Proportion Of Acetonitrile Research Articles

Silver ion high-performance liquid chromatography of isomeric cis- and trans-octadecenoic acids : Effect of the ester moiety and mobile phase composition

The effects of the ester moiety and of the mobile phase composition on the resolution of cis and trans positional isomers of octadecenoates have been studied by silver ion HPLC with UV detection. The efficiency of the separation increases in the order phenethyl<phenacyl< p-methoxyphenacyl esters. Retention and resolution are substantially affected by small changes in the proportion of acetonitrile in the mobile phase. Dichloromethane influences retention but has a small effect on resolution. Clear resolution of cis and trans positional isomers of octadecenoic acid in partially hydrogenated sunflower oil has been achieved after conversion into p-methoxyphenacyl esters on a silver ion column by isocratic elution with a mobile phase of hexane–dichloromethane–acetonitrile (60:40:0.2, v/v) in only 22 min.

Transference Numbers of NaCl in Aqueous Mixtures with Organic Solvents of Moderate to Low Permittivities

Electromotive forces (emf) were measured in the transference cells: Ag∣AgCl∣- Nacl (m2) in Z∥ NaCl (m1) in Z∣AgCl∣Ag and NaxHg1-x∣NaCl (m1) in Z∥ NaCl (m2) in Z∣NaxHg1-x (where NaxHg1-x denotes a flowing Na–amalgam electrode and Z an aqueous-organic solvent mixture) at various molalities m2 > m1 of NaCl in Z = (ethylene glycol + water), (acetonitrile + water) and (1,4-dioxane + water), with mass fractions of the organic components ≤0.8. The transference number of Na+ in (ethylene glycol + water) and (1,4-dioxane + water) varies little with respect to that in pure water medium, whereas in (acetonitrile + water) it increases remarkably with increasing proportion of acetonitrile so as to approach equitransference, behavior similar to that previously found in (methanol + water) and in (ethanol + water). At acetonitrile mass fraction 0.6 NaCl is sufficiently close to equitransference to emerge as a useful salt bridge, nearly at the same level as the popular aqueous KCl.

High-performance liquid chromatographic assay of a new HIV-1 protease inhibitor, LB71350, in the plasma of dogs

A reliable reversed-phase high-performance liquid chromatographic method has been developed for the determination of LB71350 in the plasma of dogs. The analyte was deproteinized with 1.5 volumes of methanol and 0.5 volumes of 10% zinc sulfate, and the supernatant was injected into a 5-μm Capcell Pak C 18 column (150×4.6 mm I.D.). The mobile phase was a stepwise gradient mixture of acetonitrile and 0.2% triethylamine–HCl with a flow-rate of 1 ml/min and detection at UV 245 nm. The proportion of acetonitrile was kept at 52% for the first 6 min, increased to 100% for the next 0.5 min, kept at 100% for the next 2 min, decreased to 52% for the next 0.5 min, and finally kept at 52% for the next 7 min. The retention time of LB71350 was 6.9 min. The calibration was linear over the concentration range of 0.1–100 mg/l for dog plasma ( r>0.997) and the limit of quantitation was 0.1 mg/l using 0.1 ml plasma. The quality control samples were reproducible with acceptable accuracy and precision at 0.1, 1, 10 and 100 mg/l concentrations. The within-day recovery ( n=5) was 90.2–93.9%, the between-day recovery ( n=5) was 89.5–93.5%, and the absolute between-day recovery ( n=5) was 77–81%. The within-day precision ( n=5) and between-day precision ( n=5) were 2.59–5.82% and 3.17–4.55%, respectively. No interferences from endogenous substances were observed. Taken together, the above HPLC assay method by deproteinization and UV detection was suitable for the determination of LB71350 in the preclinical pharmacokinetics.

