscopy. The results showed that the synthesized N-CDs had an extreme small size ((1.62±0.35) nm), good water solubility and excellent fluorescent stability. The addition of nitrite (NO2-) caused a fluorescence increase of N-CDs. Based on this phenomenon, a new fluorescence analysis method for detecting NO2- was established. The linear range for detection of nitrite was 8-100 μmol/L, and the detection limit was 0.65 μmol/L. The possible fluorescence enhancement mechanism was presented. Furthermore, the constructed fluorescence sensing system was applied to the detection of NO2- in sausage, pickle and tap water samples with satisfactory results.
Orange luminescent nitrogen doped carbon dots (N-CDs) were prepared via one-step hydrothermal treatment by using p-phenylenediamine and citric acid as precursors. The morphology and optical properties of the N-CDs were characterized by transmission electron microscopy, fourier transform infrared spectra, ultraviolet-visible absorption spectroscopy and fluorescence spectroscopy. The results showed that the synthesized N-CDs had an extreme small size ((1.62±0.35) nm), good water solubility and excellent fluorescent stability. The addition of nitrite (NO2-) caused a fluorescence increase of N-CDs. Based on this phenomenon, a new fluorescence analysis method for detecting NO2- was established. The linear range for detection of nitrite was 8-100 μmol/L, and the detection limit was 0.65 μmol/L. The possible fluorescence enhancement mechanism was presented. Furthermore, the constructed fluorescence sensing system was applied to the detection of NO2- in sausage, pickle and tap water samples with satisfactory results.
2019, 47(4): 567-575
doi: 10.19756/j.issn.0253-3820.191013
Abstract:
Aptamers have similar functions as antibodies, and have attracted increasing attentions in the field of specific recognition and detection of target of interest. Small molecule substances are usually closely related to environmental pollution and human health. It is particularly difficult to screen aptamers for specifically binding to those small molecule targets, because they have less active sites for immobilization as well as have little difference in properties to nucleic acid libraries. Herein, the random nucleic acid libraries were firstly immobilized on the surface of streptavidin-coated magnetic beads through hydrogen bonds complementary to a biotin-labeled sequence with 12 bases. Subsequently, the magnetic beads were incubated with different concentrations of paraquat and the ssDNA sequences with high affinity to paraquat molecules were obtained by elution. The enriched ssDNA libraries for the next screening were purified from the products of above sequences after asymmetric PCR amplification. After 9 rounds of screening, 15 ssDNA sequences with specific affinity to paraquat were obtained through cloning and sequencing. 6 ssDNA sequences were selected to determine their affinity to paraquat based on the cluster analysis and secondary structure prediction of the above 15 sequences. These results showed that PQ-15 aptamer sequence had the highest affinity to paraquat with a dissociation constant (Kd) of (54±4) nmol/L. Finally, a novel aptasensor for colorimetric detection of paraquat pesticides was established for the first time, in which PQ-15 aptamer sequence was used as the target specific recognition molecule and the aggregation of gold nanoparticles mediated by cationic compound was employed as the signal transmit element. The proposed aptasensor had a detection limit as low as 25.2 nmol/L for paraquat, and displayed high selectivity against other competitive pesticides. Moreover, the aptasensor also exhibited excellent accuracy in detection of paraquat in real samples with recoveries from 91.13% to 99.60%.
Aptamers have similar functions as antibodies, and have attracted increasing attentions in the field of specific recognition and detection of target of interest. Small molecule substances are usually closely related to environmental pollution and human health. It is particularly difficult to screen aptamers for specifically binding to those small molecule targets, because they have less active sites for immobilization as well as have little difference in properties to nucleic acid libraries. Herein, the random nucleic acid libraries were firstly immobilized on the surface of streptavidin-coated magnetic beads through hydrogen bonds complementary to a biotin-labeled sequence with 12 bases. Subsequently, the magnetic beads were incubated with different concentrations of paraquat and the ssDNA sequences with high affinity to paraquat molecules were obtained by elution. The enriched ssDNA libraries for the next screening were purified from the products of above sequences after asymmetric PCR amplification. After 9 rounds of screening, 15 ssDNA sequences with specific affinity to paraquat were obtained through cloning and sequencing. 6 ssDNA sequences were selected to determine their affinity to paraquat based on the cluster analysis and secondary structure prediction of the above 15 sequences. These results showed that PQ-15 aptamer sequence had the highest affinity to paraquat with a dissociation constant (Kd) of (54±4) nmol/L. Finally, a novel aptasensor for colorimetric detection of paraquat pesticides was established for the first time, in which PQ-15 aptamer sequence was used as the target specific recognition molecule and the aggregation of gold nanoparticles mediated by cationic compound was employed as the signal transmit element. The proposed aptasensor had a detection limit as low as 25.2 nmol/L for paraquat, and displayed high selectivity against other competitive pesticides. Moreover, the aptasensor also exhibited excellent accuracy in detection of paraquat in real samples with recoveries from 91.13% to 99.60%.
