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Selected papers from the latest issue:
Detection of ketamine and its metabolites in human hair using an integrated nanoflow liquid chromatography column and electrospray emitter fritted with a single porous 10μm bead
28 January 2013,
02:18:42
15 February 2013
Publication year: 2013
Source:Journal of Chromatography A, Volume 1277
Targeting metabolites incorporated into hair following drug administration is useful for evidential purposes as this approach can aid in differentiating between administration and passive exposure. Greater analytical sensitivity is required than for targeting the parent drug alone. A 20μm i.d. fused silica capillary column with an integrated electrospray emitter fritted with a single porous 10μm polymeric bead has been successfully fabricated to facilitate this purpose. The sensitivity gains through the use of these integrated single fritted columns coupled to a nanoelectrospray source (nanoflow–LC nanoESI) over conventional liquid chromatography–tandem mass spectrometry (LC–MS/MS) columns was explored by their application to the detection of ketamine and its phase I metabolites in human hair. Hair was collected from 4 volunteers following the administration of a small oral dose of ketamine (50mg) and subsequently analysed by the capillary–LC nanoESI approach. The drug and its metabolites were extracted from hair using solid phase extraction following a methanolic wash, pulverisation with a ball mill and acid digestion. From a 50μL extract, 1μL was injected and the method provided a limit of detection estimated to be 5fg on column for ketamine and norketamine and 10fg for dehydronorketamine. The single porous frit minimises extra column band broadening and offers an alternative fritting approach which reduces the blocking of the electrospray emitter, in comparison with other approaches such as sintering and polymerisation.
Publication year: 2013
Source:Journal of Chromatography A, Volume 1277
Targeting metabolites incorporated into hair following drug administration is useful for evidential purposes as this approach can aid in differentiating between administration and passive exposure. Greater analytical sensitivity is required than for targeting the parent drug alone. A 20μm i.d. fused silica capillary column with an integrated electrospray emitter fritted with a single porous 10μm polymeric bead has been successfully fabricated to facilitate this purpose. The sensitivity gains through the use of these integrated single fritted columns coupled to a nanoelectrospray source (nanoflow–LC nanoESI) over conventional liquid chromatography–tandem mass spectrometry (LC–MS/MS) columns was explored by their application to the detection of ketamine and its phase I metabolites in human hair. Hair was collected from 4 volunteers following the administration of a small oral dose of ketamine (50mg) and subsequently analysed by the capillary–LC nanoESI approach. The drug and its metabolites were extracted from hair using solid phase extraction following a methanolic wash, pulverisation with a ball mill and acid digestion. From a 50μL extract, 1μL was injected and the method provided a limit of detection estimated to be 5fg on column for ketamine and norketamine and 10fg for dehydronorketamine. The single porous frit minimises extra column band broadening and offers an alternative fritting approach which reduces the blocking of the electrospray emitter, in comparison with other approaches such as sintering and polymerisation.
Highlights
► A 20μm i.d. capillary column with was fritted with a single 10μm porous bead. ► The column consisted of an integrated electrospray emitter. ► Dehydronorketamine was detected in hair samples for the first time.Effects of injection volume on chromatographic features and resolution in the process of counter-current chromatography
28 January 2013,
02:18:42
15 February 2013
Publication year: 2013
Source:Journal of Chromatography A, Volume 1277
Counter-current chromatography is a high efficiency separation and purification technique. As a preparative separation technique, the final goal that we are concerned about is acquisition of maximum yields of the separated compounds under specific conditions. In this paper, the theory of counter current extraction table (TCCET), a numerical model for counter-current chromatography, was employed firstly to investigate the effects of injection volume on chromatographic features (retention time, peak height and peak width) and resolution between the separated compounds from theoretical point of view. Moreover, a series of experiments were performed to evaluate the effectiveness of the TCCET model when used for analysis of the influences of the injection volume on a counter-current chromatography separation process. Both the theoretical analysis and experiments show that: (1) the retention time or retention volume increases with the injection volume linearly; (2) the peak height increases with increase of the injection volume, and when the injection volume is smaller than ten percent of V m (volume occupied by mobile phase in a CCC column), the relationship between the peak height and the injection volume is a kind of linear relationship; and (3) the peak width also increases with increase of the injection volume, and obvious linear relationship between the peak width and the injection volume can be observed when the injection volume is smaller than a certain volume. In contrast, the resolution between the separated compounds decreases with increase of the injection volume.
