Chromium speciation in liquid matrices: a survey of the literature

A thorough review of the literature published (1983 - March 1999) on chromium speciation in liquid samples is presented, and analytical techniques used in the 404 articles are summarized. The discussion focuses on atomic spectrometric techniques, which are mainly employed for chromium speciation in liquid matrices (134 articles). Details on the type of pretreatment, species, samples, techniques and analytical features of the methodologies proposed are given.     

Analytical methodologies for chromium speciation in solid matrices: a survey of literature

The analytical literature about chromium speciation in solid samples has been surveyed. From 451 articles published on the speciation of chromium from 1983 to 1997, the methodologies to do speciation in solids after sample pretreatment are discussed, through consideration of the types of samples and their dissolution, the analytical techniques employed for chromium measurement, and the figures of merit of the 86 papers reported in the Analytical Abstracts data base.     

Traceability and analytical chemistry

 The basic concepts of traceability as they are defined by the Comité Consultatif pour la Cluantité de Matière are contrasted with the practical exploitation in chemical analysis. The applicability of traceability concepts are tested for their practical applicability on four different analytical methodologies, neutron activation analysis, plasma mass spectrometry, beam microscopical analysis and speciation analysis of organometallic compounds. Received: 31 March 1998 · Accepted: 6 June 1998     

Coupling continuous flow systems to instruments based on discrete sample introduction

The interfaces between low-pressure continuous sample treatment systems and high-level information instruments such as gas chromatographs, capillary electrophoresis equipment and graphite furnace atomic spectroscopic instruments, which are characterized by conventional discrete sample introduction devices, are presented. The present and future developments are discussed of (directly) linking real samples and those analytical equipments with the main objective of avoiding or minimizing manually implemented preliminary operations of the analytical process. Received: 27 January 1998 / Revised: 5 March 1998 / Accepted: 7 March 1998     

Effect of sample preparation on the operational speciation of cadmium and lead in a freshwater sediment

The three-stage sequential extraction procedure recommended by BCR has been applied in the operational speciation of cadmium and lead in a relatively unpolluted freshwater sediment, following various types of sample pre-treatment. Changes in speciation occurred when the sediment was air-dried, oven-dried or frozen. Cadmium speciation was particularly perturbed by freezing, whilst lead was more affected by oven-drying. Metals were determined by electrothermal atomic absorption spectrometry, using direct calibration with reagent-matched standard solutions. Received: 18 March 1998 / Revised: 22 June 1998 / Accepted: 26 June 1998     

Electrothermal atomic absorption spectrometry in the study of metal ion speciation

The literature on the use of electrothermal atomic absorption spectrometry (ETAAS) in the determination of metals in speciation studies of different samples is comprehensively reviewed. The methods of extraction, preconcentration, etc. in connection with speciation studies have been highlighted. The ETAAS programmes and other details of the developed methodologies are discussed. On critical examination it becomes obvious that chromium is the metal which has been analysed by most workers. Study of other metals falls in the following order: Pb, Sn, Cu, As, Al, Cd, Zn, Fe, Ni and Se. It is clearly evident that the major work on metal ion speciation has been carried out in natural water, followed by biological materials. There are also many reports on the speciation analysis of soil and sediment. Only a few papers have been published on metal speciation in airborne particulates. The analytical details of the developed methodologies have been examined in terms of limit of detection, precision and accuracy. Received: 27 December 1995 / Revised: 20 May 1996 / Accepted: 26 May 1996     

Electrothermal atomic absorption spectrometry in the study of metal ion speciation

The literature on the use of electrothermal atomic absorption spectrometry (ETAAS) in the determination of metals in speciation studies of different samples is comprehensively reviewed. The methods of extraction, preconcentration, etc. in connection with speciation studies have been highlighted. The ETAAS programmes and other details of the developed methodologies are discussed. On critical examination it becomes obvious that chromium is the metal which has been analysed by most workers. Study of other metals falls in the following order: Pb, Sn, Cu, As, Al, Cd, Zn, Fe, Ni and Se. It is clearly evident that the major work on metal ion speciation has been carried out in natural water, followed by biological materials. There are also many reports on the speciation analysis of soil and sediment. Only a few papers have been published on metal speciation in airborne particulates. The analytical details of the developed methodologies have been examined in terms of limit of detection, precision and accuracy. Received: 27 December 1995 / Revised: 20 May 1996 / Accepted: 26 May 1996     

Speciation of organotin in sediments by multicapillary gas chromatography with atomic emission detection after microwave-assisted leaching and solvent extraction-derivatization

