Influence of solute polarity in column-switching chromatography for the assay of drugs in plasma and urine

The polarity of a drug is one of the most important parameters for the elaboration of switching systems. If the polarity of the drug is low or medium, "reversed-phase" chromatography is well adapted. The plasma or urine sample is diluted with water, centrifuged and injected first into a column of medium polarity (C2, CN or diol bonded phases). The compounds of interest are stopped on the top of the column and rinsed with water, then eluted and chromatographed on a C8 or C18 analytical column. A third column of still lower polarity can be added to improve the specificity of the system. In each successive step, the polarities of the mobile phases and columns should be decreased to reconcentrate the sample and reduce the band broadening that occurred in the previous step. Compounds of high polarity show almost no retention on reversed-phase columns, and normal-phase chromatography should be used. Aqueous solutions cannot be injected into polar bonded-phase columns as they lead to excessive band broadening. This problem can be solved by diluting plasma or urine with a large volume of a water-miscible organic solvent and injecting the clear supernatant. The compounds to be assayed are first reconcentrated on a polar column (NH2 or N(CH3)2 bonded phase) and then eluted. The selected "heart cut" of the eluate is chromatographed on another, more polar column. The influence of the polarity of drugs on the choice of switching systems is exemplified by assay methods for drugs of low, medium and high polarity.

Pyrrolidine ring conformations in prolyl peptides from 13C spin-lattice relaxation times

A method was developed in the framework of a bistable jump model to obtain the pyrrolidine ring conformations in proline peptides from 13C spin-lattice relaxation times. Equations are presented expressing the ring torsions in terms of the 13C spin-lattice relaxation times of the ring carbons. This method was applied to 26 pyrrolidine ring systems and acceptable conformations were obtained.

[Hydrolysis of the antiemetic alizapride]

First order rate constants of the hydrolysis of N-[(1-allyl-2-pyrrolidinyl)-methyl]-6-methoxy-1H-benzotriazole-5-carboxa mide (alizapride, Vergentan) in acid and alkaline medium were determined. The activation energy observed in alkaline solution was 60.3 kJ X mol-1. The substance was not hydrolized in vitro by esterase, liver homogenate and plasma.

Presence of N-methyl-D-aspartate-like and kainate-like activities in bovine brain

Searching for the natural ligands interacting with brain excitatory amino acid receptors, we have isolated from cow brain a low-Mr ampholyte fraction containing molecules with excitatory properties similar to those of N-methyl-D-aspartate and kainate, which cannot be accounted for by any of the known brain excitants. This finding supports the hypothesis of the existence of excitatory neurotransmitters other than L-glutamate and L-aspartate.

High-performance liquid chromatographic determination of alizapride, a new antiemetic compound, and its application to a dose-dependent pharmacokinetic study

An assay was developed to measure alizapride (a new antiemetic compound) in biological specimens. The method involved reversed-phase high-performance liquid chromatography and fluorescence detection. The detection limit was 5 ng/ml in plasma or urine samples. The value of the assay was demonstrated with a dose-dependent pharmacokinetic study. It showed a two-phase decrease in plasma concentrations, after intravenous injection, with half-lives of 7.5-min and 2.5-hr, respectively. From plasma and urine results, pharmacokinetic parameters remained constant in the dose range of 50-200 mg.

Analysis of methadone and metabolites in biological fluids with gas chromatography--mass spectrometry

The analysis of methadone and its metabolites in biological fluids by gas chromatography--mass spectrometry is described with deuterated methadone and metabolites as internal standards. The method allowed the determination of 20 ng methadone in 0.5 ml of plasma or saliva. Mean saliva to plasma ratio of methadone for two patients was determined to be 0.51 +/- 0.13. Methadone and 2-ethylidene-1,5-dimethyl-3,3-diphenylpyrrolidine (EDDP) in urine were measured by selected ion monitoring. Gas chromatography--mass spectrometry was found to have advantages over conventional gas chromatographic methods in terms of ratio analysis. 1,5-Dimethyl-3,3-diphenyl-2-pyrrolidone previously reported as a metabolite was shown to result primarily from the decomposition of EDDP free base.

Analysis of endogenous pyrrolidine levels by mass fragmentography

Pyrrolidine, one of biogenic volatile amines, possesses nicotine-like synaptotropic actions on the nervous systems. In the present study, pyrrolidine levels in the tissues were examined by using mass fragmentographic technique. High concentrations of pyrrolidine were found in the seminal vesicle and lung of rabbits. Only trace amounts of pyrrolidine existed in the brain of mice and rats, although higher concentrations were detected in the brain of rabbits. In the rat brain, however, high levels of pyrrolidine were found in the pineal gland, pituitary gland and corpus striatum.

