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Photometric Detection (photometric + detection)
Kinds of Photometric Detection Selected AbstractsTrace determination of arsenic species by capillary electrophoresis with direct UV detection using sensitivity enhancement by counter- or co-electroosmotic flow stacking and a high-sensitivity cellELECTROPHORESIS, Issue 12-13 2003Baoguo Sun Abstract Stacking techniques used independently and also with a high-sensitivity cell (HSC) were employed to optimise sensitivity and detection limits in the direct photometric detection of the following eight arsenic species by capillary zone electrophoresis (CZE): arsenite, arsenate, monomethylarsonic acid (MMA), dimethylarsinic acid (DMA), 4-hydroxy-3-nitrophenylarsonic acid (Roxarsone), p -aminophenylarsonic acid (p -ASA), 4-nitrophenylarsonic acid (4-NPAA), and phenylarsonic acid (PAA) (target analytes). The stacking mechanisms, optimised stacking and separation conditions, and concentration sensitivity enhancement factors were discussed and compared for (i) normal stacking mode (NSM, sometimes also referred to as field-amplified stacking) in an uncoated fused-silica capillary in the counter-electroosmotic flow (EOF) mode, (ii) large-volume sample stacking (LVSS) with polarity switching, and (iii) the less often applied stacking method of co-EOF NSM stacking with EOF reversal using a poly(diallydimethylammonium chloride) (PDDAC)-coated capillary. The optimal injection volumes were 7.4, 60 and 17.2% of the total capillary volume, for the above three methods, respectively. LVSS with polarity switching gave the lowest limit of detection (LOD). The use of the HSC further reduced the LOD of each target analytes by a factor of 5,8 times. By combining LVSS and HSC, LODs of the target analytes could be reduced by a factor of 218,311, to 5.61, 9.15, 11.1, and 17.1 ,g/L for As(III), DMA, MMA, and As(V), respectively. The method was demonstrated to be applicable to the determination of the target analytes in tap water and lake water, with recoveries in the range of 89.4,103.3%. [source] Miniaturized movable contactless conductivity detection cell for capillary electrophoresisELECTROPHORESIS, Issue 12-13 2003Miroslav Macka Abstract A miniaturized capacitively coupled contactless conductivity detector (mini-C4D) cell has been designed which is small enough to allow it to slide along the effective capillary length inside the capillary cassette of an Agilent capiillary electrophoresis system (CE) (or other CE brand of similar construction), including the possibility of positioning it close to the point of optical detection (4 cm), or even putting two such detector cells in one cassette. The cell was tested and the performance characteristics (noise, sensitivity, and peak width) were compared with those obtained with the previously used large C4D cell. No significant differences were observed. The mini-C4D was used in simultaneous separations of common cations and anions where its advantage over a larger C4D cell is the ability to vary the point of detection with the mini-C4D cell continuously at any point along the capillary length, so that the optimum apparent selectivity can be chosen. Other applications include providing a convenient second point of detection in addition to photometric detection, such as to measure accurately the linear velocity of a zone, or to allow placement of two mini-C4D cells in one capillary cassette simultaneously. [source] Enhancement of detection sensitivity for indirect photometric detection of anions and cations in capillary electrophoresisELECTROPHORESIS, Issue 12-13 2003Cameron Johns Abstract This review focuses on the indirect photometric detection of anions and cations by capillary electrophoresis. Special emphasis has been placed on the sensitivity of the technique and approaches taken to enhance detection limits. Theoretical considerations and requirements have been discussed, including buffering, detection sensitivity, separation of cations, and detector linearity. A series of tables detailing highly absorbing probes and the conditions of their use for indirect photometric detection are included. [source] Determination of trace organophosphorus pesticides in water samples with TiO2 nanotubes cartridge prior to GC-flame photometric detectionJOURNAL