Publication year: 2013
Source:Journal of Chromatography A, Volume 1277
Counter-current chromatography is a high efficiency separation and purification technique. As a preparative separation technique, the final goal that we are concerned about is acquisition of maximum yields of the separated compounds under specific conditions. In this paper, the theory of counter current extraction table (TCCET), a numerical model for counter-current chromatography, was employed firstly to investigate the effects of injection volume on chromatographic features (retention time, peak height and peak width) and resolution between the separated compounds from theoretical point of view. Moreover, a series of experiments were performed to evaluate the effectiveness of the TCCET model when used for analysis of the influences of the injection volume on a counter-current chromatography separation process. Both the theoretical analysis and experiments show that: (1) the retention time or retention volume increases with the injection volume linearly; (2) the peak height increases with increase of the injection volume, and when the injection volume is smaller than ten percent of V m (volume occupied by mobile phase in a CCC column), the relationship between the peak height and the injection volume is a kind of linear relationship; and (3) the peak width also increases with increase of the injection volume, and obvious linear relationship between the peak width and the injection volume can be observed when the injection volume is smaller than a certain volume. In contrast, the resolution between the separated compounds decreases with increase of the injection volume.
Highlights
► TCCET model was used to investigate the effects of injection volume on CCC separation. ► The relationship between chromatographic features and injection volume was studied. ► Retention time, peak height and width change with the variation of injection volume. ► The resolution of separated compounds decreases with increase of injection volume. ► The injection volume has significant effects on chromatographic features.An improved approach to hydrophilic interaction chromatography of peptides: Salt gradients in the presence of high isocratic acetonitrile concentrations
28 January 2013,
02:18:42
15 February 2013
Publication year: 2013
Source:Journal of Chromatography A, Volume 1277
Hydrophilic interaction chromatography (HILIC) for separations of peptides has been employed infrequently, particularly considering that this technique was introduced over 20years ago. The present manuscript describes a radical departure from the traditional HILIC elution approach, where separations are achieved via increasing salt (sodium perchlorate) gradients in the presence of high isocratic concentrations (>80%) of acetonitrile, denoted HILIC/SALT. This initial study compared to reversed-phase chromatography (RPC), HILIC and HILIC/SALT for the separation of mixtures of synthetic peptide standards varying in structure (amphipathic α-helix, random coil), length (10–26 residues), number of positively charged residues (+1 to +11) and hydrophilicity/hydrophobicity. Results showed a marked superiority of the HILIC/SALT approach compared to traditional HILIC and excellent complementarity to RPC for peptide separations. We believe these initial results offer a new dimension to HILIC, enabling it to transform from an occasional HPLC approach for peptide separations to a more generally applicable method.
Publication year: 2013
Source:Journal of Chromatography A, Volume 1277
Hydrophilic interaction chromatography (HILIC) for separations of peptides has been employed infrequently, particularly considering that this technique was introduced over 20years ago. The present manuscript describes a radical departure from the traditional HILIC elution approach, where separations are achieved via increasing salt (sodium perchlorate) gradients in the presence of high isocratic concentrations (>80%) of acetonitrile, denoted HILIC/SALT. This initial study compared to reversed-phase chromatography (RPC), HILIC and HILIC/SALT for the separation of mixtures of synthetic peptide standards varying in structure (amphipathic α-helix, random coil), length (10–26 residues), number of positively charged residues (+1 to +11) and hydrophilicity/hydrophobicity. Results showed a marked superiority of the HILIC/SALT approach compared to traditional HILIC and excellent complementarity to RPC for peptide separations. We believe these initial results offer a new dimension to HILIC, enabling it to transform from an occasional HPLC approach for peptide separations to a more generally applicable method.
