A. Sanz Medel

Speciation of D,L-selenomethionine enantiomers on a β-cyclodextrin column with fluorimetric and on-line hydride generation inductively coupled plasma mass spectrometric detection

O-Phthalaldehyde (OPA) and 2,3-naphthalenedicarbox-aldehyde (NDA) were investigated as pre-column derivatizating reagents in order to achieve the chiral separation of D,L-selenomethionine enantiomers on a β-cyclodextrin column using fluorimetric detection. Good resolution was achieved between the NDA-derivatized enantiomers with a mobile phase of 60% v/v methanol–0.5% triethylammonium acetate (pH 5). The sensitivity and selectivity of the fluorimetric detection of the derivatives were compared with selenium-specific detection by on-line microwave-HG-ICP-MS. Limits of detection of 2.7 and 70 µg l–1, respectively, were obtained. This sensitivity allowed the detection of small amounts (0.1–1%) of D-selenomethionine in commercially pure L-selenomethionine samples using both detectors. The HG-ICP-MS detector proved to be superior in terms of selectivity to selenium, as demonstrated by preliminary results obtained for D,L-selenomethionine determination in complex samples (selenium-enriched yeast). Selenomethionine could not be determined in such samples by fluorimetric detection owing to the presence of many other interfering amino acids at concentrations higher than that of selenomethionine which react with OPA and NDA.

Speciation of mercury by continuous flow liquid-liquid extraction and inductively coupled plasma atomic emission spectrometry detection

An accurate, precise, sensitive and automated non-chromatographic method for methylmercury speciation based on a selective continuous liquid-liquid extraction of methylmercury, into xylene, as bromide and cold mercury vapour generation directly from the organic phase and final ICP-AES mercury detection is proposed. Both separation steps, liquid-liquid and gas-liquid are accomplished in a continuous mode and on line with ICP-AES as detector. The detection limit attained for methylmercury was 4ng·ml−1 (as mercury). The precision of the determination at a concentration level around 20 times the detection limit was +-5%. The proposed methodology has been applied successfully to the speciation of methylmercury and inorganic mercury in spiked sea water and spiked urine samples.

Improved Determination of Aluminium Species in Waters Using FIA Separation/Fluorimetric Detection Techniques

Abstract A Flow Injection fluorimetric detection system, based on the reaction between aluminum and 8-hydroxyquinoline-5-sulphonic acid (8-HQS) in a micellar medium (cetyltrimethylammonium bromide (CTAB)) has been incorporated into the Driscoll fractionation method for the speciation of aluminium in waters. Improved analytical performance over a standard batch Driscoll/Pyrocatechol Violet (PCV) method is demonstrated. Detection limits (0.9 μg 1−1), speed of analysis (20 s), linear range (0-10,000 μg 1−1), and sample volume (100 μl) are all superior to the batch PCV technique. A serious positive interference from Zinc, occurring in the 8-HQS method, has been overcome by the addition of 0.1% m/v 1,10 phenanthroline to the post-column reagent. Good agreement between the conventional batch technique and our continuous flow determination for the important labile monomeric aluminium fraction in a series of waters has been demonstrated.

Spectroscopic determination of fundamental parameters in an argon microwave-induced plasma (surfatron) at atmospheric pressure

Abstract Some fundamental properties, of microwave-induced plasmas produced in a surfatron by a surface wave at a frequency of 2450 MHz and atmospheric pressure, were determined by spectroscopic techniques under various experimental conditions. These properties include electron number density and excitation, and electron and rotational temperatures. These spectroscopic diagnostics permit the characterization of departure from Local Thermodynamic Equilibrium (LTE) in this plasma.

High-performance liquid chromatographic determination of major organic acids in apple juices and ciders

SummaryA reversed-phase high-pressure liquid chromatographic method is presented for the simultaneous separation and determination of malic, citric, lactic, succinic and ascorbic acids in apple juices and ciders. After filtration and/or degasification, the organic acids in the sample are separated on a LiChrosorb/C18 column and quantified by using a rapid diode array detector.The method is considered to be a suitable choice for the accurate and precise determination (C.V. 5%) of these compounds.

