Liquid chromatographic determination of sulindac and metabolites in serum

An improved liquid chromatographic procedure is described for the quantitative determination of sulindac, sulindac sulfone, and sulindac sulfide from serum. The procedure makes use of acetonitrile extraction of the compounds of interest from acidified serum samples. Under these conditions extraction efficiencies in the 85 percent range are obtained for each of the compounds. The liquid chromatographic separation of the compounds of interest and the internal standard (indomethacin) is accomplished in an isocratic elution procedure using a nitrile (CN) stationary phase. The HPLC separation procedure is completed in less than 10 minutes, giving excellent resolution and peak shape.     

Gas chromatographic analysis of methiocarb and its metabolites in soil and rice

Summary A new method to determine the amount of methiocarb and its two metabolites, the sulfoxide and sulfone in soil and rice plant is described. The method consists of extraction of samples with acetone, filtration, separation of methiocarb and its metabolites through a Florisil column, and gas chromatographic determination. Since the degradation of methiocarb to 3,5-dimethyl-4-methylthiophenol (DMMP) is commonly observed during GC analysis, methiocarb was converted to DMMP via chemical hydrolysis after column chromatography. Reasonable recoveries for routine analysis were obtained and the limit of quantitation (LOQ) with GC/FPD were 0.5, 2 and 2 ng for DMMP sulfoxide and sulfone, with a signal to noise ratio of 4. In all rice samples, no detectable residues were found, however DMMP and methiocarb sulfoxide were found in some straw samples. In field soil samples, no sulfone was detected in all samples and methiocarb showed typical degradation curves with a half life of 8 days after treatment. A five-fold longer half life was observed in indoor studies.     

Liquid chromatographic analysis of oxcarbazepine and its metabolites in plasma and saliva after a novel microextraction by packed sorbent procedure

A rapid and reliable analytical method suitable for the simultaneous determination of the antiepileptic drug, oxcarbazepine and its metabolites in human plasma and saliva by means of liquid chromatography with diode array detection (DAD) has been developed. Oxcarbazepine and its metabolites (10,11-dihydro-10-hydroxycarbamazepine, trans-10,11-dihydro-10,11-dihydroxycarbamazepine and 3-hydroxycarbamazepine) were baseline separated within 6.5 min on a reversed-phase C18 column with a phosphate buffer-acetonitrile-triethylamine mixture as the mobile phase. The DAD detector was set at 240 nm. A sample preparation method for biological samples using a microextraction by packed sorbent technique has been implemented, employing a C18 sorbent inserted into a microvolume syringe and using only a small volume (25 μL) of plasma or saliva. The extraction yield values were satisfactory for all analytes (>86.5%) as well as the precision data, which were always in the low percentage of relative standard deviation values (<4.6%). The method was successfully applied to both plasma and saliva samples drawn from psychiatric and neurological patients undergoing treatment with oxcarbazepine (Tolep^®) tablets.     

Liquid chromatographic analysis of prednisolone, prednisone and their 20-reduced metabolites in perfusion media

A reversed-phase liquid chromatographic assay was developed to quantitate prednisolone, prednisone and the 20 alpha-dihydro and 20 beta-dihydro reduced metabolites of both parent compounds in tissue culture media from in vitro perfusions of the human placental lobule. Steroids were extracted from perfusate, using reversed-phase cartridges, with average recoveries of 95.2% or greater. The internal standard for the analyses was 6 alpha-methylprednisolone. In this assay cortisol coelutes with prednisolone, however, no other significant interferences were found. Assay of each steroid was linear in the range 0-1 microgram/ml. Intra-assay coefficients of variation were measured at 10 and 750 ng/ml with ranges of 3.4% (20 alpha-dihydroprednisone) to 8.8% (20 beta-dihydroprednisolone) and 4.1% (20 beta-dihydroprednisone) to 8.8% (prednisone). The corresponding inter-assay coefficients of variation were 3.3% (20 alpha-dihydroprednisone) to 9.1% (20 beta-dihydroprednisolone) and 1.9% (prednisolone) to 3.5% (prednisone). The analyses utilized two C18 columns which were linked together and maintained at 40 degrees C.     

