R. G. Wuilloud

Sensitive determination of mercury in tap water by cloud point extraction pre-concentration and flow injection-cold vapor-inductively coupled plasma optical emission spectrometry

A pre-concentration and determination methodology for mercury at trace levels in water samples was developed. Cloud point extraction was successfully employed for the pre-concentration of mercury prior to inductively coupled plasma optical emission spectrometry coupled to a flow injection with cold vapor generation system. The mercury was extracted as mercury-2-(5-bromo-2-pyridylazo)-5-diethylaminophenol [Hg(II)-(5-Br-PADAP)] complex, at pH 9.2 mediated by micelles of the non-ionic surfactant polyethyleneglycolmono-p-nonylphenylether (PONPE 5). Cold vapor generation was developed from 100 μl of the extracted surfactant-rich phase by means of a stannous chloride (SnCl2) solution as reluctant. An exhaustive study of the variables affecting the cloud point extraction with PONPE 5 and cold vapor mercury generation from the surfactant phase was performed. The 50-ml sample solution pre-concentration allowed us to raise an enrichment factor of 200-fold. The lower limit of detection obtained under the optimal conditions was 4 ng l−1. The precision for 10 replicate determinations at the 0.5-μg l−1 Hg level was 3.4% relative standard deviation (R.S.D.), calculated with the peak heights. The calibration graph using the pre-concentration system for mercury was linear with a correlation coefficient of 0.9998 at levels near the detection limits up to at least 50 μg l−1. The method was successfully applied to the determination of mercury in tap water samples.

Cloud point extraction of vanadium in parenteral solutions using a nonionic surfactant (PONPE 5.0) and determination by flow injection-inductively coupled plasma optical emission spectrometry

A preconcentration and determination methodology for vanadium at trace levels in parenteral solutions was developed. Cloud point extraction was successfully employed for the preconcentration of vanadium prior to inductively coupled plasma atomic optical emission spectrometry (ICP-OES) coupled to a flow injection (FI) system. The vanadium was extracted as vanadium-2-(5-bromo-2-pyridylazo)-5-diethylaminophenol [V-(5-Br-PADAP)] complex, at pH 3.7 mediated by micelles of the nonionic surfactant polyoxyethylene (5.0) nonylphenol (PONPE 5.0). The extracted surfactant-rich phase (100 mul) was mixed with 100 mul of ethanol and this final volume injected into ICP-OES for the vanadium determination. Under these conditions, the 50 ml sample solution preconcentration allowed raising an enrichment factor of 250-fold; however, it was possible to obtain a theoretical enrichment factor of 500-fold. The lower limit of detection (LOD) obtained under the optimal conditions was 16 ng l(-1). The precision for 10 replicate determinations at the 2.0 mug l(-1) V level was 2.3% relative standard deviation (RSD), calculated with the peak heights. The calibration graph using the preconcentration system for vanadium was linear with a correlation coefficient of 0.9996 at levels near the detection limits up to at least 50 mug l(-1). The method was successfully applied to the determination of vanadium in parenteral solution samples.

Speciation and preconcentration of vanadium(V) and vanadium(IV) in water samples by flow injection-inductively coupled plasma optical emission spectrometry and ultrasonic nebulization

An on-line separation, preconcentration and determination system for vanadium(IV) and vanadium(V) comprising inductively coupled plasma optical emission spectrometry (ICP-OES) coupled to a flow injection (FI) method with an ultrasonic nebulization (USN) system was studied. The vanadium species were retained on an Amberlite XAD-7 resin as a vanadium-2-(5-bromo-2-pyridylazo)-5-diethylaminophenol (V-5-Br-PADAP) complex at pH 3.7. Enhanced selectivity was obtained with the combined use of the formation on-line of the complexes and 1,2-cyclohexanediaminetetraacetic acid (CDTA) as masking agent. The vanadium complexes were removed from the microcolumn with 25% v/v nitric acid. A sensitivity enhancement factor of 225 was obtained with respect to ICP-OES using pneumatic nebulization (15-fold for USN and 15-fold for the microcolumn). The detection limit for the preconcentration of 10 mL of aqueous solution was 19 ng L-1. The precision for 10 replicate determinations at the 5 micrograms L-1 V level was 2.3% relative standard deviation (RSD), calculated from the peak heights obtained. The calibration graph using the separation and preconcentration system for vanadium species was linear with a correlation coefficient of 0.9992 at levels from near the detection limits up to at least 100 micrograms L-1. The method was successfully applied to the speciation of vanadium in river water samples.

