Stable isotope dilution negative ion chemical ionization gas chromatography-mass spectrometry for the quantitative analysis of paroxetine in human plasma

A sensitive and specific method for the quantitative determination of paroxetine in human plasma is presented. After solvent extraction from plasma with hexane/ethyl acetate (1 : 1) at alkaline pH and derivatization to the pentafluorobenzyl carbamate derivative, paroxetine was measured by gas chromatography-negative ion chemical ionization mass spectrometry. The carboxylate anion at m/z 372 was obtained at high relative abundance. [2H6]-labeled paroxetine was used as an internal standard and its rapid and facile preparation from the unlabeled compound is described. Calibration graphs were linear within a range of 0.094-12.000 ng x ml(-1) using 1 ml of plasma and 0.469-60 ng x ml(-1) using 200 microl of plasma. Intra-day precision was 1.47% (0.375 ng x ml(-1)), 3.16% (3 ng x ml(-1)) and 1.37% (9 ng x ml(-1)) for the low-level method, and 3.37% (1.875 ng x ml(-1)), 2.72% (15 ng x ml(-1)) and 2.22% (45 ng x ml(-1)) for the high-level method. Inter-day precision was 1.65% (0.375 ng x ml(-1)), 2.13% (3 ng x ml(-1)) and 1.66% (9 ng x ml(-1)) for the low-level method, and 1.10% (1.875 ng x ml(-1)), 1.56% (15 ng x ml(-1)) and 1.90% (45 ng x ml(-1)) for the high-level method. At the limit of quantification (0.094 ng x ml(-1)), intra-day precision was 4.30% (low-level method) and 2.56% (high-level method), and inter-day precision was 3.23% (low-level method) and 3.00% (high-level method). The method is rugged, rapid and robust and has been applied to the batch analysis of paroxetine during pharmacokinetic profiling of the drug.     

Quantitative determination of fluvastatin in human plasma by gas chromatography/negative ion chemical ionization mass spectrometry using [18O2]-fluvastatin as an internal standard

A sensitive and specific method for the quantitative determination of fluvastatin in human plasma is presented. The drug was isolated from plasma by extractive alkylation with pentafluorobenzyl bromide and further derivatized to the bis-trimethylsilyl derivative. [18O2]-Fluvastatin was prepared from unlabelled fluvastatin and used as an internal standard. Gas chromatography/mass spectrometry under negative ion chemical ionization conditions was used for quantitative measurement of the drug, using m/z 554.26 and 558.26 for target and internal standard, respectively. Calibration graphs were linear within a range of 2 and 512 ng mL(-1) plasma. Intra-day precision was 0.94% (2 ng mL(-1)), 2.53% (8.2 ng mL(-1)), 2.16% (81.9 ng mL(-1)) and 3.26% (409.6 ng mL(-1)); inter-day variability was found to be 1.64% (2 ng mL(-1)), 0.97% (8.2 ng mL(-1)), 1.97% (81.9 ng mL(-1)) and 2.01% (409.6 ng mL(-1)). Intra-day accuracy showed deviations of 0.6% (2 ng mL(-1)), 0.37% (8.2 ng mL(-1)), -1.52% (81.9 ng mL(-1)) and -1.67% (409.6 ng mL(-1)); inter-day accuracy was of -1.64% (2 ng mL(-1)), -1.13% (8.2 ng mL(-1)), -2.28% (81.9 ng mL(-1)) and -0.46% (409.6 ng mL(-1)). The stable isotope labelled standard was found to be stable under the analytical conditions.     

