M. Burguera

Determination of chromium in urine by electrothermal atomic absorption spectrometry using different chemical modifiers

The effects of the chemical modifiers Eu, Mg(NO 3 ) 2 , Pd, Eu-Pd and Ni and the use of longitudinally (with deuterium lamp background correction) and transversally (with Zeeman effect background correction) heated atomizers on the determination of chromium in urine samples were studied. When longitudinally heated atomizers were used, the background absorption was too high for the addition of most species, such as Mg(NO 3 ) 2 , Pd, Eu-Pd and Ni, rendering its use unsuitable for the determination of chromium in urine. The addition of Eu led to lower background signals. However, when longitudinally heated atomizers were used larger background absorption signals were observed on addition of a modifier. In contrast, with transversally heated atomizers the background absorption signals were low and were not influenced by the addition of a modifier, except when Mg(NO 3 ) 2 was added. In this case, the atomization signal shapes and the sensitivity were improved. The characteristic masses (m 0 ) and limits of detection (3σ) were 2.2 and 3.3 pg and 0.02 and 0.04 µg Cr l –1 for the longitudinally (using Eu as modifier) and transversally [using Mg(NO 3 ) 2 ] heated atomizers, respectively. Recovery studies and analysis of standard reference materials certified for chromium were performed to asses the accuracy. The results for the determination of chromium in real samples with both background correction procedures agreed well with a precision between 0.8 and 2.5%. Both procedures can be recommended and the choice will depend on instrument availability.

Flow injection–electrothermal atomic absorption spectrometry for arsenic speciation using the Fleitmann reaction

A hybrid procedure was developed for the selective determination of inorganic As species, based on the generation of arsine in a flow injection system by the Fleitmann reaction with its subsequent trapping in a graphite furnace coated with microgram amounts of possible absorbers. Efficient trapping of the arsine was achieved on Pd at 200 °C, although other elements, such as Ru, Ce, Ag and Pt, can also be used to sequestrate the hydride, but with lower sensitivity. Optimization of the experimental parameters affecting the generation and trapping of the arsine and the arsenic atomization resulted in improved sensitivity, which allowed an absolute detection limit of 10 pg of As. The recommended method was satisfactorily applied to the determination of inorganic As species in various types of water samples and of total As in a variety of certified reference materials.

In vivo sample uptake and on-line measurements of cobalt in whole blood by microwave-assisted mineralization and flow injection electrothermal atomic absorption spectrometry

An on-line automated microwave-assisted mineralization and flow injection system was developed for the determination of cobalt in whole blood with in vivo sample uptake by electrothermal atomic absorption spectrometry. The samples were drawn and at the same time pumped directly from the vein of a patients forearm to a timed injector, which is automatically controlled to inject the sample–nitric acid–anticoagulant mixture into the carrier stream. Volumes (20 µl) of the mineralized samples, collected in a capillary of a sampling arm assembly, were introduced by means of positive displacement with air through a time-based solenoid injector (TBSI) into the graphite tube atomizer. The spectrometer autosampler, used for the introduction of 10 µl of the chemical modifier, magnesium nitrate, and the furnace programme were re-programmed to synchronize with the operation of the flow system. The linear range was from 0 to 50 µg l–1 of cobalt, achieving a precision of 2.6 and 3.1% for 10 replicate analyses of a 5 µg l–1 cobalt standard solution and a certified sample, respectively, with a detection limit of 0.3 µg l–1. The agreement between the observed and certified values obtained from Seronorm Whole Blood Standard Reference Materials was good. The results obtained by using an in-batch procedure were found to linearly increase by 5% during the time interval between sample collection and analysis for the first hour; after this time the results for cobalt levelled off and were then in close agreement with those obtained by the on-line procedure proposed here.

Atomic absorption spectrometric analysis of solids with on-line microwave-assisted digestion

A procedure was developed for the on-line microwave-assisted digestion of solid samples and their analysis by flame atomic absorption spectrometry. The method involves the transport of a slurry of the sample in a 1 + 1 mixture of concentrated HNO3 and H2O2, which provides quantitative extraction of Cu and Mn in a few minutes. Real samples of sewage sludges dispersed in 20 cm3 of HNO3 and H2O2 can be digested in 4 min and other matrices, such as artichoke and diet samples dispersed in 10 cm3 of HNO3 and H2O2 are digested in only 2 min. A closed flow injection system permits the on-line digestion to be carried out; the use of two interconnected injection valves allows the measurement of standards during the digestion of samples. The method permits the analysis of more than 15 samples per hour and provides accurate results, as demonstrated by the analysis of certified samples of sewage sludges ad tomato leaves.