Highlights
► We describe a radical departure from traditional HILIC of peptides. ► Elution is by a salt gradient in the presence of a high acetonitrile concentration. ► This HILIC/SALT method is superior to HILIC and complements RPC for peptides. ► Our results offer a new dimension to HILIC as a mainstream peptide analytical tool.Optimized chromatographic conditions for separation of halogenated acetic acids by ultra-performance liquid chromatography–electrospray ionization-mass spectrometry
28 January 2013,
02:18:42
15 February 2013
Publication year: 2013
Source:Journal of Chromatography A, Volume 1277
Emerging halogenated acetic acids (HAAs), especially mixed halogenated acids such as chlorobromo-, chloroiodo- and bromoiodo-acetic acids, are unregulated disinfection by-products in drinking water. Because these compounds are hydrophilic and strongly acidic, they are difficult to detect at trace levels using approved analytical methods. In the present study, 13 HAAs were effectively separated on three ultra-performance liquid chromatography columns. The effects of changing in the aqueous mobile phase, acidic solutions and cationic volatile ion pair reagents were investigated. The samples were pretreated by filtration, and extraction, while derivatization and concentration procedures were not required. The limits of quantitation for regulated HAAs were between 0.5μg/L and 1.7μg/L and for unregulated HAAs were 1.2 and 5.8μg/L, especially for the iodinated acetic acids were 1.5 and 2.1μg/L. The method was applied to two finished water samples collected in China (Shanghai and Xuzhou) from water treatment plants that use chlorine for disinfection. Multiple unregulated HAAs were found in the two samples, but iodoacids were only detected in the water sample from Shanghai, which could be attributed to the characteristics of the source water. The presence of unregulated HAAs, especially mixed bromo- and iodoacetic acids, in the finished water samples could affect human health, and this warrants further investigation.
Publication year: 2013
Source:Journal of Chromatography A, Volume 1277
Emerging halogenated acetic acids (HAAs), especially mixed halogenated acids such as chlorobromo-, chloroiodo- and bromoiodo-acetic acids, are unregulated disinfection by-products in drinking water. Because these compounds are hydrophilic and strongly acidic, they are difficult to detect at trace levels using approved analytical methods. In the present study, 13 HAAs were effectively separated on three ultra-performance liquid chromatography columns. The effects of changing in the aqueous mobile phase, acidic solutions and cationic volatile ion pair reagents were investigated. The samples were pretreated by filtration, and extraction, while derivatization and concentration procedures were not required. The limits of quantitation for regulated HAAs were between 0.5μg/L and 1.7μg/L and for unregulated HAAs were 1.2 and 5.8μg/L, especially for the iodinated acetic acids were 1.5 and 2.1μg/L. The method was applied to two finished water samples collected in China (Shanghai and Xuzhou) from water treatment plants that use chlorine for disinfection. Multiple unregulated HAAs were found in the two samples, but iodoacids were only detected in the water sample from Shanghai, which could be attributed to the characteristics of the source water. The presence of unregulated HAAs, especially mixed bromo- and iodoacetic acids, in the finished water samples could affect human health, and this warrants further investigation.
Highlights
► Parameters for the separation of emerging halogenated acetic acids are optimized. ► Separation depends on the acid and volatile ion pair reagent in the mobile phase. ► Tandem mass spectrometry has good sensitivity for unregulated halogenated acids. ► Unregulated bromo- and iodoacetic acids are present in drinking water.Development of isotope dilution-liquid chromatography tandem mass spectrometry for the accurate determination of fluoroquinolones in animal meat products: Optimization of chromatographic separation for eliminating matrix effects on isotope ratio measurements
28 January 2013,
02:18:42
15 February 2013
Publication year: 2013
Source:Journal of Chromatography A, Volume 1277
Isotope dilution-liquid chromatography/tandem mass spectrometry (ID-LC–MS/MS) has been established as a candidate reference method for the accurate determination of three representative fluoroquinolone antibiotics (enrofloxacin, ciprofloxacin, and norfloxacin) in meat products. Enrofloxacin-d 5, ciprofloxacin-13C3 15N, and norfloxacin-d 5 were used as internal standards. After extraction and SPE clean-up, samples were analyzed by using LC–MS/MS in positive ion mode. We observed that the deuterium-labeled internal standards have slightly different LC retention time from their native analogues, which reduces the benefits of using isotope dilution techniques as ion suppression/enhancement effects caused by co-eluting matrix interferences are not completely compensated. In this study, LC conditions were optimized to minimize matrix effects causing different ionization efficiency between the target analytes and their isotope analogues by separating them from significant matrix interferences. The analytical method was validated by measuring samples (chicken breast, bovine muscle, and porcine muscle) gravimetrically fortified in various levels with the target analytes. The method provided accurate analytical results of the target analytes in the range of 5–50μg/kg with the relative expanded uncertainty of 1–5%.
