Simultaneous determination of low-molecular-weight organic acids and chlorinated acid herbicides in environmental water by a portable CE system with contactless conductivity detection

This report describes a method to simultaneously determine 11 low-molecular-weight (LMW) organic acids and 16 chlorinated acid herbicides within a single run by a portable CE system with contactless conductivity detection (CCD) in a poly(vinyl alcohol) (PVA)-coated capillary. Under the optimized condition, the LODs of CE-CCD ranged from 0.056 to 0.270 ppm, which were better than for indirect UV (IUV) detection of the 11 LMW organic acids or UV detection of the 16 chlorinated acid herbicides. Combined with an on-line field-amplified sample stacking (FASS) procedure, sensitivity enhancement of 632- to 1078-fold was achieved, with satisfactory reproducibility (RSDs of migration times less than 2.2%, and RSDs of peak areas less than 5.1%). The FASS-CE-CCD method was successfully applied to determine the two groups of acidic pollutants in two kinds of environmental water samples. The portable CE-CCD system shows advantages such as simplicity, cost effectiveness, and miniaturization. Therefore, the method presented in this report has great potential for onsite analysis of various pollutants at the trace level.     

Quantification of low molecular weight fatty acids in cave drip water and speleothems using HPLC-ESI-IT/MS — development and validation of a selective method

This study presents a novel method for the analysis of low molecular weight (LMW) fatty acids in cave drip water and speleothems. The method development included optimization of sample preparation procedures, e.g., blank reduction, solid phase extraction, concentration of extracts as well as liquid chromatography coupled to electrospray ion-trap mass spectrometry (HPLC-ESI-IT/MS) measurement parameters. Retention times for five analytes (lauric acid, myristic acid, palmitic acid, stearic acid and arachidic acid) were between 5 and 13.5 min. Spiking experiments were performed to accomplish external calibrations which ranged from 12.5 to 75 ng per spiked water sample. The correlation coefficient ranged from 0.9558 to 0.9989. Inter-batch precision, expressed as the relative standard deviation of three replicates, was <7 %. Limits of detection ranged from 0.77 to 55.97 ng for the diverse analytes; obtained recoveries varied from 30 to 103 %. For a first application, cave drip water and stalagmite samples from Herbstlabyrinth-Adventhöhle cave system were analyzed. Concentrations ranged from 38.37 to 9,982.54 ng L^?1 for water samples and 2.52 to 1,344.96 ng g^?1 for the stalagmite. Thereby, the different fatty acids showed a distinctive variation. Whereas shorter-chained fatty acids exhibited similarities, arachidic acid showed opposite trends. Diverse correlations were found, which could improve the understanding of different organic sources of the lipids transported by drip water and preserved in speleothems. This new method provides a more selective extraction process, particularly adjusted to LMW fatty acids and therefore reduces the required sample size. Furthermore, it is applicable to stalagmite as well as cave drip water samples.     

Analysis of therapeutic peptides in human urine by combination of capillary zone electrophoresis-electrospray mass spectrometry with preparative capillary isotachophoresis sample pretreatment

The presented study deals with the off-line coupling of preparative isotachophoresis (pITP) with on-line combination of capillary zone electrophoresis with electrospray mass spectrometric detection (CZE-ESI-MS) used for the analysis of therapeutic peptides (anserine, carnosine, and buserelin) in complex matrix (urine). Preparative capillary isotachophoresis, operating in a discontinuous fractionation mode in column-coupling configuration, served as a sample pretreatment technique to separation, and fractionation of mixture of therapeutic peptides present in urine at low concentration level. The fractions isolated by pITP procedure were subsequently analyzed by capillary zone electrophoresis with electrospray mass spectrometric detection. Acetic acid at 200 mmol L(-1) concentration served as background electrolyte in CZE stage and it is compatible with MS detection in positive ionization mode. In pITP fractionation procedure, sodium cation (10 mmol L(-1) concentration) as leading ion and beta-alanine as terminating ion (20 mmol L(-1) concentration) were used. While using CZE-ESI-MS, the limits of detection were 0.18 μg mL(-1) for carnosine, 0.17 μg mL(-1) for anserine and 0.64 μg mL(-1) for buserelin in water and 0.19 μg mL(-1) for carnosine, 0.50 μg mL(-1) for anserine and 0.74 μg mL(-1) for buserelin in 10 times diluted urine, respectively. The cleaning power of pITP sample pretreatment was proved as the peptides provided the higher MS signals at lower concentration levels resulting from the minimized matrix effects. The quality of obtained MS/MS spectra was very good so that they can provide information about the structure of analytes, and they were used for verification of the analytes identities. The pITP pretreatment improved the detection limits of the analyzed therapeutic peptides at least 25 times compared to the CZE-ESI-MS itself.     

