Internal Standard Peak Research Articles

Gas Chromatographic Determination of Fluazifop-butyl in Formulations: Collaborative Study

Abstract A method is described for the determination of butyl 2-(4-(5-trifluoromethyl- 2-pyridinyloxy)phenoxy) propanoate in technical and formulated material by gas chromatography (GC). Samples of technical or formulated material are dissolved in methylene chloride containing dibenzyl succinate as internal standard. The solution is injected into a gas chromatograph fitted with a flame ionization detector and a 6 ft × 2 mm glass column. The column is packed with 3% OV-17 on 100–120 mesh Chromosorb WHP and is maintained at 230°C. Peak areas obtained at the retention times of the internal standard and the active ingredient are measured with an integrator. The quantity of fluazifop-butyl is determined by comparing the internal standard and active ingredient peak areas with the peak areas obtained from a calibration solution containing known amounts of internal standard and pure active ingredient. Four samples were chosen for collaboration: technical fluazifop-butyl, a 4 lb/US gal. emulsifiable concentrate, a 560 g/L oil concentrate, and a 5% granular. Fourteen collaborators carried out replicate determinations on each sample. Coefficients of variation between laboratories were 0.80 for the technical, 0.88 for the emulsifiable concentrate, 1.03 for the oil concentrate, and 2.04 for the granular. Parallel peak height determinations showed substantially higher coefficients of variation for all except the granular sample. The method has been adopted official first action.

The interaction between water and cephalexin in the crystalline and noncrystalline states.

Solid cephalexin (CEX) has been obtained as crystals, the noncrystalline solid (NC) produced by freeze-drying and the noncrystalline solid (GNC) produced by grinding in a centrifugal mill for 4 h. Each product formed an anhydride, monohydrate and dihydrate. The interaction between water and CEX in the crystalline and noncrystalline states was studied by the infrared (IR) spectral method and the thermal kinetic analytical method (Criado method) using differential scanning calorimetry. In the IR spectrum of CEX, the hydroxyl vOH band was observed at 3400 cm-1, the amido vNH band at 3100 cm-1, the amine vNH3+ band at 2600 cm-1, the β-lactam vC=O band at 1760 cm-1, the amido vC=O band at 1680 cm-1, and the carboxylate vCO2- band at 1600 cm-1. The IR spectral intensity ratios were calculated from the peak heights of the bands with respect to the band at 1280 cm-1 as an internal standard peak. The changes of the IR spectral intensity ratios with increasing water content led us to the following conclusions. In the crystalline monohydrate (phase IV), the first water molecule interacted with the amine and carboxylate groups of different molecules in the crystal of CEX. In the crystalline dihydrate (phase II), the second water molecule interacted with NH and C=O of the amido group of CEX. In NC-H2O, the water molecule is adsorbed at the carboxylate group of CEX, while in NC-2H2O, the second water molecule is adsorbed at the amine group. The dehydrations of phase IV, GNC-H2O, GNC-2H2O and NC-2H2O followed first-order kinetics and the activation energies (E) were 15.67, 14.83, 14.58 and 12.50 kcal/mol, respectively, while that of NC-H2O followed three-dimensional diffusion kinetics and its E value was 15.81 kcal/mol. The E of phase II (second water molecule) was 11.74 kcal/mol as determined by the Kissinger method. These results suggest that the binding energies between the various forms of CEX and water reflect the characteristics of the groups of the CEX molecule to which water is actually bound in each case.

