Internal standards nitrogen

Ethanol production in the fermentation process was detected with gas chromatography, HP 5890 series II (Hewlett-Packard, Avondale, PA, USA) equipped with a flame ionisation detector (FID) and GC column Porapak QS (Alltech Associates Inc., Deerfield, IL, USA) 100/120 mesh. The oven and detector temperature were 175 and 185 °C, respectively. Nitrogen gas was used as a carrier. Isopropanol was used as an internal standard. 

Standard preparation Dissolve an accurately weighed quantity of USP Miconazole Nitrate RS in a mixture of chloroform and methanol (1 1) to obtain a solution having a known concentration of about 0.8 mg/mL. Transfer 5 mL of this solution to a test tube, add 2 mL of Internal standard solution, and evaporate at a temperature not higher than 40 °C with the aid of a current of nitrogen to dryness. Dissolve the residue in 2 mL of a mixture of chloroform and methanol (1 1), and mix to obtain a Standard preparation having a known miconazole nitrate concentration of about 2 mg/mL. 

Wrobel et al. [29] described a simple method for the determination miconazole in pharmaceutical creams, based on extraction and second-derivative spectrophotometry. In the presence of sodium lauryl sulfate (0.5%) and sulfuric acid (0.4 mol/L), the miconazole and internal standard (methylene blue) were extracted to 100 pL of methylene chloride. The organic phase was evaporated in the nitrogen stream and the dry residue was dissolved in methanol (1.5 mL). The analytical signal was obtained as the ratio between second-derivative absorbances measured at 236.9 nm... 

Szathmary and Luhmann [50] described a sensitive and automated gas chromatographic method for the determination of miconazole in plasma samples. Plasma was mixed with internal standard l-[2,4-dichloro-2-(2,3,4-trichlorobenzyloxy) phenethyl]imidazole and 0.1 M sodium hydroxide and extracted with heptane-isoamyl alcohol (197 3) and the drug was back-extracted with 0.05 M sulfuric acid. The aqueous phase was adjusted to pH 10 and extracted with an identical organic phase, which was evaporated to dryness. The residue was dissolved in isopropanol and subjected to gas chromatography on a column (12 m x 0.2 mm) of OV-1 (0.1 pm) at 265 °C, with nitrogen phosphorous detection. Recovery of miconazole was 85% and the calibration graph was rectilinear for 0.25 250 ng/mL. 

Dean et al. [93] used a high performance liquid chromatographic method for the simultaneous determination of primaquine and carboxyprimaquine in plasma with electrochemical detection. After the addition of the internal standard, plasma was deproteinized by the addition of acetonitrile. Nitrogen-dried supernatants, resuspended in mobile phase were analyzed on a C8 reversed-phase column. Limits of detection for primaquine and carboxyprimaquine were 2 and 5 ng/mL with quantitation limits of 5 and 20 ng/mL, respectively. The assay sensitivity and specificity are sufficient to permit quantitation of the drug in plasma for pharmacokinetics following low dose (30 mg, base) oral administration of primaquine, typically used in the treatment of malaria and P. carinii pneumonia. 

General Methods. Methanol used in kinetic runs was distilled from sodium methoxide or calcium hydride in a nitrogen atmosphere before use. Freshly distilled cyclohexanol was added to the methanol in the ratio 6.0 ml cyclohexanol/200 ml MeOH and was used as an internal standard for gas chromatographic (GC) analysis. Benzaldehyde was distilled under vacuum and stored under nitrogen at 5°. Other aldehydes (purchased from Aldrich) were also distilled before use. The corresponding alcohols (purchased from Aldrich) were distilled and used to prepare GC standards. All metal carbonyl cluster complexes were purchased from Strem Chemical Company and used as received. Tetrahydrofuran (THF) was distilled from sodium benzophenone under nitrogen before use. 

Since the product slowly darkens on exposure to air, it should be stored under nitrogen in a refrigerator. The compound solidifies on cooling m.p. 16.0-16.5°. Nuclear magnetic resonance spectrum (neat, tetramethylsilane internal standard) singlets at d 7.00 (aromatic protons), 3.93 (CH2), and 2.24 p.p.m. (NH). 

General Procedure for PTC Catalyzed Arvl Bisplacement, Reactions. Alkali phenolate or thiolate, substrate, phase transfer catalyst, and a magnetic stirring bar were weighed into a dry stoppered flask under nitrogen. Solvent was added, and the reaction mixture was stirred and heated under the conditions described in the tables. Hydrocarbon internal standards (n-alkanes for VPC... 

General. All reactions were performed under nitrogen. H NMR and NMR spectra were recorded in ppm (5) on a 300 MHz instrument using TMS as internal standard. Elemental analyses were performed by Robertson Micolit Laboratories. Anhydrous THE, toluene, and tert-butyllithium in pentane (1.7 M) were purchased. Flash chromatography was performed with silica gel 60 (230-400 mesh). Melting points were determined and are uncorrected. 

We obtained the best results with the Carbopack B-DA/4% Carbowax 20M, 80-120 mesh Supelco column, 2000 x 2 mm. It was initially conditioned for 21 h at 245°C, but the normal running temperature is 175°C. The injector/detector temperature is 200°C and a flame ionization detector is used. A glass sleeve is fitted to the injector and the glass wool plug removed from the column inlet. The carrier gas is nitrogen with a flowrate of 40 ml min at 310 kN m. The sample solution (9 ml) is mixed with 1 ml of pivalic acid solution (1.5% m/v) as internal standard. Then 1 ml of this solution is mixed with 1 ml 0.3 M oxalic acid solution and 3 ml deionized water before injecting 1 pi into the septum. 

The quaternary ammonium compounds paraquat and diquat are widely used non-selective contact herbicides, which are extremely toxic to humans. Fee et al. [112] established an HPLC-MS-MS procedure for the determination of these herbicides in whole blood and urine using ethyl paraquat as internal standard. After extraction with Sep-Pak C18 cartridges, analytes were separated using ion pair chromatography with heptafluorobutyric acid in 20 mM ammonium acetate and acetonitrile gradient elution. Detection was carried out in ESI MS-MS SRM mode. Using similar separation and detection conditions, paraquat, diquat, difenzoquat, and a number of structurally related quaternary nitrogen muscle relaxants (see Section 20.2.1.3) were determined in whole blood by Ariffin and Anderson [113]. 

Sane et al. reported the determination of diloxanide furoate in pharmaceuticals by gas chromatography [36]. A sample of powdered tablets equivalent to 250 mg of drug was dissolved in chloroform and diluted to a concentration of 5 mg/mL. A mixture of 2 mL of the sample solution and 1 mL of bromhexine hydrochloride solution (the internal standard) was diluted to 5 mL with chloroform, was used for the analysis. The injection volume was 400 nL, which was analyzed at 265°C on a stainless steel column (3 m x 2 mm) containing 3% OV-13 on Chromosorb W-HP (80-100 mesh). Nitrogen was used as the carrier gas at a flow rate of 50 mL/min, and analyte detection was effected using a dual flame ionization detector. 

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