On-line monitoring of electroosmotic flow for capillary electrophoretic separations

A recently developed technique for monitoring electroosmotic flow (EOF) in capillary electrophoresis by periodic photobleaching of a neutral fluorophore added to the running buffer has been further characterized and optimized and then applied to monitoring EOF during a typical capillary electrophoresis separation. The concentration of neutral fluorophore (rhodamine B) added to the running buffer for monitoring EOF has been decreased by one order of magnitude. The rate at which EOF can be measured has been increased from 0.2 to 1.0 Hz by decreasing the distance between the bleaching beam and the laser-induced fluorescence detector from 6.13 to 0.635 mm. The precision of the measured EOF ranges from 0.2 to 1.8%. Under typical experimental conditions, the dynamic range for flow measurements is 0.066 to 0.73 cm s(-1). Experimental factors affecting precision, signal-to-noise (S/N) ratio and dynamic range for EOF monitoring have been examined. This technique has been applied to measure EOF during a separation of phenolic acids with analyte detection by UV/VIS absorbance. The EOF monitoring method has been shown not to interfere with UV/VIS absorbance detection of analytes.

Capillary electrophoretic analysis of alkaline phosphatase inhibition by theophylline

An analytical method for studying enzyme inhibition has been developed using capillary electrophoresis with laser-induced fluorescence detection. This technique is based on electrophoretic mixing of zones of enzyme and inhibitor in substrate-filled capillaries. Enzyme catalytic activity is measured by detecting the fluorescent reaction product as it migrates past the detector. Reversible enzyme inhibition is indicated by a transient decrease in product formation. The enzyme, alkaline phosphatase, has been studied using the fluorogenic substrate AttoPhos ([2,2'-bibenzothiazol]-6-hydroxy-benzthiazole phosphate). This assay has been used to quantify theophylline, a noncompetitive, reversible inhibitor of alkaline phosphatase. The detection limit for theophylline is estimated at 3 microM, and 8.6 amole of alkaline phosphatase are required for each assay. The calculated K(i) for theophylline is 90 microM for the capillary electrophoretic enzyme-inhibitor assays.

HPLC-accelerator MS measurement of atrazine metabolites in human urine after dermal exposure

Metabolites of atrazine were measured in human urine after dermal exposure using HPLC to separate and identify metabolites and accelerator mass spectrometry (AMS) to quantify them. Ring-labeled [14C]atrazine was applied for 24 h with a dermal patch to human volunteers at low (0.167 mg, 6.45 muCi) and high (1.98 mg, 24.7 muCi) doses. Urine was collected for 7 days. The urine was centrifuged to remove solids, and the supernatant was measured by liquid scintillation counting prior to injection on the HPLC to ensure that < 0.17 Bq (4.5 pCi) was injected on the column. A reversed-phase gradient of 0.1% acetic acid in water and 0.1% acetic acid in acetonitrile became less polar with increasing time and separated the parent compound and major atrazine metabolites over 31 min on an octadecylsilane column. Peaks were identified by coelution with known standards. Elution fractions were collected in 1-min increments; half of each fraction was analyzed by AMS to obtain limits of quantitation of 14 amol. Mercapturate metabolites of atrazine and dealkylated atrazine dominated the early metabolic time points, accounting for approximately 90% of the 14C in the urine. No parent compound was detected. The excreted atrazine metabolites became more polar with increasing time, and an unidentified polar metabolite that was present in all samples became as prevalent as any of the known ring metabolites several days after the dose was delivered. Knowledge of metabolite dynamics is crucial to developing useful assays for monitoring atrazine exposure in agricultural workers.

Analytical performance of accelerator mass spectrometry and liquid scintillation counting for detection of 14C-labeled atrazine metabolites in human urine

Accelerator mass spectrometry (AMS) has been applied to the detection of 14C-labeled urinary metabolites of the triazine herbicide, atrazine, and the analytical performance of AMS has been directly compared to that of liquid scintillation counting (LSC). Ten human subjects were given a dermal dose of 14C-labeled atrazine over 24 h, and urine from the subjects was collected over a 7-day period. Concentrations of 14C in the samples have been determined by AMS and LSC and range from 1.8 fmol/mL to 4.3 pmol/mL. Data from these two methods have a correlation coefficient of 0.998 for a linear plot of the entire sample set. Accelerator mass spectrometry provides superior concentration (2.2 vs 27 fmol/mL) and mass (5.5 vs 54,000 amol) detection limits relative to those of LSC for these samples. The precision of the data provided by AMS for low-level samples is 1.7%, and the day-to-day reproducibility of the AMS measurements is 3.9%. Factors limiting AMS detection limits for these samples and ways in which these can be improved are examined.

