Simultaneous determination of inorganic anions, carboxylic and aromatic carboxylic acids by capillary zone electrophoresis with direct UV detection

Co-electroosmotic capillary zone electrophoresis (CZE) with direct UV detection was developed for simultaneous determination of inorganic anions, carboxylic and aromatic carboxylic acids. These solutes were separated using a 30 mM phosphate buffer containing 1.0 mM tetradecyltrimethylammonium bromide (TTAB) and 20% (v/v) acetonitrile at pH of 6.5 and directly detected by UV at 190 nm. Calibration curves were linear in the range 0.01-2.0 mM, depending of the solutes. The detection limits ranged from 1.0 to 8.0 microM and the relative standards deviations (n=5) in range from 1.9 to 3.6% for the peak area. The proposed method was used to determine inorganic anions and carboxylic and aromatic acids in soil and plant tissue extracts.     

Thermodynamic Study of the Extraction of Inorganic Mercury Compounds in Fish Species of the International Anzali Wetland,Iran

Inorganic mercury concentration was measured in the muscle tissues of four types of fish in the aquatic international Anzali Wetland ecosystem in Guilan. In the same ecosystem, the northern pike is able to concentrate inorganic mercury in its body more than other fish. In each species, a fish with the highest amount of inorganic mercury was selected for determination of thermodynamic parameters of inorganic mercury extraction using calculation of the equilibrium constant and fitting of ln K_c versus inverse temperature at the atmospheric pressure. The origins of thermodynamic parameters were discussed. The extraction processes were done in the range of temperatures from 331.15 to 365.15 K and at atmospheric pressure. Results show that the extraction of mercury compounds from SH groups of sulfhydryl proteins in fish muscle tissue is an endothermic process with a positive value for entropy and Gibbs free energy changes at room temperature.     

Application of co-electroosmotic capillary electrophoresis for the determination of inorganic anions and carboxylic acids in soil and plant extract with direct UV detection

Summary Indirect UV detection in capillary zone electrophoresis (CZE) is frequently used for the determination of inorganic anions and carboxylic acids. However, there are few reports on direct UV detection of these solutes in real samples. This paper describes the use of direct UV detection of inorganic anions and organic acids in environmental samples using co-electroosmotic capillary zone electrophoresis (co-CZE) at 185 nm. The best separation and detection of the solutes was achieved using a fused silica capillary with an electrolyte containing 25 mM phosphate, 0.5 mM tetradecyltrimethylammonium bromide (TTAB) and 15% acetonitrile (v/v) at pH 6.0. Four common inorganic anions (Cl⁻, NO₂ ⁻, NO₃ ⁻ and SO₄ ²⁻) and 11 organic acids (oxalic, formic, fumaric, tartaric, malonic, malic, citric, succinic, maleic, acetic, and lactic acid), were determined simultaneously in 15 min. Linear calibration plots for the test solutes were obtained in the range 0.02–0.5 mM with detection limits ranging from 1–9 μM depending on the analyte. The proposed method was successfully used to determine inorganic anions and carboxylic acids in soil and plant tissue extracts with direct injection of the sample.     

Determination of functionalised carboxylic acids in atmospheric particles and cloud water using capillary electrophoresis/mass spectrometry

A capillary electrophoresis/electrospray ionisation mass spectrometry (CE/ESI-MS) method was developed for the determination of 38 organic acids in atmospheric particles and cloud water. The target analytes include many functionalised carboxylic acids, such as carboxylic acids with additional oxo-, hydroxy- or nitro-groups. These compounds are of large interest as their determination might give new insights into the atmospheric multiphase chemistry. OASIS HLB sorbent material (Waters) was used to extract and enrich polar carboxylic acids from aqueous solutions with recoveries greater than 80% for most analytes. Relative standard deviations in the range of 4-20% for peak areas (n=5), including the SPE step, and 0.2-0.5% (n=8) for migration times were found. The limits of detection (S/N=3) ranged from 0.005 to 0.6 micromol l(-1) for an ion-trap mass spectrometer and from 0.0004 to 0.08 micromol l(-1) for a time-of-flight mass spectrometer. These detection limits translate into atmospheric concentrations in the low pg m(-3) range based on the experimental conditions in this study. Severe matrix effects were observed for real samples, arising from complex co-extracted organic material. However, using the method of standard addition, most of the analytes could successfully be quantified in samples of ambient particles and cloud water with concentrations in the low ng m(-3) to high pg m(-3) range. These results demonstrate the suitability of the proposed method for the determination of a wide range of polar carboxylic acids at low concentrations in complex samples of different atmospheric phases.     

