Arbutin determination in medicinal plants and creams.

A simple flow injection (FI) manifold with spectrophotometric detection was fabricated and tested for arbutin determination. It is based on the measurement of a red-coloured product at 514 nm formed by the complexation reaction between arbutin and 4-aminoantipyrine (4-AP) in the presence of hexacyanoferrate (III) in an alkaline medium. On injecting 300 microL standard solutions at various concentrations of arbutin into the FI system under optimum conditions, a linear calibration graph over the range of 1.0-30.0 microg mL(-1) arbutin was established. It is expressed by the regression equation y = 0.2188 +/- 0.0036x + 0.1019 +/- 0.0366 (r(2) = 0.9990, n = 5). The detection limit (3sigma) and the limit of quantitation (10sigma) were 0.04 microg mL(-1) and 0.13 microg mL(-1), respectively. The RSD of intraday and interday precisions were found to be 1.2-1.4% and 1.7-2.7%, respectively. The method was successfully applied in the determination of arbutin in four selected fruits and three commercial whitening cream extracts with the mean recoveries of the added arbutin over the range of 96.2-99.0%. No interference effects from some common excipients used in commercial whitening creams were observed. The method is simple, rapid, selective, accurate, reproducible and relatively inexpensive.

A new flavonoid from Chromolaena odorata.

Fractionation of the aerial parts of Chromolaena odorata afforded a new flavonoid, 5,7-dihydroxy-6,4'-dimethoxyflavanone, in addition to 14 known flavonoid compounds, six of which had not been isolated previously from this plant. The structure of the new compound was determined by spectroscopic methods particularly 2D-NMR analysis.

Constituents of the essential oil from aerial parts of Chromolaena odorata from Thailand.

The chemical composition of the essential oil from the aerial parts of Chromolaena odorata, collected from Phitsanulok, Thailand was analyzed by means of GC-(FID) and GC-MS. Twenty-two constituents were identified. The major components were pregeijerene (17.6%), germacrene D (11.1%), alpha-pinene (8.4%), beta-caryophyllene (7.3%), vestitenone (6.5%), beta-pinene (5.6%), delta-cadinene (4.9%), geijerene (3.1%), bulnesol (2.9%), and trans-ocimene (2.2%).

A simple flow injection spectrophotometric procedure for the determination of diazepam in pharmaceutical formulation.

A single-channel flow injection (FI) manifold with spectrophotometric detection has been designed and fabricated for diazepam determination. A 100 microl sample and/or standard solution containing diazepam was injected into a flowing stream of 0.1 mol L(-1) hydrochloric acid with the optimum flow rate of 6.8 mL min(-1). As soon as the sample reached the detector, the FI signal as a peak was recorded at 360 nm. The optimum conditions for microg amounts of diazepam were achieved. A linear calibration graph over the range of 2-110 mg L(-1) diazepam was obtained with the regression equation Y = 0.2926X + 0.5896 (r2 = 0.9929). The method was very sensitive, since as little as 0.60 mg L(-1) could be detected; very reproducible with an RSD of 3.3% (n=11); and very rapid with a sampling rate of 100 h(-1). The limit of quantitation (10 sigma) was 2.0 mg L(-1). The proposed FI procedure has been satisfactorily applied to the quantitation of diazepam in commercial pharmaceutical formulations. The obtained results were in excellent agreement with those obtained by the conventional spectrophotometric method, verified by the student t-test at the 95% confidence level.

Simultaneous determination of tolperisone and lidocaine by high performance liquid chromatography.

A reversed phase high performance liquid chromatographic (RP-HPLC) method for the simultaneous determination of tolperisone (TP) and lidocaine (LD) has been developed. The drugs were separated on a column (4.60 x 250 mm(2)) Spherisorb ODS (5 microm) using 5.5% triethylamine in 70/30 v/v acetonitrile/water as mobile phase 0.7 ml min(-1)and UV detection at 254 nm. The detection limits for Tolperisone hydrochloride (TP-HCl) and lidocaine hydrochloride (LD-HCl) were 0.20 ng/20 microl and 100 ng/20 microl and the quantitation limits were 0.50 ng/20 microl and 250 ng/20 microl, respectively. Linear calibration curves over the ranges of 1-10, 10-100 and 150-500 microg ml(-1) for TP-HCl and 10-500 microg ml(-1) for LD-HCl were established. Different calibration slopes were found for TP probably owing to changes in refractive index due to increase in TP concentration. The average recoveries of the added TP in the samples (TP-HCl tablets and injection liquid). A solutions spiked with standard TP-HCl were 99.9 and 99.7% with the RSD (n=11) of 0.66 and 0.67%, respectively. The average recovery of the added LD in the sample (injection) spiked with standard LD-HCl was 98.9% with the RSD (n=11) of 0.59%. The proposed method has been applied to the determination of TP-HCl and LD-HCl in commercial products available in Thailand. Comparative determination of TP by UV spectrophotometry and LD by colorimetry were also carried out. The results obtained by both methods were in good agreement of those obtained by the proposed method verified by using t-test. The proposed RP-HPLC method is simple, accurate, reproducible and suitable for routine analysis.

Univariate and simplex optimization for the flow-injection spectrophotometric determination of copper using nitroso-R salt as a complexing agent.

A simple colorimetric flow-injection system for the determination of Cu(II) based on a complexation reaction with nitroso-R salt is described. The chemical and FIA variables were established using the univariate and simplex methods. A small volume of Cu(II) was mixed with merged streams of nitroso-R salt and acetate buffer solutions. The absorbance of the complex was continuously monitored at 492 nm. The calibration curve over the concentration range 1.0-7.0 microg ml(-1) was obtained. The relative standard deviation for determining 4.0 microg ml(-1) Cu(II) was 0.47% (n = 11). The detection limit (3sigma) was 0.68 microg ml(-1) and the sample throughput was 150 h(-1). The validity of the method has been satisfactorily examined for the determination of Cu(II) in wastewater and copper ore samples. The accuracy was found to be high, because the student t-values were calculated to be less than the theoretical values when the results were compared with those obtained by FAAS.

Titrimetric determination of microgram amounts of bismuth after precipitation as Bi[Cr(SCN)(6)] followed by thiocyanate amplification.

Bismuth (10-100 mug) is precipitated as Bi[Cr(SCN)(6)]. After filtration, the precipitate is treated with bicarbonate solution, and the thiocyanate dissolved is oxidized by iodine in alkaline medium to sulphate. After acidification, the excess of iodine is extracted into chloroform, and the iodide in the aqueous solution is amplified by bromine oxidation and subsequent treatment with more iodide. The titrimetric procedure provides 228 iodine atoms for each original bismuth ion. Only Hg(2+)(2), Hg(2+) and AsO(3-)(4) interfere seriously.