Muhammad Idiris Saleh

In situ derivatization hollow fibre liquid-phase microextraction for the determination of biogenic amines in food samples.

Hollow fibre liquid-phase microextraction with in situ derivatization using dansyl chloride has been successfully developed for the high-performance liquid chromatography-ultraviolet (HPLC-UV) determination of the biogenic amines (tryptamine, putrescine, cadaverine, histamine, tyramine, spermidine) in food samples. Parameters affecting the performance of the in situ derivatization process such as type of extraction solvent, temperature, extraction time, stirring speed and salt addition were studied and optimized. Under the optimized conditions (extraction solvent, dihexyl ether; acceptor phase, 0.1M HCl; extraction time, 30 min; extraction temperature, 26 degrees C; without addition of salt), enrichment factors varying from 47 to 456 were achieved. Good linearity of the analytes was obtained over a concentration range of 0.1-5 microg mL(-1) (with correlation coefficients of 0.9901-0.9974). The limits of detection and quantification based on a signal-to-noise ratio of 3-10, ranged from 0.0075 to 0.030 microg mL(-1) and 0.03 to 0.10 microg mL(-1), respectively. The relative standard deviations based on the peak areas for six replicate analysis of water spiked with 0.5 microg mL(-1) of each biogenic amine were lower than 7.5%. The method was successfully applied to shrimp sauce and tomato ketchup samples, offering an interesting alternative to liquid-liquid extraction and solid phase extraction for the analysis of biogenic amines in food samples.

Solvent extraction of lanthanum(III) from acidic nitrate-acetato medium by Cyanex 272 in toluene

Abstract The extraction behavior of La(III) from acidic nitrate-acetato medium by bis(2,4,4-trimethylpentyl)phosphinic acid (Cyanex 272, H 2 A 2 ) in toluene either alone or in combination with trioctylphospine oxide (TOPO, B) has been investigated as a function of contact time, aqueous phase concentration of La 3+ , H + , NO 3 − and Ac − (acetate), Cyanex 272 and TOPO concentration in the organic phase and temperature. The distribution coefficient is found to decrease with increasing La 3+ concentration up to 7.34 mM La 3+ in the aqueous phase, after which it increases up to 9.79 mM La 3+ concentration and again decreases. The pH and log extractant concentration dependencies suggest that [La(Ac) 2 A·3HA] and [La(Ac)A 2 ·B] are extracted in the system without and with TOPO, respectively. The pH dependence of 1 indicates that one hydrogen ion is liberated in forming the complex for both the extraction system with TOPO and without TOPO. The distribution coefficient decreases with increasing acetate ion concentration at higher acetate ion concentrations with and without TOPO but is less dependent at low acetate concentrations. The synergistic effect of TOPO is found only at higher TOPO concentrations. These results suggest that the [La(Ac) 2 A·3HA] (o) and [La(Ac)A 2 ·B] (o) species are extracted in the system without and with TOPO, respectively. The temperature dependence data give the enthalpy of extraction, Δ H , of 60 kJ/mol. The equilibrium constant, K ex , is 10 −2.16 with a standard deviation of log K ex of 0.096 in the system without TOPO and 10 −2.58 with a standard deviation of log K ex of 0.21 for the extraction system with TOPO. The loading capacity of Cyanex 272 is found to be 15.97 g La(III)/100 g Cyanex 272. The phosphorus to lanthanum ratio of the solid complex obtained is 3.

Analysis of anions and cations in drinking water samples by Capillary Ion Analysis

Abstract The use of capillary ion electrophoresis (CIE, Waters’ tradename: Capillary Ion Analysis, CIA) for the analysis of four anions and four cations in drinking water samples available on the Malaysian market, such as natural mineral water, bottled drinking water and tap water, was investigated. In addition, zam-zam water (an underground water, much sought-after by Muslims and only available in Mekah, Saudi Arabia) was also analyzed. The anions analyzed were chloride, sulphate, nitrate and fluoride while the cations analyzed were potassium, calcium, sodium and magnesium. Results of this determination generally show a low content of anions and high content of calcium and magnesium in natural mineral water and non-detectable amounts of anions and cations in bottled drinking water. Out of the 15 mineral waters of different brands that were analyzed, four brands show anionic and cationic levels almost similar to that of tap water. With the exception of fluoride, an abnormally high level of both anions and cations were detected in all the zam-zam water samples analyzed, as compared to the other drinking waters.

Determination of underivatized long chain fatty acids using RP-HPLC with capacitively coupled contactless conductivity detection.

A reversed-phase high-performance liquid chromatographic method with capacitively coupled contactless conductivity detector (C(4)D) has been developed for the separation and the simultaneous determination of five underivatized long chain fatty acids (FAs), namely myristic, palmitic, stearic, oleic, and linoleic acids. An isocratic elution mode using methanol/1mM sodium acetate (78:22, v/v) as mobile phase with a flow rate of 0.6 mL min(-1) was used. The separation was effected by using a Hypersil ODS C(18) analytical column (250 mm x 4.6 mm x 5 microm) and was operated at 45 degrees C. Calibration curves of the five FAs were well correlated (r(2)>0.999) within the range of 5- 200 microg mL(-1) for stearic acid, and 2-200 microg mL(-1) for the other FAs. The proposed method was tested on four vegetable oils, i.e., pumpkin, soybean, rice bran and palm olein oils; good agreement was found with the standard gas chromatographic (GC) method. The proposed method offers distinct advantages over the official GC method, especially in terms of simplicity, faster separation times and sensitivity.