Simultaneous Determination of Inorganic Anions and Organic Acids in Environmental Samples by Capillary Zone Electrophoresis with Indirect UV Detection

Capillary zone electrophoresis (CZE) with indirect UV detection was developed for the simultaneous determination of inorganic anions and organic acids in environmental samples. Various aromatic acids (benzoic, phthalic, trimellitic, and pyromellitic acids) were evaluated as background electrolytes (BGEs) to give high resolution and detection sensitivity. Co-electroosmotic conditions such as the concentration of BGE, electrolyte pH, and EOF modifier were systematically investigated. Three inorganic anions and ten organic acids were determined simultaneously in 10 min using an electrolyte containing 10 mM phthalic acid, 0.5 mM myristyltrimethylammonium bromide (MTAB), and 5% methanol (MeOH) (v/v) at pH 5.60. Linear plots for the test solutes were obtained in the concentration range 0.01–1.0 mM with detection limits in the range 5–30 μM. The proposed method was successfully demonstrated for the determination of inorganic anions and organic acids in natural water, soil, and plant extracts after direct sample injection.     

Optimization and validation of a capillary electrophoresis methodology for inorganic anions in atmospheric aerosol samples

Optimization and validation of a method for the determination of inorganic anions, such as chloride, nitrate, sulphate, fluoride and phosphate, in atmospheric particulate matter is described. Ultrasonic extraction followed by CE, using CTAB as EOF modifier, has been established for this separation using chromate as visualization reagent for the indirect UV/vis detection. Optimization of the experimental chemical conditions (pH, surfactant concentration, chromate concentration and acetonitrile concentration) and instrumental parameters (temperature, applied voltage and injection time) is described. Linear calibrations plots are obtained for the five ions, with detection limits in the high ng/mL range. A standard reference material, SRM 1648 Urban Particulate Matter, has been used to validate the proposed method. Satisfactory reproducibility and acceptable agreement to the matter atmospheric samples has been found (recoveries ranging from 86 to 96%). Application to real particulate matter atmospheric samples, collected on high volume samplers from the air quality surveillance network of Extremadura, southwest Spain, is shown.     

Simultaneous determination of the herbicides isoproturon, dichlorprop-p, and bifenox in soils using RP-HPLC

Summary A simple and fast analytical method for the simultaneous determination of the herbicides isoproturon (N-(4-isopropylphenyl)-N'N'-dimethyl-urea), dichlorprop-p ((+)-2-(2,4-dichlorophenoxy)-propionic acid), bifenox (methyl-5-(2,4-dichlorophenoxy)-2-nitro-benzoate), and its main metabolite bifenox acid (5-(2,4-dichloro-phenoxy)-2-nitro-benzoic acid) in soils is described. The herbicides differ substantially in their physical and chemical properties. The soil extraction with a mixture of CH₂Cl₂, C₂H₅OH, and acetone, followed by an isocratic RP-HPLC determination yields high, reproducible recoveries for all compounds. The method can be used for different soil moisture and pH conditions. The detection limits range from 0.01 to 0.03 mg active compound/kg dry soil. An additional clean-up using size exclusion techniques can improve the detection limits to 0.003 to 0.007 mg active compound/kg dry soil. The method is suitable for routine residue analyses and applicable to other herbicides as well.     

Determination of microtraces of Bi, Co, Cu, Fe, Mn, In, Ni, Pb, Sb and Zn in phosphoric acid and ammonium phosphate

Summary Methods for the determination of Bi, Co, Cu, Fe, Mn, In, Ni, Pb, Sb and Zn in phosphoric acid by ETA-AAS using the platform technique were developed. The detection limits are in the range of 1 to 30 ppb for conc. H₃PO₄. Relative standard deviations of 5–10% at 10 times the detection limits were achieved. The results obtained by five different atomic spectroscopic methods are in good agreement (direct Zeeman-ETA-AAS, D₂-ETA-AAS and FAAS; OES and FAAS after trace extraction).     