Nevirapine quantification in human plasma by high-performance liquid chromatography coupled to electrospray tandem mass spectrometry. Application to bioequivalence study

A rapid, sensitive and specific method to quantify nevirapine in human plasma using dibenzepine as the internal standard (IS) was developed and validated. The method employed a liquid-liquid extraction. The analyte and the IS were chromatographed on a C(18) analytical column, (150 x 4.6 mm i.d. 4 microm) and analyzed by tandem mass spectrometry in the multiple reaction monitoring mode. The method had a chromatographic run time of 5.0 min and a linear calibration curve over the range 10-5000 ng ml(-1) (r(2) > 0.9970). The between-run precision, based on the relative standard deviation for replicate quality controls was 1.3% (30 ng ml(-1)), 2.8% (300 ng ml(-1)) and 3.6% (3000 ng ml(-1)). The between-run accuracy was 4.0, 7.0 and 6.2% for the above-mentioned concentrations, respectively. This method was employed in a bioequivalence study of two nevirapine tablet formulations (Nevirapina from Far-Manguinhos, Brazil, as a test formulation, and Viramune from Boehringer Ingelheim do Brasil Química e Farmacêutica, as a reference formulation) in 25 healthy volunteers of both sexes who received a single 200 mg dose of each formulation. The study was conducted using an open, randomized, two-period crossover design with a 3 week washout interval. The 90% confidence interval (CI) of the individual ratio geometric mean for Nevirapina/Viramune was 96.4-104.5% for AUC((0-last)), 91.4-105.1% for AUC((0-infinity)) and 95.3-111.6% for C(max) (AUC = area under the curve; C(max) = peak plasma concentration). Since both 90% CI for AUC((0-last)) and AUC((0-infinity)) and C(max) were included in the 80-125% interval proposed by the US Food and Drug Administration, Nevirapina was considered bioequivalent to Viramune according to both the rate and extent of absorption.     

Quantitative analysis of memantine in human plasma by gas chromatography/negative ion chemical ionization/mass spectrometry

A sensitive and specific method for the determination of memantine in human plasma is presented. Memantine was extracted from plasma and derivatized to the pentafluorobenzoyl derivative in a one-step procedure avoiding any sample concentration steps. Amantadine was used as an internal standard. The compounds were measured by gas chromatography/negative ion chemical ionization mass spectrometry without any further processing. Using this detection mode, the fragment ions at m/z 353 and 325 were obtained at high relative abundance. Calibration graphs were linear over the range 0.117-30 ng ml(-1). At the limit of quantification (LOQ), the inter-assay precision was 2.00% and the intra-assay variability was 3.22%. The accuracy at the LOQ showed deviations of -1.42% (intra-assay) and -2.47% (inter-assay). The method is rugged, rapid and robust and was applied to the batch determination of memantine during pharmacokinetic profiling of the drug.     

Gabapentin quantification in human plasma by high-performance liquid chromatography coupled to electrospray tandem mass spectrometry. Application to bioequivalence study

A rapid, sensitive and specific analytical method was developed and validated to quantify gabapentin in human plasma using acetaminophen as an internal standard. The method employs a single plasma protein precipitation. The analytes are chromatographed on a C4 reversed-phase chromatographic column and analyzed by mass spectrometry in the multiple reaction monitoring (MRM) mode. The method has a chromatographic run time of 4 min and a linear calibration curve over the range 50-10 000 ng x ml(-1) (r > 0.999). The between-run precision, based on the relative standard deviation for replicate quality controls, was < or = 4.8 % (200 ng x ml(-1)), 6.0% (1000 ng x ml(-1)) and 4.4% (5000 ng x ml(-1)). The between-run accuracy was +/-2.6, 4.4 and 0.5% for the above-mentioned concentrations, respectively. This method was employed in a bioequivalence study of two gabentin capsule formulations (Progresse from Biosintética, Brazil, as a test formulation, and Neurotin from Parke-Davis, as a reference formulation) in 24 healthy volunteers of both sexes who received a single 300 mg dose of each formulation. The study was conducted using an open, randomized, two-period crossover design with a 7-day washout interval. The 90% confidence interval (CI) of the individual ratio geometric mean for Progresse/Neurotin was 87.9-115.6% for AUC(0-36 h) and 88.6-111.7% for Cmax. Since both 90% CI for AUC(0-36 h) and Cmax were included in the 80-125% interval proposed by the US Food and Drug Administration, Progresse was considered bioequivalent to Neurotin according to both the rate and extent of absorption.     

