Analysis of methylphenidate and its metabolite ritalinic acid in monkey plasma by liquid chromatography/electrospray ionization mass spectrometry.

Methylphenidate (MP, Ritalin) is a psychotropic drug widely prescribed to children for treating the symptoms of attention deficit disorder with and without hyperactivity. Because little information exists about the effects of chronic MP administration on cognitive function in children, measures of behavior changes in non-human primates are important surrogates. An essential component of such studies is the determination of MP plasma levels under chronic and acute dosing conditions. An analytical method was developed that provided sufficient sensitivity to measure low levels of the active parent drug (lower limit of quantitation = 0.25 ng/mL) and the inactive metabolite, ritalinic acid (RA), in monkey plasma as well as the ability to conveniently analyze large numbers of samples. The method uses a polymeric reversed-phase sorbent for solid phase extraction, an efficient reverse-phase high performance liquid chromatography (HPLC) separation, deuterated internal standards for isotope dilution quantification of MP and RA, and detection by sensitive electrospray ionization mass spectrometry (ES-MS) with a single quadrupole instrument. The method responses are linear over the range of plasma concentrations of MP and RA observed in monkeys, gives respective analyte recoveries of 75 and 60% with reasonable precision and accuracy, and demonstrates robust MS performance for rapid determination of MP/RA plasma levels. The average peak MP concentration (ca. 16 ng/mL) and half-lives for MP and RA elimination in monkeys (1.79 and 2.31 h, respectively) were not significantly different under acute vs. chronic dosing conditions and were comparable to values previously reported from human studies.

Analysis of erythromycin by liquid chromatography/mass spectrometry using involatile mobile phases with a novel atmospheric pressure ionization source.

A critical limitation of electrospray ionization (ESI) liquid chromatography/mass spectrometry (LC/MS) sources is the susceptibility to blockage of interface orifices due to the deposition of involatile components from the sample and/or mobile phase. These components, including salts, buffers, and ion-pairing agents, can be essential to the performance of the chosen analytical method. We report here the performance enhancements provided by a novel atmospheric pressure ionization (API) source in the analysis of erythromycin A (ERY) using mobile phases that contain involatile components. The enhanced robustness of the new source is derived from the use of a continuous flow of aqueous solvent at the sampling cone orifice that maintains unobstructed ion transmission. The ESI mass spectral responses measured for ERY, using an LC separation that incorporates 10 mM sodium phosphate with and without 10 mM octane sulfonate, were monitored by repeated injections over 13-15 h total analysis time. Minimal effects on ESI mass spectral responses (integrated peak area) or chromatographic performance (peak shape, retention time) were observed during these studies. In the absence of the aqueous cleaning flow, complete loss of mass spectral responses and total blocking of the sampling cone was observed in less than 30 min. Responses for ERY spiked into chicken and beef liver, and catfish muscle at or below the regulatory level of interest (100 ppb), were quantified by internal standard calibration using this procedure. These results demonstrate the ability of a novel API-MS ion source to perform analyses that require the use of involatile mobile phase additives.

Detection and confirmation of beta-agonists in bovine retina using LC/APCI-MS.

Beta-adrenergic receptor agonists are growth-promoting drugs with the potential for illegal use in livestock, and human toxicity has resulted from consumption of contaminated meat. On-line liquid chromatography with atmospheric pressure chemical ionization mass spectrometry (LC/APCI-MS) was used for sensitive detection of several beta-agonists in retina, a tissue reported to concentrate and retain such residues for extended periods. Multiresidue extraction, separation, detection, and confirmation procedures were developed for retinal tissue and applied to eyes from cattle treated with clenbuterol (69-201 ppb) and to control eyes spiked with salbutamol (100 ppb) and terbutaline (25-100 ppb). Rapid switching of the potential difference between sampling cone and skimmer in the transport region of the API source was used to optimize acquisition of the protonated molecules and characteristic fragment ions obtained by collision-induced dissociation reactions. The respective selected ions were simultaneously acquired using a single quadrupole mass spectrometer. The accurate and precise agreement observed for diagnostic ion intensity ratios between beta-agonists in retinal samples and authentic standards suggests that LC/APCI-MS can be used for confirmation of analyte structure at trace levels and does not require the use of a triple-stage quadrupole mass analyzer.

Confirmation of gentian violet and its metabolite leucogentian violet in catfish muscle using liquid chromatography combined with atmospheric pressure ionization mass spectrometry.

