Quantitative determination of trace metals in single yeast cells by time-resolved ICP-MS using dissolved standards for calibration.

Time-resolved inductively coupled plasma mass spectrometry (ICP-MS) for studying cellular heterogeneity or detecting metals in single cells draws increasing attention in the recent years. Considering the full width of a single-cell event is about 0.5-0.9 ms, dependent on the duration of the ion plume generation in typical ICP condition, dwell time shorter than the transient event was suggested for fully profiling it. Herein we investigated the effect of dwell time (0.1-10.0 ms) on the signal profiles of single-cell events, signal-to-background ratio, duty cycle of detection, the limit of detection, and the ability of cell counting by the time-resolved ICP-MS, using yeast (Saccharomyces cerevisiae) cells as example. Two calibration equations with respect to the length of dwell time (0.1 ms or 5.0 ms), simply using dissolved metal standard solutions, were constructed and successfully applied to the determination of K, Mg, Zn, Mn, and Cu in single yeast cells. The limit of detection (LOD, fg per cell) obtained at dwell time 0.1 ms was 1.68 (K), 0.29 (Mg), 0.17 (Zn), 0.01 (Mn), and 0.02 (Cu) for single-cell analysis of yeast cells; the LOD (fg per cell) at 5.0 ms was 80.0 (K), 10.3 (Mg), 1.6 (Zn), 0. 14 (Mn), and 0.24 (Cu), respectively. The results showed that a short dwell time leading to high signal-to-background ratio and low LOD was a prerequisite for the quantitative analysis of ultra-trace content of metals in single cells.

Low-density solvent-based dispersive liquid-liquid microextraction combined with single-drop microextraction for the fast determination of chlorophenols in environmental water samples by high performance liquid chromatography-ultraviolet detection.

A new format of fast three-phase microextraction by combining low-density solvent-based dispersive liquid-liquid microextraction (DLLME) and single-drop microextraction (SDME) was for the first time developed for the determination of chlorophenols in environmental water samples. The extraction procedure includes a 2 min DLLME pre-extraction and a 10 min SDME back-extraction. A portion of low-density solvent (toluene) was used as organic phase and injected into the aqueous sample (donor phase) with methanol as disperser. The analytes were pre-extracted into the organic phase within 2 min. A thin layer of the organic phase formed on the top of the aqueous phase by a 2 min centrifugation. Then a drop of acceptor solution was introduced into the upper layer and SDME was carried out for the back-extraction. The stirring step typically involved in SDME and LLLME is avoided with the benefit of the high speed and efficiency of DLLME pre-extraction. After extraction, the acceptor drop was withdrawn and directly injected into a high performance liquid chromatography instrument with ultraviolet detection for analysis. Five chlorophenols, 4-chlorophenol, 2-chlorophenol, 2,4-dichlorophenol, 2,4,6-trichlorophenol, and pentachlorophenol, were selected as model compounds for developing and evaluating the method. Factors affecting extraction efficiency were studied, including the organic solvent, the disperser solvent, the composition of donor phase and acceptor phase, the volume of acceptor microdrop, and the extraction time. At optimal conditions, the method showed low detection limit (0.016-0.084 µg/L) for the five chlorophenols, good linearity (from 0.2-250 to 1.0-250 µg/L, depending on the analytes) and repeatability (RSD below 8.2, n=5). The simple, fast, and efficient feature of the proposed method was demonstrated by the analysis of chlorophenols in environmental water samples.

Bioavailability of methyl parathion adsorbed on clay minerals and iron oxide.

