Isocratic HPLC method

Normal-phase chromatography is still widely used for the determination of nonpolar additives in a variety of commercial products and pharmaceutical formulations, e.g. the separation of nonpolar components in the nonionic surfactant Triton X-100. Most of the NPLC analyses of polymer additives have been performed in isocratic mode [576]. However, isocratic HPLC methods are incapable of separating a substantial number of industrially used additives [605,608,612-616], Normal-phase chromatography of Irgafos 168, Irganox 1010/1076/3114 was shown [240]. NPLC-UV has been used for quantitative analysis of additives in PP/(Irganox 1010/1076, Irgafos 168) after Soxhlet extraction (88%... 

Rustan et al. (123) used an isocratic HPLC method for the determination of alpha-, gamma-, and delta-tocopherol, BHT, BHA, PG, OG, DG, NDGA, TBHQ, ascorbyl palmitate, and beta-carotene in foods. An RP18 column was used in experiments, and seven mobile phases based on various combinations of acetonitrile, methanol, water, and tetrahydrofuran were tested. Trials with carrot juice, dried milk formula for infants, and aperitif cakes showed that all 12 antioxidants could be determined by a single isocratic HPLC analysis. The optimum mobile phase... 

The OPP malathion is widely used because of its low persistence in the environment and its high insecticide activity. Pure malathion has moderate toxicity, but crude malathion and its formulations contain impurities, which are far more toxic to mammals. These impurities not only are formed during commercial production but can also develop in the grains during storage. The most toxic of these products is the oxidation product malaoxon. An isocratic HPLC method indicated the degradation of malathion in stored wheat (55) and the presence of malathion and malaoxon in maize and bean samples (56). Isomalation and malation monocarboxylic acid metabolites were also detected. 

Chollet et al. [39] developed an isocratic HPLC method for simultaneous determination of vigabatrin and gabapentin in human serum after precolumn derivatization with o-phthaldialdehyde and fluorimetric detection at 435 nm with excitation at 235 nm. A column (25 cm x 3.0 mm) of Nucleosil Ci8 (5 /im) with a mixture of 0.022 M phosphoric acid (pH 2)-acetonitrile (45 55) as a mobile phase (flow rate 0.6 ml/min) was used. The calibration graph was rectilinear from 2.0 to... 

An isocratic HPLC method for screening plasma samples for sixteen different non-steroidal anti-inflammatory drugs (including etodolac) has been developed [29]. The extraction efficiency from plasma was 98%. Plasma samples (100-500 pL) were spiked with internal standard (benzoyl-4-phenyl)-2-butyric acid and 1 M HC1 and were extracted with diethyl ether. The organic phase was separated, evaporated, the dry residue reconstituted in mobile phase (acetonitrile-0.3% acetic acid-tetrahydrofuran, in a 36 63.1 0,9 v/v ratio), and injected on a reverse-phase ODS 300 x 3.9 mm i.d. column heated to 40°C. A flow rate of 1 mL/min was used, and UV detection at 254 nm was used for quantitation. The retention time of etodolac was 30.0 minutes. The assay was found to be linear over the range of 0.2 to 100 pg/mL, with a limit of detection of 0.1 pg/mL. The coefficients of variation for precision and reproducibility were 2.9% and 6.0%, respectively. Less than 1% variability for intra-day, and less than 5% for inter-day, in retention times was obtained. The effect of various factors, such as, different organic solvents for extraction, pH of mobile phase, proportion of acetonitrile and THF in mobile phase, column temperature, and different detection wavelengths on the extraction and separation of analytes was studied. 

The described isocratic HPLC method is validated and shown to be precise and accurate. This method can be used in quality control departments for the simultaneous determination of metformin and glibenclamide in the combined dosage form. 

A stability-indicating high performance liquid chromatographic method is available for the formulated product of diltiazem hydrochloride. Diltiazem hydrochloride is separated from its major potential degradate, desacetyl diltiazem using an isocratic HPLC method. The method utilizes a Phenomenex IB... 

HPLC-MS analysis Samples of broth were prepared for HPLC-MS analysis by mixing with an equal volume of acetonitrile containing trifluoroacetic acid (5 mL/L). The samples were centrifuged and the supernatant analyzed by an isocratic HPLC method (Spherisorb ODS2 [5-pm particle size, 150 x 4.5 mm] acetonitrile/water [55 45] with trifluoroacetic acid [0.1%, v/v], flow rate... 

Nygard, G. Wahba Kahlil, S.K. An isocratic HPLC method for the determination of cephalosporins in plasma. J.Liq.Chromatogr., 1984, 7, 1461—1475 [plasma cephapirin (IS) column temp 45 extracted cefamandole, cefazolin, cefonicid, cefoperazone, cefoxitin, cephalothin]... 

The majority of breakfast cereals in the United States are fortified with PN, and additional PN is also added to infant formula products to ensure adequate vitamin Be supply to the infant. Gregory (100) reported an isocratic HPLC method for the determination of PN in breakfast cereals (Table 5). Other investigators attempted simultaneous determination of PN and other vitamins used in food fortification. Wehling and Wetzel used ion pair HPLC to separate pyridoxine, riboflavin and thiamine from each other after acid extraction of the vitamins from cereals (101). Using a dual fluorescence detector setup, pyridoxine and riboflavin were monitored by the first detector. After the column eluate had passed the first detector, an alkaline ferricyanide solution was introduced, resulting in the formation of a fluorescent thiochrome derivative of thiamine, which was detected by the second fluorescence detector. A similar method for simultaneous determination of pyridoxine and riboflavin in infant formula products has also been described (102). 

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