Flow injection spectrophotometric determination of trace amounts of selenium

A simple, rapid and sensitive flow injection spectrophotometric method for determination of selenium (0.005-1.5 mug ml(-1)) is described. The method is based on the catalytic effect of Se(IV) on the reduction reaction of thionine (TN) with sulphide ion, monitored spectrophotometrically at 598 nm. The detection limit is 5 ng ml(-1) the relative standard deviation for eight replicate measurements is 1.1% for 1 mug ml(-1) of selenium. The sampling rate is 25-30 samples h(-1). The procedure was applied successfully to the determination of selenium in real samples.     

Sensitive flow injection colorimetry of nitrite by catalytic coupling of N-phenyl-p-phenylenediamine with N,N-dimethylaniline

A rapid, sensitive and selective flow-injection colorimetry method is proposed for the determination of trace amounts of nitrite. It is based on the nitrite's catalytic effect on the oxidative coupling of N-phenyl-p-phenylenediamine with N,N-dimethylaniline to produce a green dye (lambda(max)=735 nm) in the presence of bromate. The change in absorbances of the dye were monitored in continuos flow mode. Linear calibration curves were obtained for the nitrite concentration range 2.0-100 ng ml(-1). The proposed method had a low detection limit (0.6 ng ml(-1)) and high sample throughput (approximately 30 samples h(-1)). The RSD for 10 and 50 ng ml(-1) nitrite were 2.4 and 1.3% (n=10), respectively. The method has been successfully applied to the determination of nitrite in river water samples.     

Development and validation of a liquid chromatographic/electrospray ionization mass spectrometric method for the quantitation of prazepam and its main metabolites in human plasma

A method was developed and fully validated for the quantitation of prazepam and its major metabolites, oxazepam and nordiazepam, in human plasma. Sample pretreatment was achieved by solid-phase extraction using Oasis HLB cartridges. The extracts were analysed by high-performance liquid chromatography (HPLC) coupled with single-quadrupole mass spectrometry (MS) with an electrospray ionization interface. The MS system was operated in the selected ion monitoring mode. HPLC was performed isocratically on a reversed-phase XTerra MS C18 analytical column (150 x 3.0 mm i.d., particle size 5 microm). Diazepam was used as the internal standard for quantitation. The assay was linear over a concentration range of 5.0-1000 ng ml(-1) for all compounds analyzed. The limit of quantitation was 5 ng ml(-1) for all compounds. Quality control samples (5, 10, 300 and 1000 ng ml(-1)) in five replicates from three different runs of analysis demonstrated an intra-assay precision (CV) of < or = 9.1%, an inter-assay precision of < or = 6.0% and an overall accuracy (relative error) of < 4.6%. The method can be used to quantify prazepam and its metabolites in human plasma covering a variety of pharmacokinetic or bioequivalence studies.     

Determination of the active metabolite of molsidomine in human plasma by reversed-phase high-performance liquid chromatography

A reversed-phase high-performance liquid chromatographic method, with ultraviolet detection, is proposed for the plasma determination of SIN-1, the active metabolite of molsidomine, which involves propoxycarbonyl derivatization. The internal standard is the ethoxycarbonyl derivative of SIN-1 (i.e. molsidomine). Derivatization and extraction are each performed in one step (2 min) with 70% yield. The nature of a by-product is discussed. The method provides rapid elution (less than 15 min), linearity over the range 0.4-200 ng/ml, day-to-day precision between 2.5 and 11.3% and a limit of determination of 0.5 ng/ml. This method is also suitable for the simultaneous determination of molsidomine and SIN-1. In this case the internal standard is an ethoxycarbonyl derivative of a piperazino-3-sydnonimine, a SIN-1 analogue.     

