M. Llobat-Estellés

Preconcentration and speciation of chromium in waters using solid-phase extraction and atomic absorption spectrometry.

A method for the preconcentration and speciation of chromium was developed. After formation of an anionic compound with ethylenediaminetetraacetic acid (CrY(-)), Cr (VI) and Cr (III) are retained on a strong anionic phase (SAX) and controlled elution with 0.5 M NaCl permits their speciation. The retention and elution conditions were optimised, and interferences due to the presence of other ions such as Mg(II), Mn(II), Sn(II), Fe(III), Ba(II), Al(III), Ca(II), chloride, iodine, bromide, fluoride, sulphate, phosphate, bicarbonate and nitrate were studied. The detection limits were 0.4 mug l(-1) and 1.1 mug l(-1) for Cr(III) and Cr(VI), respectively, and reproducibility was 9%. The results obtained for speciation of chromium by the proposed method in wastewaters are in agreement with the values obtained by a reference method for a 95% confidence level.

Detection of bias errors in ETAAS Determination of copper in beer and wine samples.

A method that evidences changes in the shape of the absorbance profiles obtained by graphite furnace atomic absorption spectrometry (ETAAS) is proposed. The method is based upon the apparent content curves model previously described for molecular spectroscopy and it permits the detection of possible sources of bias errors. Moreover, a procedure that allows to detect the existence of constant and/or proportional errors is also described. Both models has been applied to the determination of copper in wine and beer samples with and without pre-treatment of the samples. Results obtained evidence the usefulness of the proposed models.

Comparative evaluation of liquid chromatography versus gas chromatography using a β-cyclodextrin stationary phase for the determination of BTEX in occupational environments

An HPLC method for the determination of benzene, toluene, ethylbenzene and o-xylene, m-xylene and p-xylene in occupational environments was developed and compared with a GC-MS method. Chromatographic analysis using a beta-cyclodextrin stationary phase was performed after active and passive air sampling by adsorption on activated charcoal and pressurized fluid extraction. The analytes were completely separated and quantified using both methods, although GC-MS provided better resolutions and lower detection limits than HPLC. The HPLC method was unsuccessfully applied to the determination of benzene in real samples because its sensitivity was too low. Both methods were applied to the analysis of certified reference materials and air samples collected in several workplaces. Statistical comparison showed that HPLC and GC-MS provided analogous accuracy.

Kinetic and chemometric studies of the determination of creatinine using the Jaffé reaction. Part 2. Application to human serum samples: kinetic behaviour and chemometric evaluation of the determination

The kinetic behaviour of the reaction of alkaline picrate with creatinine in human serum samples was found to be similar to that for standard creatinine solutions containing albumin. A chemometric evaluation of the kinetic determination of creatinine using the Jaffé reaction was carried out. The analysis of variance (ANOVA) method applied to the delta A45,180 values, obtained from two replicates of three different serum samples over a period of 10 d, showed that the between-day and between-replicate variations added a component to the total variability, the residual error (delta R2) being 5 X 10(-5). A study of the accuracy of the determination was carried out by means of percentage recovery experiments, Youdens method and the standard additions method. Percentage recovery experiments showed that albumin has a marked effect on the results obtained. The application of Youdens method to four serum samples indicated that the method does not have a constant bias error, but, by applying the standard additions method it was concluded that the method has a proportional bias error. The recovery factor, defined as the ratio of the slope of the standard additions graph to that of the standard response graph, was also calculated for the four serum samples. The best values were obtained with different standard response graphs (7.7, 15.4 and 25.6 g l-1 of albumin) for each sample. A modification of the routine procedure used in clinical laboratories is proposed. This modification is based on the principles of the standard additions method and gives better results for creatinine content than those obtained with the routine procedure.

Samplers for VOCs in air based on cyclodextrin–silica hybrid microporous solid phases

Samplers for VOCs in air based on cyclodextrin-silica hybrid microporous solid phases are proposed. The solid phase preparation is very easy and inexpensive. Proposed samplers compared with other solid phases present the advantages of a wider range of operative conditions for VOCs desorption. Samplers are tested based on results for the determination of benzene, toluene, ethylbenzene and o-xylene, m-xylene and p-xylene (BTEX) in air. Operational parameters are optimized and quantitative recovery is obtained using a solid phase from 2-hydroxypropyl-β-cyclodextrin and acetonitrile as the extraction solvent. The recoveries obtained are 89 ± 4%, 90 ± 6%, 91 ± 2%, 87.0 ± 0.9%, 88 ± 4%, and 88 ± 4% for benzene, toluene, ethylbenzene, o-xylene, m-xylene and p-xylene, respectively. Moreover results indicate a good reproducibility with a coefficient of variation below 6% and no significant difference between the reproducibility intra-synthesis and inter-synthesis. The proposed procedure has been applied to the determination of BTEX in several contaminated air samples and compared with results provided by a reference method.

Kinetic and chemometric studies of the determination of creatinine using the Jaffé reaction. Part I. Kinetics of the reaction: analytical conclusions

A kinetic-spectrophotometric study of the Jaffé reaction was carried out and the kinetic behaviour, calibration step and interfering effect of albumin on creatinine standard solutions were studied. It was concluded that there is a variation in the kinetic behaviour of the system when higher concentrations of creatinine, picrate or sodium hydroxide are tested. The experimental conditions for quantifying creatinine must be chosen so that the kinetic behaviour is the same in the dynamic concentration range. Changes in the absorbance (delta A) versus concentration equations were chosen as the most suitable for calibration graphs. It was also shown that creatinine results will have a proportional bias error if the interfering effect of albumin is not taken into consideration.

Chromatographic Separation of Cresol Isomers by a β‐Cyclodextrin: Application for the Determination of Volatile Phenols in Alcoholic Beverages

Abstract The chromatographic separation of o‐cresol, m‐cresol, and p‐cresol by using β‐cyclodextrin as a chiral reagent has been studied. Conditions for the chromatographic separation of these isomers by using the cyclodextrin in the mobile phase or bonded in the stationary phase were optimized, and both procedures provided good results for the resolution of the chromatographic peaks. The use of fluorimetric detection (λexc 275 nm λem 300 nm) allows detection and quantification limits of the µg/L for eight studied phenols by using both procedures. The determination of volatile phenols in alcoholic beverages must be carried out using the cyclodextrin in the mobile phase because of the co‐elution of phenol and ethylguaiacol with other compounds of some studied matrix.

Spectrophotometric determination of the theophylline in plasma by the apparent content curves method

A direct spectrophotometric procedure for the determination of theophylline in plasma is proposed. This procedure is based on the apparent content curves method and it is not necessary to know the nature and contents of interferent substances. Bias errors introduced by plasma and metabolites are avoided. The results obtained are in agreement with those provided by an immunofluoroassay used as a reference method.