Gold nanoparticle-enhanced target (AuNPET) as universal solution for laser desorption/ionization mass spectrometry analysis and imaging of low molecular weight compounds

Preparation is described of a durable surface of cationic gold nanoparticles (AuNPs), covering commercial and custom-made MALDI targets, along with characterization of the nanoparticle surface properties and examples of the use in MS analyses and MS imaging (IMS) of low molecular weight (LMW) organic compounds. Tested compounds include nucleosides, saccharides, amino acids, glycosides, and nucleic bases for MS measurements, as well as over one hundred endogenous compounds in imaging experiment. The nanoparticles covering target plate were enriched in sodium in order to promote sodium-adduct formation. The new surface allows fast analysis, high sensitivity of detection and high mass determination accuracy. Example of application of new Au nanoparticle-enhanced target for fast and simple MS imaging of a fingerprint is also presented.     

Determination of haloacetic acids by the combination of non-aqueous capillary electrophoresis and mass spectrometry

The applicability of capillary electrophoresis (CE) in combination with atmospheric pressure ionization mass spectrometry (API-MS) is demonstrated for the determination of organic acids and in particular for haloacetic acids. CE-conditions, sheath flow and MS-parameters were optimized with respect to the separation of the analytes and mass spectrometric sensitivity. CE/MS turned out to be an attractive alternative for the determination of haloacetic acids to existing methods based on GC-ECD. Employing CE/MS derivatization is not necessary which saves time and avoids possible sources of errors. In the present work the sample pre-treatment is performed by liquid-liquid extraction using methyl tert.-butyl ether as the extraction solvent. The organic phase is brought to dryness in a stream of nitrogen gas and the residue is dissolved in methanol and analyzed by CE/MS using a mixture of 2-propanol/water 80?:?20 containing triethylamine as the sheath liquid in the interface. Best results for the separation of all nine possible bromo- and chloroacetic acids together with two internal standards are obtained with a carrier electrolyte consisting of ammonium acetate/acetic acid in methanol; to resolve the strongly acidic trihaloacetic acids as well as the less acidic monohaloacetic acids, a careful optimization of the acetic acid content is necessary. The method was applied to the determination of haloacetic acids in real water samples. With optimized CE and MS conditions detection limits between 0.3 and 7.6 μg/L in the original water samples were achieved, employing a sample volume of 30 mL.     

Analysis of low molecular mass organic acids in natural waters by ion exclusion chromatography tandem mass spectrometry

A sensitive and selective method for the analysis of aliphatic low molecular mass organic acids (LMMOAs) in natural waters is presented. The method is based on separation with ion exclusion chromatography and detection with electrospray ionization tandem mass spectrometry (LC-MS/MS). The extra selectivity gained by applying MS/MS allows for a minimum of sample preparation and the use of a sub-optimal mobile phase regarding chromatographic resolution. Instead the mobile phase, comprising aqueous formic acid with methanol as organic modifier, was mainly optimized for maximum sensitivity and long term MS stability. Detection limits for malonic, fumaric, maleic, succinic, citraconic, glutaric, malic, alpha-ketoglutaric, tartaric, shikimic, trans-aconitic, cis-aconitic, isocitric and citric acid were in the range 1-50 nM, while the detection limits for pyruvic, oxalic and lactic acid were around 250 nM for an injection volume of 100 microL. Due to their metal-chelating properties, these LMMOAs are all considered to affect the bioavailability of metals and to be involved in soil forming processes. It is thus of interest to be able to monitor their presence in natural waters, and the method developed within this work was successfully applied for the analysis of LMMOAs in soil solution and stream water samples.     