Separation of Nonionic Compounds by CE Using A Lauryl Poly(oxyethylene) Sulfate Additive

A nonionic surfactant (Brij-30) was treated with chlorosulfonic acid to form C12H25(OCH2CH2)4OSO3-Na+. Addition of a low concentration of this material to an aqueous solution−acetonitrile electrolyte makes it possible to separate nonionic organic compounds by capillary electrophoresis. Separation is based on differences in the stabilities of analyte−additive complexes in solution. Migration times of analytes can be varied over an unusually large range by varying the additive concentration and the proportion of acetonitrile in the electrolyte. This greatly expands the scope of neutral organic compounds that can be separated by CE. Several examples are given. Some very difficult separations were achieved, such as the baseline resolution of four methylbenz[a]anthracene isomers and the separation of normal and deuterated acetophenone.

Simple HPLC determination of the concentrations of epiroprim in the serum and brains of mice.

Epiroprim, an analogue of trimethoprim, has been shown to potentiate the efficacy of dapsone in experimental parasitic infections. A simple and accurate HPLC method has been developed to estimate epiroprim in serum and brain. Blood and brains from mice were sampled 0, 30, 75, 120 and 240 min after 50 or 100 mg kg-1 oral gavage. The drug and added internal standard metoprine in serum and brain supernatant were isolated by solid-phase extraction (Superclean LC-SCX). The HPLC system consisted of a 150 x 4.6 mm Hypersil 5 microns ODS column. The mobile phases contained various proportions of acetonitrile, methanol and phosphate buffer (0.1 M). Peaks were detected by UV absorbance at 210 nm. Serum concentrations (mean +/- s.e.m.) of epiroprim were highest at 30 min for both 50 and 100 mg kg-1 doses, 173 +/- 20 and 207 +/- 25 ng mL-1, respectively, falling to 8 +/- 5 and 18 +/- 6 ng mL-1, respectively, at 240 min. Epiroprim concentrations in the brain correlated well with those in the serum, with levels of 223 +/- 69 and 265 +/- 21 ng g-1 falling to 10 +/- 10 and 31 +/- 11 ng g-1, respectively. Epiroprim is rapidly absorbed and distributed to the brain.

Analysis of erythromycin estolate by liquid chromatography

A method is described for the determination of erythromycin estolate by liquid chromatography. A C18 reversed-phase column (25 × 0.46 cm i.d.) was used with acetonitrile-tetrabutylammonium sulphate (pH 6.5, 0.2 M)-phosphate buffer (pH 6.5, 0.2 M)-water [ x:5:5:(90- x), v/v/v/v] as mobile phase. The proportion of acetonitrile ( x) has to be adapted to the type of stationary phase used. For RSil C18 LL 42.5% (v/v) was used. The column was heated at 35°C, the flow rate was 1.5 ml min −1 and UV detection was performed at 215 nm. The main component, erythromycin A propionate, was separated from all other components which were present in commercial samples. The impurities most frequently observed were the propionate ester of erythromycin C and the amide N-propionyl- N-demethylerythromycin A. Erythromycin A was shown to be present in specialties.

Silver ion high-performance liquid chromatography of derivatives of isomeric fatty acids

Silver ion high-performance liquid chromatography was used to study the retention characteristics of series of monoenoic, dienoic and polyunsaturated esters. Two columns with stationary phases consisting of bonded phenylsulphonic moieties in the silver ion form were used, with a mobile phase consisting of dichloromethane-dichloroethane (1:1) with various proportions of acetonitrile at fixed temperatures. Accurate capacity factors relative to octadecene as an internal standard were obtained. Each column had distinctive characteristics, and methyl ester derivatives were less well resolved than phenacyl derivatives. For example, baseline resolution of three naturally occurring isomers (6-, 9- and 11-18:1) was possible. The distance of the double bond from the car☐yl group was much more important than the nature of the terminal moiety in its effect on retention values. Fixed temperatures were necessary for reproducible retention times, but lowering the temperature improved the resolution merely by extending the time of chromatography. The results are discussed in terms of a hypothetical mechanism involving simultaneous interaction between one silver ion and either two double bonds, or one double bond and one other electron-rich moiety such as the ester group.