2019, 47(4): 576-582
doi: 10.19756/j.issn.0253-3820.181650
Abstract:
Ultraviolet-visible (UV-vis) absorption spectrophotometry is used to detect the concentration of mixed solution of Zn and Co ions, where the problems of spectrum overlaps and interferes with each other due to their similar chemical properties are well solved. A boosting modeling method based on least absolute shrinkage and selection operator (LASSO) regression is proposed. The method first obtains sub-data sets by weighting the calibration samples, and then uses the sub-data sets to establish LASSO sub-model sets with different penalty factors, and uses Akaike Information Criterion (AIC) to judge the sub-model sets. According to the error of sub-model to modeling sample, the sample weight is updated. The iterations are repeated until sub-model convergence. Finally, the sub-models are given different weights according to the prediction performance of the sub-model, and the final prediction model is obtained by weighting fusion of the sub-model. A total of 80 groups of UV-Vis spectral data sets of mixed solution of Zn and Co are obtained by experiments. The method is compared with PLS of the whole spectrum, Monte Carlo uniformative variable elimination- partial least square(MCUVE-PLS) and competitive adaptive reweighted sampling (CARS)-PLS, and it is found that that the proposed method can greatly retain the wavelength variables with high contribution to the model and improve both the explanatory and predictive performance of the model. The method can be used to establish a stable and efficient prediction model for spectral data analysis.
Ultraviolet-visible (UV-vis) absorption spectrophotometry is used to detect the concentration of mixed solution of Zn and Co ions, where the problems of spectrum overlaps and interferes with each other due to their similar chemical properties are well solved. A boosting modeling method based on least absolute shrinkage and selection operator (LASSO) regression is proposed. The method first obtains sub-data sets by weighting the calibration samples, and then uses the sub-data sets to establish LASSO sub-model sets with different penalty factors, and uses Akaike Information Criterion (AIC) to judge the sub-model sets. According to the error of sub-model to modeling sample, the sample weight is updated. The iterations are repeated until sub-model convergence. Finally, the sub-models are given different weights according to the prediction performance of the sub-model, and the final prediction model is obtained by weighting fusion of the sub-model. A total of 80 groups of UV-Vis spectral data sets of mixed solution of Zn and Co are obtained by experiments. The method is compared with PLS of the whole spectrum, Monte Carlo uniformative variable elimination- partial least square(MCUVE-PLS) and competitive adaptive reweighted sampling (CARS)-PLS, and it is found that that the proposed method can greatly retain the wavelength variables with high contribution to the model and improve both the explanatory and predictive performance of the model. The method can be used to establish a stable and efficient prediction model for spectral data analysis.