Microwave-assisted leaching of organotin compounds from sediment samples followed by the simultaneous extraction-derivatization of the extracted species was revisited with the goal to compare the existing procedures, improve their recoveries and extend them to phenyltin compounds. The stability of butyl- and phenyltin compounds under microwave field, real recoveries of the whole analytical procedure, effect of the extraction solvent, and the necessity for an internal standard were evaluated using two candidate reference sediments. The combination of the optimized sample preparation procedure with multicapillary chromatography resulted in a rapid (2 min leaching + 5 min extraction-derivatization + 3 min chromatographic separation) and efficient analytical procedure for speciation analysis of organotin compounds in sediment samples. The detection limit achieved with a microwave-induced plasma atomic emission detector was 2 ng g^–1. Received: 27 July 1998 / Revised: 31 August 1998 / Accepted: 4 September 1998     

Flow injection analysis of fluoride in electroplating baths with potentiometric detection

A high dispersion FIA system with a fluoride selective and a double junction reference electrode in cascade arrangement was developed for the determination of the fluoride content in chromium electroplating baths. The analyses of seven synthetic baths prepared in the laboratory and two samples provided by the industry gave results with a mean recovery value of 100.5%, and a mean variation coefficient of 1.6%. These data were better than those obtained by the EDTA complexometric titration, the reference technique, with a mean recovery of 94.0% and a mean variation coefficient of 7.5%. The sampling rate for the FIA manifold was 20 samples per hour. Received: 27 November 1997 / Revised: 24 February 1998 / Accepted: 1 March 1998     

Introduction to the EU-network on trace element speciation: preparing for the 21st century

The main objective of the EU-network is to bring together scientists with a background in analytical chemistry interested in speciation method development with potential users from industry and representatives from legislative bodies. The network started on 1/10/1997 for a duration of 2 years. A series of meetings are being organised to debate all the important questions for collecting information on environmental, food and occupational health aspects of speciation and to define possible future projects. The findings and conclusions will be summarised as a series of general papers that will be published in the open literature, recapitulating the essential information gathered to date, outlining the state of the art for each topic and recommending legislative actions. A first meeting was held in Überlingen, Germany on 5–6 December 1997. The representatives from industry explained their interest in the network and the participants from the academic and national institutes gave a state-of-the-art presentation of their research. Out of this, a program was compiled for the following meeting in Segovia from 16 to 20 March 1998. The topics dealt with were: organotin compounds in the environmental session; the speciation and bioavailability of trace element species (Cr, Fe, Se), the quality of the data and new legislation in the food session; and identification of inhaled particles and the search for bioindicators for exposure to Ni and Pt in the occupational health/hygiene session. In each session about half of the participants came from industry. The delegates agreed on a list of priorities in speciation analysis. A www-page has been created: hhtp://www. speciation 21.plymouth.ac.uk. Everybody interested in adding information to the page is requested to mail this to lpitts@plymouth.ac.uk     

Determination of the plasticizer N-butylbenzenesulfonamide and the pharmaceutical Ibuprofen in wastewater using solid phase microextraction (SPME)

A rapid, inexpensive and solvent-free method for the simultaneous determination of the polyamide plasticizer N-butylbenzenesulfonamide (NBBS) and the widely used pharmaceutical Ibuprofen by solid phase microextraction (SPME) combined with gas chromatography/mass spectrometry (GC/MSD) in wastewater samples was developed. Besides the optimized analytical conditions, results of investigations with varying analytical parameters are reported. Problems, which may occur during the analytical procedure (e.g. salt deposits, adsorption phenomena, carry-over), are discussed. For the determination of Ibuprofen, it is important to carry out the extraction under acidic conditions with sufficiently buffered samples; the GC/MSD system must be very clean and well maintained. SPME allows an extraction of Ibuprofen without derivatization of its carboxylic group. For quantification in complex matrices, the standard addition technique is necessary. Limit of detection and limit of determination are 0.1 μg/L for both analytes. NBBS and Ibuprofen were detected in several raw and treated wastewater samples from municipal wastewater treatment plants in the range from < 0.1 to 3.5 μg/L. Received: 13 March 1998 / Revised: 16 June 1998 / Accepted: 19 June 1998     

Simultaneous determination of chromium(VI) and chromium(III) at trace levels by adsorptive stripping voltammetry

A new methodology was proposed for the speciation of chromium by differential pulse adsorptive stripping voltammetry (DPAdSV) using pyrocatechol violet (PCV) and N-(2-hydroxyethyl)ethylenediamine-N,N′,N′-triacetic acid (HEDTA) as complexing agents. In this procedure, a partial least squares (PLS) regression was used for the resolution of the strongly overlapping voltammetric signals from mixtures of Cr(III) and Cr(VI) in the presence of PCV and HEDTA. The relative error in absolute value was <6% when concentrations of several mixtures were calculated. The analysis of the possible effect of the presence of foreign ions in the solution was performed. The procedure was successfully applied to the speciation of chromium in different samples of natural water.     