High-performance liquid chromatographic determination of prifinium quaternary ammonium ion in human serum and urine

A simple, sensitive method for the determination of the prifinium ion, a quaternary ammonium ion, in human serum and urine is described. The method is based on extraction of the test solution with chloroform in the presence of saturated potassium bromide solution and normal-phase high-performance liquid chromatography using aqueous methanol as the mobile phase at pH 10. To prevent the dissolution of silica from the analytical column, the mobile phase is pre-saturated with silica by using a silica saturation column. Quantitation is possible down to 0.5 ng/ml of prifinium ion using 2 ml of serum and down to 5 ng/ml using a 1 ml of urine. The coefficients of variation of the method are less than 1.3% in both serum and urine. Serum levels and urinary excretion data obtained with this method are given for three healthy volunteers who had received a 60-mg oral dose of prifinium bromide.

Xilobam: analysis, determination of decomposition products, and assessment of stability

A stability-indicating UV assay was developed for xilobam, a member of a new class of CNS agents. The method was specific, precise, and accurate. TLC and high-pressure liquid chromatography were used to support method specificity. Xilobam is sensitive to heat, moisture, and basic conditions. The degradation products were identified as N-methylpyrrolidone, 2,6-dimethylaniline, and N,N'-bis(2,6-dimethyl-phenyl)urea. At high temperatures, the incorporation of molecular sieves into glass bottles of xilobam tablets was effective in preventing decomposition caused by moisture or volatile decomposition products.

Determination of buflomedil hydrochloride [2',4',6'-trimethoxy-4-(pyrrolidinyl)butyrophenone hydrochloride] by reversed-phase ion-pair high-performance liquid chromatography

A simple and rapid method for the determination of buflomedil hydrochloride [2',4',6'-trimethoxy-4-(pyrrolidinyl)butyrophenone hydrochloride] in pharmaceutical formulations by reversed-phase ion-pair high-performance liquid chromatography is described. The sample is dissolved in methanol and 1,3,5-trimethoxybenzene is added as an internal standard. The resulting solution is chromatographed on an octadecylsilane column using ion-pair partition chromatography with lauryl sulphate as the counter ion. A 25-microliter injection (containing 3.5 micrograms of buflomedil hydrochloride) produces a 60% full-scale peak (0.2 a.u.f.s.) at the absorbance maximum (275 nm). The relative standard deviation of the method ranges from 1 to 3%, depending on the particular tablet formulation examined. Excipients present in the preparations do not interfere.

New derivatives of prostaglandin A1 and specific detection of prostaglandin A's and 190hydroxylated prostaglandin A's in human semen

The derivatization of prostaglandins of the A series with 1:1 mixtures of bis-(trimethylsilyl)trifluoroacetamide and nitrogen-containing non-aromatic heterocyclics such as piperidine, pyrrolidine, morpholine and hexamethylenimine (1--4 h at 60--70 degrees C) gives new types of derivatives, designated as 11-heterocycle, 9-enol PGA (TMS)3. These derivatives show very simplified and characteristic mass spectral patterns strikingly dominated by a common [M-173]+ fragment ion and easily detectable by selected ion monitoring. This feature allows the concurrent analytical detection of both prostaglandin A's and 19-hydroxy prostaglandin A's in biological samples. In this case 2 ml samples of human semen were extracted by direct ultrafiltration on a Pellicon membrane with a nominal molecular weight limit of 1000. The prostaglandins in the approximately or equal to 1.6 ml of ultrafiltrate thus obtained were recovered in ethyl acetate, derivatized as indicated above and detected by monitoring of the corresponding [M-173]+ ions.

Direct gas chromatographic analysis of cyclic N-nitrosamines

A rapid gas chromatographic technique has been developed for quantitative estimation of cyclic N-nitrosamines. Cumbersome clean-up procedures are unnecessary and quantitative estimation can be done by injecting hexane extract without further pretreatment. The detection limit for the procedures is ca. 0.5 ng.

Identification of some basic extractable compounds produced by Neisseria gonorrhoeae and Neisseria meningitidis in a defined medium

Electron capture gas-liquid chromatography and mass spectrometry have been used to identify some of the basic extractable heptafluorobutyric anhydride reactive compounds found in a defined medium after 20 h of growth by Neisseria gonorrhoeae and N. meningitidis. Acetoin, 2,3-butanediol, pyrroline, and 1,3-diaminopropane were identified by both gas chromatography and mass spectrometry; 2-hydroxy-pyrrolidine and 3-aminomethyl-pyrrolidine were tentatively identified by mass spectrometry. A possible origin of the amines is through enzymatic oxidation of polyamines.