Detection of trace levels of thiodiglycol in blood, plasma and urine using gas chromatography-electron-capture negative-ion chemical ionisation mass spectrometry

A sensitive method has been developed for the detection and quantitative determination of thiodiglycol in blood, plasma and urine. Samples were extracted from Clin Elut columns and cleaned up on C18 Sep-Pak cartridges (blood, plasma) or Florisil Sep-Pak cartridges (urine). Tetradeuterothiodiglycol was added to the sample prior to extraction as internal standard. Thiodiglycol was converted to its bis-(pentafluorobenzoate) derivative and analysed by capillary gas chromatography-electron-capture negative-ion chemical ionisation mass spectrometry using selected ion monitoring. Levels of thiodiglycol down to 1 ng/ml (1 ppb) could be detected in 1-ml spiked blood and urine samples; calibration curves were linear over the range 5- or 10-100 ng/ml. Blood and urine samples from a number of control subjects were analysed for background levels of thiodiglycol. Concentrations up to 16 ng/ml were found in blood, but urine levels were below 1 ng/ml.     

Stability indicating methods for determination of Donepezil Hydrochloride according to ICH guidelines

Stability indicating assays for determination of Donepezil Hydrochloride in presence of its oxidative degradate were developed and validated. The first three are spectrophotometric methods depending on using zero order (D(0)), first order (D(1)) and second order (D(2)) spectra. The absorbance was measured at 315 nm for (D(0)) while the amplitude was measured at 332.1nm for (D(1)) and 340 nm for (D(2)) using deionized water as a solvent. Donepezil Hydrochloride (I) can be determined in the presence of up to 70% of its oxidative degradate (II) using (D(0)), 80% using (D(1)) and 90% using (D(2)). The linearity range was found to be 8-56 microg ml(-1) for (D(0)), (D(1)) and (D(2)). These methods were applied for the analysis of I in both powder and tablet form. Also, a spectrofluorimetric method depending on measuring the native fluorescence of I in deionized water using lambda excitation 226 nm and lambda emission 391 nm is suggested. The linearity range was found to be 0.32-3.20 microg ml(-1) using this method, I was determined in the presence of up to 90% of II. The proposed method was applied for the analysis of I in tablet form as well as in human plasma. The last method depends on using TLC separation of I from its oxidative degradate II and I was then determined spectrodensitometrically. The mobile phase was methanol : chloroform : 25% ammonia (16 : 64 : 0.1 by volume). The linearity range was found to be 2-15 microg/spot. This method was applied to the analysis of I in both powder and tablet form using acetonitrile as a solvent.     

Capillary column gas chromatographic method using electron-capture detection for the simultaneous determination of nicardipine and its pyridine metabolite II in plasma

A rapid, specific and direct method based on capillary column gas chromatography with electron-capture detection is described for the simultaneous determination of nicardipine, a new calcium antagonist, and its pyridine metabolite II in human plasma. In this method, the nicardipine, its pyridine metabolite II and internal standard are extracted from the plasma and then partially purified by acid-base partitioning prior to the final injection onto the capillary column gas chromatograph for quantification by means of an electron-capture detector. The quantification limit of the method is 1 ng/ml of plasma for both nicardipine and its pyridine metabolite II. The coefficients of variation for nicardipine and the pyridine metabolite II at concentrations of 1-50 ng/ml are less than 7% and less than 9% (n = 4), respectively. The method has been validated against a previously developed high-performance liquid chromatographic method (sensitivity 5 ng/ml).     