Assay of mixtures of phenylpropanolamine hydrochloride and caffeine in appetite suppressant formulations by high-performance liquid chromatography

A simple assay method for the quality control of appetite suppressant products containing phenylpropanolamine hydrochloride and caffeine has been developed. A methanolic extract of the product was evaporated to dryness and the residue was treated with aqueous solutions of sodium metaperiodate and disodium phosphate. Following addition of methyl p-hydroxybenzoate as internal standard and subsequent filtration, an aliquot of the filtrate was subjected to high-performance liquid chromatography on a 10-μm Partisil ODS-2 column with acetonitrile-water (30:70) as mobile phase. The drug: internal standard peak height ratio at 254 nm was linear over the ranges 0.3–2.0 μg of phenylpropanolamine hydrochloride and 1.1–16.0 μg of caffeine injected. All peaks were well-resolved. The heights equivalent to a theoretical plate (± S.D.) for phenylpropanolamine (as benzaldehyde) and caffeine were ( n  10) 0.42 ± 0.08 and 1.31 ± 0.23 mm, respectively. Overall per cent recoveries (± S.D.) from simulated formulations ( n  6) were 100.7 ± 1.6% phenylpropanolamine hydrochloride and 99.1 ± 1.4% caffeine. The method was applied to marketed products and is also applicable for single dose analysis.

Determination of clofilium, a new antifibrillatory agent, in plasma by gas chromatography—mass spectrometry

A sensitive and selective method for the assay of the new quaternary amine antifibrillatory agent clofilium is described. Plasma samples were extracted with dichloromethane (98.5 ± 0.2% recovery) and analyzed by gas chromatography—mass spectrometry operating in the electron-impact mode. The method involves a Hofmann elimination of an N-alkyl radical from clofilium and the internal standard in the presence of a strong nucleophile in the injector of the gas chromatograph. The resulting tertiary amines are chromatographed and detected by selective ion monitoring. The ratio of the clofilium base peak ( m/z 224) to the internal standard peak ( m/z 210) was linear relative to the plasma clofilium concentration over the range of 25–1000 ng/ml plasma.

Chromatographic determination of thiodiglycolic acid - a metabolite of vinyl chloride.

The determination of thiodiglycolic acid (TDGA) In urine by gas chromatography (GC) is described. The analytical procedure includes addition of internal standard (o-phthalic acid), ethyl acetate extraction, evaporation of the solvent and silylation of TDGA with N-trimethylsilyl-diethylamine in pyridine (1:1). The results are calculated from the ratio of TDGA and internal standard peak heights. The detection limit of the method is 10 mg/l and the coefficient of various is +/- 5%.

Evidence for the influence of fCH 4 on the crystallinity of disseminated carbon in greenschist facies rocks, Rhode Island, USA

Disseminated carbon has been extracted from 19 samples of arkosic rocks from the chlorite, biotite and garnet zones in the Narragansett basin, and analysed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). XRD of these samples yields only the (002) peak which may be as much as four times wider than the silicon internal standard peak and is always skewed to low angles 2θ. All (002) peaks were digitized and the four moments calculated. The results suggest that width at half-height (W1/2) provides a poorer estimate of peak shape than coefficients of skewness and kurtosis. The positive correlation of these coefficients with grain size determined by SEM in the range of 0.1–100 μm suggest a direct relationship between peak shape and grain size.

Determination of paraquat in sunflower seeds by reversed—phase high—performance liquid chromatography

The herbicide paraquat was determined with extracts from 1-g samples of sunflower seeds. The liquid chromatography procedure utilized a microparticle (10 μm) C 18 reversed-phase column and isocratic elution with 27% acetronitrile in water, 10m M in the sodium salt of octanesulfonic acid. Eluted paraquat was detected at 254 and 280 nm and quantitated by paraquat internal standard peak height ratios. This procedure provided linear working curves over the concentration range of 0–20 μg/g of paraquat. Recovery of paraquat varied fom 89–101%, with an average recovery of 93%. Good agreement was obtained in the comparison of results of the described procedure with those from a well established UV procedure.

