Application of HPLC to measure vanadium in environmental,biological and clinical matrices

Vanadate and vanadium compounds exist in many environmental, biological and clinical matrices, and despite the need only limited progress has been made on the analysis of vanadium compounds. The vanadium coordination chemistry of different oxidation states is known, and the result of the characterization and speciation analysis depends on the subsequent chemistry and the methods of analysis. Many studies have used a range of methods for the characterization and determination of metal ions in a variety of materials. One successful technique is high performance liquid chromatography (HPLC) that has been used mainly for measuring total vanadium level and metal speciation. Some cases have been reported where complexes of different oxidation states of vanadium have been separated by HPLC. Specifically reversed phase (RP) HPLC has frequently been used for the measurement of vanadium. Other HPLC methods such as normal phase, anion-exchange, cation-exchange, size exclusion and other RP-HPLC modes such as, ion-pair and micellar have been used to separate selected vanadium compounds. We will present a review that summarizes and critically analyzes the reported methods for analysis of vanadium salts and vanadium compounds in different sample matrices. We will compare various HPLC methods and modes including sample preparation, chelating reagents, mobile phase and detection methods. The comparison will allow us to identify the best analytical HPLC method and mode for measuring vanadium levels and what information such methods provide with regard to speciation and quantitation of the vanadium compounds.     

A two-step supercritical fluid extraction of polycyclic aromatic hydrocarbons from roadside soil samples

A two-step procedure for the supercritical fluid extraction (SFE) of polycyclic aromatic hydrocarbons from soil samples was developed. The procedure consists of a static supercritical fluid treatment in a closed extraction cell at a high temperature (T=250 or 340degreesC for 20 min) and an SFE with a solvent trapping. During the static phase, the sample is exposed to a supercritical organic solvent (methanol, toluene, dichloromethane, ACN, acetone, and hexane). The solvent penetrates particles of the matrix to substitute strongly bonded molecules and dissolves the analytes in the supercritical phase. At ambient temperature, supercritical fluids became liquid and lost their solvation abilities. Most of the analytes condense on the surface of the particles or on the extraction cell walls without forming strong bonds or penetrating deep into the matrix. Thus, the pretreatment liberates the analytes and they behave similar to those in freshly spiked samples. The common SFE with toluene-modified CO2 as an extraction fluid follows the static phase. With the use of the most suitable extraction phases (toluene, ACN), the extraction efficiency of the combined procedure is much higher (approximately100%). The results of the combined procedure are compared to the SFE procedure of the same untreated sample (difference less than 5%) and to the Soxhlet extraction. The extracts were analyzed using a GC with the flame ionization detection.     

On-line preconcentration and determination of nickel in natural water samples by flow injection-inductively coupled plasma optical emission spectrometry (FI-ICP-OES)

An on-line nickel preconcentration and determination system implemented with inductively coupled plasma optical emission spectrometry (ICP-OES) associated to flow injection (FI) was studied. Trace amounts of nickel were preconcentrated by sorption on a conical minicolumn packed with activated carbon (AC) at pH 5.0. The nickel was removed from the minicolumn with 20% nitric acid. An enrichment factor of 80-fold for a sample volume of 50 ml was obtained. The detection limit (DL) value for the preconcentration method proposed was 82 ng l⁻¹. The precision for ten replicate determinations at the 0.5 μg l⁻¹ Ni level was 3.0% relative standard deviation (R.S.D.), calculated from the peak heights obtained. The calibration graph preconcentration method for nickel was linear with a correlation coefficient of 0.9997 at levels near the detection limits (DL) up to at least 100 μg l⁻¹. The method was successfully applied to the determination of nickel in natural water samples.     

Analysis of organic compounds in environmental samples by headspace solid phase microextraction

The analysis of samples contaminated by organic compounds is an important aspect of environmental monitoring. Because of the complex nature of these samples, isolating target organic compounds from their matrices is a major challenge. A new isolation technique, solid phase microextraction, or SPME, has recently been developed in our laboratory. This technique combines the extraction and concentration processes into one step; a fused silica fiber coated with a polymer is used to extract analytes and transfer them into a GC injector for thermal desorption and analysis. It is simple, rapid, inexpensive, completely solvent-free, and easily automated. To minimize matrix interferences in environmental samples, SPME can be used to extract analytes from the headspace above the sample. The combination of headspace sampling with SPME separates volatile and semi-volatile analytes from non-volatile compounds, thus greatly reducing the interferences from non-target compounds. This paper reports the use of headspace SPME to isolate volatile organic compounds from various matrices such as water, sand, clay, and sludge. By use of the technique, benzene, toluene, ethyl-benzene, and xylene isomers (commonly known as BTEX), and volatile chlorinated compounds can be efficiently isolated from various matrices with good precision and low limits of detection. This study has found that the sensitivity of the method can be greatly improved by the addition of salt to water samples, water to soil samples, or by heating. Headspace SPME can also be used to sample semi-volatile compounds, such as PAHs, from complex matrices.     