Determination of didanosine in human serum by on-line solid-phase extraction coupled to high-performance liquid chromatography with electrospray ionization tandem mass spectrometric detection: application to a bioequivalence study

A method based on solid-phase extraction coupled to liquid chromatography with positive ion electrospray ionization and tandem mass spectrometric detection was developed for the determination of didanosine in human serum, using lamivudine as internal standard. The acquisition was performed in the multiple reaction monitoring mode, monitoring the transitions m/z 237 --> 136.7 for didanosine and m/z 230 --> 111.7 for lamivudine. The method was linear over the range studied (10-1500 ng ml(-1)), with r(2) > 0.98, and the run time was 5 min. The intra- and inter-assay precisions were < or =10% and the intra- and inter-assay accuracies were >95%. The absolute recoveries were 99.8% (10 ng ml(-1)), 98.4% (30 ng ml(-1)), 91.5% (700 ng ml(-1)) and 94.7% (1200 ng ml(-1)). The limits of detection and quantitation were 5 and 10 ng ml(-1), respectively. The method was applied to a bioequivalence study, in which 24 healthy adult volunteers (12 men) received single oral doses (200 mg) of reference and test didanosine formulations (buffered powder for oral solutions), in an open, two-way, randomized, crossover protocol. The 90% confidence interval of the individual ratios (test formulation/reference formulation) for C(max) (peak serum concentration) and AUC(0-inf) (area under the serum concentration versus time curve from time zero to infinity) were within the range 80-125%, which supports the conclusion that the two formulations are bioequivalent regarding the rate and extent of didanosine absorption.     

Determination of RSD921 in human plasma by high-performance liquid chromatography-tandem mass spectrometry using tri-deuterated RSD921 as internal standard: application to a phase I clinical trial.

A fast, sensitive and specific method is presented for the quantification of RSD921 in human plasma by liquid chromatography coupled with tandem mass spectrometry using tri-deuterated RSD921 (3d-RSD921) as an internal standard. A single-step liquid/liquid extraction was performed with diethyl ether/hexane (80 : 20, v/v) using 0.5 ml of plasma. The plasma calibration curves were linear from 0.1 to 20 ng ml(-1) (r > 0.999). Between-run precision, based on the percent relative deviation for replicate (n = 40) quality controls, was < or =7.27% (0.5 ng ml(-1)), < or =7.39% (5.0 ng ml(-1)), and < or =5.06% (20.0 ng ml(-1)). Between-run accuracies, based on the relative error, were +/-2.59%, +/-1.23% and +/-1.64% respectively. The method was developed to evaluate the pharmacokinetic profile after 15 min of intravenous stepwise-ascending infusion dose of RSD921 in 18 healthy volunteers. A dissociation study of protonated RSD921 and 3d-RSD921 by collision-induced dissociation using in-source fragmentation and tandem mass spectrometry is also presented.     

Sensitive high-performance liquid chromatographic assay using 9-fluorenylmethylchloroformate for monitoring controlled-release lidocaine in plasma

A sensitive high-performance liquid chromatographic (HPLC) assay using fluorescence detection for quantifying lidocaine levels in plasma (in the ng/ml range) was developed. This novel HPLC assay has made possible the simultaneous monitoring of lidocaine levels in coronary and peripheral plasma obtained after myocardial controlled-release matrix administration (0.92 mg/kg during 4 h) in the arrhythmic dog. The method employed extracts the drug from plasma using 1-chlorobutane and a subsequent derivatization with 9-fluorenylmethylchloroformate in acetonitrile at 110 degrees C. The derivative was chromatographed on a C18 reversed-phase column and measured with fluorescence detection (excitation 254 nm, emission 313 nm). N-Methylephedrine was found to be suitable as an internal standard, post-derivatization. The derivatization product of lidocaine was identified and characterized by mass spectral analysis. It was found to have a unique and reproducible dicarbamate structure, which was stable for at least three days at room temperature. The method was tested with human plasma as well as on dog plasma. Analytical recoveries were 88.6 +/- 3.6 and 77.4 +/- 3.0% (mean +/- S.E.), respectively, at levels ranging from 25 to 200 ng/ml. The lower detection limit was 1 ng/ml lidocaine. In conclusion, this rapid and convenient analysis was found to be suitable for the bioavailability pharmacokinetic assessment of lidocaine following low-dose regional drug administration.     