Determination of polymer additives by liquid chromatography coupled with mass spectrometry. A comparison of atmospheric pressure photoionization (APPI), atmospheric pressure chemical ionization (APCI), and electrospray ionization (ESI)

A method for the determination of polymer additives like antioxidants, UV absorbers and processing stabilizers using liquid chromatography (LC) coupled with atmospheric pressure photoionization mass spectrometry (APPI-MS) is presented. Ion source parameters were optimized regarding temperatures, gas flow rates, and voltages applied. Detection limits were determined using APPI with or without dopant and were compared with electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI). Differences between APPI, ESI and APCI are pointed out and the effect of the dopant toluene and acetone is discussed. The optimized method yielded detection limits between 0.001 mg L⁻¹ and 0.022 mg L⁻¹ for 15 different analytes. Linear calibration plots could be obtained for all solutes over a wide concentration range showing satisfying repeatability with standard deviations of peak areas between 3.4% and 7.6%. The results indicate that the developed method can be regarded as suitable for the quantitative determination of polymer additives even at low concentration levels.     

Fabrication of Cu−CeO2 Coated Multiwall Carbon Nanotube Composite Electrode for Simultaneous Determination of Guanine and Adenine

A copper nano particles and cerium (IV) oxide modified carbon nanotube based composite on glassy carbon electrode (Cu−CeO₂/MWCNT/GCE) was fabricated for simultaneous determination of guanine and adenine. The surface morphology, chemistry and conductance of the prepared electrodes were characterized by scanning electron microscopy (SEM), energy dispersion X‐ray (EDX), X‐Ray photoelectron spectroscopy (XPS) and electrochemical impedance spectroscopy (EIS). The Cu−CeO₂/MWCNT/GCE improved electrochemical behaviour of guanine and adenine compared to other electrodes. The modified electrode was also used for individual and simultaneous determination of guanine and adenine. Under optimized conditions, the calibration curves were obtained linearly in the range of 0.20 to 6.00 μM for the guanine and 0.10 to 8.0 μM for the adenine by differential pulse voltammetry. The limits of detection of guanine and adenine were calculated as 0.128 and 0.062 μM, respectively. Interferences studies were also performed in the presence of inorganic and organic compounds. Moreover, the determination of guanine and adenine contents were carried out in a calf thymus DNA sample by the developed method with satisfactory results.     

Direct atmospheric pressure chemical ionization-tandem mass spectrometry for the continuous real-time trace analysis of benzene, toluene, ethylbenzene, and xylenes in ambient air

Real-time monitoring of benzene, toluene, ethylbenzene, and xylenes (BTEX) in ambient air is essential for the early warning detection associated with the release of these hazardous chemicals and in estimating the potential exposure risks to humans and the environment. We have developed a tandem mass spectrometry (MS/MS) method for continuous real-time determination of ambient trace levels of BTEX. The technique is based on the sampling of air via an atmospheric pressure inlet directly into the atmospheric pressure chemical ionization (APCI) source. The method is linear over four orders of magnitude, with correlation coefficients greater than 0.996. Low limits of detection in the range 1–2 μg/m³ are achieved for BTEX. The reliability of the method was confirmed through the evaluation of quality parameters such as repeatability and reproducibility (relative standard deviation below 8% and 10%, respectively) and accuracy (over 95%). The applicability of this method to real-world samples was evaluated through measurements of BTEX levels in real ambient air samples and results were compared with a reference GC-FID method. This direct APCI-MS/MS method is suitable for real-time analysis of BTEX in ambient air during regulation surveys as well as for the monitoring of industrial processes or emergency situations.     

Automated system for on-line determination of dimethylarsinic and inorganic arsenic by hydride generation–atomic fluorescence spectrometry

A multisyringe flow-injection approach has been coupled to hydride generation-atomic fluorescence spectrometry (HG-AFS) with UV photo-oxidation for dimethylarsinic (DMA), inorganic As and total As determination, depending on the pre-treatment given to the sample (extraction or digestion). The implementation of a UV lamp allows on-line photo-oxidation of DMA and the following arsenic detection, whereas a bypass leads the flow directly to the HG-AFS system, performing inorganic arsenic determination. DMA concentration is calculated by the difference of total inorganic arsenic and measurement of the photo-oxidation step. The detection limits for DMA and inorganic arsenic were 0.09 and 0.47 μg L(-1), respectively. The repeatability values accomplished were of 2.4 and 1.8%, whereas the injection frequencies were 24 and 28 injections per hour for DMA and inorganic arsenic, respectively. This method was validated by means of a solid reference material BCR-627 (muscle of tuna) with good agreement with the certified values. Satisfactory results for DMA and inorganic arsenic determination were obtained in several water matrices. The proposed method offers several advantages, such as increasing the sampling frequency, low detection limits and decreasing reagents and sample consumption, which leads to lower waste generation.     