Development of capillary zone electrophoresis-electrospray ionization-mass spectrometry for the determination of lamotrigine in human plasma

A method of coupling capillary zone electrophoresis (CZE) with electrospray ionization-mass spectrometry (ESI-MS) detection has been developed for monitoring an antiepileptic drug, lamotrigine (LTG) in human plasma. The CZE-MS was developed in three stages: (i) CZE separation and ESI-MS detection of LTG and tyramine (TRM, internal standard) were simultaneously optimized by studying the influence of CZE background electrolyte (BGE) pH, BGE ionic strength, and nebulizer pressure of the MS sprayer; (ii) sheath liquid parameters, such as pH, ionic strength, organic modifier content, and flow rate of the sheath liquid, were systematically varied under optimum CZE-MS conditions developed in the first stage; (iii) MS sprayer chamber parameters (drying gas temperature and drying gas flow rate) were varied for the best MS detection of LTG. The developed assay was finally applied for the determination of LTG in plasma samples. The linear range of LTG in plasma sample assay was between 0.1-5.0 microg/mL with a limit of detection as low as 0.05 microg/mL and run time less than 6 min. Finally, the concentration-time profile of LTG in human plasma sample was found to correlate well when CZE-ESI-MS was compared to a more established method of high-performance liquid chromatography with ultraviolet detection.     

Determination of haloacetic acids by the combination of non-aqueous capillary electrophoresis and mass spectrometry

The applicability of capillary electrophoresis (CE) in combination with atmospheric pressure ionization mass spectrometry (API-MS) is demonstrated for the determination of organic acids and in particular for haloacetic acids. CE-conditions, sheath flow and MS-parameters were optimized with respect to the separation of the analytes and mass spectrometric sensitivity. CE/MS turned out to be an attractive alternative for the determination of haloacetic acids to existing methods based on GC-ECD. Employing CE/MS derivatization is not necessary which saves time and avoids possible sources of errors. In the present work the sample pre-treatment is performed by liquid-liquid extraction using methyl tert.-butyl ether as the extraction solvent. The organic phase is brought to dryness in a stream of nitrogen gas and the residue is dissolved in methanol and analyzed by CE/MS using a mixture of 2-propanol/water 80 : 20 containing triethylamine as the sheath liquid in the interface. Best results for the separation of all nine possible bromo- and chloroacetic acids together with two internal standards are obtained with a carrier electrolyte consisting of ammonium acetate/acetic acid in methanol; to resolve the strongly acidic trihaloacetic acids as well as the less acidic monohaloacetic acids, a careful optimization of the acetic acid content is necessary. The method was applied to the determination of haloacetic acids in real water samples. With optimized CE and MS conditions detection limits between 0.3 and 7.6 μg/L in the original water samples were achieved, employing a sample volume of 30 mL. Received: 4 May 1999 / Revised: 9 June 1999 / Accepted: 12 June 1999     

Determination of some acidic drugs in surface and sewage treatment plant waters by capillary electrophoresis-electrospray ionization-mass spectrometry

We describe an analytical method involving solid-phase extraction (SPE) and capillary zone electrophoresis-electrospray ionization-mass spectrometry (CZE-ESI-MS) for determining some pharmaceutical compounds - naproxen, clofibric acid and bezafibrate - in real water samples. The electrospray parameters were optimized to maximize sensitivity. When a mixed aqueous-organic solvent and CZE-ESI-MS were used to analyze these drugs in water samples, the capillary was coated with hexadimethrin bromide (HDB) to permanently reverse the EOF. The method was developed from off-line SPE-CZE-MS and was validated with surface water. The detection limits were 100 ng.L(-1) for all analytes. The method was applied to analyze water samples from the influent and effluent of a sewage treatment plant. A liquid-liquid extraction step was required before SPE, and the compounds studied were found, some of them between detection and quantification limits.     

