M. Luisa Cervera

Metal speciation in solid matrices

The literature on metal ion speciation in solid matrices is reviewed, taking into account its applications in the analysis of soil, sediment, biological materials, foodstuff and other solid samples. The pretreatment methods of various solid materials required for carrying out speciation studies have been highlighted. The basis of the methods of separation of different species from matrices, such as sequential extraction, selective extraction, etc. is discussed. The instrumental techniques used for the characterization of different chemical species in solid matrices have been mentioned. The literature survey reveals the analytical details of the developed methodologies, and these have been examined in terms of the limit of detection, precision and accuracy.

Literature survey of on-line elemental speciation in aqueous solutions

The literature about the on-line speciation in water has been comprehensively studied. Critical examination of this subject reveals that a great deal of work has been performed in this area for inorganic metal species and some organic compounds. The topic studied mainly includes the speciation of chromium, selenium, copper, arsenic, lead, cadmium, mercury, iron, aluminium, nickel, tin, antimony, phosphorus, nitrogen and others. The present literature survey includes also comments about the possibilities and problems of speciation as a function of analytical steps, general strategies involved and methods proposed in the literature for each element or a series of elements.

Mechanism of porous core electroosmotic pump flow injection system and its application to determination of chromium(VI) in waste-water

An electroosmotic pump flow injection system is introduced in this paper. According to electroosmotic theory, the pumps properties were described. A large flow range (mul min(-1)-ml min(-1)), moderate carrier pressure (>0.15 MPa), reduced performance voltage (<500 V) and stable flow rate (RSD<3.0% in 4 h) are the main properties of the pump. NH(4)OH (0.35 mM) was used as carrier for improving the pumps flow stability. The electroosmotic efficiency of the pumps medium, porous core, can be recovered and regenerated. A sandwich zone was used for sample and reagent introduction in order to adapt to the pump performance. Flow injection-spectrophotometry was employed for the determination of Cr(VI) in waste-water, based on the formation of the complex with 1,5-diphenylcarbazide and absorbance measurement at 540 nm. Within the calibration range of 0-7.0 mg l(-1) of Cr(VI), the RSD was 0.4% (n=5). The recovery of 0.70 mg l(-1) Cr(VI) added to the waste-water sample was 94.5+/-2.0% (n=5).

Determination of arsenic and antimony in milk by hydride generation atomic fluorescence spectrometry.

A highly sensitive procedure has been developed for total arsenic and antimony determination in milk samples by hydride generation atomic fluorescence spectrometry after microwave-assisted sample digestion. The discrete introduction of 2 ml of digested sample in the automated continuous flow hydride generation system allows us to reduce drastically the sample and HCl consume and to determine several elements from a same sample digestion. The method provides detection limits of 0.006 and 0.003 ng ml(-1), a sensitivity of 2390 and 2840 fluorescence units per ng ml(-1) for As and Sb respectively, and average relative standard deviation of 2.3% for As and 4.8% for Sb. The analysis of cow milk samples, obtained from the Spanish market evidenced the presence of As at concentration levels from 3.4 to 11.6 ng g(-1) and Sb levels from 3.5 to 11.9 ng g(-1), thus in a proportion near to 1:1, which is in contrast with the 10:1 natural ratio between As and Sb and could evidence the effect of the introduction of new alloys and polymer materials in the industrial process of milk. The method was validated by the comparison of data found for commercial samples by using the proposed procedure and reference methods based on dry-ashing and AFS, and microwave-assisted digestion and inductively coupled plasma mass spectrometry determination.

Determination of mercury in rice by cold vapor atomic fluorescence spectrometry after microwave-assisted digestion

A cold vapor atomic fluorescence spectrometry method (CV-AFS) has been developed for the determination of Hg in rice samples at a few ngg(-1) concentration level. The method is based on the previous digestion of samples in a microwave oven with HNO(3) and H(2)O(2) followed by dilution with water containing KBr/KBrO(3) and hydroxylamine and reduction with SnCl(2) in HCl using external calibration. The matrix interferences and the effect of nitrogen oxide vapors have been evaluated and the method validated using a certified reference material. The limit of detection of the method was 0.9ngg(-1) with a recovery percentage of 95+/-4% at an added concentration of 5ngg(-1). The concentration level of Hg found in 24 natural rice samples from different origin ranged between 1.3 and 7.8ngg(-1).