2019, 47(4): 583-590
doi: 10.19756/j.issn.0253-3820.181808
Abstract:
合成了谷胱甘肽GSH包覆的荧光金纳米簇AuNCs，基于Hg2+-Au+间的高亲合作用实现对汞离子Hg2+的高灵敏性、高选择性荧光检测，线性检测范围为4~200 nmol/L，检出限LOD，S/N=3为2.4 nmol/L。常见的金属离子Ni2+，Mn2+，Co2+，Na+，Ba2+，Cu2+，Zn2+，Mg2+，Cd2+，Ca2+，K+，Fe3+，Al3+，Pb2+和阴离子F-，C2O42-，Cl-，H2PO4，NO3--，SO42-，HCOO-，I-，C5H7O5COO-，CH3COO-，Br-，CO32-对检测没有干扰。基于GSH-AuNCs构筑了两种纸型便携式AuNCs器件：半定量试纸和纸型横向流动检验LFA试剂盒，并成功用于可视化检测自来水样中Hg2+。
合成了谷胱甘肽GSH包覆的荧光金纳米簇AuNCs，基于Hg2+-Au+间的高亲合作用实现对汞离子Hg2+的高灵敏性、高选择性荧光检测，线性检测范围为4~200 nmol/L，检出限LOD，S/N=3为2.4 nmol/L。常见的金属离子Ni2+，Mn2+，Co2+，Na+，Ba2+，Cu2+，Zn2+，Mg2+，Cd2+，Ca2+，K+，Fe3+，Al3+，Pb2+和阴离子F-，C2O42-，Cl-，H2PO4，NO3--，SO42-，HCOO-，I-，C5H7O5COO-，CH3COO-，Br-，CO32-对检测没有干扰。基于GSH-AuNCs构筑了两种纸型便携式AuNCs器件：半定量试纸和纸型横向流动检验LFA试剂盒，并成功用于可视化检测自来水样中Hg2+。
2019, 47(4): 591-596
doi: 10.19756/j.issn.0253-3820.181541
Abstract:
Carbon quantum dots (CQDs) were prepared from litchi rind. CQDs could catalyze the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) in the presence of H2O2 to form oxidized TMB (ox-TMB) with an absorption peak at 652 nm. However, the introduction of cysteine (CySH) could cause the reduction of ox-TMB, resulting in a decrease of the absorbance at 652 nm. Based on this, a colorimetric method using CQDs as mimetic peroxidase was developed for determination of CySH. With TMB as a substrate, the effect of experiment conditions including pH of system and reaction temperature on catalytic activity of the obtained CQDs was studied. Under the optimal conditions, e.g. pH 3.5, reaction temperature of 40℃, reaction time of 10 min, 0.5 mmol/L H2O2, 0.5 μg/mL CQDs and 0.25 mmol/L TMB, the response was linearly proportional to the concentration of CySH in the range of 0.05-4.00 μmol/L with a detection limit of 0.02 μmol/L(3σ/k). The method proposed here exhibited excellent selectivity and common amino acids in serum did not interfere with detection of CySH. This method was successfully applied to determination of CySH in human serum sample with recoveries of 94.0%-104.0%.
Carbon quantum dots (CQDs) were prepared from litchi rind. CQDs could catalyze the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) in the presence of H2O2 to form oxidized TMB (ox-TMB) with an absorption peak at 652 nm. However, the introduction of cysteine (CySH) could cause the reduction of ox-TMB, resulting in a decrease of the absorbance at 652 nm. Based on this, a colorimetric method using CQDs as mimetic peroxidase was developed for determination of CySH. With TMB as a substrate, the effect of experiment conditions including pH of system and reaction temperature on catalytic activity of the obtained CQDs was studied. Under the optimal conditions, e.g. pH 3.5, reaction temperature of 40℃, reaction time of 10 min, 0.5 mmol/L H2O2, 0.5 μg/mL CQDs and 0.25 mmol/L TMB, the response was linearly proportional to the concentration of CySH in the range of 0.05-4.00 μmol/L with a detection limit of 0.02 μmol/L(3σ/k). The method proposed here exhibited excellent selectivity and common amino acids in serum did not interfere with detection of CySH. This method was successfully applied to determination of CySH in human serum sample with recoveries of 94.0%-104.0%.
2019, 47(4): 597-604
doi: 10.19756/j.issn.0253-3820.181765
Abstract:
The detection limit is an important parameter for evaluating the sensitivity of an analytical method. Compared with normally fluorescence probes, the calculation of detection limit of ratio fluorescence probes is more complicated. When the ratio fluorescence probe is used for pH detection, there is no universal definition of detection limit. The ratio fluorescence probes are classified into three categories based on the data types. A simulating probe with an excitation wavelength of 365 nm and an emission wavelength of 600 nm/450 nm is fabricated. Based on the calculation of detection limit for spectral method, a reasonable process is proposed for definition of detection limit for ratio fluorescence probe, which paves the way for comparing the sensitivity of different kinds of pH ratio fluorescence probes.