Mass spectrometric identification of C20 fatty acids in bovine lens using the pyrrolidide derivative

Unsaturated C20 fatty acids from bovine lens have been examined via gas chromatography-mass spectrometry of their pyrrolidide derivatives. The presence of arachidonic acid and 5,8,11-20:3 in bovine lens has been confirmed by this study. In addition, the 10-, 11-, 12-, and 13-isomers of 20:1 and the 7,13-, 18,14-, and 12,15-isomers of 20:2 were identified.

Simultaneous semiautomated assay of pyrrobutamine phosphate, cyclopentamine hydrochloride, and methapyrilene hydrochloride in pharmaceutical mixtures

Antihistamine preparations containing methapyrilene hydrochloride, pyrrobutamine phosphate, and cyclopentamine hydrochloride were assayed by introducing an aqueous sample solution into the appropriate automated system. Methapyrilene hydrochloride was determined by UV spectrophotometry. Pyrrobutamine phosphate was extracted as an ion-pair and quantitated colorimetrically by forming the bromcresol purple acid-dye complex. Cyclopentamine hydrochloride was determined colorimetrically by using the copper dithiocarbamate reaction for secondary amines.

The metabolic fate of the coronary vasodilator 4-(3,4,5-Trimethoxycinnamoyl)-1-(N-pyrrolidinocarbonylmethyl)piperazine (cinepazide) in the rat, dog and man

1. An oral dose of the coronary vasodilator 4-(3,4,5-trimethoxy[14C]cinnamoyl)-1-(N-pyrrolidinocarbonylmethyl)piperazine was well absorbed and more than 60% of the dose was excreted within 24 h. In 5 days, rats, dogs, and man excreted in the urine and faeces respectively 36.7% and 58.3%, 33.4% and 68.6%, and 61.3% and 38.1% dose. Faecal radioactivity was probably excreted via the bile. 2. Plasma concentrations of radioactivity reached a maximum within about 1 h in all three species and declined fairly rapidly (t0.5 less than 3 h). For several hours, more than 50% of the plasma radioactivity was due to unchanged drug. After correction for dose and body weight (normalization), peak plasma concentrations of unchanged drug in man, rat and dog were in the approximate ratio 100 :30:1. 3. Similar metabolites were excreted by the three species, but the relative proportions differed. Rats and man excreted 17.2% and 15.9% respectively as unchanged drug in the urine whereas dogs excreted only 3.6%. Rat bile and urine contained 4.3% and 9.8% dose respectively as glucuronides of the mono-O-demethylated compounds and dog and human urine contained 9.0% and 2.6% respectively of these metabolites. The corresponding pyrrolidone accounted for 2.5%, 5.5% and 5.1% respectively in rat, dog and human urine. Complete O-demethylation also occurred since 4-(3,4,5-trihydroxycinnamoyl)-1-(N-pyrrolidinocarbonylmethyl)piperazine was present in rat faeces (22.1% dose).

Trace analysis of volatile N-nitroso compounds by combined gas chromatography and thermal energy analysis

Thermal energy analysis (TEA) has been combined with gas chromatography (GC). The new GC-TEA technique is highly specific to compounds which contain heat labile nitrosyl groups. Because of the specificity of the technique, full use may be made of the TEA sensitivity. Analysis by direct injection of solutions containing less than 1 ng/ml N-nitroso compound is demonstrated.

Chemical studies on tobacco smoke. XXXIII. N' -nitrosonornicotine in tobacco: analysis of possible contributing factors and biologic implications

A chemical analytic method to determine N'-nitrosonornicotine (NNN) and N' -nitrosoanabasine (NAB) in tobacco was developed. NNN was found in the unburned tobacco of commercial products at concentrations betweeen 0.3 and 88.6 mug/g. The highest levels were observed in highly fermented snuff (29.1 mug/g) and fine-cut chewing tobacco (88.6 mug/g). NAB was not detected (smaller than 0.5 ng/g) in any tobacco examined. Two new tobacco components, N' -carbomethoxynornicotine and N' -carbomethoxyanabasine,were found. Possible origins of NNN in tobacco were discussed, especially in relation to concentrations of nitrite, nitate, and alkaloids, and in relation to pH and curing. Biologic implications, including the possible function of NNN (the first organic carcinogen isolated from unburned tobacco) as a causative factor in cancer of the oral cavity in tobacco chewers and betel quid chewers, were also discussed.

Investigation of Erythrina spp. VII. Chemical constituents of Erythrina variegata var. orientalis bark

The petroleum ether extractive of the bark of Erythrina variegata var. orientalis was fractionated and shown to be composed of wax alcohols and wax acids, alkyl ferulates, alkyl phenolates, stigmasterol, sitosterol, campesterol and possibly citrostadienol/24-methylenelophenol. The ethanol extractive yielded chloroform-soluble and water-soluble bases, identified as erysovine and stachydrine, respectively.