Publication year: 2013
Source:Journal of Chromatography A, Volume 1277
Isotope dilution-liquid chromatography/tandem mass spectrometry (ID-LC–MS/MS) has been established as a candidate reference method for the accurate determination of three representative fluoroquinolone antibiotics (enrofloxacin, ciprofloxacin, and norfloxacin) in meat products. Enrofloxacin-d 5, ciprofloxacin-13C3 15N, and norfloxacin-d 5 were used as internal standards. After extraction and SPE clean-up, samples were analyzed by using LC–MS/MS in positive ion mode. We observed that the deuterium-labeled internal standards have slightly different LC retention time from their native analogues, which reduces the benefits of using isotope dilution techniques as ion suppression/enhancement effects caused by co-eluting matrix interferences are not completely compensated. In this study, LC conditions were optimized to minimize matrix effects causing different ionization efficiency between the target analytes and their isotope analogues by separating them from significant matrix interferences. The analytical method was validated by measuring samples (chicken breast, bovine muscle, and porcine muscle) gravimetrically fortified in various levels with the target analytes. The method provided accurate analytical results of the target analytes in the range of 5–50μg/kg with the relative expanded uncertainty of 1–5%.
Highlights
► Development of ID-LC/MS/MS method for the analysis of fluoroquinolones in meat. ► Slight separation of deuterated internal standards from their target analytes by LC. ► The R.T. difference causes bias in isotope ratio measurement due to matrix effects. ► LC conditions were optimized to get rid of biases from matrix effects in ID-LC/MS/MS. ► Method was validated for samples of bovine and porcine muscles, and chicken breast.Evaluation of a liquid chromatography method for quality control of methylated cyclodextrins
28 January 2013,
02:18:42
15 February 2013
Publication year: 2013
Source:Journal of Chromatography A, Volume 1277
Halo C18 column (fused core particles) and Chromolith RP18 column (monolith) were evaluated in liquid chromatography in order to analyze methylated-β-cyclodextrins (Me-β-CD) with various degrees of substitution, DS such as the number of methyl groups per cyclodextrin ring. Chromolith RP18 enables a performing analysis of Me-β-CD with low DS but is not suitable for dimethyl-β-cyclodextrins (DM-β-CD). On the other hand, Halo C18 column allows an improved fingerprint of CDs having a DS from 4.9 up to a value major than 14 and avoiding the use of various chromatographic systems. Thus, liquid chromatography performed with this column and an evaporative light scattering detector can be used as a generic system for methylated CD analysis. Moreover, fused core particles of Halo C18 column enables a rapid analysis and liquid chromatography coupled with electrospray-mass spectrometry appears as a powerful tool to determine co-elution and to characterize various isomers of complex methylated-β-cyclodextrin mixtures.
Publication year: 2013
Source:Journal of Chromatography A, Volume 1277
Halo C18 column (fused core particles) and Chromolith RP18 column (monolith) were evaluated in liquid chromatography in order to analyze methylated-β-cyclodextrins (Me-β-CD) with various degrees of substitution, DS such as the number of methyl groups per cyclodextrin ring. Chromolith RP18 enables a performing analysis of Me-β-CD with low DS but is not suitable for dimethyl-β-cyclodextrins (DM-β-CD). On the other hand, Halo C18 column allows an improved fingerprint of CDs having a DS from 4.9 up to a value major than 14 and avoiding the use of various chromatographic systems. Thus, liquid chromatography performed with this column and an evaporative light scattering detector can be used as a generic system for methylated CD analysis. Moreover, fused core particles of Halo C18 column enables a rapid analysis and liquid chromatography coupled with electrospray-mass spectrometry appears as a powerful tool to determine co-elution and to characterize various isomers of complex methylated-β-cyclodextrin mixtures.
