Analysis of some selected catechins and caffeine in green tea by high performance liquid chromatography.

Green tea seems to have a positive impact on health due to the catechins-found as flavanols. Thus, the present study was aimed to develop a low cost reversed phase high performance liquid chromatographic (HPLC) method for simultaneous determination of flavanol contents, namely catechin (C), epicatechin (EC), epigallocatechin (EGC), epicatechin 3-gallate (ECG) and epigallocatechin 3-gallate (EGCG) and caffeine in 29 commercial green tea samples available in a Saudi Arabian local market. A C-18 reversed-phase column, acetonitrile-trifluoroacetic acid as a mobile phase, coupled with UV detector at 205 nm, was successfully used for precise analysis of the tested analytes in boiled water of digested tea leaves. The average values of N (No. of theoretical plates), HETP (height equivalent of theoretical plates) and R(s) (separation factor) (at 10 µg ml(-1) of the catechins EC, EGC, EGCG and ECG) were 2.6×10(3)±1.2×10(3), 1.7×10(-3)±4.7×10(-4) cm and 1.7±5.53×10(-2), respectively. The developed HPLC method demonstrated excellent performance, with low limits of detection (LOD) and quantification (LOQ) of the tested catechins of 0.004-0.05 µg ml(-1) and 0.01-0.17 µg ml(-1), respectively, and recovery percentages of 96-101%. The influence of infusion time (5-30 min) and temperature on the content of the flavanols was investigated by HPLC. After a 5 min infusion of the tea leaves, the average concentrations of caffeine, catechin, EC, EGC, ECG and EGCG were found to be in the ranges 0.086-2.23, 0.113-2.94, 0.58-10.22, 0.19-24.9, 0.22-13.9 and 1.01-43.3 mg g(-1), respectively. The contents of caffeine and catechins followed the sequence: EGCG>EGC>ECG>EC>C>caffeine. The method was applied satisfactorily for the analysis of (+)-catechin, even at trace and ultra trace concentrations of catechins. The method was rapid, accurate, reproducible and ideal for routine analysis.

Development of an analytical method for trace gold in aqueous solution using polyurethane foam sorbents: kinetic and thermodynamic characteristic of gold(III) sorption.

The kinetic parameters of gold(III) sorption by unloaded polyurethane foams (PUFs) and PUFs impregnated with some onium cations e.g. tetramethylammonium perchlorate (TMA(+)ClO(4)(-)), tetrabutylammonium iodide (TBA(+)I(-)), and tetraheptylammonium bromide (THA(+)Br(-)), have been determined. The retention steps were found to be fast, reached equilibrium in a few minutes and followed a first-order rate equation with an overall rate constant, k, of 0.0076 and 0.007 min(-1), respectively. The thermodynamic characteristics of gold(III) retention by the unloaded PUFs and THA(+)Br(-) immobilized PUFs have been critically studied. The negative values of DeltaH and DeltaS are interpreted as the exothermic and spontaneous reaction of gold(III) sorption onto unloaded PUFs and foams impregnated with THA(+)Br(-). The cellular structure of the PUFs sorbent offer unique advantages over conventional bulk-type sorbents in the rapid, versatile effective separation and/or preconcentration of gold ions.

Extractive liquid-liquid spectrophotometric procedure for the determination of thiocyanate ions employing the ion pair reagent amiloride monohydrochloride.

An accurate, inexpensive and less laborious liquid-liquid extractive spectrophotometric procedure for the determination of thiocyanate ions in aqueous media has been developed. The method has been based upon the formation of a yellow colored complex ion associate of the ion-pairing reagent 1-(3, 5-diamino-6-chloropyrazinecarboxyl) guanidine hydrochloride monohydrate, namely amiloride hydrochloride, DPG+.Cl- and the thiocyanate ions in aqueous media containing HNO3 (0.5 mol L(-1)) and subsequent extraction with 4-methyl-2-pentanone. The absorption electronic spectrum of the ion associate showed one well-defined peak at lambda(max) 366 nm. The stoichiometric mole ratio of DPG+.Cl- to the thiocyanate ions is 1:1. The effective molar absorptivity (epsilon) of the ion associate at lambda(max) 366 nm is 1.1+/-0.1x10(4) L mol(-1) cm(-1). The extraction constants (K(d), K(ex), and beta) enabled a simple and convenient use of the developed binary ion associate for the extractive spectrophotometric determination of traces of thiocyanate ions in the aqueous media. Beer's law and Ringbom's plots are obeyed in the concentration range 0.05-10 and 0.1-7 microg mL(-1) of the thiocyanate ions, respectively with a relative standard deviation of +/-2.3%. The calculated lower limits of detection (LOD) and quantitation (LOQ) of the developed procedure for the thiocyanate ions were found equal to 0.02 and 0.066 microg mL(-1), respectively. The developed method has been applied for the determination of trace amounts of thiocyanate ions in tap-, waste- and natural water samples and compared successfully with the reported methods at the 95% confidence level. The proposed method was also applied successfully for the determination of thiocyanate ions in saliva samples.

