José A. Gásquez

Preconcentration and speciation of chromium in drinking water samples by coupling of on-line sorption on activated carbon to ETAAS determination

An on-line flow injection (FI) preconcentration-electrothermal atomic absorption spectrometry (ETAAS) method is developed for trace determination of chromium in drinking water samples by sorption on a conical minicolumn packed with activated carbon (AC) at pH 5.0. The chromium was removed from the minicolumn with 1.0% (v/v) nitric acid. An enrichment factor (EF) of 35-fold for a sample volume of 10ml was obtained. The detection limit (DL) value for the preconcentration method proposed was 3.0ngl(-1). The precision for 10 replicate determinations at the 0.5mugl(-1) Cr level was 4.0% relative standard deviation (R.S.D.), calculate with the peak heights obtained. The calibration graph using the preconcentration system for chromium was linear with a correlation coefficient of 0.9992 at levels near the detection limits up to at least 50mugl(-1). The method was successfully applied to the determination of Cr(III) and Cr(VI) in drinking water samples.

On-line preconcentration and determination of nickel in natural water samples by flow injection-inductively coupled plasma optical emission spectrometry (FI-ICP-OES)

An on-line nickel preconcentration and determination system implemented with inductively coupled plasma optical emission spectrometry (ICP-OES) associated to flow injection (FI) was studied. Trace amounts of nickel were preconcentrated by sorption on a conical minicolumn packed with activated carbon (AC) at pH 5.0. The nickel was removed from the minicolumn with 20% nitric acid. An enrichment factor of 80-fold for a sample volume of 50 ml was obtained. The detection limit (DL) value for the preconcentration method proposed was 82 ng l(-1). The precision for ten replicate determinations at the 0.5 microg l(-1) Ni level was 3.0% relative standard deviation (R.S.D.), calculated from the peak heights obtained. The calibration graph preconcentration method for nickel was linear with a correlation coefficient of 0.9997 at levels near the detection limits (DL) up to at least 100 microg l(-1). The method was successfully applied to the determination of nickel in natural water samples.

On-line preconcentration and determination of vanadium in tap and river water samples by flow injection-inductively coupled plasma-optical emission spectrometry (FI-ICP-OES)

A flow injection system coupled to an inductively coupled plasma optical emission spectrometer (ICP-OES) was used for the on-line preconcentration and subsequent determination of vanadium. Trace amounts of V were preconcentrated by sorption on a conical minicolumn packed with immobilised yeast cells in the absence of complexing reagent at pH 7.0. Vanadium was removed from the minicolumn with a 50% HCl solution. An enrichment factor of 45-fold for a sample volume of 10 ml was obtained. The detection limit (LoD) for the preconcentration method proposed was 0.06 μg l−1. The precision for 10 replicate determinations at the 5 μg l−1 V level was 3.4% relative standard deviation (RSD), calculated from the peak heights obtained. The calibration graph of the preconcentration method for V was linear with a correlation coefficient of 0.9997 at levels near the detection limits up to at least 100 μg l−1. The method was successfully applied to the determination of V in tap and river water samples.

Determination of scandium in river water by ICP-OES with flow-injection on-line preconcentration using knotted reactor and ultrasonic nebulization

An on-line scandium preconcentration and determination system implemented with inductively coupled plasma optical emission spectrometry (ICP-OES) associated with flow injection (FI) with an ultrasonic nebulization system (USN) was studied. The scandium was retained as the scandium-2-(5-bromo-2-pyridylazo)-5-diethylaminophenol, Sc-(5-Br-PADAP), complex, at pH 9.5. The 5-Br-PADAP solution concentration was 1 × 10−4 mol l−1 and it was dissolved in a 17% (v/v) ethanol–water solution. The scandium complex was removed from the knotted reactor (KR) with 30% (v/v) nitric acid. A total enhancement factor of 1120 was obtained with respect to ICP-OES using pneumatic nebulization –Meinhard, Pneumatic Nebulizer– (25 for USN and 45 for KR) with a preconcentration time of 300 s. The value of the detection limit for the preconcentration of 30 ml of sample solution was 0.45 ng l−1. The precision for 10 replicate determinations at 10 ng l−1 Sc level was 3.5% relative standard deviation (RSD), calculated from the peak heights obtained. The calibration graph using the preconcentration system for scandium was linear with a correlation coefficient of 0.9996 at levels near the detection limits up to at least 50 µg l−1. The method was successfully applied to the determination of scandium in river water samples.

On-Line Preconcentration/Determination of Lead Traces in Bee Honey by Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES) Using a Conical Minicolumn Packed with Activated Carbon

Abstract In this study, the preconcentration of Pb2+ using a conical minicolumn packed with activated carbon (AC) was studied for preconcentration of Pb2+. The experiments showed that Pb2+ reacts with 8-hydroxyquinoline to form a complex at pH 10.0 and can be retained “on-line” on a conical minicolumn packed with activated carbon, then eluted with 20% (v/v) nitric acid. The conditions for the quantitative and reproducible preconcentration and subsequent ICP-OES determination with ultrasonic nebulization system (USN) were studied. A total enhancement factor (N) of 500 was obtained with respect to ICP-OES using pneumatic nebulization (10 for USN and 50 for enrichment factor) for a sample volume of 25 mL. The detection limit (DL) was 0.04 µg L−1. The relative standard deviation (RSD) were 3.0%. The optimized procedure was successfully applied to the determination of trace levels of Pb+2 in bee honey samples.

