Capillary zone electrophoretic separation of neutral species of chloro-s-triazines in the presence of cationic surfactant monomers.

Chloro-s-triazines are difficult to separate by capillary zone electrophoresis (CZE), due to their low pKa values. However, these analytes can be effectively separated by CZE in the presence of cationic surfactant monomers, such as tetradecylammonium bromide (TTAB) and dodecyltrimethylammonium bromide (DTAB). The separation mechanism based on a 1:1 binding of analytes to cationic surfactant monomers is proposed. The binding constants of chloro-s-triazines to cationic surfactant monomers are estimated. The results show that the strength of the interactions of these analytes with TTAB monomers is considerably strong, whereas that of the corresponding analyte with DTAB monomers is about 12- to 14-fold weaker. A linear correlation of binding constants with log P(ow) (the logarithm of the partition coefficient of analytes between 1-octanol and aqueous phases) indicates that the migration order of these chloro-s-triazines depends primarily on their hydrophobicity. Moreover, the skewed peaks of chloro-s-triazines observed may reveal the occurrence of adsolubilization of these analytes in the adsorbed cationic surfactant layer on the capillary surface.

Indirect electrochemical detection of type-B trichothecene mycotoxins.

Trichothecene mycotoxins in animal feed and human food can cause fatalities in livestock and disease in humans. In addition, these toxins are suspected chemical warfare agents. Therefore, development of a simple and sensitive method for the screening of trichothecenes is important to prevent economic loss and health hazards. A simple and inexpensive method for the detection of type-B trichothecene mycotoxins has been developed in our laboratory. By hydrolyzing the toxin under basic conditions at 80 degrees C for 1 h it is possible to detect the toxin with simple electrochemical techniques. Deoxynivalenol (DON), commonly known as vomitoxin, was used as a representative compound for type-B trichothecenes in this detection scheme. The detection limit for DON using our procedures was determined to be 9.1 microM in solution, corresponding to 0.24 ppm in a 25-g grain sample if the final extraction volume is 2.2 mL. The linear dynamic detection range was determined to be from 0.32 ppm to greater than 32 ppm. In addition to standard solutions, this method was used on rice samples spiked with DON. It was demonstrated that there is no electrochemical interference from rice extract and that 1 ppm of DON in rice samples can be quantified. This method may be ideal for toxin screening in animal feeds or in runoff from sites that produce the compounds as chemical warfare agents. Since the active moiety in DON is common to virtually all type-B trichothecenes, our approach may be ideal for type-specific screening.

Possibilities and limitations in miniaturized sensor design for uric acid.

Uric acid (UA) has been under intensive investigation by electrochemists owing to its important role as a metabolite in biological fluids. One of the major problems in biological determinations of uric acid comes from electrochemical interferences such as ascorbic acid (AA), which has a similar oxidation potential, E1/2 approximately 200 mV versus SCE, at graphite electrodes, and is present at high concentrations in biological systems. UA undergoes a 2 H+, 2 e- oxidation in aqueous buffers. The oxidation product, a diimine, is an unstable intermediate with a half-life of less than 22 ms. A follow-up hydration reaction converts the diimine to an imine alcohol. Results of previous work show that UA weakly adsorbs and undergoes a fast electron transfer reaction, ks = 54 s-1, at carbon fiber electrodes. These characteristics make UA an excellent candidate for fast scan voltammetric (FSV) determinations. This paper presents the results of FSV at bare carbon fiber electrodes. The results show good selectivity and sensitivity in the determination of low concentrations of UA in the presence of high concentrations of AA. By increasing the scan rate above 500 V s-1, voltammograms of UA in the presence of AA can be resolved because of the kinetic differences in the response of the two anions, without the need for a permselective film on the electrode. Results are also presented that demonstrate an effective way to reach a stable background current at bare carbon fiber electrodes, which is required in FSV because the signal from the analyte is smaller than the electrochemical signal from the background current. Signal-to-noise ratios at bare carbon fiber electrodes in FSV are improved, because the high temporal resolution in fast scan methods allows the acquisition of a large number of scans that can be signal averaged in a short period of time. In addition, large signals can be measured because the voltammetric peak current increases with increase in scan rate.