Enzymatic amperometric procedures for measuring arsenic, based on the inhibitive action of this metal on acetylcholinesterase enzyme activity, have been developed. Screen-printed carbon electrodes (SPCEs) were used with acetylcholinesterase covalently bonded directly to its surface. The amperometric response of acetylcholinesterase was affected by the presence of arsenic ions, which caused a decrease in the current intensity. The experimental optimum working conditions of pH, substrate concentration and potential applied, were established. Under these conditions, repeatability and reproducibility of biosensors were determined, reaching values below 4% in terms of relative standard deviation. The detection limit obtained for arsenic was 1.1 × 10⁻⁸ M for Ach/SPCE biosensor. Analysis of the possible effect of the presence of foreign ions in the solution was performed. The method was applied to determine levels of arsenic in spiked tap water samples.

A new strategy to approach multiresponse optimization in conjunction to a D-optimal design for simultaneously optimizing a large number of experimental factors is proposed. The procedure is applied to the determination of biogenic amines (histamine, putrescine, cadaverine, tyramine, tryptamine, 2-phenylethylamine, spermine and spermidine) in swordfish by HPLC-FLD after extraction with an acid and subsequent derivatization with dansyl chloride. Firstly, the extraction from a solid matrix and the derivatization of the extract are optimized. Ten experimental factors involved in both stages are studied, seven of them at two levels and the remaining at three levels; the use of a D-optimal design leads to optimize the ten experimental variables, significantly reducing by a factor of 67 the experimental effort needed but guaranteeing the quality of the estimates. A model with 19 coefficients, which includes those corresponding to the main effects and two possible interactions, is fitted to the peak area of each amine. Then, the validated models are used to predict the response (peak area) of the 3456 experiments of the complete factorial design. The variability among peak areas ranges from 13.5 for 2-phenylethylamine to 122.5 for spermine, which shows, to a certain extent, the high and different effect of the pretreatment on the responses. Then the percentiles are calculated from the peak areas of each amine. As the experimental conditions are in conflict, the optimal solution for the multiresponse optimization is chosen from among those which have all the responses greater than a certain percentile for all the amines. The developed procedure reaches decision limits down to 2.5 μg L-1 for cadaverine or 497 μg L-1 for histamine in solvent and 0.07 mg kg-1 and 14.81 mg kg-1 in fish (probability of false positive equal to 0.05), respectively.

In this work, a headspace solid-phase microextraction and gas chromatography coupledwith mass spectrometry\ud (HS-SPME-GC/MS) method for trace determination of primary aromatic amines was developed. The following\ud analytes were investigated: aniline (A), 4,4′-diaminodiphenylmethane (4,4′-MDA) and 2,4-diaminotoluene\ud (2,4-TDA) using 3-chloro-4-fluoroaniline (3C4FA) and 2-aminobiphenyl (2ABP) as internal standards. Prior to\ud extraction the analytes were derivatized in the aqueous solution by diazotation and subsequent iodination.\ud The derivativeswere extracted byHS-SPME using a PDMS/DVB fiber and analyzed by GC/MS. A D-optimal design\ud was used to study the parameters affecting the HS-SPME procedure and the derivatization step. Two experimental\ud factors at two levels and one factor at three levels were considered: (i) reaction time, (ii) extraction temperature,\ud and (iii) extraction time in the headspace. The interaction between the extraction temperature and\ud extraction time was considered in the proposed model. The loadings in the sample mode estimated by a\ud PARAFAC (parallel factor analysis) decomposition for each analyte were the response used in the design because\ud they are proportional to the amount of analyte extracted. The optimum conditions for the best extraction of the\ud analytes were achieved when the reaction time was 20 min, the extraction temperature was 50 °C and the\ud extraction time was 25 min. The interaction was significant.\ud A calibration based on a PARAFAC decomposition provided the following values of decision limit (CCα): 1.07 μgL−1\ud for A, 1.23 μg L−1 for 2,4-TDA and 0.83 μg L−1 for 4,4′-MDA for a probability of false positive fixed at 5%. Also, the\ud accuracy (trueness and precision) of the procedurewas assessed. Furthermore, all the analyteswere unequivocally\ud identified.\ud Finally, the method was applied to spiked water samples and polyamide cooking utensils (spoons). 3% (w/v)\ud acetic acid in aqueous solution was used as food simulant for testing migration from polyamide kitchenware.\ud Detectable levels of 4,4′-diaminodiphenylmethane and aniline were found in food simulant from some of the\ud investigated cooking utensils.Ministerio de Economía y Competitividad (CTQ2011-26022) and Junta\ud de Castilla y León (BU108A11-2