A. Padró

Arsenic speciation using HPLC-HG-ICP-AES with gas-liquid separator

SummaryThe determination of different chemical species of arsenic in aquatic media has been carried out using several separation and detection techniques. As separation techniques GC, HPLC, HG and cold trap-selective thermal desorption are the most frequently used. As detection techniques FAAS, ETAAS or, to a lesser extent, ICP-AES are applied. In this work the optimization conditions are presented for As(III), As(V), monomethylarsonic acid (MMA) and dimethylarsinic acid (DMA) determination using (IC)HPLC coupled to HG with gas-liquid separator, and using ICP-AES as detector is presented. The gas-liquid separator impedes the entrance of mobile phase into the nebulizer and consequently into the plasma torch. The experimental conditions for HG (kind of acids and concentration, borohydride concentration, reagent flows) as well as plasma conditions have been optimized.The quality parameters: LOD, precision and accuracy are reported for all the species studied.

Speciation of arsenic in mussels by the coupled system liquid chromatography-UV irradiation-hydride generation-inductively coupled plasma mass spectrometry.

A method has been developed for the determination of seven arsenic species in mussel tissues by liquid chromatography-hydride generation-UV photo-oxidation and detection by inductively coupled plasma mass spectrometry. In order to determine the different species, two ion-exchange columns (anionic and cationic) were used with phosphate and nitric acid/ammonium nitrate as mobile phases, respectively. The optimisation of the conditions for separation, photo-oxidation and hydride generation is described. For each of these species, the limits of detection and repeatability are reported with the entire system coupling. This system was applied to the analysis of certified reference material (CRM 278) and mussels collected from Barcelona harbour. Extractions were achieved in methanol/water (1:1) using low-power focused microwaves as leaching process. As expected, arsenobetaine was the main compound extracted from both materials; the typical concentrations found were between 1 and 7 mg kg(-1). Other organoarsenical compounds, probably arsenosugars, were extracted in a concentration range of 0.3-1.5 mg kg(-1) in both cases. Amounts of dimethylarsinate (DMA) were found to be significant in the CRM 278, but very low in mussels from Barcelona harbour. The low limits of detection of the coupled system allow us to quantify low contents of other species (As(V), arsenocholine and monomethylarsonate (MMA)).

Speciation of organic and inorganic arsenic by HPLC-HG-ICP

This paper deals with the application of high performance liquid chromatography (HPLC), hydride generation (HG) and inductively coupled plasma atomic emission spectrometry (ICP) to determine four species of arsenic: As(III), As(V), monomethylarsonic acid (MMA) and dimethylarsinic acid (DMA). The coupling conditions of HPLC-HG-ICP are given. Two anionic exchange columns (Nucleosil-5SB and Hamilton PRP X-100) are tested and the separation conditions optimized. Two acids (H2SO4 and HCl at different concentrations) are tested to obtain the hydrides. The proposed method is applied to determine four arsenic species in a synthetic matrix simulating a fish extract.

Determination of arsenic speciation by liquid chromatography—hydride generation inductively coupled plasma atomic emission spectrometry with on-line UV photooxidation

Abstract The determination is described of the six arsenic species arsenite, arsenate, monomethylarsonate (MMA), dimethylarsinate (DMA), arsenobetaine and arsenocholine by hydride generation inductively coupled plasma atomic emission spectrometry after liquid chromatographic separation and on-line photooxidation. An anion-exchange polymer-based column is used for separation. The details of the photoreactor designed to transform arsenobetaine and arsenocholine into simpler species that can be reduced are presented. The reducing conditions to obtain the arsine from arsenate (as the final product of the photooxidation process) are optimized. The overall assembly is presented and using the optimized operating condition the quality parameters (detection limits, precision and accuracy) for all the arsenic species are reported. These parameters for arsenic, arsenate, MMA and DMA are compared with those obtained without photooxidation. The introduction of a new step on-line in the coupling does not produce any loss of quality of information or a significant increase in analysis time.

Organic and inorganic selenium speciation using high-performance liquid chromatography with UV irradiation and hydride generation-quartz cell atomic absorption spectrometric detection

Abstract We propose a new on-line method for organic and inorganic selenium speciation, consisting of liquid chromatography–UV irradiation–hydride generation-quartz cell atomic absorption spectrometry. Unlike other methods, UV irradiation for the derivatization of all selenium species to selenite, before hydride generation, is a simpler and cleaner method, since it does not require any additional reagent. The reaction time is also much shorter. A good resolution between the four species (selenite, selenate, selenocystine and selenomethionine) is achieved in less than 15 min. The optimisation of operating conditions, including those used during separation and UV irradiation, is described. Detection limits, precision, linear ranges and recovery are reported. The technique can be considered a reliable, straightforward system for selenium speciation.