Inductively Coupled Plasma Optical Emission Spectrometric Determination of Gadolinium in Urine Using Flow Injection On‐Line Sorption Preconcentration in a Knotted Reactor

Abstract An on‐line gadolinium preconcentration and determination system, implemented with ultrasonic nebulization coupled to inductively coupled plasma optical emission spectrometry (ICP‐OES), associated with flow injection (FI) was studied. Gadolinium was retained as Gd‐2‐(5‐bromo‐2‐pyridilazo)‐5‐diethylaminophenol complex (Gd‐5‐Br‐PADAP) at pH 9.0, on the inner walls of the knotted reactor (KR). The collected analyte complexes were quantitatively eluted from the 200 cm KR with 30% (v/v) nitric acid. An enhancement factor of 255‐fold was obtained (17 for KR and 15 for USN). The detection limit (DL) value for the preconcentration of 15 mL of sample was 4.0 ng L−1. The relative standard deviation (RSD) was 3.5%, calculated from the peak heights obtained. The calibration graph using the preconcentration system for gadolinium was linear, with a correlation coefficient of 0.9996 at levels near the detection limit up to at least 200 µg L−1. The method was successfully applied to the determination of gadolinium in urine samples.

A fast method for apatite selective leaching from granitic rocks followed through rare earth elements and phosphorus determination by inductively coupled plasma optical emission spectrometry.

Rare earth elements (REE) and phosphorus (P) in apatite were determined using inductively coupled plasma optical emission spectrometry (ICP-OES) after partial dissolution of the granitic rocks and pure apatite. The dissolution was performed with nitric acid in an open system and the matrix elements were separated by a cation exchange procedure. Samples of pure apatite from granitic rocks were dissolved with, 0.14 mol L(-1) nitric acid. The results showed that the release of REE is due to apatite leaching because it could be assessed by comparing the chondrite-normalised pattern corresponding to the rocks and the pure apatite. Similar results were found for absolute REE abundance from the partial dissolution of the rocks and pure apatite. This simple and rapid method can be applied for the determination of REE in apatite as an indicator for mineral exploration, although its use in petrology could be possible.

On‐Line Preconcentration and Analysis of Zinc in Water by Flow Injection‐Knotted Reactor: Application to Geological and Environmental Exploration

Abstract A preconcentration on‐line system composed of flow injection (FI) and a knotted reactor (KR), associated with inductively coupled plasma atomic emission spectrometry (ICP‐AES) has been used to determine Zn concentrations in river water. The zinc was retained as Zn‐2(5‐bromo‐2‐pyridilazo)5‐diethylaminofenol precipitated complex on the knotted reactor (KR). The limit of detection (0.09 µg L−1 of Zn) of this method makes it particularly suitable for hydrochemical exploration in geological and environmental projects. This application has been validated in the volcanogenic gold (copper, zinc, lead) deposit of La Carolina in the province of San Luis, Argentina. The Carolina Stream and the Grande River have been sampled for water downstream this deposit. The regional background in river water is 2 µg L−1. Six times this concentration has been observed at more than 6.5 km from the source, La Carolina mine.

Online Copper Removal for Selenium Determination by Hydride Generation–Inductively Coupled Plasma Optical Emission Spectrometry

Abstract Selenium determination in samples with a high copper content by hydride generation–inductively coupled plasma optical emission spectrometry (HG‐ICP‐OES) after online copper removal and selenium (VI) reduction is described. An activated carbon minicolumn was used for the retention of copper and its subsequent separation of Se. Se(VI) was then online reduced by heating into a PTFE coiled reactor with 12 M HCl. The analyte was introduced into a water stream containing sodium tetrahydroborate (NaBH4) in order to generate selenium hydride (H2Se). The detection limit (DL) obtained was 0.8 µg L−1, and the precision, expressed by the relative standard deviation (RSD), was 2.5% (n=10; 10 µg L−1 selenium level). The current method was applied to the Se determination in two copper reference materials, MBH‐39DK 3601 (with a Se content of 90 mg kg−1) and MBH‐39 DK 3604 (with a Se content of 15 mg kg−1). The authors were invited to contribute this paper to a special issue of the journal entitled “Spectroscopy and Automation”. This special issue was organized by Miguel de la Guardia, Professor of Analytical Chemistry at Valencia University, Spain.

Correction of line interference in X-ray fluorescence trace analysis. Application to yttrium determination in silicate rocks

An empirical method is proposed for the correction of spectral interference between characteristic lines in XRF. The procedure is based on a coefficient which includes instrumental parameters and atomic properties and is obtained with the same standards as those used in calibration. This method has shown to be valid in the range of concentration studied. The application of the method to the interference of Rb Kβ1 on Y Kα in silicate rocks is described. Experimental proof was demonstrated using Certified Reference Materials (CRMs) and samples analysed in other laboratories.