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Preconcentration Technique (preconcentration + technique)
Selected AbstractsElectrokinetic supercharging-electrospray ionisation-mass spectrometry for separation and on-line preconcentration of hypolipidaemic drugs in water samplesELECTROPHORESIS, Issue 7 2010Mohamed Dawod Abstract Electrokinetic supercharging, a powerful on-line preconcentration technique in CE, was for the first time hyphenated with ESI-MS for the on-line concentration and separation of five hypolipidaemic drugs. The electrophoretic separation was performed in a co-EOF mode using the EOF reversal agent, hexadimethrine bromide, in ammonium bicarbonate electrolyte, pH 9.00. The ionic strength and the amount of methanol in the buffer were optimised in a multivariate manner using artificial neural networks, with the optimal conditions being 60,mM ammonium bicarbonate containing 60% methanol, providing baseline resolution of the five hypolipidaemics within 20,min. Using electrokinetic supercharging, the sensitivity of the method was improved 1000-fold over a conventional injection under field-amplified sample stacking conditions with LODs of 180,ng/L. This is the first report of the separation of hypolipidaemics by CE. The developed method was validated and then applied to the determination of the target drugs in water samples from Hobart city. [source] Sensing of toxic metals through pH changes using a hybrid sorbent material: Concept and experimental validationAICHE JOURNAL, Issue 11 2009Prasun K. Chatterjee Abstract This article reports a new hybrid sorbent material that is capable of detecting trace concentration of toxic metals, such as zinc, lead, copper, nickel, etc., through pH changes only. The material is essentially a composite granular material synthesized through rapid fusion of a mixture of amorphous hydrated ferric oxide (HFO) and akermanite or calcium magnesium silicate (Ca2MgSi2O7). When a water sample is rapidly passed through a mini-column containing this hybrid material, effluent pH at the exit always remains alkaline (,9.0) because of slow hydrolysis of akermanite and steady release of hydroxyl (OH,) ions. This exit solution turns pink through the addition of a phenolphthalein indicator. Commonly encountered electrolytes containing sodium, calcium, chloride, and sulfate have no impact on the exit pH from the mini-column. However, when trace concentration of a heavy metal (say lead) is present in the sample water, a considerable drop in pH (>2 units) is observed for the exiting solution. At this point, the solution turns colorless through the addition of a phenolphthalein indicator. Moreover, the change in the slope of pH, i.e., ,dpH/dBV, provides a sharp, noticeable peak for each toxic metal where BV is the bed volumes of solution fed. The technique allowed detection of zinc and lead through pH swings in synthesized samples, spiked Bethlehem City water, and also in Lehigh River water in the presence of phosphate and natural organic matter (NOM). Using a simple preconcentration technique, lower than 10 ,g/l of lead was detected with a significant peak. From a mechanistic viewpoint, high sorption affinity of HFO surface sites toward toxic metal cations, ability of akermanite to maintain near-constant alkaline pH for a prolonged period through slow hydrolysis and labile metal-hydroxy complex formation causing dissipation of OH, ions from the aqueous phase provide a synergy that allows detection of toxic metals at concentrations well below 100 ,g/l through pH changes. Nearly all previous investigations pertaining to toxic metals sensing use metal-selective enzymes or organic chromophores. This simple-to-operate technique using an inexpensive hybrid material may find widespread applications in the developing world for rapid detection of toxic metals through pH changes. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source] A new approach to determine method detection limits for compound-specific isotope analysis of volatile organic compoundsRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 24 2006Maik A. Jochmann Compound-specific isotope analysis (CSIA) has been established as a useful tool in the field of environmental science, in particular in the assessment of contaminated sites. What limits the use of gas chromatography/isotope ratio mass spectrometry (GC/IRMS) is the low sensitivity of the method compared with GC/MS analysis; however, the development of suitable extraction and enrichment techniques for important groundwater contaminants will extend the fields of application for GC/IRMS. So far, purge and trap (P&T) is the most effective, known preconcentration technique for on-line CSIA with the lowest reported method detection limits (MDLs in the low,µg/L range). With the goal of improving the sensitivity of a fully automated GC/IRMS analysis method, a commercially available P&T system was modified. The method was evaluated for ten monoaromatic compounds (benzene, toluene, para -xylene, ethylbenzene, propylbenzene, isopropylbenzene, 1,2,3-trimethylbenzene, 1,2,4-trimethylbenzene, 1,3,5-trimethylbenzene, fluorobenzene) and ten halogenated volatile organic compounds (VOCs) (dichloromethane, cis -1,2-dichloroethene, trans -1,2-dichloroethene, carbon tetrachloride, chloroform, 1,2-dichloroethane, trichloroethene, tetrachlorethene, 1,2-dibromoethane, bromoform). The influence of method parameters, including purge gas flow rates and purge times, on ,13C values of target compounds was evaluated. The P&T method showed good reproducibility, high linearity and small isotopic fractionation. MDLs were determined by consecutive calculation of the ,13C mean values. The last concentration for which the ,13C value was within this iterative interval and for which the standard deviation was lower than ±0.5, for triplicate measurements was defined as the MDL. MDLs for monoaromatic compounds between 0.07 and 0.35,µg/L are the lowest values reported so far for continuous-flow isotope ratio measurements using an automated system. MDLs for halogenated hydrocarbons were between 0.76 and 27,µg/L. The environmental applicability of the P&T-GC/IRMS method in the low-µg/L range was demonstrated in a case study on groundwater samples from a former military air field contaminated with VOCs. Copyright © 2006 John Wiley & Sons, Ltd. [source] Analysis of exhaled breath from smokers, passive smokers and non-smokers by solid-phase microextraction gas chromatography/mass spectrometryBIOMEDICAL CHROMATOGRAPHY, Issue 5 2009Bogus, aw Buszewski Abstract In this study, 38 samples of expired air were collected and analyzed from 20 non-smoking volunteers, four passive smokers and 14 smokers (21 women and 17 men). Measurements were carried out using solid-phase microextraction (SPME) as an isolation and preconcentration technique. The determination and identification were accomplished by gas chromatography coupled with mass spectrometry (GC/MS). Our data showed that ca 32% of all identified compounds in the breath of healthy non-smokers were saturated hydrocarbons. In the breath of smoking and passive smoking volunteers hydrocarbons were predominant, but also present were more exogenous analytes such as furan, acetonitrile and benzene than in the breath of non-smokers. Acetonitrile, furan, 3-methylfuran, 2,5-dimethylfuran, 2-butanone, octane and decane were identified in breath of smoking and passive smoking persons. Copyright © 2008 John Wiley & Sons, Ltd. [source] | ||||||||||