The detection limit is an important parameter for evaluating the sensitivity of an analytical method. Compared with normally fluorescence probes, the calculation of detection limit of ratio fluorescence probes is more complicated. When the ratio fluorescence probe is used for pH detection, there is no universal definition of detection limit. The ratio fluorescence probes are classified into three categories based on the data types. A simulating probe with an excitation wavelength of 365 nm and an emission wavelength of 600 nm/450 nm is fabricated. Based on the calculation of detection limit for spectral method, a reasonable process is proposed for definition of detection limit for ratio fluorescence probe, which paves the way for comparing the sensitivity of different kinds of pH ratio fluorescence probes.
2019, 47(4): 605-612
doi: 10.19756/j.issn.0253-3820.181623
Abstract:
An electrochemical sensor based on palladium-copper nanoparticles/three-dimensional reduced graphene oxide ([PdCu/3DRGO]) was constructed for detection of a p-nitrophenol (4-NP) with wide detection range and high stability.[PdCu/3DRGO] were synthesized by hydrothermal method using a solution containing palladium ions, copper ions and graphene oxide, which were characterized by scanning electron microscope (SEM), X-ray diffration (XRD), energy dispersive spectroscopy (EDS) and Fourier transform infrared spectroscopy (FT-IR). As-made composite was dropped on the surface of glassy carbon electrode to make the modified electrode ([PdCu/3DRGO]/GCE), of which electrochemical behavior was characterized by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Under the optimized experimental conditions, the modified electrode was used to detect 4-NP using differential pulse voltammetry (DPV) and current-time curve (i-t). The limit of detection was 0.050 μmol/L(S/N=3), the sensitivity was 0.372 μA/(μmol/L cm2), and the linear range was 10-3000 μmol/L. The sensor represented good stability and strong anti-interference performance which the common inorganic ions and structural analogues in water did not interfere with the determination of 4-NP.
An electrochemical sensor based on palladium-copper nanoparticles/three-dimensional reduced graphene oxide ([PdCu/3DRGO]) was constructed for detection of a p-nitrophenol (4-NP) with wide detection range and high stability.[PdCu/3DRGO] were synthesized by hydrothermal method using a solution containing palladium ions, copper ions and graphene oxide, which were characterized by scanning electron microscope (SEM), X-ray diffration (XRD), energy dispersive spectroscopy (EDS) and Fourier transform infrared spectroscopy (FT-IR). As-made composite was dropped on the surface of glassy carbon electrode to make the modified electrode ([PdCu/3DRGO]/GCE), of which electrochemical behavior was characterized by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Under the optimized experimental conditions, the modified electrode was used to detect 4-NP using differential pulse voltammetry (DPV) and current-time curve (i-t). The limit of detection was 0.050 μmol/L(S/N=3), the sensitivity was 0.372 μA/(μmol/L cm2), and the linear range was 10-3000 μmol/L. The sensor represented good stability and strong anti-interference performance which the common inorganic ions and structural analogues in water did not interfere with the determination of 4-NP.
2019, 47(4): 613-619
doi: 10.19756/j.issn.0253-3820.181782
Abstract:
A novel disposable surface-enhanced Raman scattering (SERS) sensor based on enzyme-catalyzed oxidation was developed for detecting tyrosinase (TYR) activity. The SERS sensor was fabricated by assembling the synthesized 4-thiol-catechol onto the surface of silver nanoparticles (AgNPs) which were screen printed on supporting material, and then the detection of TYR activity was accomplished according to SERS spectral changes of the SERS senor caused by the reaction between 4-thiol-catechol and TYR. The results showed that the SERS sensor had fast response to TYR (less than 5 min), and there was a linear relationship between the characteristic SERS signal and TYR concentration from 1 U/mL to 100 U/mL with limit of detection (LOD) of 0.28 U/mL (3σ). Moreover, resulting from the fingerprinting advantage of SERS technique and the specific property of the employed sensing-reaction, the developed SERS sensor had good selectivity towards TYR, which could be used for detection and evaluation of TYR and TYR inhibitor in serum.
A novel disposable surface-enhanced Raman scattering (SERS) sensor based on enzyme-catalyzed oxidation was developed for detecting tyrosinase (TYR) activity. The SERS sensor was fabricated by assembling the synthesized 4-thiol-catechol onto the surface of silver nanoparticles (AgNPs) which were screen printed on supporting material, and then the detection of TYR activity was accomplished according to SERS spectral changes of the SERS senor caused by the reaction between 4-thiol-catechol and TYR. The results showed that the SERS sensor had fast response to TYR (less than 5 min), and there was a linear relationship between the characteristic SERS signal and TYR concentration from 1 U/mL to 100 U/mL with limit of detection (LOD) of 0.28 U/mL (3σ). Moreover, resulting from the fingerprinting advantage of SERS technique and the specific property of the employed sensing-reaction, the developed SERS sensor had good selectivity towards TYR, which could be used for detection and evaluation of TYR and TYR inhibitor in serum.
