Qiantao Cai

Antimony speciation by inductively coupled plasma mass spectrometry using solid phase extraction cartridges

A novel and simple method for inorganic antimony speciation is described based on selective solid phase extraction (SPE) separation of antimony(III) and highly sensitive inductively coupled plasma mass spectrometric (ICP-MS) detection of total antimony and antimony(V) in the aqueous phase of the sample. Non-polar SPE cartridges, such as the Isolute silica-based octyl (C8) sorbent-containing cartridge, selectively retained the Sb(III) complex with ammonium pyrrolidine dithiocarbamate (APDC), while the uncomplexed Sb(V) remained as a free species in the solution and passed through the cartridge. The Sb(III) concentration was calculated as the difference between total antimony and Sb(V) concentrations. The detection limit was 1 ng L(-1) antimony. Factors affecting the separation and detection of antimony species were investigated. Acidification of samples led to partial or complete retention of Sb(V) on C8 cartridge. Foreign ions tending to complex with Sb(III) or APDC did not interfere with the retention behavior of the Sb(III)-APDC complex. This method has been successfully applied to antimony speciation of various types of water samples.

Simultaneous speciation of inorganic selenium and tellurium by inductively coupled plasma mass spectrometry following selective solid-phase extraction separation

A new method was developed for the simultaneous determination of inorganic tellurium and selenium species in waters by inductively coupled plasma mass spectrometry (ICP-MS) following selective solid-phase extraction (SPE) separation. Under acidic conditions, only selenium(IV) and tellurium(IV) formed complexes with ammonium pyrrolidine dithiocarbamate (APDC), and the complexes were completely retained on a non-polar C18 cartridge. Te(VI) and Se(VI) passed through the cartridge and remained as free species in the solution, thereafter being determined by ICP-MS. Se(IV) and Te(IV) concentrations were obtained as the respective differences between total selenium and Se(VI), and total tellurium and Te(VI) concentrations. The detection limits (3σ) are 7 ng L−1 selenium and 3 ng L−1 tellurium. Factors affecting the separation and detection were investigated. Coexisting ions did not show significant interferences. This method has been successfully applied to the inorganic selenium and tellurium speciation analysis of water samples with spiked recoveries of 82.3–106%.

Determination of trace aluminium by differential pulse adsorptive stripping voltammetry of aluminium(II) -8-hydroxyquinoline complex

Abstract A rapid and sensitive differential-pulse adsorptive stripping voltammetric method, based on the formation of an electroactive complex between aluminium(III) and 8-hydroxyquinoline (HOx), is presented for the determination of trace levels of aluminium. The complex showed an oxidative peak potential at +0.876 V vs. Ag/AgCl (saturated KCl) at a glassy carbon (GC) electrode in aqueous ammonium acetate (0.024 M, pH 6.8. A good linear relationship between the peak current and Al(III) concentration in the ranges 4.00 X 10 −8 –5.00 X 10 −6 and 8.00 X 10 −6 –4.00 X 10 −5 M were observed. In the lower Al(III) concentration region, the anodic peak was the result of the stripping of the absorbed Al(III)-HOx complex, whereas in the higher concentration range, the diffusional oxidation current of the solution species predominated. A surface saturation region was observed from 5.00 X 10 −6 to 8.00 X 10 −6 M Al(III). Relatively few interferences were found and these were easily masked. The detection limit for Al(III) for this method is 1.00 X 10 −8 M and ten determinations of Al(III) at 1.00 X 10 −7 M gave a relative standard deviation of 6.2%. The method was employed in the analysis of Al(III) in a US Environmental Protection Agency water pollution quality control sample (WP 386) and excellent agreement with the certified value was obtained.

Determination of trace thallium after accumulation of thallium(III) at a 8-hydroxyquinoline-modified carbon paste electrode

Thallium(III) was selectively accumulated, in an open circuit, from a stirred Britton–Robinson buffer solution (pH 4.56) onto a carbon paste electrode incorporating 8-hydroxyquinoline. The ensuing measurement was carried out by differential pulse anodic stripping voltammetry after reducing the thallium(III) to metallic thallium in ammonia–ammonium chloride buffer (pH 10.00). Factors affecting the accumulation, reduction and stripping steps were investigated and an optimized procedure was developed. Under optimized conditions, a calibration plot for thallium(III) concentration in the range 5.00 × 10–10–1.60 × 10–5 mol l–1 gave two linear regions arising from different controlling factors during the accumulation step. A detection limit of 2.30 × 10–10 mol l–1(0.047 ppb)(S/N = 3) was found for a 2 min accumulation. For 10 successive determinations of 1.00 × 10–6 mol l–1 and 1.00 × 10–7 mol l–1 TIIII, relative standard deviations, sr, of 2.8 and 4.8% were obtained, respectively. Interferences from other ions and organic substances were examined. The developed method was applied to thallium determinations in sea-water and human urine samples.

Determination of bromate and bromoacetic acids in water by ion chromatography-inductively coupled plasma mass spectrometry

A new method for the simultaneous determination of bromate and six bromoacetic acids in water was developed by online coupling anion-exchange chromatography separation to element-specific inductively coupled plasma mass spectrometry (ICP-MS) detection. Factors affecting the chromatographic and ICP-MS performances were systematically investigated. The separation was achieved on a Dionex IonPac® AS11-HC column (4.0 × 250 mm) by elution with 100 mM ammonium nitrate. The detection limits (3σ) of the analytes were 0.13–0.36 µg L−1 based on a 500-µL sample injection. The possible masking of bromochloroacetic acid by the relatively high level of bromide in the chromatogram was avoided by sample pretreatment with Dionex OnGuard® Ag and H cartridges. The sample matrix did not show significant influence on the analysis. The method has been applied to analysis of various waters with good precisions and spiked recoveries of 80.8–113.8%.

Determination of Water-Soluble Organophosphorus Herbicides by Ion Chromatography With Inductively Coupled Plasma Mass Spectrometry Detection

There is a high risk for human exposure to organophosphorus pesticides through contaminated drinking water. Glyphosate, glufosinate, fosamine and ethephon are among the water-soluble herbicides used currently. Sensitive and rapid analytical methodologies are critical for evaluating their residuals in a broad variety of samples, including environmental waters. However, challenges arise from the inherent chemical properties of the herbicides: strong polarity, high solubility in water, insolubility in organic solvent (except ethephon), absence of chromophore or fluorophore in their molecular structures. So far very rare analytical methods are available for ethephon [1] and fosamine [2], while glyphosate and glufosinate are often determined by gas chromatography [3], high performance liquid chromatography (HPLC) [4] and capillary electrophoresis (CE) [5]. Inductively coupled plasma mass spectrometry (ICP-MS) is sensitive, rapid, selective, and is more powerful when hyphenated with appropriate separation. For the analysis of glufosinate, glyphosate and its metabolite aminomethylphosphonic acid (AMPA), ICP-MS was recently coupled to CE [6] or ion-pairing reversed-phase LC [7].Copyright