Development of a capillary electrophoresis-mass spectrometry method for the determination of rivastigmine in human plasma--optimization of the limits of detection and quantitation

A capillary zone electrophoresis-electrospray ionization-mass spectrometry (CZE-ESI-MS) method was developed for the analysis of the acetylcholinesterase inhibitor rivastigmine. Several electrophoretic and ESI-MS parameters were investigated in order to improve sensitivity. These parameters were categorized in three areas: (i) background electrolyte (BGE) parameters, (ii) sheath liquid parameters, and (iii) spray chamber parameters. The optimized results were obtained by using 40-mM ammonium acetate at pH 9 as BGE, a sheath liquid of 1% acetic acid in water:MeOH (50:50 v/v) at a flow rate of 10?μL/min, and a drying gas flow rate that was set at 6 L/min and at a temperature of 200°C. These parameters provided limit of detection and limit of quantitation of 2.8?ng/mL and 8.4?ng/mL, respectively. The optimal CZE-ESI-MS conditions were applied to a plasma sample obtained from an Alzheimer's disease patient following rivastigmine patch administration, and the mean (±standard deviation) plasma concentration was estimated to be 14.6 (±1.7)?ng/mL. Several sample preparation procedures were examined, and solid-phase extraction using a C18 cartridge proved to be the most effective procedure, since higher sensitivity and recovery were obtained. In addition, precision was evaluated based on migration time and peak area in plasma, and the relative standard deviations were in the range of 0.10-0.16% and 0.62-9.0%, respectively.     

Capillary electrophoresis-electrospray ionization-mass spectrometry method to determine the phenolic fraction of extra-virgin olive oil

We describe the first analytical method involving SPE and CZE coupled to ESI-IT MS (CZE-ESI-MS) used to identify and characterize phenolic compounds in olive oil samples. The SPE, CZE and ESI-MS parameters were optimized in order to maximize the number of phenolic compounds detected and the sensitivity of their determination. To this end we have devised a detailed method to find the best conditions for CE separation and the detection by MS of the phenolic compounds present in olive oil using a methanol-water extract of Picual extra-virgin olive oil (VOO). Electrophoretic separation was carried out using an aqueous CE buffer system consisting of 60 mM NH(4)OAc at pH 9.5 with 5% of 2-propanol, a sheath liquid containing 2-propanol/water 60:40 v/v and 0.1% v/v triethylamine. This method offers to the analyst the chance to study important phenolic compounds such as phenolic alcohols (tyrosol (TY), hydroxytyrosol (HYTY) and 2-(4-hydroxyphenyl)ethyl acetate), lignans ((+)-pinoresinol and (+)-1-acetoxypinoresinol), complex phenols (ligstroside aglycon (Lig Agl), oleuropein aglycon, their respective decarboxylated derivatives and several isomeric forms of these (dialdehydic form of oleuropein aglycon, dialdehydic form of ligstroside aglycon, dialdehydic form of decarboxymethyl elenolic acid linked to HYTY, dialdehydic form of decarboxymethyl elenolic acid linked to TY) and 10-hydroxy-oleuropein aglycon) and one other phenolic compound (elenolic acid) in extra-VOO by using a simple SPE before CE-ESI-MS analysis.     