Development of a rapid and specific assay for detection of busulfan in human plasma by high-performance liquid chromatography/electrospray ionization tandem mass spectrometry

A sensitive and specific assay for detection of busulfan in human plasma was developed. The assay is based on rapid isolation of busulfan by liquid-liquid extraction with ethyl acetate, and detection by high-performance liquid chromatography with electrospray ionization and tandem mass spectrometry. 1,6-Bis(methanesulfonyloxy)hexane, a synthesized analogue of busulfan, was used as the internal standard (IS). The acquisition was performed in the multiple reaction monitoring mode; busulfan and the IS were detected with no interferences from plasma matrix. The method was linear over the range 5-2500 ng mL(-1), with r2 > 0.99 and a run time of only 3.5 min. The intra- and inter-assay precisions were in the ranges 2.1-11.9% and 3.2-10.1%, respectively, and the intra- and inter-assay accuracies were 92.2-107.6% and 94.7-104.1%, respectively. The absolute recoveries were 82.0% (20 ng mL(-1)), 90.6% (1000 ng mL(-1)) and 80.0% (2000 ng mL(-1)) for busulfan, and 89.1% for the IS (1000 ng mL(-1)). The limits of detection and quantification were 2 and 5 ng mL(-1), respectively. The validated method was successfully applied to analyze plasma samples obtained from six adults receiving doses of 1 mg kg(-1) in a conditioning regimen prior to bone marrow transplantation. A marked intra-patient variation in busulfan concentrations during the steady state was observed, which limits the application of pharmacokinetic modeling and suggests that continuous therapeutic monitoring is necessary for adequate individualized dosing. In this regard, the present assay brings important advantages relative to other methods described in the literature, i.e., it is highly specific and simple to perform, with a rapid chromatographic run time (3.5 min), and the whole procedure can be completed in 4-5 h, which would permit dose corrections after the third dose allowing earlier and better dosing adjustments towards the target level of busulfan.     

Analysis of lorazepam and its glucuronide metabolite by electron-capture gas--liquid chromatography. Use in pharmacokinetic studies of lorazepam.

This paper describes a rapid and sensitive method for analysis of lorazepam and its glucuronide metabolite in plasma and urine following therapeutic doses of lorazepam in humans. After addition of the structurally related benzodiazepine derivative, oxazepam, as the internal standard, 1-ml samples of plasma or urine are extracted twice at neutral pH with benzene (containing 1.5% isoamyl alcohol). The combined extracts are evaporated to dryness, reconstituted, and subjected to gas chromatographic analysis using a 3% OV-17 column and an electron-capture detector. Lorazepam glucuronide in urine is similarly analyzed following enzymatic cleavage with Glusulase. The sensitivity limits are 1--3 ng of analyzed following enzymatic cleavage with Glusulase. The sensitivity limits are 1--3 ng of lorazepam per ml of original sample, and the variability of identical samples is 5% or less. The applicability of the method to pharmacokinetic studies of lorazepam is demonstrated.     

Determination of cefquinome in pig plasma and bronchoalveolar lavage fluid by high-performance liquid chromatography combined with electrospray ionization mass spectrometry

