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  • Author or Editor: S. Ravi x
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Summary  

A highly efficient and an optimized synthesis of [1-14C]lauric acid with high specific activity (50 mCi/mmol) is described. [1-14C]lauric acid was prepared from [1-14C]lauronitrile, in 2 minutes with a mixture of concentrated hydrochloric acid: propionic acid (1: 2 v/v) under microwave irradiation, in quantitative yield.

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A new sensitive and specific isocratic RP-HPLC-UV method was developed and validated for the determination of ondansetron in rabbit plasma using risperidone as an internal standard (IS). The sample preparation involved a simple deprotenization procedure with a mixture of 1 mL of acetonitrile and 50 μL of 10% w/υ zinc sulfate. Analysis was performed on a Phenomenex CN column (250 mm × 4.6 mm, 5 μm) with 50 mM ammonium acetate (pH 3.5) and acetonitrile (35:65, υ/υ) as mobile phase at a flow rate of 1.0 mL min−1. Column eluent was monitored at 310 nm. The calibration curve was linear over the concentration range of 25–1000 ng mL−1 (r 2 = 0.9999) with a limit of quantification (LOQ) 25 ng mL−1. The intraday and interday precision and accuracy were between 0.93% and 3.41% and −3.63% and 1.01%, respectively. The mean recoveries of ondansetron and risperidone were 85.87% and 99.80%, respectively. Ondansetroncontaining plasma samples were stable at −20°C for 14 days. The validated method was successfully applied for a pharmacokinetic study after a single oral administration of ondansetron (8 mg) to rabbits.

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Abstract  

129I content of batches of Na131I vials, used for nuclear medicine procedures, was estimated by neutron activation analysis. The average value of the129I/131I activity ratio /corresponding to zero decay time of the latter/ was /4.98±2.8/x10–9. It is concluded that the contribution of129I from medical applications of131I in India is insignificant in relation to that from nuclear fuel cycle activities.

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Abstract  

Carbon-14 labelled p-fluorophenylacetic acid was prepared by heating its sodium salt with14CO2 at 325 °C. The labelled acid after isolation from the reaction mixture was degraded by reaction with sodium azide. From the radioactivity measurements it was observed that no scrambling of14C had taken place and the acid could be designated as carboxyl-14C.

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Abstract  

Deoxyadenosine-5'-monophosphite was treated with excess of trimethylsilyl chloride. One equivalent of trimethylsilyl chloride treated phosphite in pyridine and one equivalent of elemental 35S in toluene solution (specific activity > 1000 Ci/mmol) were stirred together with gradual removal of solvents under vacuum, over a period of one hour, to give deoxyadenosine-5'-(35S)-thiomonophosphate [dAMP(35S)] in high yields.

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4,6-dimethoxy-2-methylsulphonylpyrimidine is a key intermediate for the synthesis of pyrithiobac-sodium, a selective herbicide for cotton plant. 14C labeled pyrithiobac-sodium is required for studying the translocation and metabolism in cotton plants. It was prepared by oxidation of 4,6-dimethoxy-[2-14C]-2-methylmercaptopyrimidine with H5IO6/CrO3 in ethyl acetate at room temperature to give 4,6-dimethoxy-[2-14C]-2-methylsulphonylpyrimidine in high yields.

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Abstract  

Microwave assisted direct aromatic substitution of 3-bromopyridine with K14CN as the cyanide source and catalytic amount of tetrabutylammonium bromide afforded [3-14C]-cyanopyridine 3 in 90% yield. Microwave assisted hydrolysis of 3 with a mixture of concentrated hydrochloric acid and propionic acid afforded [carboxyl-14C]-nicotinic acid in 95% yield whereas microwave assisted hydrolysis of 3 with a mixture of concentrated sulfuric acid and propionic acid afforded [carbonyl-14C]-nicotinamide in 85% yield.

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Abstract  

Two modifications of the existing method of determining free acidity in highly concentrated uranyl nitrate solutions by alkalimetric titrations in neutral potassium oxalate medium have been carried out to improve the reliability of the method. Free acidities of several synthetic solutions containing uranium and nitric acid in a wide range of concentration ratios were determined by all the three methods and compared with the results obtained by a more accurate ion exchange method. Interference from other hydrolyzable ions and the precision and accuracy were studied and compared.

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An isocratic RP-HPLC-UV method for analysis of sumatriptan succinate in pharmaceutical dosage forms has been developed and validated. Best separation was achieved on a Thermo Hypersil C4 column (250 mm × 4.6 mm, 5 µm) using a mobile phase of 20 mM potassium dihydrogen phosphate adjusted to pH 4.0 with orthophosphoric acid and acetonitrile (65:35, v/v) at a flow rate of 1.0 mL min−1. UV detection was performed at 227 nm. The method was validated for specificity, linearity, precision, accuracy, limit of quantification, limit of detection, robustness, and solution stability. The calibration plot was linear over the concentration range 25–600 ng mL−1 (r 2 = 0.9998) and the limits of detection and quantification were 10 and 25 ng mL−1, respectively. Intra-day and inter-day precision and accuracy were between 1.25 and 2.95% and between −1.15 and 2.47%, respectively. The method was successfully used for analysis of sumatriptan succinate, in the presence of excipients, in orally disintegrating tablets prepared in our laboratory and in commercially available tablets (Imigran) and nasal spray (Suminat).

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Abstract  

Copper activated zinc sulphide phosphor was coated with tritiated polystyrene to give self-sustained light sources. The stability of the zinc sulphide phosphor coated with polystyrene was studied. It is suggested that the drastic reduction in light output over a period of two years may be due to the phosphor damage rather than loss of radioactivity.

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