Chromatography electrochemical detector

The chromatographic pumps and flow path used in IEC must be resistant to corrosion. For this reason, polymers such as poly(etheretherketone) (PEEK , ICI Americas Wilmington, DE) have entered into widespread usage in ion chromatography. Electrochemical detectors may also be subject to corrosion by certain ions. This chapter will review the chromatographic materials, detectors, and applications of ion exchange chromatography. For some classes of compounds, where reversed phase or normal phase alternatives may have been developed, alternative separation techniques will be presented. 

Fig. 14.8 A thin-layer cell for use as a high pressure liquid chromatography electrochemical detector (courtesy of Bioanalytical Systems).

Aminosalicylic acid in assessment of reactive oxygen species formation by in vitro Fenton and ozonation reactions and by in vivo ozone-exposure experiments in rats revealed oxidation products as follows salicylic acid, by deamination 2,3-dihydro-xybenzoic acid and 2,5-dihydroxybenzoic acid, from radical or enzymatic hydroxylation 5-amino-2 - hydroxy-N,W-bis(3 - carboxy- 4- hydroxyphenyl)-1,4-benzoquinonediimine, a condensation product of oxidised 5-aminosalicylic acid and 5-amino-2,3,4,6-tetrahydroxybenzoic acid, attributed to hydroxyl radical attack without deamination, identified by high-pressure liquid chromatography electrochemical detector system analysis and by gas chromatography-mass spectrometry analysis of trimethyl silyl derivatives (Kumarathasan et al. 2001). 

Liquid chromatography was performed on symmetry 5 p.m (100 X 4.6 mm i.d) column at 40°C. The mobile phase consisted of acetronitrile 0.043 M H PO (36 63, v/v) adjusted to pH 6.7 with 5 M NaOH and pumped at a flow rate of 1.2 ml/min. Detection of clarithromycin and azithromycin as an internal standard (I.S) was monitored on an electrochemical detector operated at a potential of 0.85 Volt. Each analysis required no longer than 14 min. Quantitation over the range of 0.05 - 5.0 p.g/ml was made by correlating peak area ratio of the dmg to that of the I.S versus concentration. A linear relationship was verified as indicated by a correlation coefficient, r, better than 0.999. 

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. ... 

Brunt, K., Electrochemical detectors for high-performance liquid chromatography and flow analysis systems, Trace Analysis, Vol. 1, Lawrence, J. F., Ed., Academic Press, New York, 1981, 47-120. 

Bollet, C., Oliva, P., and Caude, M., Partial electrolysis electrochemical detector in high-performance liquid chromatography, /. Chromatogr., 149,625,1977. 

Weber, S. G., The dependence of current on flow rate in thin-layer electrochemical detectors used in liquid chromatography. A clarification, /. Electroanal. Chem., 145, 1, 1983. 

Kordorouba, V. and Pelletier, M., Ion chromatography using an electrochemical detector response to non-electroactive anions, /. Liq. Chromatogr., 11, 2271, 1988. 

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

Electrochemical detectors (ECD) gas chromatography, 4 615 liquid chromatography, 4 622 6 387, 449 supercritical fluid chromatography, 4 631... 

Shea and MacCrehan [10] determined hydrophillic thiols in sediment pore water using ion-pair chromatography coupled to an electrochemical detector. Down to 2p mole absolute of these compounds could be determined including cysteine, monothiogylcerol, glutathione, mercaptopyruvic acid, 3-mercaptopropionic acid and 2-mercaptopropionic acid. 

We have already briefly described a popular application of amperometry in Chapter 13. This was the electrochemical detector used in HPLC methods. In this application, the eluting mobile phase flows across the working electrode embedded in the wall of the detector flow cell. With a constant potential applied to the electrode (one sufficient to cause oxidation or reduction of mixture components), a current is detected when a mixture component elutes. This current translates into the chromatography peak... 

ECO = electron capture detector ED = electrochemical detector FID st flame ionization detector GC = gas chromatography HECD = Hall s electrolytic conductivity detector HPLC = high performance liquid chromatography MEC = molecular emission cavity analysis MS - mass spectrometry HD = photo-ionization detector... 

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... 

CZE = capillary zone electrophoresis EC = electrochemical detector GC = gas chromatography HCD = Hall conductivity detector HPLC = high performance liquid chromatography IDMS = isotope dilution mass spectrometry MS = mass spectrometry RSD = relative standard deviation SEE = supercritical fluid extraction SPE = solid phase extraction UV = ultraviolet absorbance detection... 

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