Boonsom Liawruangrath

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.

Design and fabrication of a low-cost flow-through cell for the determination of acetaminophen in pharmaceutical formulations by flow injection cyclic voltammetry

A low-cost electrochemical flow-through cell is designed and fabricated to use in conjunction with a flow injection (FI) system. This detector cell used a centrosymmetric radial flow thin-layer geometry with a stainless steel auxiliary electrode and a reference electrode (Ag/AgCl) without a salt bridge. The 5H pencil lead electrode used as a working electrode in the home-made cell is an extremely inexpensive electrode which performs as well as the expensive commercial glassy carbon electrode. Optimum conditions for determining acetaminophen using the proposed FI manifold was investigated. Appropriate volume of sample and/or standard solution containing acetaminophen in pH 2.2 Mcllvaine buffer solution was injected into the proposed FI system and mixed with the flowing stream of supporting electrolyte (pH 2.2 Mcllvaine buffer solution) at an optimum flow rate of 1 mlmin(-1). The cyclic voltammograms were recorded over the potential range from -0.5 to +2.0 V with a scan rate of 40 mVs(-1). Linear calibration curve over the range of 0.1-5 mM acetaminophen was established with the regression equation Y=3.68X+1.0157 (r(2)=0.9964). The recommended method has been applied to the determination of acetaminophen in 8 commercial pharmaceutical preparations. The percentage recoveries of the spiked acetaminophen in four tablet samples were ranging from 103 to 112 with the relative standard deviation in the range of 0.1-1.3%.

Sequential injection spectrophotometric determination of zinc(II) in pharmaceuticals based on zinc(II)-PAN in non-ionic surfactant medium

A sequential injection analysis (SIA) spectrophotometric method for the determination of trace amounts of zinc(II) with 1-(2-pyridylazo)-2-naphthol (PAN) is described. The method is based on the measurement of absorbance of the zinc(II)-PAN chelate solubilized with a non-ionic surfactant, Triton X-100, no extraction procedure is required in the proposed method, yielding a pink colored complex at pH 9.5 with absorption maximum at 553nm. The SIA parameters that affect the signal response have been optimized in order to get the better sensitivity and minimum reagent consumption. A linear relationship between the relative peak height and concentration was obtained in the concentration range of 0.1-1.0microg ml(-1). The limit of detection (LOD, defined as 3sigma) and limit of quantification (LOQ, defined as 10sigma) were 0.02 and 0.06microg ml(-1), respectively. The sample throughput about 40 samples/h was obtained. The repeatability were 1.32 and 1.24% (n=10) for 0.1 and 0.5microg ml(-1), respectively. The proposed method was successfully applied to the assay of zinc(II) in three samples of multivitamin tablets. The results were found to be in good agreement with those obtained by flame atomic absorption spectrophotometric method and with the claimed values by the manufactures. The t-test showed no significant difference at 95% confidence level.

Simultaneous micellar LC determination of lidocaine and tolperisone.

A micellar liquid chromatography (MLC) procedure was developed for the simultaneous separation and determination of lidocaine hydrochloride (LD HCl) and tolperisone hydrochloride (TP HCl) using a short-column C18 (12.5 mm x 4.6 mm, 5 microm), sodium dodecyl sulfate (SDS) with a small amount of isopropanol, and diode array detector. The optimum conditions for the simultaneous determination of both drugs were 0.075 mol l(-1) SDS-7.5% (v/v) isopropanol with a flow rate of 0.7 ml min(-1) and detection at 210 nm. The LOD (2S/N) of LD HCl was 0.73 ng 20 microl(-1), whereas that of TP HCl was 1.43 ng 20 microl(-1). The calibration curves for LD HCl and TP HCl were linear over the ranges 0.125-500 microg ml(-1) (r(2)=0.9999) and 1.00-500 microg ml(-1) (r(2)=0.9997), respectively. The %recoveries of both drugs were in the range 98-103% and the %RSD values were less than 2. The proposed method has been successfully applied to the simultaneous determination of TP HCl and LD HCl in various pharmaceutical preparations.

Concise synthesis of (-)-steviamine and analogues and their glycosidase inhibitory activities

A concise synthesis of (-)-steviamine is reported along with the synthesis of its analogues 10-nor-steviamine, 10-nor-ent-steviamine and 5-epi-ent-steviamine. These compounds were tested against twelve glycosidases (at 143 μg mL(-1) concentrations) and were found to have in general poor inhibitory activity against most enzymes. The 10-nor analogues however, showed 50-54% inhibition of α-L-rhamnosidase from Penicillium decumbens while one of these, 10-nor-steviamine, showed 51% inhibition of N-acetyl-β-D-glucosaminidase (from Jack bean) at the same concentration (760 μM).

Micellar liquid chromatographic determination of arbutin and hydroquinone in medicinal plant extracts and commercial cosmetic products.