Preparation and characterisation of chromium and sodium tantalate layers by anodic spark deposition

A plasma-electrochemical synthesis was used to prepare chromium and sodium tantalate layers. These layers were deposited on a tantalum anode surface as ceramic compounds from aqueous electrolytes. The typical pore structure morphology of the tantalate layer was characterised by SEM as well as fractures which provide evidence of an intimate contact between layers and substrate. An XRD-study showed that the layers are composed of a mixture of Ta₂O₅ and either NaTaO₃ or CrTaO₄ depending on the electrolyte composition. Quantitative characterisation by EPM indicated higher chromium and tantalum concentrations on the electrolyte/layer interface than at the layer/tantalum interface. The chemical state of tantalum was investigated by means of XPS. Received: 15 July 1997 / Revised: 5 March 1998 / Accepted: 9 March 1998     

Speciation,separation and enrichment of Cr(III) and Cr(VI) in environmental samples by ion-pair solvent extraction using a β-diketone ligand

A simple speciation, separation and enrichment method has been developed for the determination of Cr(III) and Cr(VI) ions in different samples by ion-pair solvent extraction with a β-diketone ligand, 2-(4-methoxybenzoyl)-N′-benzylidene-3-(4-methoxyphenyl)-3-oxo-N-phenyl-propono hydrazide (MBMP). Cr(III) was separated from Cr(VI) as Cr(III)-(MBMP)-perchlorate ternary ion-pair complex. The influences of various analytical parameters including pH, amount of reagent, shaking time, sample volume and ionic strength on the recovery of Cr(III) and/or Cr(VI) were investigated. Total chromium was obtained after reducing Cr(VI) to Cr(III) with NH₂OH?·?HCl. Recoveries were found to be higher than 95% and the relative standard deviation (RSD) was less than 2%. The method detection limit based on 3σ criterion for Cr(III) was found to be 0.32?µg?L^?1. The formed ternary ion-pair complex, Cr(III)?:?MBMP?:?2ClO₄, has a molar ratio of 1?:?1?:?2. The developed method has been applied successfully to the speciation of chromium in various natural water, soil, sediment and hair samples with satisfactory results.     

Toward chromium speciation in solids using wavelength dispersive X-ray fluorescence spectrometry Cr Kβ lines

The determination of chromium speciation in solid samples is critical for environmental and industrial purposes. Several analytical methods exist to perform such a determination either directly in solid state or liquid state after an extraction step, each of them having some limitations. In this study, the use of a high-resolution wavelength-dispersive X-ray fluorescence spectrometer to determine and quantify chromium species is investigated by looking at the differences in the Kβ transition profiles between Cr(0), Cr(III) and Cr(VI) compounds. Three different approaches were tested and compared to determine the Cr(VI) fraction of known mixtures: relative height and peak fitting using calibration mixtures, partial least square regression (PLS) of pure compounds, and principal component regression (PCR) of pure compounds. The accuracy of these methods was found to be about the same with an average relative error in the range of 15%. However, PLS and PCR can be easily implemented in an automated way contrary to peak fitting which can be sometimes perceived as analyst-dependant. Another advantage of using PLS and PCR is that information concerning the other oxidation states present in the sample can be retrieved. Finally, PLS and the peak height approach can be used up to 0.5% total chromium which make the XRF an alternative technique to X-ray induced photoelectron spectroscopy (XPS) for chromium speciation in solid state.     

Ultrasonic assisted deep eutectic solvent liquid–liquid microextraction using azadipyrromethene dye as complexing agent for assessment of chromium species in environmental samples by electrothermal atomic absorption spectrometry

A novel type of solvent named deep eutectic solvent (DES) has been considered as a green ionic liquid analogue. A novel method was developed for enrichment and speciation of chromium ion from water and food samples based on deep eutectic solvent and ultrasonic extraction. The procedure for this method was comprised of Cr(III) complex formation with a hydrophobic complexing agent (Z)‐N‐(3,5‐diphenyl‐1H‐pyrrol‐2‐yl)‐3,5‐diphenyl‐2H‐pyrrol‐2‐imine (azadipyrromethene dye). Metal complex was entrapped in a deep eutectic solvent as an extracting solvent. While Cr(III) recovery was quantitative, the recovery of Cr(VI) was found 5%. After reduction of Cr(VI) to Cr(III), the method was applied for determination of total chromium(III) ion. The amount of Cr(VI) was calculated as subtracting of Cr(III) from total chromium ion. Various analytical parameters were optimized. The certified reference materials were analyzed and standard addition method also carried out to real samples to check the accuracy of the developed method. Preconcentration factor was found to be 50. The limit of detection of chromium(III) was found to be 4.3 ng l^‐1. The precision of developed method as the relative standard deviation (RSD) was found as 3.5 %. The developed method was applied successfully for the speciation of chromium ions in water and food samples.     