Liquid chromatographic high-throughput analysis of ketamine and its metabolites in human plasma using a monolithic silica column and solid phase extraction

A rapid and sensitive liquid chromatographic (LC) assay was developed for the simultaneous determination of ketamine (KE) and its two main metabolites, namely, norketamine (NK) and dehydronorketamine (DHNK) in human plasma. Each compound together with an internal standard (Labetalol) was extracted from the plasma matrix using solid phase extraction (SPE). The applicability of monolithic LC phases in the field of quantitative bioanalysis has been evaluated. The existing method with UV detection set at 220 nm was successfully transferred from a conventional reversed phase column to a 10 cm × 4.6 mm i.d. monolithic silica column. By simply increasing the mobile phase flow-rate, run times were about six-fold reduced and consumption of mobile phase were about two-fold decreased, while the chromatographic resolution of the analytes remain unaffected. The method was validated over the range 25-2000 ng/mL for KE, 25-1500 ng/mL for NK, and 15-750 ng/mL for DHNK. The method proved to be precise (within-run precision ranges from 2.2 to 7.2% and between-run precision ranges from 3.7 to 8.2%) and accurate (within-run accuracies ranged from 1.3 to 7.2% and between-run accuracies ranged from 1.5 to 8.7%). The mean absolute recoveries were 95.3, 96.9, and 103.9% for KE, NK and DHNK, respectively. The limit of quantitation (LOQ) and limit of detection (LOD) for KE and NK in human plasma were 25 and 12.5 ng/mL, respectively, and for DHNK were 15 and 7.5 ng/mL (S/N = 3). The assay should be suitable for use in routine determination of KE and its metabolites in human plasma.     

Liquid chromatographic method for the simultaneous determination of sulphasalazine and its main metabolites in biological fluids

Summary An HPLC procedure was developed for the simultaneous determination of salicylazosulphapyridine, and its main metabolites 5-aminosalicylic acid and sulphapyridine, in human serum and synovial fluid. The analytical procedure consisted of a single ion-pair extraction step for an Extrelut column with methylene chloride. The investigated compounds and the added sulphadimidine internal standard were eluated from a Hypersil-MOS reversed-phase column by stepwise gradient; mobile phase was methanol-0.01 M potassium dihydrogenphosphate (3:7, 0.0–2.0 min and 8:2, 2.1–6.5 min).     

High-performance liquid chromatographic analysis of a linear alkylbenzenesulfonate and its environmental biodegradation metabolites

A simple and fast method is described for determining a linear alkylbezenesulfonat e (LAS) and its potential sulfonated and unsulfonated metabolites in natural waters. This method includes extraction of 60 ml of water with an octadecyl-bonded silica (C₁₈) mini-column and analysis of the extract by high-performance liquid chromatography. A reversed-phase column with a 0.008 M potassium phosphate buffer (pH 2.2)-acetonitrile gradient as the mobile phase provides the separation. A UV detector, set at 215 nm, is employed.     

Liquid chromatographic analysis of sulfornamides in foods

Summary A procedure for the simultaneous determination of several sulfonamides in different foods, such as honey, milk and eggs is proposed. The analysis is carried out using reversed phase liquid chromatography with spectrophotometric detection. Optimization of the mobile phase led to good separation and a short analysis time when an initial isocratic step with a 397 acetonitrile: water mixture was used for 5 minutes, followed by a linear gradient up to a 4060 mixture over 15 min. The proposed method is suitable for routine quality control analysis to ensure the absence of sulfonamides in foods. Recovery studies yielded good results for all food samples because there were no interferences from the matrices.     

Gas chromatographic determination of aldicarb and its metabolites in urine

A method is described for the determination of aldicarb and its metabolites (the sulphoxide and sulphone) in urine by gas chromatography with flame photometric detection (GC-FPD). The sample was concentrated with a column containing activated charcoal and Florisil, and then eluted with dichloromethane-acetone (1:1, v/v). The aldicarb and aldicarb sulphoxide in the eluate solution were oxidized to aldicarb sulphone and the total sulphone concentration was determined by GC-FPD after extraction with dichloromethane and clean-up with an activated charcoal column. The detection limit was 0.0024 mg/l. The mean recoveries from spiked urine in the range 0.04-0.12 mg/l were 90.9%, 86.6%, 92.6% for aldicarb, aldicarb sulphoxide and aldicarb sulphone, respectively.     