Analysis of domperidone in pharmaceutical formulations and wastewater by differential pulse voltammetry at a glassy-carbon electrode.

The redox characteristics of the drug domperidone at a glassy-carbon electrode (GCE) in aqueous media were critically investigated by differential-pulse voltammetry (DPV) and cyclic voltammetry (CV). In Britton-Robinson (BR) buffer of pH 2.6-10.3, an irreversible and diffusion-controlled oxidation wave was developed. The dependence of the CV response of the developed anodic peak on the sweep rate (nu) and on depolizer concentration was typical of an electrode-coupled chemical reaction mechanism (EC) in which an irreversible first-order reaction is interposed between the charges. The values of the electron-transfer coefficient (alpha) involved in the rate-determining step calculated from the linear plots of E (p,a) against ln (nu) in the pH range investigated were in the range 0.64 +/- 0.05 confirming the irreversible nature of the oxidation peak. In BR buffer of pH 7.6-8.4, a well defined oxidation wave was developed and the plot of peak current height of the DPV against domperidone concentration at this peak potential was linear in the range 5.20 x 10(-6) to 2.40 x 10(-5) mol L(-1) with lower limits of detection (LOD) and quantitation (LOQ) of 6.1 x 10(-7) and 9.1 x 10(-7) mol L(-1), respectively. A relative standard deviation of 2.39% (n = 5) was obtained for 8.5 x 10(-6) mol L(-1) of the drug. These DPV procedures were successfully used for analysis of domperidone in the pure form (98.2 +/- 3.1%), dosage form (98.35 +/- 2.9%), and in tap (97.0 +/- 3.6%) and wastewater (95.0 +/- 2.9%) samples. The method was validated by comparison with standard titrimetric and HPLC methods. Acceptable error of less than 3.3% was also achieved.

Chemical speciation and recovery of gold(I, III) from wastewater and silver by liquid-liquid extraction with the ion-pair reagent amiloride mono hydrochloride and AAS determination.

A novel and low cost liquid-liquid extraction procedure for the separation of gold(III) at trace level from aqueous medium of pH 5-9 has been developed. The method has been based upon the formation of a yellow colored ternary complex ion associate of tetrachloro gold(III) complex anion, AuCl(4)(-) with the ion-pair reagent 1-(3,5-diamino-6-chloropyrazinecarboxyl) guanidine hydrochloride monohydrate, namely amiloride, DPG(+).Cl(-). The effect of various parameters, e.g. pH, organic solvent, shaking time, etc. on the preconcentration of gold(III) from the aqueous media by the DPG(+).Cl(-) reagent has been investigated. The colored gold species was quantitatively extracted into 4-methyl pentan-2-one. The chemical composition of the ion associate of DPG(+).Cl(-) with AuCl(4)(-) in the organic solvent has been determined by the Job's method. The molar absorptivity (2.19x10(4)Lmol(-1)cm(-1)) of the associate DPG(+).AuCl(4)(-) at 362nm enabled a convenient application of the developed extraction procedure for the separation and AAS determination of traces of aurate ions. Mono-valence gold ions after oxidation to gold(III) with bromine water in HCl (1.0molL(-1)) media have been also extracted quantitatively from the aqueous media by the developed procedure. The chemical speciation of mono- and/or tri-valence gold species spiked to fresh and industrial wastewater samples has been achieved. The method has been also applied successfully from the separation of gold(I) and gold(III) species from metallic ions and silver. The developed method has also the advantage of freedom from most diverse ions.