A.M. Gutiérrez

Sequential extraction of U, Th, Ce, La and some heavy metals in sediments from Ortigas river, Spain

The extractable contents of U, Th, Ce, La, Cu, Cr, Ni and Zn in two sediment samples collected from the Ortigas river have been analysed using the three step sequential extraction procedure (SEP) described by BCR, Community Bureau of Reference (now Standards Measurements and Testing Programme) of the European Union. In order to perform a mass balance, a fourth step has been included, i.e. digestion of the residue from the third extraction step. ICP-AES was used for the determination of Cu, Cr, Ni, Zn, Th, Ce and La. Because of the inadequate sensitivity of ICP-AES for the analysis of uranium, ICP-MS was used for the determination of this element. Standard addition method was required, because of the matrix effects. Finally, SEP was applied to the Ortigas river sediments, showing that most of the elements were found mainly associated with the residual sediment fraction, except for uranium, which was found as an exchangeable species in approximately 60% of its total content. Recoveries of 86-108% have been obtained.

Selenium speciation in animal tissues after enzymatic digestion by high‐performance liquid chromatography coupled to inductively coupled plasma mass spectrometry

A procedure is described for the enzymatic digestion of tuna and mussel samples that allows the determination of selenium species by high-performance liquid chromatography in conjunction with inductively coupled plasma mass spectrometry. The species were extracted by two-step enzymatic hydrolysis with a non-specific protease (subtilisin). The selenium species were separated on a Spherisorb 5 ODS/AMINO column using two different chromatographic conditions, namely phosphate buffers at pH 2.8 and pH 6.0 as mobile phases. The method determines organic (trimethylselenonium, selenocystine, selenomethionine and selenoethionine) and inorganic selenium species (selenite and selenate), but only organic selenium species were found in the samples. The sum of identified selenium species in the sample was about 30% of the total selenium present in the enzymatic extract despite the fact that recoveries of total hydrolysed selenium were 93-102%. Trimethylselenonium ion and selenomethionine were found in both tuna and mussel samples and an unknown selenium species was also found in tuna samples.

Determination of selenocystine, selenomethionine, selenite and selenate by high-performance liquid chromatography coupled to inductively coupled plasma mass spectrometry

An analytical method has been developed for the determination of selenocystine, selenomethionine, selenite and selenate. Separation of the four Se species was achieved by HPLC on a Spherisorb 5 ODS–AMINO column using a concentration gradient from 3.5 to 7.0 mmol l–1 phosphate buffer of pH 6.0 as the mobile phase at a flow rate of 1.0 ml min–1. Detection was carried out using an on-line inductively coupled plasma mass spectrometer. The chromatographic parameters and the chemical factors affecting the separation of the Se species were optimized. The detection limits, using a 100 µl sample loop volume and expressed as Se, were found to be 2.0, 1.0, 1.6 and 1.2 µg l–1 for selenocystine, selenomethionine, selenite and selenate, respectively. The precision was better than 5% in all instances. The method was successfully applied to the determination of the four Se species in water samples certified for selenite and selenate, to which selenocystine and selenomethionine had been added.

Electrophysiological aspects of sensory conduction velocity in healthy adults. 1. Conduction velocity from digit to palm, from palm to wrist, and across the elbow, as a function of age.

The sensory conduction velocity from digit to palm and from palm to wrist was determined in median (digit 3) and ulnar (digit 5) nerves in 47 healthy subjects with age range from 21 to 77 years. The decrement of the sensory conduction as a function of age was more marked in the palm to wrist than in the digit to palm segment. Sensory conduction velocity of the ulnar nerve across the elbow was also studied. Irregularities in the shape of the sensory evoked potential recorded above the cubital sulcus were found in 12.76% of cases, especially in subjects over 50 years of age. These results suggest that aging causes decrement in sensory conduction and changes in the shape of the evoked potentials, especially at points where the nerves are more frequently compressed.

Development of a fluoroimmunosensor for theophylline using immobilised antibody

A flowthrough theophylline fluoroimmunosensor with an antibody covalently immobilised on a solid support has been developed. The immobilisation technique proposed in this paper used Protein-A on control pore glass (Protein A-CPG) in an immunoreactor and dimethylsuberimidate as a cross-linking agent. Several supports and cross-linking reagents were tested in order to obtain oriented immobilisation and thus efficiency of the immunological reaction and reusability of the immunosensor. The immunosensor performance characteristics were established. The precision expressed as RSD, was 1.6%; the detection limit was 3 mug l(-1); the immunoreactor lifetime was established in 80 assays and there were no interferences with structurally similar compounds such as aminophylline, dihydroxypropyltheophylline and caffeine in the determination of the analyte. This fluoroimmunosensor was applied to determine theophylline in human serum samples from patients of the Puerta de Hierro Hospital in Madrid. The results obtained show that there are no significant differences between the proposed immunosensor and the high-pressure liquid chromatographic method with UV detection used by the Hospital, thus demonstrating the validity of the method.