Determination of erythromycin ethylsuccinate by liquid chromatography

A method is described for the determination of erythromycin ethylsuccinate by liquid chromatography. A C 18 reversed-phase column (25 cm x 4.6 mm I.D.) was used with acetonitrile-0.2 M tetrabutylammonium sulphate (pH 6.5)-0.2 M phosphate buffer (pH 6.5)-water [ x:5:5:(90 - x)] as mobile phase. The proportion of acetonitrile ( x) has to be adapted to the type of stationary phase used. For RSil C 18 LL, 42.5% was used. The column was heated at 35°C, the flow-rate was 1.5 ml/min and UV detection was performed at 215 nm. The main component, erythromycin A ethylsuccinate, was separated from all other components which were present in commercial samples. The main impurities were erythromycin A and the ethylsuccinate esters of erythromycin B and C. The amide N-ethylsuccinyl-N-demethylerythromycin A was shown to be present in all the samples examined. The method was successfully applied to the analysis of specialties.

A fluorometric, high-performance liquid chromatographic assay for transglutaminase activity

A fluorometric, high-performance liquid chromatographic assay for transglutaminase activity is described. The method uses the small synthetic peptide benzyloxycarbonyl- l-glutaminylglycine and the fluorescent amine monodansylcadaverine as substrates. Very small amounts of substrates and enzyme are required for this assay. The reaction product is separated from substrates on a reversed-phase, C-18 column, using an isocratic elution solvent consisting of 50% methanol in water, and is detected fluorometrically with didansylcadaverine as standard. A detection limit of 31 pmol of product per injection was measured. An apparent K m of 34.7 ± 2.4 m m was determined for the peptide substrate with purified guinea pig liver enzyme. Using this assay, a series of alkyl aldehydes was shown to inhibit transglutaminase. Modification of this assay using either gradient or isocratic elution with various proportions of acetonitrile (0.1% trifluoroacetic acid)/water (0.1% trifluoroacetic acid) afforded assays for a series of glutamine-containing peptides including substance P, α-endorphin, and two small, synthetic peptides. The assay is suitable for measurement of transglutaminase activity with purified enzyme or with crude preparations. This method provides a sensitive, quantitative assay for the determination of substrate and inhibitor properties of small peptides toward transglutaminases.

Separation of derivatized glycosphingolipids into individual molecular species by high performance liquid chromatography.

The high performance liquid chromatography separation of the perbenzoyl derivatives of the neutral glycosphingolipids (GlcCer, LacCer, GbOse3Cer, GbOse4Cer, and GgOse3Cer) and the p-bromophenacyl and 2,4-dinitrophenyl hydrazide derivatives of the gangliosides (GM4, GM3, GM2, GM1, GD1a) into individual molecular species on a C18 reversed-phase column is described. Peaks were identified by comparing their relative retention times to the relative retention time of the corresponding glycosphingolipid of known molecular species composition. As little as 5 to 10 pmol of each molecular species of neutral glycosphingolipids and 3 to 5 pmol of the gangliosides can be detected. The effects of changes in the proportion of acetonitrile, methanol, and water in the mobile phase and of column temperature on the molecular species separation are described. A procedure for the tentative identification of glycosphingolipid molecular species based on their relative retention times is presented.

Comparison of bonded, polymeric and silica columns for chromatography of some penicillins