The use of emulsions for the determination of methylmercury and inorganic mercury in fish-eggs oil by cold vapor generation in a flow injection system with atomic absorption spectrometric detection

An on-line time based injection system used in conjunction with cold vapor generation atomic absorption spectrometry and microwave-aided oxidation with potassium persulfate has been developed for the determination of the different mercury species in fish-eggs oil samples. A three-phase surfactant-oil-water emulsion produced an advantageous flow when a peristaltic pump was used to introduce the highly viscous sample into the system. The optimum proportion of the oil-water mixture ratio was 2:3 v/v with a Tween 20 surfactant concentration in the emulsion of 0.008% v/v. Inorganic mercury was determined after reduction with sodium borohydride while total mercury was determined after an oxidation step with persulfate prior to the reduction step to elemental mercury with the same reducing agent. The difference between total and inorganic mercury determined the organomercury content in samples. A linear calibration graph was obtained in the range 0.1-20 micrograms l-1 of Hg2+ by injecting 0.7 ml of samples. The detection limits based on 3 sigma of the blank signals were 0.11 and 0.12 microgram l-1 for total and inorganic mercury, respectively. The relative standard deviation of ten independent measurements were 2.8 and 2.2% for 10 micrograms l-1 and 8.8 and 9.0% for 0.1 microgram l-1 amounts of total and inorganic mercury, respectively. The recoveries of 0.3, 0.6 and 8 micrograms l-1 of inorganic and organic mercury added to fish-eggs oil samples ranged from 93.0 to 94.8% and from 100 to 106%, respectively. Good agreement with those values obtained for total mercury content in real samples by electrothermal atomic absorption spectrometry was also obtained, differences between mean values were < 7%. With the proposed procedure, 22 proteropterous catfish-eggs oil samples from the northwestern coast of Venezuela were measured; while the organic mercury lay in the range 2.0 and 3.3 micrograms l-1, inorganic mercury was not detected.

Flow injection for automation in atomic spectrometry

The use of FI methods to extend the capabilities of atomic spectrometric detectors is discussed with emphasis on developments in automation. Topics such as direct sample introduction and on-line dilution, calibration, dissolution, liquid–liquid extraction, precipitation reactions, ion-exchange preconcentration, generation of volatile species and microwave sample pre-treatment are used to illustrate the versatility of coupling FI with either FAAS, ETAAS, ICP-AES, ICP-MS and/or AFS. Finally a brief overview of the advances in this research field is presented.

Determination of sodium, potassium, calcium, magnesium, iron, copper and zinc in cerebrospinal fluid by flow injection atomic absorption spectrometry

A method is proposed for the determination of sodium, potassium, calcium, magnesium, iron, copper and zinc in cerebrospinal fluid by flow injection atomic absorption spectrometry. The sample is injected as a discrete slug into a carrier stream of doubly distilled, de-ionised water. Standards are prepared in solutions containing physiological concentrations of various chemical species. Recoveries are 91–106%. The procedure is simple, quick, reliable and reproducible.

Electrothermal atomic absorption spectrometry determination of molybdenum in whole blood

Abstract A method for the determination of molybdenum in whole blood by atomic absorption spectrometry with electrothermal atomization was developed and evaluated. Erbium (25 μg) was chosen from several potential chemical modifiers (Sm, Lu, Ho, Eu and Pd+Mg) as the most appropriate for the sensitive and reliable determination of molybdenum in such sample. The process used was direct dilution of the sample in a ratio 1:2 with a 0.1% (v/v) Triton X-100 solution. The injection of 20 μl of a solution of 15% (w/v) hydrogen peroxide and running the temperature program after 5 firings greatly reduced the effect of build-up of carbonaceous residues within the atomizer. The limit of detection and working ranges, respectively, were 0.6 and 2.0–100.0 μg l−1, and the characteristic mass was 7.2 pg. The relative standard deviation varied from 0.8 to 1.5% for within and between batch determinations, respectively. The determination of molybdenum in Seronorm™ Trace Elements in Whole Blood with known added amounts of the analyte was performed to asses the accuracy. The optimized procedure has been applied to the determination of molybdenum in whole blood specimens of 20 subjects taken before and 10–12 h after receiving an over-supply of 1 mg of molybdenum. The molybdenum concentrations (±S.D.) were 10.9±0.4 μg Mo l−1 (range 9.9–11.6 μg Mo l−1) and 15.4±0.4 μg Mo l−1 (range 13.1–16.9 μg Mo l−1) for the individuals before and after the administration of molybdenum.

Determination of some organophosphorus insecticides by flow injection with a molecular emission cavity detector

Abstract The determination is based on the measurement of HPO emission at 528 nm in a H2/N2 flame. Organophosphorus insecticides are extracted with hexane/dichloromethane at pH

Flow injection-hydride generation system for the determination of arsenic by molecular emission cavity analysis

A system is described that permits the simple and rapid determination of nanogram amounts of arsenic (0.1–10 µg ml–1) in microlitre volumes of sample solutions by flow injection and hydride generation coupled with molecular emission cavity analysis. The effect of some interfering ions, including Ni, Ag, Zn, Cu, Te and Se, was eliminated or minimised by using a 0.01 M EDTA-0.2 M sodium iodide-1.5 M hydrochloric acid carrier solution in which the sample was injected. The method permits a sampling rate of ca. 100 measurements per hour. The method is illustrated by the determination of arsenic in NBS orchard leaves reference material with good accuracy.