Highly sensitive semi-quantitative field test for the determination of chromium (VI) in aqueous samples

A method for the semi-quantitative colorimetric determination of chromium(VI) at sub μg/L levels after sorptive preconcentration is presented. The method is based on the retention of the reaction product (preformed in liquid phase) between Cr(VI) and diphenylcarbazide on membrane embedded cation exchange material. The color intensity of the membrane can be correlated to Cr(VI) concentrations in the range 0.05–50 μg/L (i.e. almost three orders of magnitude lower than the conventional spectrophotometric procedure) with a detection limit of about 10 ng/L (using 50 mL of sample volume). Due to the visual inspection mode and comparative color detection the precision is only 30–80% rsd which, however, is regarded as sufficient for screening purposes. Analysis of real samples including different kinds of waters and extracts of soil and filter collected airborne particulate matter demonstrated the applicability of the method for fast and species selective screening. Recovery experiments generally gave reasonably good results, yet also revealed the risk of the conversion of chromium species during sample pretreatment procedures due to redox reactions. Received: 1 December 1997 / Revised: 23 February 1998 / Accepted: 10 March 1998     

Speciation of Cr(III) and Cr(VI) in environmental samples by using coprecipitation with praseodymium(III) hydroxide and determination by flame atomic absorption spectrometry

A speciation procedure has been established for the flame atomic absorption spectrometric determination of Cr(III) and Cr(VI) based on coprecipitation of Cr(III) by using praseodymium(III) hydroxide (Pr(OH)₃) precipitate. In the presented system, Cr(III) was quantitatively (>95%) recovered at the pH range of 10.0?C12.0 on Pr(III) hydroxide, while the recoveries of Cr(VI) were below 10%. The method was applied to the determination of the total chromium after reduction of Cr(VI) to Cr(III) by using hydroxylamine hydrochloride. The concentration of Cr(VI) is calculated by difference of total chromium and Cr(III) levels. The analytical parameters including pH of the aqueous medium, amount of Pr(III), centrifugation speed, sample volume were optimized. The influences of matrix ions were also investigated. The method was validated by the analysis of TMDA 70 fortified lake water certified reference material. The method was applied to the speciation of chromium in water samples.     

Platinum and rhodium in a polluted environment: studying the emissions of automobile catalysts with emphasis on the application of CSV rhodium analysis

An analytical approach is presented that utilizes CSV (cathodic stripping voltammetry) determination of Pt and Rh in polluted common grass, successfully discriminating trends in the imission situation. A sampling strategy was developed leading to clear spatial trends. It is shown that additional detection of Rh helps to confirm accuracy even of peak Pt concentrations. Applicability and reliability of CSV Rh (and Pt) detection is proven during comparative measurements in other laboratories. Independent instrumental methods (ICP-MS, docimasy) confirmed CSV results, particularly in the case of Rh. In 1997, concentrations of Pt and Rh in grass samples were found to be 2.7 times higher than in 1994, and in dust samples 3.9 times higher than in 1994, respectively. Percentage of cars equipped with catalytic converters, on the other hand, was 2.4 times higher in 1997 compared with 1994. Some of the first rhodium concentrations in environmental samples are reported. Received: 11 February 1998 / Revised: 30 March 1998 / Accepted: 1 April 1998     

Speciation of chromium in waste waters by coupled column ion chromatography-inductively coupled plasma mass spectrometry

An application of coupled column ion chromatography (IC)-inductively coupled plasma mass spectrometry (ICP-MS) is presented for speciation of chromium in waste waters. By coupling an anion column with a cation column, both the cationic Cr(III) and anionic Cr(VI) species can be analyzed with detection limits below 0.5 μg/1. The separation of the interfering ions (chloride, chlorate, perchlorate, sulphate, sulphite, sulphide, thiosulphate, carbonate, cyanide and some organic compounds) from the chromium peaks is discussed, and the use of different chromium isotopes for data acquisition is compared. Based on the results, m/z 52 was considered as an ideal isotope for speciation of chromium in waste waters by the coupled column IC-ICP-MS, because it did not suffer from polyatomic interferences and due to the high sensitivity for chromium. The analysis of the waste water samples should be performed as soon as possible after sampling according to the stability tests of the species.