The retention of ampicillin, amoxicillin, and penicillin G was determined on ODS and cyanopropyl (CN)-bonded to silica, on an all-organic polymeric reversed-phase column (styrene-divinylbenzene) and on bare silica. Solvents tested were 0.01 M H 3PO 4 (pH 1.6)-acetonitrile and 0.002 M KH 2PO 4 (pH 4.6)-acetonitrile in the proportions 100:0 to 10:90. Retention with 0.002 M KH 2PO 4 was weaker than with 0.01 M H 3PO 4 at all proportions of acetonitrile on all packings. With 0.01 M H 3PO 4, retention of penicillins on the polymeric column decreased rapidly from 100 to 50% aqueous phase and remained low to 10% aqueous phase. On the ODS bonded column, retention was similar, except that retention of the aminopenicillins, amoxicillin and ampicillin increased at < 30% aqueous phase. On the CN-bonded column, results were similar to those on the ODS column, except that the aminopencillins were less strongly retained when using 100% 0.01 M H 3PO 4. On the bare silica, penicillin G was poorly retained at all proportions of acetonitrile, while retention of aminopenicillins increased rapidly at < 50% 0.01 M H 3PO 4. Retention of aminopenicillins at < 50%. 0.01 M H 3PO 4 was parallel on bonded and bare silica but weaker on the bonded silica. A bonded organic layer weakened but did not prevent binding of amines to silica.

High-performance liquid chromatography of ciprofloxacin and its metabolites in serum, urine and sputum

A versatile and sensitive method requiring no internal standard was developed for quantitating ciprofloxacin in serum, urine and sputum by high-performance liquid chromatography with fluorescence detection. Acetonitrile and chloroform were employed to remove protein and lipophilic substances from an aqueous, ciprofloxacin-containing sample layer. The proportions of acetonitrile and 0.1 M potassium phosphate, pH 2.5, in the mobile phase were varied to suit the purpose of the assay. For the routine determination of ciprofloxacin pharmacokinetics, isocratic 19% acetonitrile was used. A gradient from 15 to 36% acetonitrile was chosen to show the appearance of metabolites which formed during the biodisposition of ciprofloxacin. In the latter case urine samples were diluted for assay and protein was precipitated from serum samples with trichloroacetic acid. Four fluorescent metabolites were observed in all patient specimens, and with tandem ultraviolet detection two additional ultraviolet-absorbing metabolites were readily found in urine specimens.

The separation by liquid chromatography (under elevated pressure) of phenyl, benzyl, and o-nitrophenyl glycosides of oligosaccharides. Analysis of substrates and products for four N-acetyl- d-glucosaminyl-transferases involved in mucin synthesis

Liquid chromatography under elevated pressure (h.p.l.c.) has been applied to the separation of the phenyl, benzyl, and O-nitrophenyl glycosides of 2-acetamido-2-deoxy- d-galactopyranose and of various mucin-type, di-, tri-, and tetra-saccharides. The separations were carried out with a Whatman Partisil PXS 5/25 PAC column and various proportions of acetonitrile and water in the mobile phase. These methods were subsequently used to separate the substrates and products of the following N-acetylglucosaminyltransferase reactions: UDP-GlcNAc + β-Gal-(1→3)-GalNAc-R → β-Gal-(1→3)-[β-GlcNAc-(1→6)]-GalNAc-R + UDP ( 1); UDP-GlcNAc + β-Gal-(1→3)-[β-GlcNAc-(1→6)]-GalNAc-R → β-GlcNAc-(1→3)-β-Gal-(1→3)-[β-GlcNAc-(1→6)]-GalNAc-R + UDP ( 2); UDP-GlcNAc + GalNAc-R′ → β-GlcNAc-(1→3)-GalNAc-R′ + UDP ( 3); and UDP-GlcNAc + β-GlcNAc-(1→3)-GalNAc-R′ → β-GlcNAc-(1→6)-[β-GlcNAc-(1→3)]-GalNAc-R′ + UDP ( 4), where R = benzyl or o-nitrophenyl, and R′ = benzyl or phenyl α- d-glycoside. Reaction 1 is catalyzed by a transferase in canine submaxillary glands and porcine gastric mucosa, and reaction 2 by an enzyme in porcine gastric mucosa. Enzyme activities catalyzing reactions 3 and 4 have recently been demonstrated in rat colonic mucosa. Liquid chromatography can be used at the preparative level for the purification and identification of the transferase products, and at the analytical level in the assay of glycosyltransferases.