2019, 47(4): 620-626
doi: 10.19756/j.issn.0253-3820.171349
Abstract:
Tree rings can reflect the environmental conditions during tree growing period. The celluloses of tree rings will not be reutilized for energy. The nonexchangeable organically bound tritium (NE-OBT) in celluloses has no liquidity and no exchange with other things, so it can accurately reflect the historical tritium level in the local environment. The measurement of NE-OBT in tree rings using accelerator mass spectrometer (AMS) needs only 10 mg of celluloses and a 200-s measurement time, which is more suitable compared with liquid scintillation counter (LSC). In this study, the principle of sample preparation for AMS NE-OBT measurement of tree rings was systematically studied. Through modification of the extraction methods for cellulose, the purity of cellulose was raised from 64.8% to 83.9%. With the developed two-step method, the cellulose was transformed into titanium hydride which could be measured using accelerator mass spectrometry directly. By strictly controlling the combustion cellulose amounts between 10.00 and 10.05 mg, extending the combustion time from 4 h to 10 h, strictly controlling the water transfer time in the vacuum system above 1 min and the cold trap temperature between -88℃ to -80℃, and cooling down with an open door, etc., the isotopic fraction effect during sample pretreatment was depressed and stabilized. Measurement results of 105-107 TU standard samples by LSC and AMS were treating with linear regression on the double logarithmic axis. After fitting, the correlation coefficient R2 reached 0.99912. These results proved that the prepared sample by this method could be used for measurement by accelerator mass spectrometry. Accurate measurement could be obtained after calibration with multi-level standards.
Tree rings can reflect the environmental conditions during tree growing period. The celluloses of tree rings will not be reutilized for energy. The nonexchangeable organically bound tritium (NE-OBT) in celluloses has no liquidity and no exchange with other things, so it can accurately reflect the historical tritium level in the local environment. The measurement of NE-OBT in tree rings using accelerator mass spectrometer (AMS) needs only 10 mg of celluloses and a 200-s measurement time, which is more suitable compared with liquid scintillation counter (LSC). In this study, the principle of sample preparation for AMS NE-OBT measurement of tree rings was systematically studied. Through modification of the extraction methods for cellulose, the purity of cellulose was raised from 64.8% to 83.9%. With the developed two-step method, the cellulose was transformed into titanium hydride which could be measured using accelerator mass spectrometry directly. By strictly controlling the combustion cellulose amounts between 10.00 and 10.05 mg, extending the combustion time from 4 h to 10 h, strictly controlling the water transfer time in the vacuum system above 1 min and the cold trap temperature between -88℃ to -80℃, and cooling down with an open door, etc., the isotopic fraction effect during sample pretreatment was depressed and stabilized. Measurement results of 105-107 TU standard samples by LSC and AMS were treating with linear regression on the double logarithmic axis. After fitting, the correlation coefficient R2 reached 0.99912. These results proved that the prepared sample by this method could be used for measurement by accelerator mass spectrometry. Accurate measurement could be obtained after calibration with multi-level standards.
2019, 47(4): 627-633
doi: 10.19756/j.issn.0253-3820.181599
Abstract:
Amino acids are usually analyzed by derivatization or adding ion-pair reagents. In this work, a new method was established base on a mixed-mode retention mechanism (reversed-phase and cation-exchange) to determinate 18 kinds of amino acids, using simple mobile phase without the ion-pair and derivatization. In this method, 18 kinds of amino acids could be retained on a OSAKA SODA CAPCELL PAK CR 1:4 (150 mm×2.1 mm, 5 μm; SCX:C18=1:4) column with a mobile phase of 0.1% formic acid(A)-acetonitrile (0.1% formic acid) (B) - 50 mmol/L ammonium formate (C) using a gradient elution program. Mass spectrometry (MS) detection was performed with multiple reaction monitoring (MRM) using positive electrospray ionization. The relative standard deviations (RSDs) of peak area ranged from 0.7% to 5.9%. The correlation coefficients (R2) of 18 kinds of compounds were greater than 0.993. And the recoveries of serum and urine samples from SD rats ranged from 92.2% to 113.6%. This method was proved to be simple with good reproducibility. It provides a new method and idea for determination of amino acids in biological samples or other complex matrices.