Highlights
► Halo C18 and Chromolith RP18 columns were evaluated to analyze methylated CDs by LC. ► Halo C18 column is suitable for rapid LC analysis of various CDs. ► LC-ELSD with this column was proposed as a generic system for CD analysis.Improving performance of a tandem simulated moving bed process for sugar separation by making a difference in the adsorbents and the column lengths of the two subordinate simulated moving bed units
28 January 2013,
02:18:42
15 February 2013
Publication year: 2013
Source:Journal of Chromatography A, Volume 1277
A tandem simulated moving bed (SMB) process for removal of sulfuric acid and acetic acid from sugars has been developed previously. This process consisted of two four-zone SMB units (Ring I and Ring II), in which the same adsorbent (Dowex99 resin) and the same column length were used. To improve the performance of such a tandem SMB process for sugar separation, it is worth adopting the strategy of making a difference between the column lengths of Ring I and Ring II. The results showed that such strategy could allow the adsorbent beds of both Ring I and Ring II to be fully utilized at the same time, which was impracticable in the previous tandem SMB mode. As a result, the tandem SMB based on such strategy could achieve higher productivity than the previous tandem SMB mode. In addition, the use of different adsorbents (Amberchrom-CG161C in Ring I and Dowex99 in Ring II) was proposed as the second strategy, which was confirmed to be highly effective in improving the productivity of the tandem SMB for sugar separation. Finally, a third strategy was proposed by combing the first and the second strategies. It was found that compared to the previous tandem SMB mode, the third strategy led to more than eleven times the productivity under the constraint of pressure drop ≤100psi. This was mostly because the third strategy had a remarkable advantage over the previous tandem SMB mode in the aspects of bed utilization and selectivities, which stemmed from the use of different column lengths and the use of different adsorbents respectively.
Publication year: 2013
Source:Journal of Chromatography A, Volume 1277
A tandem simulated moving bed (SMB) process for removal of sulfuric acid and acetic acid from sugars has been developed previously. This process consisted of two four-zone SMB units (Ring I and Ring II), in which the same adsorbent (Dowex99 resin) and the same column length were used. To improve the performance of such a tandem SMB process for sugar separation, it is worth adopting the strategy of making a difference between the column lengths of Ring I and Ring II. The results showed that such strategy could allow the adsorbent beds of both Ring I and Ring II to be fully utilized at the same time, which was impracticable in the previous tandem SMB mode. As a result, the tandem SMB based on such strategy could achieve higher productivity than the previous tandem SMB mode. In addition, the use of different adsorbents (Amberchrom-CG161C in Ring I and Dowex99 in Ring II) was proposed as the second strategy, which was confirmed to be highly effective in improving the productivity of the tandem SMB for sugar separation. Finally, a third strategy was proposed by combing the first and the second strategies. It was found that compared to the previous tandem SMB mode, the third strategy led to more than eleven times the productivity under the constraint of pressure drop ≤100psi. This was mostly because the third strategy had a remarkable advantage over the previous tandem SMB mode in the aspects of bed utilization and selectivities, which stemmed from the use of different column lengths and the use of different adsorbents respectively.
Highlights
► Strategy of improving the tandem SMB performance for sugar separation was proposed. ► It was to make a difference in the adsorbents and column lengths of the 2 sub-SMBs. ► The Amberchrom-CG161C and Dowex99 adsorbents were used in the 1st and 2nd sub-SMBs. ► The strategy was highly effective in improving the productivity of the tandem SMB. ► The strategy had a clear advantage in term of bed utilization and selectivities.Microcalorimetric study of the adsorption of native and mono-PEGylated bovine serum albumin on anion-exchangers
28 January 2013,
02:18:42
15 February 2013
Publication year: 2013
Source:Journal of Chromatography A, Volume 1277
The adsorption of native bovine serum albumin (BSA) and 12kDa-PEG-BSA on 12 different commercially available strong and weak anion-exchange resins is studied at 25°C and pH 7. The resins differ in their base matrix material, their functional groups and the type of polymer modification. A combination of equilibrium measurements and microcalorimetric experiments is used to determine the specific enthalpy of adsorption of the proteins. From these data, the entropic contributions to the specific Gibbs energy of adsorption are determined. The results strongly differ for different resins. They also depend on the loadings. The adsorption of BSA on strong (Q) anion-exchangers is exothermic and enthalpy-driven. The adsorption of BSA on weak (DEAE) anion-exchangers is endothermic and entropy-driven. The adsorption of PEG-BSA on strong (Q) anion-exchangers is exothermic or endothermic, depending on the resin, while the adsorption of PEG-BSA on weak (DEAE) anion-exchangers is exothermic for all studied resins. The present study provides a large body of new experimental data that contribute to the understanding of the nature of protein adsorption on ion exchange resins and the influence of the resin properties and polymer modification of the proteins on this process.