Determination of selenium species in human urine by high performance liquid chromatography and inductively coupled plasma mass spectrometry

A method developed to determine organic and inorganic selenium species in human urine samples is presented in detail. After a simple sample treatment based on elimination of non-charged organic compounds, selenium species were separated by high performance liquid chromatography (HPLC) on a Spherisorb 5 ODS/AMINO column using two different chromatographic conditions: phosphate buffers at pH 2.8 and 6.0. Detection was carried out using an on-line inductively coupled plasma mass spectrometer (ICP-MS). Trimethylselenonium ion and two unknown selenium species in urine samples were found. Selenium species were shown to have stability problems, with the maximum allowed storage time of 1 week.

Determination of lead in natural waters using flow injection with on-line preconcentration and flame AAS detection

A rapid and sensitive method has been developed for the determination of lead in water samples by flame atomic absorption spectrometry using on-line preconcentration on a microcolumn packed with silica gel treated with a mixture of Aliquat 336 and nitroso-R-salt. The lead is retained at pH 5.5. The preconcentrated lead is directly eluted from the column to the nebulizer-burner system using 150 μL of 0.1 mol/L hydrochloric acid. The optimum preconcentration conditions are given and the retention efficiency achieved is higher than 80%. The enrichment factor is 37 and 100 for sample volumes of 5 and 30 mL, respectively. The limits of detection are 10.0, 6.0 and 4.0 ng/mL when 5, 10 and 30 mL of water is preconcentrated.

On-line aluminium preconcentration on chelating resin and its FIA-spectrofluorimetric determination in foods and dialysis concentrates.

A new, sensitive and rapid spectrofluorimetric flow-injection method, is presented for the determination of trace levels of aluminium based on the formation of a fluorescent complex between aluminium and 5,7-dibromo-8-quinolinol (DBQ) and its extraction into diethylether (lambda(exc) = 400 nm, lambda(em) = 525 nm). Experimental conditions such as pH, reagent concentration, flow-rates, sample volume, extraction coil length, etc., have been optimized for on-line and batch procedures. The detection limits are 1 ppb and 0.3 ppb for batch and on-line systems respectively. The coeflicient of variation is 3.0% at the 4 ppb level for the FIA system. To remove interferences and to preconcentrate aluminium, a chelating resin microcolumn which was able to selectively complex A1(III) and was obtained by immobilizing Chromotrope 2B on AG1-X8 ion-exchange resin, was incorporated into the FIA system. The proposed method was successfully applied to determine aluminium in tap water, food samples and dialysis solutions.

Se metallomics during lactic fermentation of Se-enriched yogurt.

Selenium biotransformation by lactic acid bacteria during the preparation of Se-enriched yogurt was evaluated. The study focused on the distribution of selenium in the aqueous soluble protein fraction and the detection of selenoamino acids. Screening of selenium in Tris-buffer-urea soluble fraction was carried out by sodium dodecyl sulphate polyacrylamide gel electrophoresis after pre-fractionating with asymmetric field flow fractionation using inductively coupled plasma-mass spectrometry as the detector. Selenium-containing fractions were identified by peptide mapping using nano LC-ESI/LTQMS. Proteins such as thioredoxin, glutaredoxin, albumin, β-lactoglobulin, and lactoperoxidase were identified in the selenium-containing fraction. All these proteins were detected in both the control and the selenium-enriched yogurt except chaperones, which were only detected in the control samples. Chaperones are heat-shock proteins expressed in response to elevated temperature or other cellular stresses. Selenium may have an effect on chaperones expression in Lactobacillus. For the amino acids analysis, selenocysteine was the primary seleno-containing species.

On-line preconcentration of aluminium with immobilized Chromotrope 2B for the determination by flame atomic absorption spectrometry and inductively coupled plasma mass spectrometry

Abstract A new and rapid on-line preconcentration and matrix separation method is described for the determination of aluminium by flame atomic absorption spectrometry (FAAS) and inductively coupled plasma mass spectrometry (ICP-MS). The method is based on selective retention of aluminium in a microcolumn packed with Chromotrope 2B immobilized on AG 1-X8 ion exchange resin. All the variables that affect the efficiency of aluminium retention and elution from the microcolumn have been investigated. The resulting method is rapid, sensitive and selective. For collection times of 10 and 2 min at a flow rate of 1 ml min −1 the detection limits are 10 and 0.1 ng ml −1 for FAAS and ICP-MS, respectively. The proposed method, which is highly sensitive and selective, was successfully applied to determine aluminium in tap water and dialysis solutions.