OF SEPARATION SCIENCE, JSS, Issue 14 2010Yunrui Huang Abstract This article described a new method for the sensitive determination of organophosphorus pesticides in water samples using SPE in combination with GC-flame photometric detection. In the procedure of method development, TiO2 nanotubes were used as SPE adsorbents for the enrichment of organophosphorus pesticides from water samples. Several factors, such as eluent and its volume, sample pH, sample volume, sample flow rate, and concentration of humic acid, were optimized. Under the optimal conditions, the proposed method had good linear ranges as 0.1,40,,g/L for each of them, LOD of 0.11, 0.014, and 0.0025,,g/L, and LOQs of 0.37, 0.047, and 0.0083,,g/L for chlorpyrifos, phorate, and methyl parathion, respectively. The proposed method was validated with real environmental water samples and the spiked recoveries were over the range of 86.5,115.1%. All these results indicated that TiO2 nanotubes, as a new SPE adsorbent, would be used widespread for the preconcentraiton and determination of environmental pollutants in the future. [source] Application of programmable temperature vaporisation injection with resistive heating-gas chromatography flame photometric detection for the determination of organophosphorus pesticidesJOURNAL OF SEPARATION SCIENCE, JSS, Issue 1 2006Katan Patel Abstract The combination of a programmable temperature vaporisation (PTV) injector with resistive heating GC (RH-GC), a form of fast GC, has been applied to the analysis of organophosphorus (OP) pesticides. The PTV injector was optimised in the ,at-once' solvent vent mode for the injection of ethyl acetate (10,40 ,L) or ACN (10 ,L). The short RH-GC column (5 m×0.25 mm ID) with fast temperature ramps (up to 153°C/min) allowed the separation of a total of 20 OP pesticides in less than 6 min. Average recoveries between 67 and 119% were obtained for pesticides spiked at 0.01 mg/kg into apple and pear matrix. Extraction of orange juice with ACN provided higher recoveries (92,104%) for methamidophos, acephate and omethoate compared to ethyl acetate (62,73%). Results for analysis of OP pesticides in samples containing incurred residues were in good agreement with those obtained using GC-MS. The overall method was rapid, allowing 20 samples to be analysed in 4 h. British Crown Copyright © 2005 Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim [source] Modified headspace-SPME-GC device for sampling volatile compounds in acidic mediumJOURNAL OF SEPARATION SCIENCE, JSS, Issue 6-7 2003W. A. Araújo Abstract Most of the existing analytical methods for determining dithiocarbamate pesticide residues utilize an acid decomposition step, which promotes the release of carbon disulfide from the pesticide molecule. After release, the CS2 is sampled by static headspace techniques using gas-tight syringes and analyzed by gas chromatography with flame photometric detection (GC-FPD). In our search for faster analytical methodologies for sampling of volatile compounds we have used solid phase microextraction (SPME). However, evaluation of the commercially available SPME system for the analysis of CS2 obtained by decomposing dithiocarbamates showed it to be unsuitable for analysis in an acidic environment. The present communication reports the development of an appropriate device for sampling volatile compounds in an acidic environment by static headspace-SPME followed by GC-FPD. On examining the limitations of using a standard metal needle in HS-SPME sampling of analytes in acidic medium, a corrosion process was observed in both needle and fiber. A new double-needle device which avoids such corrosion problems was developed and built. The successful application of this device to the analysis of mancozeb in water samples is described. [source] Emission to air of volatile organotins from tributyltin-contaminated harbour sedimentsAPPLIED ORGANOMETALLIC CHEMISTRY, Issue 5 2002Alfred J. Vella Abstract An analytical method for determining the presence in air of volatile forms (e.g. chlorides) of tributyltin (TBT) and that of methylbutyltins MenBu(4,n)Sn (n,=,1,3) was developed and used to establish whether dredged harbour sediments contaminated with TBT served as sources of air pollution with respect to organotin compounds. The method was based on active sampling