Determination of 4-nonylphenol and 4-tert.-octylphenol in water samples by stir bar sorptive extraction and thermal desorption-gas chromatography-mass spectrometry

A simple and highly sensitive method called thermal desorption (TD)-gas chromatography-mass spectrometry (GC-MS), which is used for the determination of trace amounts of 4-nonylphenol (NP) and 4-tert.-octylphenol (OP) in water samples, is described. NP and OP in samples are extracted from water samples and concentrated by the stir bar sorptive extraction (SBSE) technique. A stir bar coated with polydimethylsiloxane (PDMS) is added to a 2.0 ml water sample and stirring is carried out for 60 min at room temperature (25 °C) in a headspace vial. Then the extract is high sensitively analyzed by TD-GC-MS without any derivatization step. The optimum SBSE conditions are realized at an extraction time of 60 min. The detection limits are 0.02 ng ml⁻¹ for NP and 0.002 ng ml⁻¹ for OP. The method shows good linearity over the concentration range of 0.1-10 ng ml⁻¹ for NP and 0.01-10 ng ml⁻¹ for OP, and the correlation coefficients are higher than 0.999. The average recoveries of NP and OP are higher than 97% (R.S.D.: 3.6-6.2%) with correction using the added surrogate standards, 4-(1-methyl) octylphenol-d₅ and deuterium 4-tert.-octylphenol. This simple, accurate, sensitive and selective analytical method may be used in the determination of trace amounts of NP and OP in tap and river water samples.     

Quantitative determination of taurine in real samples by high-performance anion-exchange chromatography with integrated pulsed amperometric detection

As taurine is a very important compound involved in a large number of metabolic processes, it is naturally present in the mammal tissues and is often deliberately added in some foods as a fortifying component. A detailed knowledge of taurine metabolic roles in biological systems can be obtained only if a sensitive, reliable and rapid analytical method is available. This article describes the successful application of high-performance anion-exchange chromatography coupled with integrated pulsed amperometric detection (HPAEC-IPAD) for taurine determination in egg white and yolk samples, as well extracts of human serum and urine. Applications are shown for determination of taurine in soft drinks and pharmaceutical preparations where the taurine content was evaluated by standard additions. These results were achieved without prior derivatization of taurine.     

Application of microwave-assisted micellar extraction combined with solid-phase microextraction and high-performance liquid chromatography with UV detection for the determination of organochlorine pesticides in different mud samples

Abstract

A sequential injection analysis method for the simultaneous spectrophotometric determination of phosphate and silicate has been developed. The method is based on the different reaction rates of the heteropolymolybdate formation reactions. Concentrations within the range 0.026—0.485 mmol P l^?1 and 0.125—2.848 mmol Si l^?1 have been determined at a frequency of 30 samples per hour. An R.S.D. of 2.1% was obtained for 0.162 mmol P l^?1 and of 1.1% for 1.424 mmol Si l^?1. The method was found to be suitable for the determination of phosphate and silicate in wastewater.     

Screening and determination of drugs in human saliva utilizing microextraction by packed sorbent and liquid chromatography–tandem mass spectrometry

This study presents a new method for collecting and handling saliva samples using an automated analytical microsyringe and microextraction by packed syringe (MEPS). The screening and determination of lidocaine in human saliva samples utilizing MEPS and liquid chromatography–tandem mass spectrometry (LC‐MS/MS) were carried out. An exact volume of saliva could be collected. The MEPS C₈‐cartridge could be used for 50 extractions before it was discarded. The extraction recovery was about 60%. The pharmacokinetic curve of lidocaine in saliva using MEPS‐LC‐MS/MS is reported. Copyright © 2013 John Wiley & Sons, Ltd.     

Separation of Hydrocarbon Mixtures in the Microgram Range by Inclusion in a Urea-packed Mini Column

Abstract

The use of classical urea inclusion techniques for the separation of straight chain hydrocarbons from branched and cyclic compounds is satisfactory when applied to mixtures in the milligram to gram ranges, but leads to low separation efficiencies when quantities in the microgram to milligram range are involved. In this study, a modified inclusion technique using an urea-packed milli-bore column and a catalytic eluent is described. Examples of its use for the separation of mixtures of linear and cyclic hydrocarbons from 30μg up to a few milligrams are given. The versatility of this technique for the analyses of low amounts of environmental samples is described, and an application to the hydrocarbon fraction of surface sediment from lake Leman (Switzerland) is presented.     

Collection and Identification of Trace Organic Compounds in Atmospheric Deposition from a Semi-Rural Site in the U.K.

Abstract

The collection of rainwater, aerosol and vapour samples at a semi-rural site in the UK was achieved using a PTFE-lined wet-only rainfall collector and a high-volume filter/adsorption trap air sampler, respectively. Analysis of atmospheric deposition revealed the presence of several hundred compounds, many of which were of anthropogenic origin, e.g.: PAH, phenols and alkylbenzenes. Amounts of compounds varied from low nanograms to tens of micrograms per litre in rainwater samples and from low picograms to high nanograms per cubic metre in aerosols. Phenolic compounds were the most abundant group of organics identified in rainwater and were present at total concentrations of >20μg1^?1 in some of the samples analysed. In the high-volume air samples most anthropogenic compounds were detected in the adsorbent rather than the filter extract. Seasonal variations in the PAH content of the adsorbent extracts were observed. The presence of siloxanes in the air samples was thought to be the result of contamination.