On-line photolytic decomposition for the determination of organoarsenic compounds

Abstract In arsenic speciation with the use of coupled techniques (separation-atomic spectroscopic detection) the generation of arsines improves sensitivity. This article focuses on the incorporation of on-line UV photolysis to transform arsenobetaine and arsenocholine into simpler species which are able to generate arsines. The couplings of LC-UV-HG-ICP-OES (liquid chromatography-photolysis-hydride generation-inductively coupled plasma optical emission spectroscopy) or LC-UV-HG-QCAAS (liquid chromatography-photolysis-hydride generation-quartz cuvette atomic absorption spectroscopy) are proposed and were used to analyze Dorm-1 dogfish muscle Certified Reference Material with total arsenic certified. The results are compared with those reported in the literature by using LC-ICP-MS (liquid chromatography-inductively coupled plasma mass spectrometry).

Validation of mineralisation procedures for the determination of selenium, zinc, iron and copper in chicken meat and feed samples by ICP-AES and ICP-MS

Mineralisation procedures for determining Fe, Zn, Cu and Se in chicken meat and feed samples were studied. We employed three different sample preparation procedures to determine these elements by ICP-AES and ICP-MS. An open vessel wet mineralisation procedure was used for chicken meat analysis. Here, in the case of the trace elements Cu and Se, it was necessary to concentrate and reduce the acid matrix effects so samples were heated to dryness. However, this procedure causes Se volatilisation losses leading to low recoveries and high variability. Therefore, a closed vessel microwave mineralisation procedure was developed for chicken meat samples. The results obtained using this procedure presented a much lower variability (2.5, 2.0 and 3.1% of RSD for Zn, Fe and Se, respectively) and were consistent with the certified values for the reference material being assessed. Cu content, despite presenting a relatively high variability (RSD = 11%) also agreed with the certified value for the reference material. Recoveries in spiked chicken meat were 103–105% for Zn, 107–108% for Fe, 97–100% for Se and 89–94% for Cu. However, when this procedure was used with feeds, some mineralised samples presented siliceous particles which led to a lower recovery of Zn compared with that recorded when using another microwave mineralisation procedure in which these particles had been dissolved with hydrofluoric acid. This alternative mineralisation procedure for feeds was validated by assessing the precision, recovery and sensitivity when determining each element.

Photoreduction-hydride generation: a new on-line system for the determination of selenate and selenite

Abstract Here we propose the on-line photoreduction of selenate to selenite in coupled systems. Simultaneous determination of both selenate and selenite is achieved by using LC-UV-HG-QCAAS (Liquid Chromatography-UV irradiation-Hydride Generation-Quartz cuvette Atomic Absorption Spectrometry) and LC-UV-HG-ICP/OES (Liquid Chromatography-UV irradiation-Hydride Generation-Inductively Coupled Plasma/Optical Emission Spectrometry). The two methods proposed have the advantages of not requiring the addition of a reducing agent to the eluate and only use 10 min for determination. The detection limits (expressed as μg 1 −1 of selenium and calculated as 2σ the background signal) are 6.8 for selenite and 16 for selenate, when using ICP/OES as detector, and 15 for selenite and 33 for selenate when using QCAAS as detector. Precision, expressed as %RSD and calculated at concentrations of about ten times the detection limits, ranges between 4% and 6%.

LC-HG-QCAAS versus LC-HG-ICP/OES in arsenic speciation

The coupled technique LC-HG-QCAAS has been used to perform the speciation of arsenite, arsenate, monomethylarsonate and dimethylarsinate in aqueous samples. An optimization of the operating conditions, especially those for atomization, is described. The analytical signals have been collected and processed using a microcomputer. Results of limits of detection, precision, recovery and linear ranges when using peak area and peak height are reported. The technique can be considered cheap enough to be applied to metal speciation analysis in most laboratories.

Determination of mixtures of alpha emitting isotopes (242Pu, 239+240Pu, 238Pu) by using liquid scintillation–moving curve fitting

Abstract A new method for the simultaneous determination of alpha emitting plutonium isotopes based on liquid scintillation spectrometry and moving curve fitting (LS–MCF) is presented. This method overcomes the instability of the spectrum position by introducing in the model some freedom in the band location. The method proposed has a higher detection efficiency than that of the classical semiconductor alpha spectrometry. Therefore, it can be used to process smaller samples and has the additional advantage of being a relatively quick procedure. With regard to the use of multivariate calibration, LS–MCF reduces the data treatment time because it does not require a previous spectrum position correction. LS–MCF can also be applied to samples with low activity levels.