Separation and preconcentration of inorganic and organomercury species in water samples using a selective reagent and an anion exchange resin and determination by flow injection-cold vapor atomic absorption spectrometry

An on-line inorganic (InHg) and organomercury (OrHg) species separation, preconcentration and determination system consisting of cold vapor atomic absorption spectrometry (CV-AAS) coupled to a flow injection (FI) method was studied. The inorganic mercury species was retained on a column (id, 3 mm; length, 80 mm) charged with a Dowex 1X-8 resin (particle size 50–100 mesh) as the anionic complex formed with Methylthymol Blue (MTB), at pH 6.3. Previous oxidation of the organomercurial species permitted the determination of total mercury. Therefore, the separation of mercury species was obtained with the combined use of on-line selective formation of the InHg–MTB complex and the retention of this anionic compound on the anion exchange resin. The difference between total and inorganic mercury determined the organomercury content in the samples. The inorganic mercury was removed on-line from the micro-column nwith 3 M nitric acid. The mercury cold vapor generation was performed in an on-line system with 7.0% n(w/v) SnCl2 and 20% n(v/v) HCl as reducing solution. A preconcentration factor of 180 was obtained for the preconcentration of 250 ml of aqueous solution. The detection limit for InHg and OrHg was 0.8 ng l−1. The precision for ten replicate determinations at the 15 ng l−1 Hg level was 4.4% relative standard deviation (RSD), calculated from the peak heights obtained. The calibration graph using the separation and preconcentration system for mercury species was linear, with a correlation coefficient of 0.9994 at levels near the detection limit up to at least 100 µg l−1. The accuracy of the method was evaluated by the analysis of a certified reference material QC Metal LL3 Mercury in Water. The method was successfully applied to the speciation of mercury in water samples.

Determination of lead in tap water by ICP-AES with flow-injection on-line adsorption preconcentration using a knotted reactor and ultrasonic nebulization

An on-line lead preconcentration and determination system implemented with inductively coupled plasma atomic emission spectrometry (ICP-AES) combined with a flow injection (FI) method with ultrasonic nebulization (USN) was studied. The lead was retained as the lead-diethyldithiocarbamate complex at pH 9.5. The lead complex was eluted from the knotted reactor (KR) with 4.0 mol l n –1 n hydrochloric acid. A total enhancement factor of 140 was obtained with respect to ICP-AES using pneumatic nebulization ( 14.8 for USN and 9.5 for KR). The detection limit for the preconcentration of 10 ml of aqueous solution was 0.2 ng ml n –1 n. The precision for ten replicate determinations at the 20 µg l n –1 n lead level was 2.7% relative standard deviation, calculated with the peak heights obtained. The calibration graph using the preconcentration system for lead was linear with a correlation coefficient of 0.9993 at levels near the detection limits up to at least 100 ng ml n –1 n. The method was successfully applied to the determination of lead in tap water samples.

Determination of vanadium (V) in drinking water by flow injection and pre-concentration in a knotted reactor by inductively coupled plasma optical emission spectrometry with ultrasonic nebulization

Abstract An on-line vanadium pre-concentration and determination system implemented with inductively coupled plasma optical emission spectrometry (ICP-OES) associated with a flow injection (FI) method with ultrasonic nebulization (USN) system was studied. The vanadium was retained as vanadium-2-(5-bromo-2-pyridylazo)-5-diethylaminophenol V(V)-(5-Br-PADAP) complex, at pH 3.2. The vanadium complex was removed from the knotted reactor (KR) with 30% v/v nitric acid. A sensitivity enhancement factor of 180 was obtained with respect to ICP-OES using pneumatic nebulization (15 for USN and 12 for KR). The value of detection limit for the pre-concentration of 10 ml of aqueous solution was 19 ng l −1 . The precision for 10 replicate determinations at the 5 μg l −1 V(V) level was 2.6% relative standard deviation (R.S.D.), calculated with the peak heights obtained. The calibration graph using the pre-concentration system for vanadium was linear with a correlation coefficient of 0.9995 at levels near the detection limits up to at least 100 μg l −1 . The method was successfully applied to the determination of vanadium in drinking water samples.