离子转换色谱-紫外检测法测定啤酒中的无机阴离子和有机酸

建立了离子转换色谱与紫外检测器联用检测啤酒中无机阴离子与有机酸的新方法。在传统的离子色谱基础上引入两根离子转换柱,无机阴离子与有机酸经过两步转换,定量转换成有相同紫外响应的碘酸盐,然后用紫外检测器代替电导检测器进行定量分析。在Dionex AS11-HC阴离子色谱柱上,采用KOH梯度淋洗方式实现了12种无机阴离子与有机酸的分离。结果表明,12种无机阴离子和有机酸检出限（S/N=3）与定量限（S/N=10）分别为6.168~29.01 μg/L与20.56~66.30 μg/L;线性关系良好（r在0.9994以上）,回收率为89.0%~117.0%,RSD均小于1.0%,该方法与传统的电导检测器检测结果相当。该方法简单快捷,只需采用少数标准曲线,就可以实现啤酒中无机离子与有机酸的定量测定。     

Capillary zone electrophoresis for the determination of light-absorbing anions in environmental samples.

A rapid and simple method for separation and determination of inorganic anions by capillary zone electrophoresis was described. The detection was carried out directly with a diode array detector. The experimental conditions, such as concentration of carrier electrolyte, capillary length, voltage, and temperature were optimized. In order to improve selectivity, different organic modifiers were also investigated. The baseline separation of 10 light-absorbing anions was accomplished within 3.5 min with a background electrolyte consisting of 50 mM sodium tetraborate containing 5% MeOH. Linear plots were obtained in the concentration range of 0.1-10 microg/ml. With sample stacking injection, the quantitation limits of the anions were found to be in the range of 0.02-0.1 microg/ml. The proposed method was successfully applied to the determination of inorganic anions in environmental samples and in effluents of a power plant.     

Simultaneous determination of aflatoxin B1, B2, G1, and G2 in corn powder,edible oil,peanut butter,and soy sauce by liquid chromatography with tandem mass spectrometry utilizing turbulent flow chromatography

A novel fully automated method based on dual column switching using turbulent flow chromatography followed by liquid chromatography with tandem mass spectrometry was developed for the determination of aflatoxin B₁, B₂, G₁, and G₂ in corn powder, edible oil, peanut butter, and soy sauce samples. After ultrasound‐assisted extraction, samples were directly injected to the chromatographic system and the analytes were concentrated into the clean‐up loading column. Through purge switching, the analytes were transferred to the analytical column for subsequent detection by mass spectrometry. Different types of TurboFlow^TM columns, transfer flow rate, transfer time were optimized. The limits of detection and quantification of this method ranged between 0.2–2.0 and 0.5–4.0 μg/kg for aflatoxins in different matrixes, respectively. Recoveries of aflatoxins were in range of 83–108.1% for all samples, matrix effects were in range of 34.1–104.7%. The developed method has been successfully applied in the analysis of aflatoxin B₁, B₂, G₁, and G₂ in real samples.     

A Novel Carbon Nitride Nanosheets-based Electrochemical Sensor for Determination of Hydroxychloroquine in Pharmaceutical Formulation and Synthetic Urine Samples

This study introduces modified carbon paste electrodes with carbon nitride nanosheets (CNNS) and outlines their application for the determination of hydroxychloroquine sulfate (HCQ) in tablets and synthetic urine samples. CNNS were synthesized by hydrothermal route (200 °C, 10 h) using melamine and citric acid as their precursors. The carbon nitride nanosheets-based electrode (CNNS/E) presented a linear dynamic range for HCQ (LDR), ranging from 10.0 nmol l⁻¹ to 6.92 μmol l⁻¹, and detection (LOD) and quantification limits (LOQ) of 0.16 nmol l⁻¹ and 0.52 nmol l⁻¹, respectively. LOD and LOQ were calculated by the equations: LOD=3(S_d/b), and LOQ=10(S_d/b). The modified sensor presented excellent relative standard deviations for parameters such as repeatability (2.39 % and 1.87 %) and reproducibility (3.22 % and 2.32 %) in HCQ oxidation peaks (1 and 2). The CNNS/E has not shown significant variations in its anodic signal intensity in the presence of some organic and inorganic substances. It is worth bearing in mind that CNNS/E can be easily manufactured and the sensor has the lowest HCQ detection limits reported so far. The proposed sensor was successfully applied for HCQ determination in tablets and synthetic urine, showing good recovery values and an error of 0.60 % about comparative method in tablet samples, assuring the quality of the method.     