Computer Automation of X-Ray Powder Diffraction

The interfacing of a Hewlett-Packard 9825 calculator to an Enraf-Nonius microdensitometer and a Philips powder diffractometer provides automated data collection and manipulation on a routine basis. Data is acquired and stored on a floppy disk; background corrections are made; diffraction peak maxima are found, normalized and plotted; a table of approximate d-spacing (±0.0lÅ) is printed. The analyst designates the internal standard peaks. Corrected d-spacings are then computed, tabulated and printed above the appropriate peak. An accurate d-spacing scale is drawn on the plot. The total time for a scan is approximately twenty minutes with only about five minutes of operator time required. The program is conversational and requires little prior knowledge of the software by the operator. Data interpretation is further aided by supporting programs to calculate patterns from literature, determine lattice constants for observed phases, help index patterns, deconvolute overlapping peaks, carry out crystalline size determinations and perform search/match procedures. Such supporting programs are possible because, even though the system can be used in a “dedicated” manner, it is still a stand-alone computer. Thus, the desired degree of automation in data collection has been obtained without sacrificing flexibility.

Gas-Liquid Chromatographic Determination of Diethylstilbestrol Monomethyl Ether in Diethylstilbestrol

Abstract A gas chromatographic method is described for the determination of the monomethyl ether of diethylstilbestrol (MME) in diethylstilbestrol (DES). A 1 g sample of DES is dissolved in an aqueous solution of 0.5N sodium hydroxide and extracted with a chloroform solution containing benefin, the internal standard. The chloroform solution is back-extracted with sodium hydroxide, and an aliquot is chromatographed after silylation. The MME peaks (cis and trans') are measured relative to the internal standard peak. The method was tested for accuracy within the 120—2000 ppm range, and a linear plot of detector response vs. concentration was obtained. The method is also suitable for the determination of diethylstilbestrol dimethyl ether (DME) if present with MME in a DES sample.

Analysis of Adrenocortical Steroids in Pharmaceutical Preparations by High-Pressure Liquid-Liquid Chromatography

The adrenocortical steroids hydrocortisone, cortisone, hydrocortisone acetate, and cortisone acetate were separated by liquid-liquid chromatography. A commercially prepared reverse- phase cyano ethyl silicone column was used in conjunction with a UV precision photometer. Linearity studies were carried out using the internal standard technique and peak height measurements. Responses of each steroid were linear over the working range when equal injection volumes were used. The results of a study of the controlled decomposition of hydrocortisone in basic solution indicated a good separation of drug from the degradation products. Samples of adrenocortical steroids in various dosage forms, primarily creams and ointments, were analyzed by the proposed procedure, yielding a single steroid assay value and an identification and quantitation of each foreign steroid. The sample preparation was a simple dissolution of the steroid in alcohol plus the addition of an internal standard prior to injection.

Gas Chromatographic Determination of Diethylstilbestrol Dimethyl Ether in Diethylstilbestrol

Abstract A GLC method is described for the determination of the dimethyl ether of diethylstilbestrol (DME) in diethylstilbestrol (DES). A 1 g sample of DES is dissolved in an aqueous solution of 0.5N NaOH and then extracted with a chloroform solution containing benefin, the internal standard. An aliquot of the chloroform layer is chromatographed and the DME peak is measured relative to the internal standard peak. The method was tested for accuracy within the 11–110 ppm range and a linear plot of detector response vs. concentration was obtained.

Rapid Identification and Quantitative Determination of Barbiturates and Glutethimide in Blood by Gas—Liquid Chromatography

Abstract Barbiturates and glutethimide can be identified and measured in whole blood, plasma, or serum in 20 min. An internal standard containing known amounts of five common barbiturates is added to the sample, the sample is acidified, and the sedatives are extracted rapidly into toluene, then from the toluene into a small volume of aqueous tetraethylammonium hydroxide. An aliquot of this last extract is introduced directly into the gas chromatograph, where the barbiturates are converted to their ethyl derivatives and separated on a silicone column. They are identified by observing which of the internal standard peaks has increased and measured by measuring the extent of increase. Glutethimide can be determined on the same chromatogram. Mephobarbital and phenobarbital can be simultaneously determined.