Publication year: 2013
Source:Journal of Chromatography A, Volume 1277
The adsorption of native bovine serum albumin (BSA) and 12kDa-PEG-BSA on 12 different commercially available strong and weak anion-exchange resins is studied at 25°C and pH 7. The resins differ in their base matrix material, their functional groups and the type of polymer modification. A combination of equilibrium measurements and microcalorimetric experiments is used to determine the specific enthalpy of adsorption of the proteins. From these data, the entropic contributions to the specific Gibbs energy of adsorption are determined. The results strongly differ for different resins. They also depend on the loadings. The adsorption of BSA on strong (Q) anion-exchangers is exothermic and enthalpy-driven. The adsorption of BSA on weak (DEAE) anion-exchangers is endothermic and entropy-driven. The adsorption of PEG-BSA on strong (Q) anion-exchangers is exothermic or endothermic, depending on the resin, while the adsorption of PEG-BSA on weak (DEAE) anion-exchangers is exothermic for all studied resins. The present study provides a large body of new experimental data that contribute to the understanding of the nature of protein adsorption on ion exchange resins and the influence of the resin properties and polymer modification of the proteins on this process.
Highlights
► Adsorption equilibrium and thermodynamics of native BSA and PEGylated BSA on different anion-exchangers. ► Adsorption can be endo- or exothermic and driven by entropic contributions. ► Thermodynamics of adsorption highly depends on structure and properties of resin. ► Influence of PEG not predictable. Depends on resin properties.Impurity analysis of pure aldrin using heart-cut multi-dimensional gas chromatography–mass spectrometry
28 January 2013,
02:18:42
15 February 2013
Publication year: 2013
Source:Journal of Chromatography A, Volume 1277
Identification and quantification of related-structure impurity is a research focus in the purity assessment of organic compounds. Determination of the purity value and uncertainty assessment are also important in the metrological research. A method for the determination of related-structure impurity in pure aldrin sample has been developed by using heart-cut multi-dimensional gas chromatography–mass spectrometry (MDGC/MS). Compared to the traditional one-dimensional (1-D) GC system, the two separated columns in the MDGC/MS system can effectively reduce co-elution, enhance separation capability, and thus improve detectability of the trace-level impurities. In addition, MDGC/MS system was simultaneously equipped with flame ionization detector (FID) or electron capture detector (ECD) in the first GC unit and mass spectrometry (MS) detector in the second GC unit. Therefore, accurate quantitative results of the trace-level impurities can be easily achieved by isolation of principal component to the second dimension column using “heart-cut” process. The mass fraction of related-structure impurities in aldrin samples obtained using MDGC/MS system ranged from 6.8×10−3 mgg−1 to 26.47mgg−1 with five orders of magnitude, which is hard to be realized by mean of the 1-D GC. Excellent linearity with correlation coefficients of above 0.999 was achieved for each impurity analysis over a wide range of concentrations. Limits of quantification (LOQ) varied from 250ngg−1 to 330ngg−1 for FID, and from 1.0ngg−1 to 2.0ngg−1 detected by ECD. The combined standard uncertainty (u c) was lower than 0.37mgg−1 and 0.040mgg−1 detected using FID and ECD, respectively. Therefore, performance characterization of MDGC/MS used in the study is fit for quantification analysis of trace-level impurity. These results demonstrate that the MDGC/MS is extremely suitable for the purity assessment of organic compounds with medium structural complexity and low polarity.
