Detection limit electron capture

LOD, limit of detection NR, not reported MDC. mircodiffusion cell TCA, trichloroacetic acid AAS. atomic absorption spectrometry UV, ultraviolet absorbance detection ECD, electron capture detection NPD, nitrogen phosphorus detection GC-MSD, gas chromatography-mass selective detection GC, gas chromatography ATC, 2-amino-1hiazoline-4-carboxylic acid. 

GLC of mycotoxins is limited as most are non-volatile and derivatives need to be prepared, although GLC is of considerable use in the determination of the trichothecenes which are difficult to assay by TLC or HPLC. The preferred method of detection is electron capture, but increasing use is being made of GLC linked to mass spectrometry. 

In hplc, detection and quantitation have been limited by availabiHty of detectors. Using a uv detector set at 254 nm, the lower limit of detection is 3.5 X 10 g/mL for a compound such as phenanthrene. A fluorescence detector can increase the detectabiHty to 8 x 10 g/mL. The same order of detectabiHty can be achieved using amperometric, electron-capture, or photoioni2ation detectors. 

The analysis of mefloquine in blood, using packed-column sfc, a mobile phase consisting of / -pentane modified with 1% methanol and 0.15% -butylamine, and electron capture detection has been reported (92). The method compares favorably to a previously pubflshed hplc-based procedure having a detection limit of 7.5 ng/mLin 0.1 mL blood sample. 

The first bioanalytical application of LC-GC was presented by Grob et al. (119). These authors proposed this coupled system for the determination of diethylstilbe-strol in urine as a replacement for GC-MS. After hydrolysis, clean-up by solid-phase extraction and derivatization by pentafluorobenzyl bromide, the extract was separated with normal-phase LC by using cyclohexane/1 % tetrahydrofuran (THE) at a flow-rate of 260 p.l/min as the mobile phase. The result of LC-UV analysis of a urine sample and GC with electron-capture detection (ECD) of the LC fraction are shown in Ligures 11.8(a) and (b), respectively. The practical detection limits varied between about 0.1 and 0.3 ppb, depending on the urine being analysed. By use of... 

A very sensitive method for the determination of MCA in surfactants is a gas chromatographic one [249]. The method is based on the derivatization of the sample with ethanol and subsequent extraction of the derived ester with cyclohexane. The acids are identified and qualified gas chromatographically by the use of an electron capture detector and two capillary columns of varying polarities. The detection limit is 0.2 ppm. 

The method of choice for the determination of a- and P-endosulfan in blood, urine, liver, kidney, brain, and adipose tissue is gas chromatography equipped with an electron capture detector (GC/ECD) (Coutselinis et al. 1976 Demeter and Heyndrickx 1979 Demeter et al. 1977 Le Bel and Williams 1986). This is because GC/ECD is relatively inexpensive, simple to operate, and offers a high sensitivity for halogens (Griffith and Blanke 1974). After fractionation of adipose tissue extracts using gel permeation chromatography, detection limits of low-ppb (1.2 ng/g) were achieved for endosulfan and other chlorinated pesticides using GC/ECD (Le Bel and Williams 1986). 

Several methods are available for the analysis of trichloroethylene in biological media. The method of choice depends on the nature of the sample matrix cost of analysis required precision, accuracy, and detection limit and turnaround time of the method. The main analytical method used to analyze for the presence of trichloroethylene and its metabolites, trichloroethanol and TCA, in biological samples is separation by gas chromatography (GC) combined with detection by mass spectrometry (MS) or electron capture detection (ECD). Trichloroethylene and/or its metabolites have been detected in exhaled air, blood, urine, breast milk, and tissues. Details on sample preparation, analytical method, and sensitivity and accuracy of selected methods are provided in Table 6-1. 

Cyanide and thiocyanate anions in aqueous solution can be determined as cyanogen bromide after reaction with bromine [686]. The thiocyanate anion can be quantitatively determined in the presence of cyanide by adding an excess of formaldehyde solution to the sample, which converts the cyanide ion to the unreactive cyanohydrin. The detection limits for the cyanide and thiocyanate anions were less than 0.01 ppm with an electron-capture detector. Iodine in acid solution reacts with acetone to form monoiodoacetone, which can be detected at high sensitivity with an electron-capture detector [687]. The reaction is specific for iodine, iodide being determined after oxidation with iodate. The nitrate anion can be determined in aqueous solution after conversion to nitrobenzene by reaction with benzene in the presence of sulfuric acid [688,689]. The detection limit for the nitrate anion was less than 0.1 ppm. The nitrite anion can be determined after oxidation to nitrate with potassium permanganate. Nitrite can be determined directly by alkylation with an alkaline solution of pentafluorobenzyl bromide [690]. The yield of derivative was about 80t.with a detection limit of 0.46 ng in 0.1 ml of aqueous sample. Pentafluorobenzyl p-toluenesulfonate has been used to derivatize carboxylate and phenolate anions and to simultaneously derivatize bromide, iodide, cyanide, thiocyanate, nitrite, nitrate and sulfide in a two-phase system using tetrapentylammonium cWoride as a phase transfer catalyst [691]. Detection limits wer Hi the ppm range. 