Multi-elemental analysis of mussel samples by atomic absorption spectrometry after room temperature sonication

A simple procedure was developed for the room temperature leaching of several elements from mussel samples with a solution of 1.6 M HNO3, 1.2 M HCl and 0.1 M H2O2. The method involves the use of a sonication time of 120 min and determination by flame (FAAS) and electrothermal atomic absorption spectrometry (ETAAS). Ca, Cu, Fe, K, Mg, Mn, Na, V and Zn were quantitatively recovered and Cd, Co, Cr, Rb and Se were partially leached; the leaching of Cs and Sc was poor. The effect of sample mass, reagent leaching mixture and sonication time on the extraction of the elements was evaluated from the direct analysis of the acidic phase by AAS and of the remaining solids by neutron activation analysis. The results obtained by the proposed procedure were evaluated by comparison with those obtained by ICP-MS and AAS after microwave-assisted digestion and also with those found by direct analysis of the solid sample by neutron activation. The method provides a limit of detection of 0.081, 0.012, 0.059, 0.002 and 0.007 µg ml–1 for Ca, Cu, Fe, Mg and Zn, respectively, and 0.342 ng ml–1 for Mn, and RSD values from 0.6 to 7.1% as a function of the element concentration. The recovery values found in the analysis of spiked samples ranged from 92 to 109%, and relative errors lower than 9% were found in the analysis of a certified mussel tissue.

Non-chromatographic speciation of toxic arsenic in fish

A rapid, sensitive and economic method has been developed for the direct determination of toxic species of arsenic present in fish and mussel samples. As(III), As(V), dimethylarsinic acid (DMA), and monomethylarsonic acid (MMA) were determined by hydride generation-atomic fluorescence spectrometry using a series of proportional equations without the need of a chromatographic previous separation. The method is based on the extraction of arsenic species from fish through sonication with HNO(3) 3moll(-1) and 0.1% (m/v) Triton and washing of the solid phase with 0.1% (m/v) EDTA, followed by direct measurement of the corresponding hydrides in four different experimental conditions. The limit of detection of the method was 0.62ngg(-1) for As(III), 2.1ngg(-1) for As(V), 1.8ngg(-1) for MMA and 5.4ngg(-1) for DMA, in all cases expressed in terms of sample dry weight. The mean relative standard deviation values (R.S.D.) in actual sample analysis were: 6.8% for As(III), 10.3% for As(V), 8.5% for MMA and 7.4% for DMA at concentration levels from 0.08mgkg(-1) As(III) to 1.3mgkg(-1) DMA. Recovery studies provided percentages greater than 93% for all species in spiked samples. The analysis of SRM DORM-2 and CRM 627 certified materials evidenced that the method is suitable for the accurate determination of arsenic species in fish.

A review on molybdenum determination in solid geological samples

This review highlights the necessity for the development of proper sampling and storage, fast pretreatment methodology followed by highly sensitive detection for the determination of molybdenum in geological samples. Distribution of concentration and chemical speciation of molybdenum analysis in solid geological matrices have also been discussed.

Metal speciation in biological fluids — a review

The literature on the speciation of metal ions in biological fluids is comprehensively reviewed. Critical examination on this subject reveals that major work has been done in blood and urine. Speciation in materials like milk has not yet been widely studied. On the other hand, only few references could be found on sweat, saliva, cell lysate, cerebrospinal, seminal, tear and bronchoalveolar fluids. The topics studied for these fluids were mainly the speciation of arsenic, mercury, aluminium and selenium. Work on the speciation of other elements like zinc, chromium, cadmium, lead, copper, iron etc. have also been carried out in such matrices. The present literature survey includes also a critical comment about the sampling and storage of the fluids, general methodologies and analytical details of the developed methods for studying such metal ion speciation.

Determination of As, Sb, Se, Te and Bi in milk by slurry sampling hydride generation atomic fluorescence spectrometry.

A simple and fast analytical procedure has been developed for the determination of As, Sb, Se, Te and Bi in milk samples by hydride generation atomic fluorescence spectrometry (HG-AFS). Samples were treated with aqua regia for 10min in an ultrasound water bath and pre-reduced with KBr for total Se and Te determination or with KI and ascorbic acid for total As and Sb, the determination of Bi being possible in all with or without pre-reduction. Slurries of samples, in the presence of antifoam A, were treated with NaBH(4) in HCl medium to obtain the corresponding hydrides, and AFS measurements were processed in front of external calibrations prepared and measured in the same way as samples. Results obtained by the developed procedure compare well with those found after microwave-assisted complete digestion of samples. The proposed method is simple and fast, and only 1ml of milk is needed. The values obtained for detection limit are 2.5, 1.6, 3, 6 and 7ngl(-1) for As, Sb, Se, Te and Bi respectively in the diluted samples, with average relative standard deviation values of 3.8, 3.1, 1.9, 6.4 and 1.2% for three independent analysis of a series of commercially available samples of different origin. Data found in Spanish market samples varied from 3.2+/-0.3 to 11.3+/-0.2ngg(-1) As, from 3.1+/-0.2 to 11.6+/-0.4ngg(-1) Sb, from 10.7+/-0.5 to 25.5+/-0.4ngg(-1) Se, from 0.9+/-0.2 to 9.4+/-0.6ngg(-1) Te and from 11.5+/-0.1 to 27.7+/-0.4ngg(-1) Bi.