Publication year: 2013
Source:Journal of Chromatography A, Volume 1277
Identification and quantification of related-structure impurity is a research focus in the purity assessment of organic compounds. Determination of the purity value and uncertainty assessment are also important in the metrological research. A method for the determination of related-structure impurity in pure aldrin sample has been developed by using heart-cut multi-dimensional gas chromatography–mass spectrometry (MDGC/MS). Compared to the traditional one-dimensional (1-D) GC system, the two separated columns in the MDGC/MS system can effectively reduce co-elution, enhance separation capability, and thus improve detectability of the trace-level impurities. In addition, MDGC/MS system was simultaneously equipped with flame ionization detector (FID) or electron capture detector (ECD) in the first GC unit and mass spectrometry (MS) detector in the second GC unit. Therefore, accurate quantitative results of the trace-level impurities can be easily achieved by isolation of principal component to the second dimension column using “heart-cut” process. The mass fraction of related-structure impurities in aldrin samples obtained using MDGC/MS system ranged from 6.8×10−3 mgg−1 to 26.47mgg−1 with five orders of magnitude, which is hard to be realized by mean of the 1-D GC. Excellent linearity with correlation coefficients of above 0.999 was achieved for each impurity analysis over a wide range of concentrations. Limits of quantification (LOQ) varied from 250ngg−1 to 330ngg−1 for FID, and from 1.0ngg−1 to 2.0ngg−1 detected by ECD. The combined standard uncertainty (u c) was lower than 0.37mgg−1 and 0.040mgg−1 detected using FID and ECD, respectively. Therefore, performance characterization of MDGC/MS used in the study is fit for quantification analysis of trace-level impurity. These results demonstrate that the MDGC/MS is extremely suitable for the purity assessment of organic compounds with medium structural complexity and low polarity.
Highlights
► Application of heart-cut multi-dimensional gas chromatography-mass spectrometry. ► Method for determination of related-structure impurity in aldrin sample has been developed. ► Separation and qualitative analysis could be fulfilled in a simple cycle. ► Accurate quantitative results of trace-level impurities can be easily achieved. ► The method is fit for compounds with medium structural complexity and low polarity.Prediction of retention times in temperature programmed gas chromatography using the retention equation derived from crystallization behavior of polymer
28 January 2013,
02:18:42
15 February 2013
Publication year: 2013
Source:Journal of Chromatography A, Volume 1277
Based on the enlightenment from the crystallization behavior of polymer, a novel retention equation constructed with only three pairs of isothermal retention data was proposed to predict retention times in temperature programmed gas chromatography (TPGC). The new retention equation worked beautifully in both the single- and the multiple-ramp temperature-programmed modes, yielding the average absolute relative errors of 0.65% for single-ramp TPGC across all the 18 analytes in 3 temperature programmed experiments and 0.30% for multiple-ramp TPGC across all the 8 analytes in 6 temperature programmed experiments tested in this work. Moreover, to compare with the new retention equation systematically and thoroughly, another 13 retention equations determined by two or three parameters were derived from a universal formula ln k = a 0 + a 1/T + a 2/T 2 + a 3 ln T + a 4 T + a 5 T 2 as a combination of the relationships between ln k and T with reference to four widely used retention equations in publications. Calculated by these 14 retention equations with the same experimental data, the absolute relative errors of prediction retention times for single-ramp TPGC mode were compared by means of statistical analysis. At a very high significance level of 1%, statistical evidences of paired t-test strictly implied that the new retention equation yielded the best prediction results among all of the 14 retention equations. In addition, remarkably, among the 13 retention equations, three seldom used in publications retention equations also worked nicely, yielding satisfactory average absolute relative errors of 0.78%, 0.81% and 0.84% for single-ramp TPGC.
Publication year: 2013
Source:Journal of Chromatography A, Volume 1277
Based on the enlightenment from the crystallization behavior of polymer, a novel retention equation constructed with only three pairs of isothermal retention data was proposed to predict retention times in temperature programmed gas chromatography (TPGC). The new retention equation worked beautifully in both the single- and the multiple-ramp temperature-programmed modes, yielding the average absolute relative errors of 0.65% for single-ramp TPGC across all the 18 analytes in 3 temperature programmed experiments and 0.30% for multiple-ramp TPGC across all the 8 analytes in 6 temperature programmed experiments tested in this work. Moreover, to compare with the new retention equation systematically and thoroughly, another 13 retention equations determined by two or three parameters were derived from a universal formula ln k = a 0 + a 1/T + a 2/T 2 + a 3 ln T + a 4 T + a 5 T 2 as a combination of the relationships between ln k and T with reference to four widely used retention equations in publications. Calculated by these 14 retention equations with the same experimental data, the absolute relative errors of prediction retention times for single-ramp TPGC mode were compared by means of statistical analysis. At a very high significance level of 1%, statistical evidences of paired t-test strictly implied that the new retention equation yielded the best prediction results among all of the 14 retention equations. In addition, remarkably, among the 13 retention equations, three seldom used in publications retention equations also worked nicely, yielding satisfactory average absolute relative errors of 0.78%, 0.81% and 0.84% for single-ramp TPGC.
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