An ion mobility spectrometer offers to prospective users an attractive detector for a GC, from the perspective of detection limits and specificity. A mobility spectrometer, even with low resolution, allows interrogation of compound identities and imparts better specificity than the electron-capture detector. When gaseous analytes are delivered individually to IMS, the mobility spectrum contains information for identification, provided that operating conditions are kept constant for the unknown and reference spectra. The connection of a GC column to an ion mobility spectrometer is... 

Shimoishi [ 555 ] determined selenium by gas chromatography with electron capture detection. To 50-100 ml seawater was added 5 ml concentrated hydrochloric acid and 2 ml 4-nitro-o-phenylenediamine (1%) and, after 2 hours, the product formed was extracted into 1 ml of toluene. The extract was washed with 2 ml of 7.5 M hydrochloric acid, then a sample (5 pi) was injected into a glass gas-liquid chromatography column (lm x 4 mm) packed with 15% of SE-30 on Chromosorb W (60-80 mesh) and operated at 200 °C with nitrogen (53 ml/min) as carrier gas. There is no interference from other substances present in seawater. The detection limit is 5 ng/1 with 200 ml samples, and the precision at a Se level of 0.025 pg/1 is 6%. 

Detectors range from the universal, but less sensitive, to the very sensitive but limited to a particular class of compounds. The thermal conductivity detector (TCD) is the least sensitive but responds to all classes of compounds. Another common detector is the flame ionization detector (FID), which is very sensitive but can only detect organic compounds. Another common and very sensitive detector is called electron capture. This detector is particularly sensitive to halogenated compounds, which can be particularly important when analyzing pollutants such as dichlorodiphenyltrichloroethane (DDT) and polychlorobiphenyl (PCB) compounds. Chapter 13 provides more specific information about chromatographic methods applied to soil analysis. 

One of the most commonly used detection systems in a gas chromatography laboratory is the electron capture detector. The first paper [25] to be published demonstrating the use of an electron capture detector with supercritical fluid chromatography showed that with supercritical fluid chromatography sensitivity to about 50pg minimum detection limit on column was obtainable. 

Onuska and Terry [14] have described a method for the determination of chlorinated benzenes in bottom sediment deposits. Sample preparation methods using Soxhlet extraction, ultrasonic extraction or steam distillation were compared. The chlorinated benzenes were characterized by open tubular column gas chromatography with electron capture detection. In recovery studies using sediments with different organic matter contents, the steam distillation method was the most efficient. Detection limits were in the range 0.4-10pg kgy1. 

Lee [42] determined pentachlorophenol and 19 other chlorinated phenols in sediments. Acidified sediment samples were Soxhlet extracted (acetone-hexane), back extracted into potassium bicarbonate, acetylated with acetic anhydride and re-extracted into petroleum ether for gas chromatographic analysis using an electron capture or a mass spectrometric detector. Procedures were validated with spiked sediment samples at 100,10 and lng chlorophenols per g. Recoveries of monochlorophenols and polychlorophenols (including dichlorophenols) were 65-85% and 80-95%, respectively. However, chloromethyl phenols were less than 50% recovered and results for phenol itself were very variable. The estimated lower detection limit was about 0.2ng per g. 

Downer et al. [212] reported comparable sensitivity with electron capture gas chromatography and specific ion monitoring of characteristic ions of residues of these compounds in soils. For both herbicides, the detection limit was reported to be 50pg, but less clean-up was required for specific ion monitoring than for electron capture gas chromatography. 

Elimination of wet chemical sample preparation enables a complete analysis to be performed and data to be quickly analyzed. The detection limits are in the low part-per-million range using mass spectrometric detection. Alternatively, detection of compounds can be achieved by all common gas chromatography detectors (flame ionization detector, electron capture detector and flame photometric detector), and detection limits are determined by the method of detection employed. 

Low detection limits (low ng/mL) have been achieved using a headspace/gas chromatographic (GC) technique (Seto et al. 1993). The sample is acidified and incubated, and the headspace analyzed by GC with a nitrogen-specific detector (NPD) (Carseal et al. 1993 Levin et al. 1990 Seto et al. 1993). Reported recovery is good (>90%) (Carseal et al. 1993), and precision is good as well (<15% RSD) (Carseal et al. 1993 Levin et al. 1990 Seto et al. 1993). Blood samples may be treated with chloramine T priorto incubation to produce a derivative which can be determined by GC with electron capture detection (ECD). Cyanate and thiocyanate do not interfere in this method (Odoul et al. 1994). The detection limit is 5 pg/L (ppb) precision is good (<15% RSD) (Odoul et al. 1994). 

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