Liquid chromatographic method for the analysis of buspirone HCl and its potential impurities

An accurate, reproducible, and sensitive method for the determination of buspirone HCl and its potential impurities is developed and validated. The validated liquid chromaography method is conducted to meet the Food and Drug Administration/ International Conference on Harmonization requirements for the analysis of buspirone HCI in the presence of its impurities. Five buspirone HCI potential impurities, including 1-(2-pyrimidinyl)-piperazine (I), propargyl chloride (II), 3,3'-tetramethylene glutarimide (III), propargyl glutarimide (IV), and the Mannich base-condensate of I-IV fumarate (V), are separated using a microBondapack C18 column by gradient elution with a flow rate 2.0 mL/min. The initial mobile phase composition is 90:10 (v/v) 10mM KH2PO4 (pH 6.1)-acetonitrile. After a 1-min initial hold, a linear gradient is performed in 26 min to 35:65 (v/v) 10mM KH2PO4 (pH 6.1)-acetonitrile. The samples are detected at 210 and 240 nm using a photo-diode array detector. The linear range of detection for buspirone HCI was between 1.25 ng/microL and 500 ng/microL, with a limit of quantification of 1.25 ng/microL. The linearity, range, peak purity, selectivity, system performance parameters, precision, accuracy, and robustness for all of the impurities were also shown to have acceptable values.     

Liquid chromatographic analysis of cinchona alkaloids in beverages

A method for the determination of Cinchona extract (whose main components are the alkaloids cinchonine, cinchonidine, quinidine, and quinine) in beverages by liquid chromatography was developed. A beverage with an alcohol content of more than 10% was loaded onto an OASIS HLB solid-phase extraction cartridge, after it was adjusted to pH 10 with 28% ammonium hydroxide. Other beverages were centrifuged at 4000 rpm for 5 min, and the supernatant was loaded onto the cartridge. The cartridge was washed with water followed by 15% methanol, and the Cinchona alkaloids were eluted with methanol. The Cinchona alkaloids in the eluate were chromatographed on an L-column ODS (4.6 mm id x 150 mm) with methanol and 20 mmol/L potassium dihydrogen phosphate (3 + 7) as the mobile phase. Cinchona alkaloids were monitored with an ultraviolet (UV) detector at 230 nm, and with a fluorescence detector at 405 nm for cinchonine and cinchonidine and 450 nm for quinidine and quinine (excitation at 235 nm). The calibration curves for Cinchona alkaloids with the UV detector showed good linearity in the range of 2-400 microg/mL. The detection limit of each Cinchona alkaloid, taken to be the concentration at which the absorption spectrum could be identified, was 2 microg/mL. The recovery of Cinchona alkaloids added at a level of 100 microg/g to various kinds of beverages was 87.6-96.5%, and the coefficients of variation were less than 3.3%. A number of beverage samples, some labeled to contain bitter substances, were analyzed by the proposed method. Quinine was detected in 2 samples of carbonated beverage.     

High-performance liquid chromatographic analysis of tiaprofenic acid and its metabolites in plasma and urine by direct injection

A rapid, convenient, sensitive and selective reversed-phase high-performance liquid chromatographic method was developed to measure tiaprofenic acid, its reduced and oxidized metabolites and their conjugates in biological fluids. The method involved direct injections of plasma and urine samples into the chromatograph before and after alkaline hydrolysis of the conjugates. Concentrations as low as 0.5 micrograms/ml of the drug in plasma and urine were quantifiable. The method was suitable for analysis of tiaprofenic acid and its metabolites in biological fluids after administration of therapeutic doses. Several other non-steroidal anti-inflammatory drugs which were applied to the system did not interfere with the assay.     

Gas chromatographic analysis of chlorophenylmercapturic acid lindane metabolites

An analytical method for phenols has been adapted for the analysis of chlorophenylmercapturic acids in rat urine. Chlorothiophenols were produced from the mercapturic acids by hydrolytic cleavage with sodium hydroxide. Acetate esters of the chlorothiophenols were formed by addition of acetic anhydride to the aqueous alkaline solution. After acylation, the acetate derivatives were extracted into hexane. Forming the acetate esters of the chlorothiophenols prevented their oxidation to disulfides and significantly improved their chromatographic properties. Electron-capture gas chromatographic analysis of the stable acetate esters was performed on a mixed phase column, 4% SE-30 + 6% OV-210. Recoveries of four chlorothiophenols ranged from 82 to 93%. This method required no sample transfer steps; therefore, sample loss and analysis time were minimized.     

Liquid chromatographic analysis of low-alloy steel samples

The isolation of transition and rare earth elements from low-alloy steels by liquid chromatography (LC) with post-column reaction detection is described. The eluted metal ions are detected with a UV-visible spectrophotometric detector after post-column complexation with 4-(2-pyridylazo)resorcinol and Arsenazo-III. The requirements and characterization of the post-column reaction for the sensitive detection of metal ions after LC separation are discussed. The results are compared with those of other methods such as atomic absorption spectrometry and inductively coupled plasma atomic emission spectrometry.