Valerio Porta

Determination of ultra-trace levels of metal ions in sea-water with on-line pre-concentration and electrothermal atomic absorption spectrometry

An on-line pre-concentration system for electrothermal atomic absorption spectrometry was developed. A miniature silica C18 column was inserted at the tip of the autosampler arm. A modification of the tubing line of the autosampler allowed either the flow of the sample through the column or the operation of the autosampler in the normal mode. The retention of the metal ions in the form of complexes on the microcolumn was achieved by using pyrrolidin-l-yl dithioformate as the complexing agent; acetonitrile was then used for the elution. The direct injection of the eluate into the graphite furnace gave high pre-concentration factors, ranging between 20 and 225, which are sufficient for the determination of Cd, Pb, Cu, Ni, Co and Fe in Antarctic sea-water. The blank level was very low and the detection limits ranged from 0.4 ng l–1(Cd) to 25 ng l–1(Fe).

On-line preconcentration system for inductively coupled plasma atomic emission spectrometry with quinolin-8-ol and Amberlite XAD-2 resin

An on-line preconcentration system implemented with inductively coupled plasma atomic emission spectrometry (ICP-AES) was studied. For the retention of metal ions 8-hydroxyquinoline and Amberlite XAD-2 resin were used. This system improved the detection limits of Cd, Cu, Fe, Mn, Ni and Zn by a factor of 100 compared with ICP-AES alone. Owing to this sensitivity and the excellent selectivity towards the transition metal ions with respect to salt matrices, the method was successfully applied to the determination of the above metals in Antarctic sea water. The concentration found ranged between 16 ng l−1 (Mn) and 0.4 μg l−1 (Ni) with a precision of 10%.

Aliphatic monoamines, diamines, polyamines: An HPLC method for their identification and separation by a dansylation reaction; The study of separation factors in homologous series

SummaryAn analytical method is presented for the identification and separation of aliphatic monoamines, diamines and polyamines. Dansyl chloride as the derivatizing agent and fluorimetric detection were employed. The behaviour of different column packings and eluent compositions was tested and compared. The interaction mechanisms of the dansylated compounds with stationary and mobile phases are discussed on the basis of the analysis of the capacity factors evaluated in the homologous series of monoamines CH3(CH2)nNH2, with n varying up to 9 and diamines NH2(CH2)nNH2, with n varying up to 12. An application of this method to a real sample is presented.

Comparison of different pre-concentration methods for the determination of trace levels of arsenic, cadmium, copper, mercury, lead and selenium

Three methods have been considered for trace metal concentration: (a) liquid-liquid extraction using either ammonium pyrrolidinedithiocarbamate or 8-hydroxyquinoline-5-sulphonic acid; (b) the use of a synthetic poly(dithiocarbamate) resin; and (c) reductive precipitation with NaBH4. The suitability of method (a) for the determination of metal ions in samples with a complex matrix and high salinity has been investigated. Method (b) was especially useful for speciation studies of trace levels of AsIII, AsV, SeIV and SeVI. Method (c) gave 1000-fold pre-concentration factors with total recoveries.

CHROMATOGRAPHIC BEHAVIOUR OF HOMOLOGOUS AMINES : COMPARISON OF DERIVATIZING AGENTS, COLUMNS AND MOBILE PHASES

SummaryThe liquid chromatographic behaviour of aliphatic mono- and polyamines belonging to different homologous series has been investigated using various pre-column derivatizing agents (OPA and CNB), mobile phases (water-MeOH and water-ACN), RP columns (different packing sizes and shapes) and detectors (UV and fluorescence) in order to characterize the different contributions to retention and the different selectivities under the conditions investigated. The parameters derived allowed computation of capacity factors in good agreement with experiments. The chromatographic method optimized with respect to OPA derivatization has been successfully utilized for the determination of putrescine, cadaverine and 2-phenyl-ethylamine in cheese samples under different ageing conditions.

Preconcentration and inductively coupled plasma atomic emission spectrometric determination of metal ions with on-line chelating ion exchange

An on-line preconcentration method utilizing a microcolumn of XAD-2 resin functionalized with 1-(2-thiazolylazo)-2-naphthol has been developed. Preconcentration factors of 125 were easily obtained for injection times of 5 min. The detection limit ranged between 2 ng l–1 for Mn and 40 ng l–1 for Ni. The resin has been used to preconcentrate Cd, Cu, Fe, Mn, Ni and Zn from river water and Antarctic sea-water (Ross Bay) prior to their determination by inductively coupled plasma atomic emission spectrometry. The precision of the technique is around 10% relative standard deviation at concentrations below the µg l–1 level and 5% for higher concentrations.

Simultaneous ion chromatographic determination of selenium and metal ions in waters at trace level

SummaryAn ion-chromatographic procedure is described for the determination of selenium (VI) at μg L−1 level in the presence of anions and heavy metal ions. Maximum permissible concentrations and effects from each interfering substance were investigated for the Se concentration range 12.5–1,000 μg L−1. The method, optimized for the detection of SeO42−, gives results suitable for speciation analysis. Total selenium can be determined after complete conversion to selenate ion by oxidation with KMnO4. The detection limit of selenium is 4.8 μg L−1 (0.96 ng for 200 μL sample).

Reversed-Phase Ion-Interaction Chromatography of Metal Ions by EDTA Precomplexation

SummaryConditions for the isocratic separation by reversed-phase ion-interaction chromatography of Bi(III), Fe(III), Co(III), Ni(II), Cu(II) and Pb(II) chelates with ethylenediaminetetraacetic acid have been studied using UV-Vis detection. Both chromatographic and spectrophotometric conditions for the determination of these metal chelates are discussed including ion-interaction reagent concentration, water/methanol ratio, ionic strength, pH and absorbing wavelengths. Detection limits are particularly satisfactory for Bi(III), Fe(III) and Co(III) chelates.

Ion-pair liquid—solid extraction for the preconcentration of trace metal ions Optimization of experimental conditions

Cu(II) has been recovered from dilute solutions (0.1 mug/ml) by adsorbing the ion-pairs formed between different quaternary ammonium salts and the Cu-8-hydroxyquinoline-5-sulphonic acid complex on adsorbent resins, namely XAD 8 and S 862. Both batch and column techniques have been used, the first of which gave superior recovery and precision. It has also been shown that XAD 8 resin can be transformed into an ion-exchanger suitable for preconcentration of Cu(II). The results obtained have been compared with those of reversed-phase ion-pair chromatography and a model is proposed.

Nitrilotriacetic acid, thiourea and cysteine ligands immobilized on cellulose for the uptake of trace metal ions

Abstract Functionalized celluloses containing nitrilotriacetic acid, thiourea and cysteine have been prepared for the uptake of a series of trace metal ions, namely Al(III), Ca(II), Cd(II), Co(II), Cu(II), Fe(III), Hg(II), Mg(II), Ni(II), Pb(II) and Zn(II). The recovery has been evaluated as a function of pH, and the capacities determined at the pH of maximum yield. The experimental yields obtained for the metal recoveries have been compared with the ones calculated with the aid of the computed distribution of metal-ligand species. The materials obtained may be utilized for the enrichment of trace metals, for the demetalization of solutions, and for speciation studies.