Chutima Phechkrajang

Fluorescent labelling of ciprofloxacin and norfloxacin and its application for residues analysis in surface water.

Sensitivity enhancement for residue analysis of ciprofloxacin and norfloxacin in surface water was performed by liquid chromatography with fluorescent detection (LC-FD). Labelling of both drugs were studied with fluorescent probes (e.g. Nile blue perchlorate (NBP) and 4- (N,N-Dimethylaminosulfonyl)-7-(N-chloroformylmethyl-N-methylamino)-2,1,3-benzoxadiazole (DBD-COCl). Factors affecting the derivatization (e.g. stoichiometric ratios, reaction time and base catalysts) were optimized. The derivatization was achieved in 15min using a stoichiometric ratio between the substrate and DBD-COCl of 1:3, whereas NBP gave unsatisfactory results. Separation of the derivatives by LC was achieved (resolution (RS) > 1.8) on a C8 column using a mobile phase consisting of 50mM formic acid and acetonitrile (ACN) (68:32% v/v) in 20min. The method was linear (r(2) > 0.99) in a range of 200-2,000µg/L, precise (%RSD < 9.17) and accurate (%recovery of 102.5-122.2%) for the determination of the derivatives. The uses of fluoroquinolone molecularly imprinted polymer in conjunction with hydrophilic-lipophilic balance sorbents demonstrated an efficient procedure for sample pre-concentration and clean-up for water sample resulting in the improved percent recovery. Applications of the proposed method was shown in surface water samples in Thailand.

Forced Degradation Studies of Candesartan Cilexetil and Hydrochlorothiazide Using a Validated Stability-Indicating HPLC-UV Method

Forced degradation studies of candesartan cilexetil (CCX) and hydrochlorothiazide (HCTZ) were performed by using stressed drugs under acid, alkaline, and neutral hydrolysis; oxidation; photolysis; and thermal degradation conditions. A simple and specific method of high-performance liquid chromatography with UV detection was developed for simultaneous determination of CCX, HCTZ, and their degradation products. Optimum conditions were achieved with a running buffer mixture of acetonitrile and 10 mM phosphate buffer (pH 7.0; 32 : 68, v/v) at a flow rate of 1.0 mL/min using a Zorbax stable-bond cyano (SB CN) column (4.6 × 150 mm, 5 μm), 25°C column temperature, and 254 nm UV detection wavelength. This method was validated for linearity, range, accuracy, precision, and specificity according to International Conference on Harmonization (ICH) guidelines. All figures of merit for method validation are acceptable. The method proved to be stability-indicating because it also analyzed drugs in the presence of their degradation products with a resolution of the critical peak pair at least 1.5 and peak purity values greater than 990. CCX was stable under neutral hydrolysis, photolysis, and thermal degradation conditions but degraded under acid and alkaline hydrolysis and oxidation conditions. HCTZ was stable under oxidation, photolysis, and thermal degradation conditions but degraded under neutral, acid, and alkaline hydrolysis conditions.

Chemometrics-assisted cross injection analysis for simultaneous determination of phosphate and silicate

ABSTRACT This work presents a novel method for simultaneous spectrophotometric determination of phosphate and silicate by using a cross injection analysis (CIA) coupled with the use of partial least squares (PLS) for data evaluation. The detection principle is based on the well-known ‘molybdenum blue’ method. The molybdate ions in the presence of stannous chloride in acidic medium give phosphomolybdenum blue and silicomolybdenum blue as products. In this work, all the liquids, including sample and reagents were simultaneously introduced into a CIA platform by using two peristaltic pumps for controlling the x-channel and y-channel flow which was automatically manipulated by using in-house control board. Crossflow provides sufficient mixing inside the platform prior detection of the absorption spectra of blue complexes in the wavelength of 400–900 nm. Since spectra of the blue colour product of phosphate and silicate are resemblant, these two analytes therefore reciprocally interfere with one another. This results in difficulty in simultaneous analysis of phosphate and silicate. In this work, PLS was utilised as assistor of CIA system for simultaneous analysis of phosphate and silicate using molybdenum blue reaction without using any modification of reagents and addition of selective masking agent. The calibration ranges are 0.1–6 mgP L−1 and 5–100 mgSi L−1 for phosphate and silicate, respectively. By using CIA coupled with PLS for data evaluation, the analysis of two analytes was achieved within 1.5 min with only single injection. The developed system was applied to natural water samples and the system was validated with the conventional methods. By statistical paired t-test, there was no evidence of significant difference at 95% confidence level (tstat = 2.28, tcritical = 2.31 and tstat = 0.62, tcritical = 2.31 for phosphate and silicate, respectively). This implied that the chemometrics-assisted CIA system was successfully developed for simultaneous spectrophotometric determination of phosphate and silicate.

Validated visible spectrophotometry for quantitative analysis of pirenoxine in the presence of paraben preservatives in eye drop preparations

The aim of this work were to develop and validate a visible spectrophotometry for quantitative analysis of pirenoxine in the presence of methylparaben and propylparaben. The proposed method was also applied for real samples of eye drop preparations. The developed method was validated in terms of linearity, range, accuracy, precision, limits of detection (LOD) and limits of quantification (LOQ) by using standard mixture solutions. Method validation was performed according to the United State Pharmacopeia (USP 36) and International Conference on Harmonization Q2(R1) guidelines for the analytical performance parameters. The results of validation illustrated good linearity with the squares of correlation coefficient (r2) greater than 0.99 in the concentration ranges of 2.0-10.0 μg/mL. The method was accurate with average recovery was 100.6%. The relative standard deviation (RSD) of intra-day and inter-day precission were less than 2.00%. LOD and LOQ were found to be 0.40μg/mL and 1.2μg/mL, respectively. The visible spectrophotometric method was found to be precise, accurate, rapid, simple, and inexpensive. The developed and validated method was suitable for quantitation of pirenoxine in real samples of eye drop preparations and could be transferred to quality control laboratories.