Capillary electrophoresis--electrospray ionization--mass spectrometry for the characterization of natural organic matter: an evaluation with free flow electrophoresis-off-line flow injection electrospray ionization-mass spectrometry

The separation of Suwannee River natural organic matter (NOM) with capillary zone electrophoresis hyphenated to electrospray ionization-mass spectrometry (CZE-ESI-MS) is presented. The obtained electropherograms and signal distributions are comparable to the mobility distributions obtained with more classical UV detection. A direct comparison of the results was possible with free-flow electrophoresis (FFE), which allows an upscaling of the CZE method and the analysis of the collected fractions in an off-line modus with flow-injection electrospray ionization-mass spectrometry (FI-ESI-MS). The changes of the m/z distributions with mobility are very similar with both methods and show a decrease of the m/z with increasing electrophoretic mobility in the humic hump at alkaline pH; superimposed on this hump a low-molecular-weight fraction migrates at lower mobility. The analysis of benzene carboxylic acids, glycerrhycic acid as well as oligomers of polystyrene sulfonic acid and polyacrylic acid additionally illustrates possible fragmentation, formation of adducts and multiplicity of the charges of the molecules prior to MS detection. These hardly controllable difficulties add a challenge to the interpretation of the obtained m/z distributions of NOM in terms of charge and mass distributions of molecules present in the NOM mixture.     

离子色谱-串联质谱法检测酒类产品中10种有机酸

建立了一种离子色谱-串联质谱(IC-MS/MS)测定白酒、黄酒、干红葡萄酒3种酒类样品中10种有机酸含量的方法。白酒样品氮吹后,经去离子水稀释,用IC-MS/MS分析检测;干红葡萄酒样品和黄酒样品,对比不同固相萃取小柱净化能力,最终选择石墨化炭黑固相萃取小柱进行净化,经去离子水稀释,用IC-MS/MS分析检测。选用高容量、强亲水性的Dionex IonPac^TM AS11-HC型阴离子分析柱进行分离,以淋洗液自动发生器在线产生的KOH水溶液为淋洗液,进行梯度淋洗。淋洗液经抑制器抑制后直接进入电喷雾电离串联质谱(ESI-MS/MS),采用负离子模式电离,多反应监测(MRM)模式检测,外标法定量。在该实验条件下:草酸、富马酸、马来酸、苹果酸、酒石酸、柠檬酸、奎尼酸和乌头酸在0.05~2 mg/L范围内线性关系良好;琥珀酸在0.05~5 mg/L范围内线性关系良好;乳酸在0.05~10 mg/L范围内线性关系良好(相关系数r²>0.99)。10种有机酸的检出限(S/N=3)在1.0~8.0 μg/L范围内,定量限(S/N=10)在3.5~26.5 μg/L范围内,在3个不同浓度的添加水平下,平均回收率在83.0%~112.1%之间,相对标准偏差≤9.1%,满足检测要求。该方法前处理简单,不使用有机溶剂,不需进行衍生化处理,测定快速、准确,灵敏度高,适用于3种酒类样品中10种有机酸的定量分析,为酒类食品的风味及品质测定提供方法支持。     

Microemulsion electrokinetic chromatography hyphenated to atmospheric pressure photoionization mass spectrometry

CZE is an appropriate technique for separating charged species, but lacks selectivity for neutral compounds. Alternative approaches such as microemulsion electrokinetic chromatography (MEEKC) have been developed to broaden its range of applications. Hyphenation of MEEKC with MS is an attractive perspective since it can enhance sensitivity and selectivity. The on-line coupling of MEEKC with MS, however, is not straightforward due to the low compatibility of non-volatile surfactant additives (e.g. SDS) and the commonly used API source, namely ESI. In order to hyphenate MEEKC with MS detection, the atmospheric pressure photoionization (APPI) source was investigated. Possibilities offered by the coupling of MEEKC with APPI-MS were highlighted for the complex separation of ionized and neutral compounds in both the positive and negative modes. MEEKC-APPI-MS performance, in terms of selectivity, efficiency and sensitivity was compared to CZE-ESI-MS and MEEKC-ESI-MS for the screening of doping substances (beta-blockers, central stimulants, diuretics, etc). Relevant selectivity and detectability, particularly for neutral, structurally related and isobaric compounds was demonstrated with the MEEKC-APPI-MS approach opening new avenues for CE-MS, in addition to the well-established CZE-ESI-MS technique.     