The aim of this study was to develop a rapid and sensitive method for the quantification of cefquinome in animal plasma and bronchoalveolar lavage (BAL) fluid using high-performance liquid chromatography combined with electrospray tandem mass spectrometry (LC-ESI-MS/MS). Cefadroxil is used as internal standard. For plasma, the sample preparation includes a simple deproteinization step with a Microcon filter. This allows detecting the unbound cefquinome concentration, which is correlated with the concentration in other body fluids, such as BAL fluid. To be able to detect the total plasma concentration, deproteinization with acetonitrile, followed by a back-extraction of actonitrile with dichloromethane was performed. The BAL fluid is centrifuged to precipitate floating particles. Chromatographic separation is achieved on a PLRP-S column using 0.005% formic acid and methanol as mobile phase. For plasma, good linearity was observed in the range of 5-2500 ng ml(-1) for both the unbound and total concentration. The response in BAL fluid was linear in the range of 4-1000 ng ml(-1). The limit of quantification (LOQ) was set at 5.00 ng ml(-1) for plasma and at 4.00 ng ml(-1) for BAL fluid. The limit of detection (LOD) was 3.12 ng ml(-1) and 0.41 ng ml(-1) for the unbound and total concentration in plasma, respectively, and was 1.43 ng ml(-1) for BAL fluid. The method was shown to be of use in a pharmacokinetic study in pigs, where the correlation between cefquinome concentrations in plasma and BAL fluid of pigs was studied.     

Simple, sensitive and rapid liquid chromatographic/electrospray ionization tandem mass spectrometric method for the quantification of lacidipine in human plasma

A simple, sensitive and rapid liquid chromatographic/electrospray ionization tandem mass spectrometric method was developed and validated for the quantification of lacidipine in human plasma using its structural analogue, amlodipine, as internal standard (IS). The method involves a simple single-step liquid-liquid extraction with tert-butyl methyl ether. The analyte was chromatographed on an Xterra MS C(18) reversed-phase chromatographic column by isocratic elution with 20 mM ammonium acetate buffer-acetonitrile (10:90, v/v; pH 6) and analyzed by mass spectrometry in the multiple reaction monitoring mode. The precursor to product ion transitions of m/z 456.4 --> 354.4 and m/z 409.3 --> 238.3 were used to measure the analyte and the I.S., respectively. The chromatographic run time was 1.5 min and the weighted (1/x(2)) calibration curves were linear over the range 0.1-25 ng ml(-1). Lacidipine was sensitive to temperature in addition to light. The method was validated in terms of accuracy, precision, absolute recovery, freeze-thaw stability, bench-top stability and re-injection reproducibility. The limit of detection and lower limit of quantification in human plasma were 50 and 100 pg ml(-1), respectively. The within- and between-batch accuracy and precision were found to be well within acceptable limits (<15%). The analyte was stable after three freeze-thaw cycles (deviation <15%). The average absolute recoveries of lacidipine and amlodipine (IS) from spiked plasma samples were 51.1 +/- 1.3 and 50.3 +/- 4.9%, respectively. The assay method described here could be applied to study the pharmacokinetics of lacidipine.     

Efficient and sensitive screening and confirmation of residues of selected polyether ionophore antibiotics in liver and eggs by liquid chromatography-electrospray tandem mass spectrometry.

A method using liquid chromatography tandem mass spectrometry (LC-MS-MS) with electrospray (ES) for the determination of traces of narasin, monensin and salinomycin in chicken liver and eggs was developed, validated and used for routine surveillance. The essence of this paper is to demonstrate that one single method can serve very well for two entirely different purposes, i.e., screening and confirmation. Highly reliable confirmation of the identity at low concentrations was demonstrated when residues of narasin were detected and quantified (0.2 to 11 ng g(-1)) in 50% of the Swedish eggs analysed in 1999. Four daughter ions were detected with ion ratios meeting suggested confirmation criteria for the European Union, even at 0.2 ng g(-1). The method was found to be highly cost-effective since both screening and confirmation of 98 liver samples were performed in only two analytical runs (the Swedish national surveillance scheme of 1999, report level 5 ng g(-1)). The high performance of the method for the different applications was possible due to a combination of the power of ES-LC-MS-MS, a procedure involving screening of pooled samples, and method optimisation of the work-up (automated solid phase extraction), LC and MS parameters. Validation data for narasin (0.5 to 20 ng g(-1)) in eggs are presented (accuracy 94 to 108%, relative standard deviation 4 to 10%, limit of detection 0.026 ng g(-1)). The time for an LC-MS-MS run was 4 min, corresponding to 48 s per sample in a pool.