A simple micellar liquid chromatographic (MLC) procedure for simultaneous determination of arbutin and hydroquinone in medicinal plant extracts and commercial cosmetic products was proposed. This method was developed and validated. The chromatographic conditions were also optimized. All analyses were performed at room temperature in an isocratic mode, using a mixture of 1% (v/v) acetonitrile and 0.006 mol L−1 Brij 35 (pH 6.0) as a mobile phase. The flow rate was set at 1.0 mL min−1. The analytical column was a 150 × 3.9 mm Nova‐Pak C‐18 column. The effluent from the analytical column was monitored by UV detection at 280 nm. Under the optimum conditions, arbutin and hydroquinone could be determined within a concentration range of 2–50 μg mL−1 of arbutin, and hydroquinone was obtained with the regression equations; y = 0.045x + 0.042 (r2 = 0.9923) and y = 0.091x + 0.050 (r2 = 0.9930) respectively. The limits of detection were found to be 0.51 μg mL−1 and 0.37 μg mL−1 for arbutin and hydroquinone respectively. The proposed MLC method was applied for the determination of arbutin and hydroquinone contents in medicinal plant extracts and commercial cosmetic products. This proposed MLC method is thus suitable for routine analysis of arbutin and hydroquinone in the pharmaceutical formulations, cosmetic products and raw medicinal plant extracts.

Sequential injection spectrophotometric determination of tetracycline antibiotics in pharmaceutical preparations and their residues in honey and milk samples using yttrium (III) and cationic surfactant.

A sequential injection analysis (SIA) spectrophotometric method for determining tetracycline (TC), chlortetracycline (CTC) and oxytetracycline (OTC) in different sample matrices were described. The method was based on the reaction between tetracyclines and yttrium (III) in weak basic micellar medium, yielding the light yellow complexes, which were monitored at 390, 392 and 395 nm, respectively. A cationic surfactant, cetyltrimethylammonium bromide (CTAB) was used to obtain the micellar system. The linear ranges of calibration graphs were between 1.0 × 10(-5) and 4 × 10(-4) mol L(-1), respectively. The molar absorptivities were 5.24 × 10(5), 4.98 × 10(4) and 4.78 × 10(4) L mol(-1)cm(-1). The detection limits (3σ) were between 4.9 × 10(-6) and 7.8 × 10(-6) mol L(-1) whereas the limit of quantitations (10σ) were between 1.63 × 10(-5) and 2.60 × 10(-5) mol L(-1) the interday and intraday precisions within a weak revealed as the relative standard deviations (R.S.D., n=11) were less than 4%. The method was rapid with a sampling rate of over 60 samples h(-1) for the three drugs. The proposed method has been satisfactorily applied for the determination of tetracycline and its derivatives in pharmaceutical preparations together with their residues in milk and honey samples collected in Chiang Mai Province. The accuracy was found to be high as the Students t-values were found to be less than the theoretical ones. The results were compared favorably with those obtained by the conventional spectrophotometric method.

Determination of gallic acid with rhodanine by reverse flow injection analysis using simplex optimization

A reversed flow injection (rFI) system was designed and constructed for gallic acid determination. Gallic acid was determined based on the formation of chromogen between gallic acid and rhodanine, resulting in a colored product with a λmax at 520 nm. The optimum conditions for determining gallic acid were also investigated. Optimizations of the experimental conditions were carried out based on the so-call univariate method. The conditions obtained were 0.6% (w/v) rhodanine, 70% (v/v) ethanol, 0.9 mol L(-1) NaOH, 2.0 mL min(-1) flow rate, 75 μL injection loop and 600 cm mixing tubing length, respectively. Comparative optimizations of the experimental conditions were also carried out by multivariate or simplex optimization method. The conditions obtained were 1.2% (w/v) rhodanine, 70% (v/v) ethanol, 1.2 mol L(-1) NaOH, flow rate 2.5 mL min(-1), 75 μL injection loop and 600 cm mixing tubing length, respectively. It was found that the optimum conditions obtained by the former optimization method were mostly similar to those obtained by the latter method. The linear relationship between peak height and the concentration of gallic acid was obtained over the range of 0.1-35.0 mg L(-1) with the detection limit 0.081 mg L(-1). The relative standard deviations were found to be in the ranges 0.46-1.96% for 1, 10, 30 mg L(-1) of gallic acid (n=11). The method has the advantages of simplicity extremely high selectivity and high precision. The proposed method was successfully applied to the determination of gallic acid in longan samples without interferent effects from other common phenolic compounds that might be present in the longan samples collected in northern Thailand.

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 μL 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 μg mL−1 arbutin was established. It is expressed by the regression equation y = 0.2188 ± 0.0036x + 0.1019 ± 0.0366 (r2 = 0.9990, n = 5). The detection limit (3σ) and the limit of quantitation (10σ) were 0.04 μg mL−1 and 0.13 μg 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.

Sequential injection analysis with lab-at-valve (SI-LAV) for the determination of solasodine in Solanum species

The development of sequential injection analysis with lab-at-valve (LAV) semi-automated system on-line liquid-liquid extraction is demonstrated for spectrophotometric determination of solasodine in various Solanum species fruits. The main proposed is semi-automated extractive determination of solasodine using methyl orange as colorimetric reagent. After optimization of the system, sample, reagent and organic solvent were sequentially aspirated into an extraction coil connected to the center of a selection valve, where extraction took place by flow reversal. The aqueous and organic phases were separated in a lab-at-valve unit attracted to one of the ports of the selection valve. The absorption of ion-pair solasodine-methyl orange complex in the organic phase was measured spectrophotometrically at 420 nm. The method performances, including reproducibility, linearity, sensitivity and accuracy, were also evaluated. The proposed method is simple, reproducible and accurate. It was successfully applied to the determination of solasodine in Solanum aculeatissimum Jacq., Solanum violaceum Ortega., Solanum melongena Linn. and Solanum indicum Linn. fruits in Solanaceae family. Results obtained were in good agreement with those obtained by batch wise spectrophotometric method. It is also suitable and useful for determination of solasodine in other medicinal plants.