Amino acids are usually analyzed by derivatization or adding ion-pair reagents. In this work, a new method was established base on a mixed-mode retention mechanism (reversed-phase and cation-exchange) to determinate 18 kinds of amino acids, using simple mobile phase without the ion-pair and derivatization. In this method, 18 kinds of amino acids could be retained on a OSAKA SODA CAPCELL PAK CR 1:4 (150 mm×2.1 mm, 5 μm; SCX:C18=1:4) column with a mobile phase of 0.1% formic acid(A)-acetonitrile (0.1% formic acid) (B) - 50 mmol/L ammonium formate (C) using a gradient elution program. Mass spectrometry (MS) detection was performed with multiple reaction monitoring (MRM) using positive electrospray ionization. The relative standard deviations (RSDs) of peak area ranged from 0.7% to 5.9%. The correlation coefficients (R2) of 18 kinds of compounds were greater than 0.993. And the recoveries of serum and urine samples from SD rats ranged from 92.2% to 113.6%. This method was proved to be simple with good reproducibility. It provides a new method and idea for determination of amino acids in biological samples or other complex matrices.
2019, 47(4): 634-639
doi: 10.19756/j.issn.0253-3820.181089
Abstract:
Rapid and efficient strategy for detection of polycyclic aromatic hydrocarbons (PAHs) metabolites in human urine is urgently demanded in evaluation of internal exposure of PAHs. In this study, the combination of magnetic solid-phase extraction and internal extractive electrospray ionization mass spectrometry was used to rapid and high-throughput quantification of 3-hydroxybenzopyrene (3-OHBaP) in undiluted human urine samples. Polypyrrole-coated Fe3O4 magnetite (termed as Fe3O4@Ppy) was employed as the sorbent for MSPE of urinary 3-OHBaP in undiluted human urine samples, and then the material was treated as a bulk sample, which was directly analyzed by internal extractive electrospray ionization mass spectrometry (iEESI-MS). The signal intensity of m/z 239 was linearly related with 3-OHBaP concentration over the range of 0.0005-2.50 μg/L (R2=0.9989). The limit of detection (LOD) of 3-OHBaP in undiluted urine sample was 0.1 ng/L (S/N=3). The relative standard deviations (RSDs) for six replicate measurements of 3-OHBaP concentration were below 8.0%. The concentration of 3-OHBaP in urine of smoking volunteers was significantly higher than that of non-smoking volunteers. Remarkable sensitivity of urinary 3-OHBaP detection was provided by the proposed method, showing the potential application in evaluation of trace level internal dose of PAHs exposure of human beings.
Rapid and efficient strategy for detection of polycyclic aromatic hydrocarbons (PAHs) metabolites in human urine is urgently demanded in evaluation of internal exposure of PAHs. In this study, the combination of magnetic solid-phase extraction and internal extractive electrospray ionization mass spectrometry was used to rapid and high-throughput quantification of 3-hydroxybenzopyrene (3-OHBaP) in undiluted human urine samples. Polypyrrole-coated Fe3O4 magnetite (termed as Fe3O4@Ppy) was employed as the sorbent for MSPE of urinary 3-OHBaP in undiluted human urine samples, and then the material was treated as a bulk sample, which was directly analyzed by internal extractive electrospray ionization mass spectrometry (iEESI-MS). The signal intensity of m/z 239 was linearly related with 3-OHBaP concentration over the range of 0.0005-2.50 μg/L (R2=0.9989). The limit of detection (LOD) of 3-OHBaP in undiluted urine sample was 0.1 ng/L (S/N=3). The relative standard deviations (RSDs) for six replicate measurements of 3-OHBaP concentration were below 8.0%. The concentration of 3-OHBaP in urine of smoking volunteers was significantly higher than that of non-smoking volunteers. Remarkable sensitivity of urinary 3-OHBaP detection was provided by the proposed method, showing the potential application in evaluation of trace level internal dose of PAHs exposure of human beings.
