Chromatography HPLC electrochemical

High-performance liquid chromatography (HPLC) with a micellar mobile phase or with a selective pre-column or reaction detection system has also been used to determine alkylenebis(dithiocarbamaes). ° Zineb and mancozeb residues in feed were determined by ion-pair HPLC with ultraviolet (UV) detection at 272 nm. These compounds were converted to water-soluble sodium salts with ethylenediaminetetra-acetic acid (EDTA) and sodium hydroxide. The extracts were ion-pair methylated with tetrabuthylammonium hydrogensulfate (ion-pair reagent) in a chloroform-hexane solvent mixture at pH 6.5-8.S. The use of an electrochemical detector has also been reported. ... 

ECD = electrochemical detection FID = flame ionization detector GC = gas chromatography HPLC = high performance liquid chromatography M = molar NaOH = sodium hydroxide NR = not reported rpm = revolutions per minute... 

Nagaosa et al. [839] simultaneously separated and determined these elements in seawater by high-performance liquid chromatography (HPLC) using spec-trophotometric and electrochemical detectors. 

Microdialysis is a sampling technique that must be coupled with an analytical method to identify and quantify chemical components of the dialysate. The samples can be analyzed immediately upon collection (i.e., online), or they can be stored (—80°C) for future analysis. Only analytical techniques sensitive enough to measure both small sample volumes and low concentrations of substances can be used to measure compounds in dialysate samples. High-performance liquid chromatography (HPLC) or capillary electrophoresis (CE) combined with ultraviolet (UV), electrochemical (EC), or laser-induced fluorescence (LIF)... 

Riggin and Howard (1979, 1982), Matsui et al. (1983), Fabre et al. (1984), and Ahuja et al. (1988) reported that High Performance Liquid Chromatography (HPLC) with UV or electrochemical detection is capable of analyzing 1,2-diphenylhydrazine. Reversed phase chromatographic columns have been used most often (Ahuja et al. 1988 Fabre et al. 1984 Riggin and Howard 1979, 1982). Cyano-amino polar bonded phase columns also have been used (Matsui et al. 1983). Using a reversed phase and UV detection, the minimum amount detected (on column amounts) is approximately 6-7 ng and the minimum amount quantifiable is less than 1 pg (Ahuja et al. 1988 ... 

GC = gas chromatography EC = electrochemical (detector ECD = electron capture (detector HCD = Hall conductivity detector HFBA = heptafluorobutyric anhydride HPLC = high performance liquid chromatography NCI-MS = mass spectrometry in the negative chemical ionization mode NPD = nitrogen-phosphorus detector ppb = parts per billion UV = ultraviolet absorption SPE = solid phase extraction wt wt = weight weight... 

The chemical properties of HVA, 5HIAA and 3-MD make them amenable to reverse-phase high-performance liquid chromatography (HPLC) with electrochemical detection. Furthermore, the composition of CSF means that little, if any, sample preparation is required prior to analysis. However, the susceptibility of these metabolites to oxidation means that careful sample collection and storage is required in order to minimise analyte degradation. 

Fig. 6.2.2a-bc High-performance liquid chromatography (HPLC) with electrochemical (EC) detection of neurotransmitter metabolites, a standard mixture b cerebrospinal fluid (CSF) sample - control c CSF sample - aromatic amino acid decarboxylase (AADC) deficiency. Peak identification 1 = 5HIAA (7.7 min), 2 = 3-MD (9.6 min), 3 = HVA (11.7 min)... 

MTHF was initially measured by microbiological and radioisotope dilution assay [12, 13], and later by high-pressure liquid chromatography (HPLC) using electrochemical (EC), ultraviolet, or fluorescence detection [14-16]. Compared to other methods, EC detection is more sensitive. 

An enzyme reactor with immobilized 3 -hydroxysteroid dehydrogenase has been successfully used for the analysis of residues of 17 -methyltestosterone in trout by high-performance liquid chromatography (HPLC) (269). Following their separation by reversed-phase chromatography, the major tissue metabolites of 17 -methyltestosterone, namely 5 -androstane-17 -methyl-3, 17 -diol, and 5 -androstane-17 -methyl-3, 17 -diol, were enzymatically modified in the presence of a coreactant, nicotinamide-adenine dinucleotide (NAD), to the corresponding ketone. The position at 3 was enzymatically oxidized, and NADH, the reduced form of NAD, was produced as a coproduct and subjected to fluorescence detection. Reoxidation of NADH to NAD provides the possibility for electrochemical detection. 

Electrochemical detection under convective conditions has been applied widely in freshwater measurements. In addition, seawater measurements have been combined with flow injection analysis (FIA) and high pressure liquid chromatography (HPLC) (D.C. Johnson et al., 1986). Well-developed commercial product lines exist, and detection limits are typically in the range of femtomoles. For in situ, shipboard, and land-based measure-... 

The irreversible inactivation of V-BrPO that occurs at low pH [55] was found to produce 2-oxohistidine as identified by high-performance liquid chromatography (HPLC) using electrochemical detection [60], Inactivation of V-BrPO and formation of 2-oxohistidine require all the components of turnover (i.e., bromide, dihydrogen peroxide, and V-BrPO) as well as low pH (Figure 5). Neither... 

We believe that this symposium on Recent Advances in Pesticide Analytical Methodology fulfills this plea. High-performance liquid chromatography (HPLC) has made the greatest advances. Chapters on HPLC cover subjects on metabolism studies automation of HPLC evaluation of LC columns the effect of the mobile phase on reversed-phase chromatography the electrochemical or amperometric detector and fluorogenic detection. 

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