The surfactant-sensitized analytical reaction of niobium with 8-hydroxyquinoline-5-sulphonic acid

Cationic surfactants, such as cetylpyridinium bromide (CPB), sensitize the colour reaction of Nb(V) with 8-hydroxyquinoline-5-sulphonic acid (H(2)L). The formation of a ternary complex of stoichiometry 1:3:3 (Nb-L-CPB) is responsible for the observed enhancement in absorptivity and the quenching in the fluorescence of the Nb-L chelate, when a surfactant is present. The ternary complex exhibits maximum absorption at 383 nm ( = 1.46 +/- 0.01 x 10(4) l.mole(-1).cm(-1)) at pH 5.7, and Beers law is obeyed up to 6-mug ml Nb concentration. Conditional formation constants of the niobium chelate in the presence and absence of CPB have been determined. On the basis of a detailed spectrophotometric and fluorimetric study the nature of the chromophoric reagent-surfactant interaction and the peculiar features of the sensitization by CPB are discussed.

Continuous flow and flow injection halogen generation for chloride, bromide and iodide determinations by microwave induced plasma atomic emission spectroscopy

Abstract Continuous flow generation of molecular, volatile halogens (I 2 , Br 2 , Cl 2 ), based on chemical oxidation, is a very useful sample introduction technique in microwave induced plasma atomic emission spectrometry (MIP-AES), which provides improved transport efficiency for sample to plasma, thus enhancing the sensitivity of the determinations. Optimum conditions for halogen generation/MIP detection (chemical oxidant system, type and size of gas-liquid separator, influence of halide concentration and MIP instrumental parameters) are discussed with an aim to improving both the intensity of the emission signal, and its stabilization time for I −1 , Br −1 and Cl −1 determinations. For continuous halogen generation, the influence on the MIP emission signal (and its stabilization time) of (i) the size and form of the gas-liquid separator, and (ii) the atomic weight and concentration of the halogen itself has been investigated in detail. Even for optimum conditions, iodine generation/transport to the plasma is rather slow (i.e. 4 min for signal stabilization). The use of flow injection analysis (FIA) however, allows an increase of the attainable sample throughput by up to 60 samples/h, but at the expense of a slight loss of sensitivity (20–30%) compared with continuous flow generation. The influence on the MIP signal that was observed with FIA parameters (such as the injected sample volume and flow rates of the different reagents) is discussed.

Determination of iodide by low power surfatron microwave induced plasma after iodine continuous generation

Abstract This paper describes an improvement of the detection capability of the surfatron-microwave induced plasma (MIP) for iodide determination based on the chemical generation of iodine. This element is continuously generated by on-line mixing of iodide-sulfuric acid and hydrogen peroxide solutions. The iodine vapour is separated from the aqueous phase by a gas-liquid separator and is desiccated by passing it through concentrated H2SO4 before feeding it into the plasma. The system was optimized for the continuous generation of iodine and for its final determination in the MIP. The detection limit attained was 20 μg l−1 and the precision was ± 0.75% (at the 200 μg l−1 level). An interference study showed that the proposed determination is very selective in the absence of oxidizing/reducing agents. The proposed procedure has been tested for iodide determination in real samples of table salt with very good agreement between the experimental results and the certified values.

Fluorimetric determination of ultratraces of lead by ion-pair extraction with cryptand 2.2.1 and eosin.

A spectrofluorimetric study of the extraction of lead into 1,2-dichloroethane, as an ion-pair formed between the cryptand 2.2.1-lead complex and the eosinate counter-ion is described. Optimum conditions for the extraction have been established and a new spectrofluorimetric determination of ultratraces of lead is proposed (detection limit 0.8 ng/ml; relative standard deviation 2.4% at the 60 ng/ml level). The metal:ligand:counter-ion molecular ratio in the extracted mononuclear ion-pair is 1:1:1. The equilibrium constants involved in the extraction have been estimated and refined by the Letagrop-DISTR program.

A comparative study of different extraction systems for the spectrophotometric determination of potassium with 18-crown-6

Abstract A comparative study on the extractive-spectrophotometric determination of potassium with 18-crown-6 employing different colored counterions and organic extraction solvents is described. Extraction systems using methyl orange/chloroform, bromcresol purple/chloroform and bromcresol green/benzene demonstrated good preliminar features for such purpose and are studied in detail. Analytical performance characteristics including: sensitivity, selectivity, precision, linearity, etc. are given for each method. The main disadvantage of this type of determinations is the lack of reproducibility. Some explanations to this fact are discussed. A new method for the determination of trace amounts of potassium based on its extraction into chloroform with 18-crown-6 and methyl orange is proposed. The linear working range goes from 0.5 to 7 ppm of potassium, the apparent molar absorptivity being 8.8 × 10 3 liters mol −1 · cm −1 , and the precision, expressed in terms of relative standard deviation, of ±4.6%.