Application of pressurized fluid extraction to determine cadmium and zinc in plants.

A procedure for the determination of Cd and Zn in plants is proposed. The metals are extracted by pressurized fluid extraction (PFE). Operational conditions are: pressure 1500 psi, temperature 75 degrees C, static time 5 min, flush volume 35%, purge time 60s, cycles 1 and 1,2-diaminocyclohexane-N,N,N',N'-tetraacetic acid (CDTA) 0.01M at pH 4.5 as extracting solution. Determination of Zn is carried out by flame atomic absorption spectroscopy and depending on the concentration level, Cd content is determined by flame or electrothermal atomic absorption spectroscopy. Certified samples of Virginia tobacco leaves, tea leaves, spinach leaves, poplar leaves, a commercial spinach sample (Spinacea oleracea) and genetically modified Arabidopsis thaliana were analysed by the proposed procedure and also by microwave acid digestion and extraction with HCl-Triton X-100. Confidence intervals for Cd and Zn content obtained by the proposed procedure overlap with the certified values. The other procedures, however, provide inaccurate results for Cd. Recoveries obtained for a confidence level of 95% are 96+/-6% and 95+/-5% for Zn and Cd, respectively. Reproducibility of Zn by the proposed procedure is 7% (n=8), similar to the other tests and the detection limit is 2.6 microg. For Cd reproducibility is 8.5% (n=8), better than with HCl-Triton X-100 and similar to acid digestion, the detection limit is 3.5 ng of Cd.

Desorption of BTEX from activated charcoal using accelerated solvent extraction: evaluation of occupational exposures.

A procedure for the determination of benzene, toluene, ethylbenzene and o-xylene, m-xylene and p-xylene (BTEX) in occupational environments is proposed. These compounds are extracted from activated charcoal using accelerated solvent extraction. Operational parameters are optimized and quantitative recovery is obtained using acetonitrile as the extraction solvent and 1-mL extraction cells, a preheat time of 2 min, a temperature of 160 degrees C, a pressure of 1,500 psi, a static period of 5 min, a flush volume of 110%, two cycles and a purge time of 90 s. Determination of BTEX compounds is carried out by gas chromatography using a flame ionization detector. The recoveries, obtained for a confidence level of 95%, are 91 +/- 4, 100 +/- 3, 104 +/- 2, 93 +/- 4, 99 +/- 2 and 99 +/- 2% for benzene, toluene, ethylbenzene, o-xylene, m-xylene and p-xylene, respectively. The detection limits are 0.5 microg for benzene, 0.7 microg for toluene and 1.0 microg for the other compounds. The proposed procedure has been applied to real samples collected in several workplaces, like a microbiology laboratory, an analytical chemistry laboratory, a printer's, a car repair shop and a petrol station. From the results obtained, it can be concluded that the occupational exposures determined are always acceptable because they are lower than the tenth part of the recommended exposure limits (VLA-ED and VLA-EC).

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.

Characterisation of quaternary mixtures by the apparent content curves method: identification of tocopherols in vegetable oils.

A procedure for identification of the compounds in quaternary mixtures has been developed. The proposed procedure is based on the apparent content curves method. From these curves and using the Q parameter, work conditions are selected and quaternary mixtures treated as "pseudoternary" mixtures.A simple strategy to test matrix effects at working wavelengths has been developed, identification limits established and following the identification table quaternary mixtures were easily characterised. The procedure has been applied to the identification of phenols in mixtures by UV-visible spectrophotometry and tocopherols in edible oils by fluorimetry. Results obtained for edible oils are in agreement with the composition obtained by use of the reference method.

Spectrophotometric determination of chromium with diphenylcarbazide in the presence of vanadium, molybdenum, and iron after separation by solid-phase extraction.

A method has been developed for the determination of chromium in presence of V(V), Mo(VI), and Fe(III). The effects of interferences were evaluated by using the apparent content curves method, and their separation was performed by solid-phase extraction with an anionic exchanger. The sample-treatment conditions and the influence of the sample conductivity were studied. Tolerance limits were established, and the proposed procedure was used to determine chromium in certified samples and for speciation of chromium in waste water. Our results were always in agreement with the theoretical content.

Application of ACC method to synchronous luminiscence: determination of alpha-tocopherol and alpha-tocopheryl acetate in beverages.

A new method based on the Q parameter, that permits the determination of the C(compound A)/C(compound B) ratio without preparing calibration graphs of the two compounds, is proposed. This method has been applied to signals obtained by synchronous luminiscence. Simultaneous determination of alpha-tocopherol and alpha-tocopheryl acetate in beverages using synchronous fluorescence has been carried out. To isolate the compounds from samples, liquid extraction with n-hexane as the organic phase was employed. The presence of interferences was tested using the apparent content curves (ACC) method and the C(alpha-tocopherol)/C(alpha-tocopheryl acetate) ratio was calculated using the Q parameter. The reproducibility and detection limit for the determination of alpha-tocopherol and alpha-tocopheryl acetate were 6.6% and 0.016 mg/L and 1.8% and 0.017 mg/L, respectively.

Determination of caffeine in pharmaceutical preparations by the linear absorbances method.

In this work a fast Linear Absorbance Method for the determination of caffeine in pharmaceutical preparations in the presence of paracetamol or acetylsalicylic acid is presented. The determination of acetylsalicylic acid or paracetamol is also possible by means of a tabulated parameter fB, which values are included in this paper. The method avoids the use of separation steps or multicalibration methods. The determination was carried out in commercial preparations with good results.

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.

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.

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.

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, Youden's method and the standard additions method. Percentage recovery experiments showed that albumin has a marked effect on the results obtained. The application of Youden's 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.