Capillary zone electrophoresis of metal-binding proteins in formic acid with UV- and mass spectrometric detection using cationic transient capillary isotachophoresis for preconcentration

A capillary zone electrophoresis (CZE) method with preceding cationic transient capillary isotachophoresis (tCITP-CZE) was developed for uncoated fused-silica capillaries to analyze metal-binding proteins (MBPs) of clinical relevance. UV detection was followed by mass spectrometry (MS). Optimization was done with model proteins of properties similar to relevant human MBPs. Using 1.0 mol x L(-1) formic acid (pH 1.78) as electrolyte resulted in up to 165000 plates m(-1) in CZE and 230000 plates m(-1) in combination with tCITP and analysis time was less than 5 min in uncoupled mode. Cationic tCITP with 125 mmol x L(-1) ammonium formate, buffered to pH 4.00, as leading electrolyte improved sample loadability considerably in comparison with sample stacking without impairing resolution. Following systematic optimization of the electrospray ionization process (ESI) the coupled system ((tCITP)-CZE-UV-ESI-MS) was tested with protein model mixtures and human MBPs. Repeatability of migration times was < 0.64% in pure CZE mode and in tCITP-CZE mode and < 0.83% in CZE-ESI-MS coupled mode. Mass accuracy was < 0.015%. Limits of detection were found to be in the range 50-160 fmol.     

Analysis of benzo[a]pyrene diol epoxide-DNA adducts by capillary zone electrophoresis- electrospray ionization-mass spectrometry in conjunction with sample stacking

Benzo[a]pyrene diol epoxide (BPDE) was reacted in vitro with (2'-deoxy)nucleotides and with calf thymus DNA. The modified DNA was enzymatically hydrolyzed to the 5'-monophosphate nucleotides using deoxyribonuclease I (DNA-ase I), nuclease P1 and snake venom phosphodiesterase (SVP). Most of the unmodified nucleotides were removed using solid phase extraction (SPE) in a polystyrene divinylbenzene copolymer. Three adducts could be detected and identified using capillary zone electrophoresis(negative)-ion electrospray ionization-mass spectrometry (CZE-(-)-ESI-MS) in conjunction with sample stacking. This way, not only a BPDE-dGMP adduct [(M-H)(-) at m/z 648], a well-known nucleotide adduct, could be retrieved, but also a BPDE-dAMP [(M-H)(-) at m/z 632] and a BPDE-dCMP adduct [(M-H)(-) at m/z 608] could be detected for the first time. The presence of the prominent ion at m/z 195 (the deoxyribose-phosphate ion) in the three low-energy collision-activated decomposition (CAD) spectra indicated that the adducts were formed through base-alkylation. CZE-positive ion ESI-MS/MS experiments were performed to obtain further information on base-alkylation. The absence of the loss of NH(3) from the nucleobase in each CAD spectrum points to an alkylated exocyclic NH(2) position of the nucleobase. So, the three adducts could be identified as BPDE-N(2)-dGMP, BPDE-N(6)-dAMP and BPDE-N(4)-dCMP using CZE-ESI-MS and CZE-ESI-MS/MS.     

Evaluation of a series of prolylamidepyridines as the chiral derivatization reagents for enantioseparation of carboxylic acids by LC–ESI–MS/MS and the application to human saliva