of the air being analysed and sorption of analytes onto Poropak-N. Sorbed methylbutyltins were extracted with dichloromethane and analysed by gas chromatography using flame photometric detection. Other butyltins were converted into butyltin hydrides prior to analysis by gas chromatography. It was shown that TBT-contaminated sediments from Marsamxett Harbour, Malta, placed in 0.5 l chambers through which air was displaced by continuous pumping for 11 days released mainly methylbutyltins, with concentrations (as tin) reaching maximum 48,h mean values of 8.7 (Me3BuSn), 22.1 (Me2Bu2Sn) and 93.0,ng m,3(MeBu3Sn) being measured. Other volatile forms of TBT, dibutyltin and monobutyltin were detected in the headspace air, but very infrequently and at much lower tin concentrations (<2,ng m,3). It was also shown that methylbutyltins dissolved in sea-water ([Sn],=,0.2 to 400,ng l,1) were very difficult to exsolve from this medium, even on prolonged evaporation of the solutions using mechanical agitation and active ventilation. The results suggest that emission of methylbutyltins from contaminated sediments probably occurs only from the surface of the material. The environmental implications of these findings in the management of TBT-polluted harbour sediments are discussed. Copyright © 2002 John Wiley & Sons, Ltd. [source] Preliminary evidence for in vitro methylation of tributyltin in a marine sedimentAPPLIED ORGANOMETALLIC CHEMISTRY, Issue 11 2001Alfred J. Vella Abstract Recent reports from our laboratory on the occurrence of methylbutyltins in marine sediments and seawater suggest that these compounds are formed in the environment by the methylation of both tributyltin (TBT) and thatof its degradation products, i.e. dibutyltin and monobutyltin, to give MenBu(4,n)Sn for which n,=,1, 2 and 3 respectively. We investigated the possibility of inducing methylation of TBT in seawater,sediment mixtures in experiments carried out in vitro using environmental materials collected from a yacht marina in Msida, Malta. Three water,sediment mixtures, which were shown to contain TBT, dibutyltin and monobutyltin but no other organotins, were spiked with tributyltin chloride (90,mg in 100,ml sea-water/100,ml sediment); to one mixture was added sodium acetate and to another methanol, to act as possible additional carbon sources, and all mixtures were allowed to stand at 25,°C in stoppered clear-glass bottles in diffused light for a maximum of 315 days. Speciation and quantification of organotins was performed using aqueous phase boroethylation with simultaneous solvent extraction followed by gas chromatography with flame photometric detection. The atmosphere inside the bottles quickly became reducing with abundant presence of H2S, and after an induction period of about 112 days, and only in the reaction mixture containing methanol, methyltributyltin (MeBu3Sn) was observed in both sediment (maximum concentration 0.87 µgSn g,1) and overlying water (maximum concentration 6.0 µgSn l,1). The minimum conversion yield of TBT into MeBu3Sn was estimated to be 0.3%. MeBu3Sn has a significantly lower affinity for sediment than TBT and, therefore, is more mobile in the marine environment, possibly also migrating into the atmosphere to generate a hitherto unsuspected flux of organotin into that phase. Copyright © 2001 John Wiley & Sons, Ltd. [source] Determination of bisphenol A and 10 alkylphenols in serum using SDS micelle capillary electrophoresis with ,-cyclodextrinBIOMEDICAL CHROMATOGRAPHY, Issue 7 2001Masatoki Katayama A new micelle capillary electrophoresis based on cyclodextrin micellar electrokinetic chromatography (MEKC) for the determination of bisphenol A and 10 alkylphenols in rat serum is reported. Several surfactants and dextrins were studied. Bisphenol A and alkylphenols were separated using a 50,µm,×,50,cm capillary with 20,mM borate phosphate buffer (pH 8.0) containing 20,mM sodium dodecylsulfate and 5,mM ,-cyclodextrin as carrier. The method could determine 0.6,2000,µg/mL of phenols in 100,µL serum by photometric detection at 214,nm. Using 2.0,mL serum, 1.0,ng/mL of phenols could be determined. The relative standards deviations were 6.3,7.7% at 10,µg/mL in serum. The recoveries were 91.8,93.0% with 10,µg/mL serum samples. Copyright © 2001 John Wiley & Sons, Ltd. [source] | ||||||||||