Determination of erythromycin A by liquid chromatography and electrochemical detection, with application to salmon tissue.

The chromatographic performance of erythromycin A (EA) is improved significantly over that achieved on polymeric columns by using a sterically shielded octyldiisopropylsilica (Zorbax Rx-C8) column and a neutral mobile phase consisting of 5 mM aqueous sodium perchlorate-acetonitrile (50:50). This mobile phase facilitates electrochemical detection of EA at the 3-pmol level. Temperature control of both column and detection cell is important for minimizing detector noise and drift. A clean-up procedure, based on aminopropylsilica solid-phase extraction, allows the detection of EA in salmon flesh down to the 0.2-ppm level. Some of the metabolites of EA that retain the tertiary amine may also be detected by this method.

Determination of erythromycin A in salmon tissue by liquid chromatography with ion-spray mass spectrometry.

A reverse-phase liquid chromatography/mass spectrometry (LC/MS) method, incorporating gradient elution, is described for the characterization of residual erythromycin A and its metabolites in salmon tissue. The method uses ion-spray, a mild atmospheric pressure ionization technique which provides an abundant protonated molecule well suited for selected ion monitoring experiments. Tandem mass spectrometry (MS/MS) using collision-induced dissociation was used to provide structural information. The LC/MS method was tested for the analysis of salmon tissue spiked with erythromycin A at levels between 0.01 and 1 p.p.m. A simple extraction and clean-up procedure, slightly modified from that described by Takatsuki et al. (J. Assoc. Off. Anal. Chem. 70, 708 (1987)), was used in this work. Using selected ion and selected reaction monitoring techniques, the LC/MS and LC/MS/MS methods provided detection limits of < 10 and 50 ng g-1, respectively. Confirmatory full-scan LC/MS and LC/MS/MS spectra were obtained at the 0.5 and 1 microgram g-1 levels, respectively. Using a combination of these techniques, the presence of residual erythromycin A was confirmed in the tissue of fish administered medicated feed containing the antibiotic. In addition, several metabolites and degradation products of erythromycin A, including anhydro-erythromycin and N-demethyl-erythromycin, were detected and where possible confirmed by comparison with authentic compounds. Although this analytical method has been shown to afford the necessary sensitivity and precision, application of these techniques to high-throughput quantitative analyses will require development of an improved clean-up procedure and preferably also of a suitable surrogate internal standard.

An evaluation of atmospheric pressure ionization techniques for the analysis of N-Methyl carbamate pesticides by liquid chromatography mass spectrometry.

Atmospheric pressure ionization (API) techniques are evaluated for the mass spectral analysis of N-methyl carbamate pesticides. Atmospheric pressure chemical ionization (APCI) using a heated nebulizer interface provided both protonated molecules and abundant, characteristic fragment ions. With ion spray (ISP; pneumatically assisted electrospray ionization), which utilizes a milder "ion evaporation" process, primarily protonated molecules were obtained, although fragment ions similar to those observed in APCI could be induced by variation of the API orifice voltage. Product ion spectra of ISP-derived protonated molecules, generated by tandem mass spectrometry using collision-induced dissociation, are also presented. The APCI and ISP spectra of the carbamates are compared to those obtained with a thermospray interface and also to their electron ionization and methane CI spectra obtained with a particle beam interface. For all four interfaces, combined liquid chromatography mass spectrometry methods using conventional (4.6 mm i.d.) columns are described for the separation and detection of pesticide mixtures. These methods are applied to the confirmatory analysis of three representative carbamate pesticides, spiked at the 0.1-ppm level in green peppers. For those carbamates amenable to gas chromatography mass spectrometry, comparative results are presented.

Correlation of urinary tract infection with urinary screening at the first antepartum visit.

Urinary tract infection contributes to the morbidity of pregnancy since 4-10 percent of antepartum patients have asymptomatic bacteriuria and 20-40 percent of these will result in pyelonephritis. A cost-effective outpatient assessment for asymptomatic bacteriuria in undelivered obstetric patients is described. In this study, 56 patients between 6-24 weeks gestation were assessed over a seven-month period by photometric urinary screening. This assessment was more accurate in identifying those patients with asymptomatic bacteriuria than prior history or symptoms. A 7 percent incidence of asymptomatic bacteriuria was noted with 75 percent being Escherichia coli and the remainder Klebsiella. Single-dose, oral antibiotic therapy was evaluated and resulted in no recurrences. Such screening for asymptomatic bacteriuria was felt to represent preventive and economic medical benefits.

Identification of a uteroglobin-like antigen in human uterine washings.

A uteroglobin-like molecule was detected with a sensitive radioimmunoassay for rabbit uteroglobin in the uterine washings of women. This antigen was detectable only in small amounts in the uterine washings obtained from women in the late luteal phase or proliferative phase, but was detected in large amounts in uterine washings of women collected during the early and midluteal phases of the ovarian-menstrual cycle. Our findings suggest that antigenically similar portions of rabbit uteroglobin have been phylogenetically conserved in women, and that endometrial production and secretion of this human uteroglobin-like antigen may be hormonally regulated.