Mass spectrometry has become a popular analytical tool because of its high sensitivity and specificity. The use of a chiral derivatization reagent for the mass spectrometry (MS) detection seems to be efficient for the enantiomeric separation of racemates. However, the number of chiral reagents for the liquid chromatography (LC)–MS/MS analysis is very limited. According to these observations, we are currently in the process of developing novel labeling reagents for chiral molecules in MS/MS analysis. The derivatization reagent that is effective for enhancing not only the electrospray ionization–MS/MS sensitivity but also the reversed-phase LC resolution of carboxylic acid enantiomers should have a highly proton-affinitive moiety and an asymmetric structure near the reactive functional group. Furthermore, the resulting derivative has to provide a characteristic product ion suitable for the selected reaction monitoring. Based upon these considerations, a series of prolylamidepyridines ((S)-N-pyrrolidine-2-carboxylic acid N-(pyridine-2-yl)amide (PCP2), (S)-N-pyrrolidine-2-carboxylic acid N-(pyridine-3-yl)amide, and (S)-N-pyrrolidine-2-carboxylic acid N-(pyridine-4-yl)amide) was synthesized as ideal labeling reagents for the enantioseparation of chiral carboxylic acids and evaluated in terms of separation efficiency and detection sensitivity by ultra-performance LC (UPLC)–MS/MS. Among the synthesized reagents, PCP2 was the most efficient chiral derivatization reagent for the enantioseparation of carboxylic acid. The Rs values and the detection limits of the derivatives of non-steroidal anti-inflammatory drugs, which were selected as the representative carboxylic acids, were in the range of 2.52–6.07 and 49–260 amol, respectively. The sensitive detection of biological carboxylic acids (detection limits, 32–520 amol) was also carried out by the proposed method using PCP2 and UPLC–MS/MS. The PCP2 was applied to the determination of carboxylic acids in human saliva. Several biological carboxylic acids, such as lactic acid (LA), 3-hydroxybutylic acid, maric acid, succinic acid, α-ketoglutalic acid, and citric acid, were clearly identified in the saliva of healthy persons and diabetic patients. Furthermore, the ratio of d-LA in diabetic patients was higher than that in normal subjects. Judging from these results, PCP2 seems to be a useful chiral derivatization reagent for the determination not only of chiral, but also achiral, carboxylic acids in real samples.

Preparation of a graphene oxide/silica composite modified with nitro‐substituted tris(indolyl)methane as a solid‐phase extraction sorbent for the extraction of organic acids

This paper describes the use of graphene oxide/silica modified with nitro‐substituted tris(indolyl)methane as a solid‐phase extraction sorbent for the determination of organic acids. The resultant graphene oxide/silica modified with nitro‐substituted tris(indolyl)methane was characterized by FTIR spectroscopy and adsorption experiments. Solid‐phase extraction parameters such as sorbent type, sample solution pH, sample loading rate, eluent salt concentration, eluent methanol concentration, elution rate, sample loading, and elution volume were optimized. The method showed good precision, accuracy, sensitivity, and linear response for organic acids analysis over a concentration range of 1–100 μg/L for benzoic acid, p‐methoxybenzoic acid, and salicylic acid and 5–100 μg/L for the remaining organic acids (cinnamic acid, p‐chlorobenzoic acid, and p‐bromobenzoic acid) with coefficients of determination (r²) of higher than 0.9957. Limits of detection from 0.50 to 1.0 μg/L for six organic acids were achieved. The developed method was successfully applied to determine organic acids in real samples.     

尿中有机酸的毛细管气相色谱—质谱轮廓分析—用于苯丙酮尿症的诊断

应用毛细管气相色谱-质谱轮廓分析方法,测定了33例2.5～4.5岁健康儿童尿中有机酸种类及含量和8例拟诊为苯丙酮尿症儿童尿中的有机酸,结果表明患儿尿样中苯丙酮酸、苯乙酸、邻羟基苯乙酸、对羟基苯乙酸高于正常值10～470倍。为苯丙酮尿症的确诊提供了可靠方法。     

Non-suppressed conductivity and indirect UV detection of carboxylic acids in environmental samples by ion-exclusion chromatography using 2,6-pyridinedicarboxylic acidic eluent

2,6-Pyridinedicarboxylic acid (PDCA) was evaluated as an eluent for indirect UV and non-suppressed conductivity detection of carboxylic acids in ion-exclusion chromatography. The effect of PDCA concentration on the separation and detection sensitivity was investigated. The reasonable resolutions between carboxylic acids were achieved using 1 mM PDCA eluent. Detection limits were 1.0-7.0 microM for conductivity detection and 8-30 microM for UV detection. Compared to the eluent containing 1 mM sulfuric acid, the method offers a high resolution and high detection sensitivity for both detectors due to its high molar absorptivity and low background conductance. The proposed method was demonstrated to be useful for the determination of carboxylic acids in environmental samples with direct sample injection.