Titanium dioxide nanotubes for solid phase extraction of benzoylurea insecticides in environmental water samples, and determination by high performance liquid chromatography with UV detection

A new, simple and sensitive method was established for solid-phase extraction of benzoylurea insecticides including diflubenzuron, chlorbenzuron, triflumuron, flufenoxuron, and chlorfluazuron in water samples using TiO₂ nanotubes cartridge prior to their determination by liquid chromatography. The parameters influencing the extraction were investigated and optimized. Under optimal conditions, a good linearity was found between the concentration and the peak area in the range from 0.2 to 40???g?L^-1 (r²?>?0.99), and detection limits were in the range from 0.062 to 0.21???g?L^-1. Real water samples were used for validating the method and recoveries of spiked samples were over the range from 82.0 to 100%. The results indicated that TiO₂ nanotubes repesented an attractive alternative sorbent for the enrichment and trace analysis of such pollutants.

The analysis of antimony species by using ESI-MS and HPLC-ICP-MS

A new method for the separation of organic antimony as trimethylantimony dichloride (TMSbCl₂) and inorganic Sb(V) and Sb(III) by using anion exchange high-performance liquid chromatography coupled with inductively-coupled plasma mass spectrometry (ICP-MS) is presented. In comparison with previous work the detection limits for both species were significantly decreased, down to 5 ngL^–1, mainly by avoiding any contamination from the chromatographic device. Using an ultrasonic nebulizer (USN) improved the detection limits for inorganic Sb species, but was useless for the HPLC method due to problems in the recovery of the TMSbCl₂. Matrix interferences of the chromatographic determination were studied in detail and the method was applied to environmental samples assumed to contain organic antimony species. Additionally, the molecular structure of the TMSbCl₂ in solution was studied by using electrospray-ionization mass spectrometry (ESI-MS) showing that this species occurs most probably as [TMSbOH]⁺ in aqueous solutions. Received: 22 September 1997 / Revised: 21 November 1997 / Accepted: 27 November 1997     

Total organochloride and organobromide determinations in aqueous samples by microwave induced plasma-optical emission spectrometry

The element specific detection of the adsorbable organic halogen (AOX) parameter in waters has been investigated by adsorption of the halogenated analytes on activated carbon, incineration to yield carbon dioxide and hydrogen halide, trapping of the halide on a 0.01 M sodium hydroxide solution and online introduction of the halogen formed by continuous oxidation into a microwave induced plasma (MIP). Detection has been carried out by optical emission spectrometry (OES) in the visible spectral region.The performance of three microwave cavities for MIP-OES running at atmospheric pressure (Beenakker, Surfatron and Microwave Plasma Torch) as well as a reduced pressure Surfatron were investigated for halide analysis. The Surfatron device operated at 30 torr provided the best detection limits: 3ng.ml^–1 for chloride and 8 ng.ml^–1 for bromide; consequently, it was the plasma chosen for AOX analysis.On-line continuous oxidation of organic compounds using KMnO₄ in H₂SO₄ medium and in batch catalytic dechlorination with a Fe/Pd system were investigated as alternatives to the incineration method for the destruction of organic halogens to render inorganic halides are also investigated.Finally, the optimized method has been applied successfully to the determination of organochloride and organobromide in spiked river waters, being the recoveries in the interval 92–105%.     

Determination of antibilharzial antimony compounds by direct current, differential pulse, square-wave and alternating current anodic stripping voltammetry

A simple, rapid and sensitive method has been developed for the determination of Sb(III) in five antimonial antibilharzial drugs using anodic stripping voltammetry. The method is based on the reduction of Sb(III) on the HMDE, followed by a selected mode of oxidative sweep, i.e. direct current, differential pulse, square-wave or first harmonic alternating current sweep, using 2 mol/L HCl as a supporting electrolyte. Voltammograms for various sample concentrations in the range 3–47 ppb Sb(III) were recorded and the respective calibration graphs constructed. To overcome the expected effect of adsorption of surface active organic compounds on the mercury drop, the standard addition technique of Sb₂O₃ solution was applied to calculate the recoveries of all the tested antimonials. The method gave reproducible results within 2% and the limit of detection for all measurement modes was 3 ppb. SW and AC modes seem to achieve lower detection limits than the other two modes. The four modes proved to be of equal accuracy and precision.