Adsorption, desorption and degradation by Pseudomonas putida of methyl parathion (O,O-dimethyl O-p-nitrophenyl phosphorothioate) on montmorillonite, kaolinite and goethite were studied. Metabolic activities of methyl parathion-degrading bacteria P. putida in the presence of minerals were also monitored by microcalorimetry to determine the degradation mechanism of methyl parathion. Montmorillonite presented higher adsorption capacity and affinity for methyl parathion than kaolinite and goethite. The percentage of degradation of methyl parathion adsorbed on minerals by P. putida was in the order of montmorillonite>kaolinite>goethite. The presence of minerals inhibited the exponential growth and the metabolic activity of P. putida. Among the examined minerals, goethite exhibited the greatest inhibitory effect on bacterial activity, while montmorillonite was the least depressing. The biodegradation of adsorbed methyl parathion by P. putida is apparently not controlled by the adsorption affinity of methyl parathion on minerals and may be mainly governed by the activity of the methyl parathion-degrading bacteria. The information obtained in this study is of fundamental significance for the understanding of the behavior of methyl parathion in soil environments.

[Crosslinked carboxymethyl konjac glucomannan microcolumn preconcentration of trace lead, cadmium and copper in water samples and determination by graphite furnace atomic absorption spectrometry].

A novel solid phase extraction technique was developed for the determination of trace lead, cadmium and copper in environmental water samples based on separation and preconcentration with a microcolumn packed with crosslinked carboxymethyl konjac glucomannan (CCMKGM)prior to its determination by graphite furnace atomic absorption spectrometry. Various influential factors on the separation and preconcentration of lead, cadmium and copper, such as the acidity of the aqueous solution, sample flow rate and volume, and eluent concentration and volume, were investigated systematically, and the optimized operation conditions were established. The analytes could be quantitatively retained by CCMKGM in the pH range of 5.0-7.0, then eluted completely with 1.0 mL 0.5 mol x L(-1) HCl. The detection limits (3sigma) for analyte ions were 0.038 microg x L(-1) for Pb2+, 0.0005 microg x L(-1) for Cd2+ and 0.014 microg x L(-1) for Cu2+ with an enrichment factor of 50, and the relative standard deviations were 3.5% for Pb2+, 9.2% for Cd2+ and 4.7% for Cu2+ (c(Pb2+) = C(Cu2+) = 1.0 microg x L(-1); c(Cd2+) = 0.1 microg x L(-1), n=11). The proposed method was successfully applied to the determination of trace lead, cadmium and copper in environmental water samples (local tap water and lake water). In order to validate the method, the developed method was applied to the determination of lead, cadmium and copper in environmental water reference materials (ERMs, GSBZ 50009-88, PR China), and the results obtained were in good agreement with the certified values.

[Determination of lead and cadmium in rapeseed and rapeseed meal with microwave digestion by graphite furnace atomic absorption spectrometry].

Comprehensive utilization of rapeseed and rapeseed meal has been increasingly emphasized, and contaminative problems of heavy metal have been attracting great attention, so it is of quite important significance to determine the contents of Pb and Cd. An effective method was developed for the rapid determination of Pb and Cd in rapeseed and rapeseed meal. Digestive dissolvent, time and pressure were discussed for sample preparation by microwave digestion technique, and the optimum condition of determination by GFAAS was studied. The determination limits were 2.172 and 0.243 microg x L(-1), and the linear arranges were 0-100 microg x L(-1) and 0-8 microg x L(-1) for Pb and Cd, respectively. The recoveries were from 80.8% to 110.7%. The RSD of determination was lower than 5.3%. The method offers traits of low detection limit, high sensitivity, speediness and exactness, and was applied to the determination of Pb and Cd in samples with satisfactory results.

[Preconcentration with crosslinked chitosan for determination of trace manganese in waters by flame atomic absorption spectrometry].

A novel method for the preconcentration with crosslinked chitosan (CCTS) and determination of trace manganese in waters by flame atomic absorption spectrometry has been presented. The absorption rate of manganese (VII) by CCTS was 98% at pH 3.00. The effect of preconcentration time, dosage of CCTS, temperature, sample volume and co-existing elements have been investigated. The mechanism of adsorption of CCTS for Mn(VII) was also discussed. The detection limit of the method was 1.86 microg x L(-1), and the relative standard deviation (RSD) was 2.0% (n = 10). The method has been applied to the determination of trace manganese in south lake and Changjiang water with satisfactory results.