Development of a highly sensitive enzyme-linked immunosorbent assay based on polyclonal antibodies for the detection of polychlorinated dibenzo-p-dioxins

The development of an enzyme-linked immunosorbent assay (ELISA) based on polyclonal antibodies for the polychlorinated dibenzo-p-dioxins is described. We previously reported the synthesis of haptens and generation of antibodies for detection of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). Antisera were screened with seven different coating antigens (hapten-protein conjugates), including trans-3-(7,8-dichlorodibenzo-p-dioxin-2-yl)-cis-2-methylpropeno ic acid (VII) and 5-(3,7,8-trichlorodibenzo-p-dioxin-2-yl)penta-trans,trans-2,4-dien oic acid (X). All inhibition screening and optimization studies were conducted using a less toxic surrogate standard for TCDD [2,3,7-trichloro-8-methyl-dibenzo-p-dioxin (TMDD; XVII)] which responded similarly to 2,3,7,8-TCDD in the ELISA. The most sensitive assay from the screening studies [coating antigen VII-BSA, 0.1 microgram/mL, and antiserum 7598 (anti-X-LPH), 1:10,000] was further optimized and characterized. It exhibited an IC50 value of 12 pg/well (240 pg/mL), with working range from 2 to 240 pg/well (40 to 4800 pg/mL). The influence of various physical and chemical factors (time, solvent, detergent) was investigated. The optimized assay was then used to assess cross-reactivity by congeners of halogenated dioxins and related structures. DMSO up to concentrations of 37.5% decreased the IC50 value in the assay, whereas methanol to concentrations of 30% did not lead to improved IC50 values.

Rapid assays for environmental and biological monitoring

Rapid, inexpensive, sensitive, and selective enzyme-linked immunosorbent assays (ELISAs) now are utilized in environmental science. In this laboratory, many ELISAs have been developed for pesticides and other toxic substances and also for their metabolites. Compounds for which ELISAs have recently been devised include insecticides (organophosphates, carbaryl, pyrethroids, and fenoxycarb), herbicides (s-triazines, arylureas, triclopyr, and bromacil), fungicides (myclobutanil), TCDD, and metabolites of naphthalene and toluene. New rapid assays have been developed for mercury.

Analysis of single cells by capillary electrophoresis with on-column derivatization and laser-induced fluorescence detection

On-column derivatization of single mammalian cells with capillary electrophoretic separation and laser-induced fluorescence detection is described. Individual cells are electrophorectically injected into the front end of the separation capillary, which is used as a chamber to lyse the cell and derivatize its contents for subsequent separation and detection. Reagents to lyse the cell and derivatize its contents are electrophoretically injected into the front end of the capillary (2.7 mm, 600-pL volume for a 17-microns-i.d. capillary) after the cell has been injected. Dopamine and five amino acids have been quantitatively determined in individual rat pheochromocytoma cells after on-column derivatization with naphthalene-2,3-dicarboxaldehyde and CN-. Average values of compounds determined in these cells range from 180 +/- 110 amol/cell for aspartic acid to 5.1 +/- 1.5 fmol/cell for taurine.

Analysis of human cerebrospinal fluid by capillary electrophoresis with laser-induced fluorescence detection

Capillary electrophoresis with laser-induced fluorescence detection is used to analyze 10 microL samples of human cerebrospinal fluid. Primary amine-containing compounds in untreated cerebrospinal fluid are labeled with 3-(4-carboxybenzoyl)-2-quinolinecarboxaldehyde prior to analysis, producing fluorescent isoindoles. Electropherograms containing approximately 50 peaks are obtained in less than 35 min from cerebrospinal fluid samples. Ten peaks in the electropherograms have been identified and quantitated: arginine, glutamine, threonine, valine, gamma-amino-n-butyric acid, serine, alanine, glycine, glutamic acid, and aspartic acid. Detection limits for these 10 amino acids range from 0.29 nM for gamma-amino-n-butyric acid to 100 nM for threonine, and separation efficiencies as high as 190,000 theoretical plates are obtained for these analytes. Electropherograms of cerebrospinal fluid samples from patients with Alzheimer's disease and from children with different neurological disorders are compared to those of healthy controls. Differences in individual amino acid levels are observed between the patient groups, and these differences appear to be disease and age related. These results indicate that analysis of cerebrospinal fluid by capillary electrophoresis will be useful as a selective, rapid, and sensitive tool for both diagnosis of central nervous system disorders and for study of the mechanisms of these disorders.