Gentian violet (GV) is a triphenylmethane dye antiseptic with potential for illegal use in livestock production, especially aquaculture where the related malachite green has been widely used. This potential misuse has regulatory importance because of the observed rodent carcinogenicity of GV. This report describes the use of online LC-APCI/MS for confirmation of incurred GV residues, and those of its principal metabolite, LGV, in catfish muscle following treatment of live catfish with GV under putative use conditions. LC with APCI/MS detection provided sensitive analysis of GV and LGV with estimated detection limits of < 1 pg observed for both compounds. Fragmentation of GV and LGV via in-source CID was effected by varying the sampling cone-skimmer voltage. Ion intensity data were collected using a rapid cone voltage switching procedure that permits selected ion acquisition under optimal conditions for the parent molecule and several selected fragment ions. For GV, four ions including the ionized molecule were used and for LGV, six ions including the protonated molecule were used. The levels of GV and LGV in muscle from fish dosed with 10 micrograms/l in aquarium water were determined by LC/VIS to be 0.5 and 44 ppb, respectively. Analysis of these samples yielded ion intensity ratios that agreed precisely between injections (< 5%) and accurately with those generated by a comparable amount of authentic GV and LGV (< 10% deviation). These results show the utility of on-line LC-APCI/MS to do both sensitive confirmatory analyses of incurred drug residues for use in monitoring the food supply.

Multiresidue determination of quinolone antibiotics using liquid chromatography coupled to atmospheric-pressure chemical ionization mass spectrometry and tandem mass spectrometry.

Liquid chromatography coupled to atmospheric-pressure chemical ionization mass spectrometry and tandem mass spectrometry (MS/MS) methods for the determination and quantification of four quinolone antibiotics were adapted from a published procedure for liquid-liquid extraction from catfish muscle and high-performance liquid chromatographic analysis. In-source collision-induced dissociation was used to optimize fragmentation to produce mass spectra consisting of the protonated molecule and two characteristic fragment ions of nearly equal intensity. Selected ion monitoring of three ions per quinolone yielded sensitive detection in catfish muscle extracts (estimated instrumental detection limits 0.8-1.7 ppb). The intensity ratios were used to confirm the presence of three of the quinolones based on the accurate agreement (< or equal to 10% deviation) between ratios derived from fortified catfish extracts and those from standard quinolones. MS/MS was used to increase the specificity and sensitivity of analysis. Scans using constant neural loss (CNL) of 18 mass units gave a sensitive response for the quinolones suggesting that CNL scans may be applicable to multiresidue screening for unknown quinolones. MS/MS with multiple reaction monitoring of the [MH - 18]+ transition for each quinolone yielded the highest sensitivity analysis in catfish extracts (estimated instrumental detection limits 0.08-0.16 ppb).

Analysis of clenbuterol in human plasma using liquid chromatography/atmospheric-pressure chemical-ionization mass spectrometry.

Clenbuterol is a beta-agonist drug used illegally as a growth stimulant in meat-producing animals and human athletes. The analysis of clenbuterol in spiked human plasma was performed using on-line liquid chromatography/atmospheric-pressure chemical-ionization mass spectrometry (LC/APCI-MS) using a conventional bore LC column (flow rate = 1.0 mL/min). At low sampling cone voltages, the mass spectrum was predominantly the [M+H]+ ion but diagnostic fragment ions were formed upon incremental increases in sampling cone voltage. The detection limit (signal-to-noise ratio of 3) using selected-ion monitoring of the [M+H]+ ion was 0.1 ng on-column (10 ppb). This is a 50-fold better sensitivity of detection than that previously reported for an on-line thermospray LC/MS method. The extraction procedures were not optimized for maximum sensitivity and the lack of interferences suggests that much lower detection limits for clenbuterol in plasma are attainable.

Indirect spectrophotometric determination of micro-amounts of Tin(II) in the presence of Tin(IV) and in dental gels.

A method for determining microgram amounts of tin(II) in synthetic samples containing tin(IV) and in dental gels has been developed. The procedure involves the oxidation of tin(II) with iron(III) in hydrochloric acid and spectrophotometric determination of the resulting iron(II) as a FerroZine complex.

Spectrophotometric determination of nitrate and nitrite in natural water and sea-water.

Nitrate and nitrite in natural waters are determined spectrophotometrically by passage through an amalgamated zinc reductor at pH 3.4 into iron(III)-Ferrozine solution. Interference by high levels of nitrite is eliminated by treatment with azide. Levels as low as 0.2 mug ml (expressed as nitrogen) can be determined with a precision of +/- 3%.

[Tactics of surgical care of closed abdominal injuries under conditions of defensive war]. / Prilog taktici hirurskog zbrinjavanja zatvorenih povreda abdomena u uslovima odbrambenog rata.

The authors are analizing the mechanism of initiation, frequency, surgical characteristics, the way of treatment and the factors affecting the prognosis of close injuries of abdomen in peace and war conditions. The discussion is about the problems of uniform surgical war-doctrine (army sanitary service, public-health service) in conditions of general civil-war defence. Own experiences are presented in surgical treatment of 179 patients with close injuries of abdomen in 10-year research on the Regional Surgical Department of Banja Luka's Medical Center.