Determination of ortho-phenylphenol, diphenyl and diphenylamine in apples and oranges using HPLC with fluorescence detection

Abstract A reversed-phase high performance liquid chromatographic (RP-HPLC) method for the determination of the fungicides ortho-phenylphenol (OPP), diphenyl (DP) and diphenylamine (DPA) is developed. A mobile phase consisting of methanol:water (70:30) and fluorescence detection ( E x and E m set at 285 and 340 nm, respectively) was used. The fungicide residues were extracted with ethyl acetate, and concentrated prior to the HPLC analysis. The proposed HPLC method was clearly superior as compared to an earlier report that was based on a mobile phase of acetonitrile:methanol:water (47:13:40 v/v) for the determination of DP, OPP and thiabendazole, especially with respect to lower detection limits and faster analysis times. Limits of detection were 0.005, 0.100 and 0.02 ppm for OPP, DP and DPA, respectively. Recovery studies that were done by fortifying apples and oranges at 0.25 and 0.50 ppm levels respectively, were satisfactory (average percent recoveries of 108.8 and 84.0%, respectively for apples and oranges). Results on the determination of these fungicides in several apple and orange samples will also be discussed.

Clean-up, detection and determination of salbutamol in human urine and serum

Salbutamol ¿2-(tert-butylamino)-1-[4-hydroxy-3- (hydroxymethyl)phenyl]ethanol¿, also known as albuterol, is clinically the most widely used beta 2-adrenoceptor agonist in the treatment of bronchial asthma. During this study, we evaluated liquid-liquid extraction (LLE) and solid-phase extraction (SPE) in order to develop a reliable extraction method followed by analysis using liquid chromatography and gas chromatography. An assay is described which involves SPE as the clean-up method followed by gas chromatography-mass spectrometry to determine salbutamol levels in human serum after oral administration. The SPE method requires the use of a hyper-cross-linked styrene-divinylbenzene bonded phase (ENV+) without involving any sample pre-treatment to obtain 60-65% recoveries for salbutamol and terbutaline as the internal standard. Distilled water and 1% trifluoroacetic acid in methanol were found to be the most suitable washing solvent and eluting solvent, respectively. A detection limit of 2 ng mL-1 was achieved by derivatization with N-methyl-N-trimethylsilyltrifluoroacetamide to form trimethylsilyl (TMS)-salbutamol (m/z 369) and TMS-terbutaline (m/z 356). The relationship between the ratio of the peak area of salbutamol to that of the internal standard and concentration was linear for the range tested (2-200 ng mL-1) and the correlation of coefficient was 0.9999 with a y-intercept not significantly different from zero. The inter-day relative standard deviation (RSD) was < 10% for all three concentrations. The intra-day RSD was 14% for 2 ng mL-1. This assay was then successfully applied to human serum samples obtained from clinical trials after oral administration of salbutamol.

Kinetics of lanthanum(III) extraction from nitrate-acetato medium by Cyanex 272 in toluene using the single drop technique

Abstract The rate of forward extraction of La(III) from nitrate-acetato medium by bis-(2,4,4-trimethylpentyl) phosphinic acid (Cyanex 272, H2A2) dissolved in toluene has been measured by the single drop technique. The rate of mass transfer per unit area is found to be proportional to [La(III)], [H2A2](o) and [H+]−1 at the interface. The forward extraction rate constant, kF, has been measured to be 10−7.0 m/s. From the temperature dependence of rate measurement, the values of Ea, ΔS±, ΔH± and ΔG300± are calculated to be 71 kJ/mol, −155 J/mol K, 69 kJ/mol and 115 kJ/mol, respectively. The rate expression can be written as; F La =10 −7.0 [ La 3+ ][ H 2 A 2 ] ( o ) [ H + ] ( i ) −1 kmol / m 2 s Analysis of the rate expression suggests that the formation of [La(HA2)]2+at interface from La3+and HA2− is the rate-determining step for the forward extraction of La(III). Negative entropy of activation suggests that the above rate-determining step occurs via the SN2 mechanism.

Sequential hollow-fiber liquid phase microextraction for the determination of rosiglitazone and metformin hydrochloride (anti-diabetic drugs) in biological fluids

A new analytical method for the simultaneous determination of the antidiabetic drugs rosiglitazone (ROS) and metformin hydrochloride (MH) with marked differences in their affinity towards organic solvents (log P of 2.4 and -1.43, respectively) was developed. Prior to the HPLC separation, the drugs were subjected to a sequential hollow fiber liquid phase microextraction (HF-LPME) procedure. Two sequential HF-LPME approaches were considered, the preferred one involves the use of two vials containing solution mixtures for the extraction of ROS (vial 1) and MH (vial 2), respectively, but using the same fiber and acceptor phase. Important parameters that affect the extraction efficiency such as extracting solvent, donor phase conditions, HCl concentration, agitation, extraction time, addition of salt, etc. were studied. Under the optimum conditions, good enrichment factors (EF, 471 and 86.6 for ROS and MH, respectively) were achieved. Calibration curves were linear over the range 1-500 (r(2)=0.998) and 5-2500 ng mL(-1) (r(2)=0.999) for ROS and MH, respectively. The relative standard deviation values (RSD%) for six replicates were below 8.4%. Detection and quantitation limits based on S/N ratio of 3 and 10 were 0.12, 1.0 and 0.36, 3.0 ng mL(-1) for ROS and MH, respectively. The proposed method is simple, sensitive and opens up new opportunities for the microextraction of analytes with contrasting properties.

Adsorption isotherms of fatty acids on rice hull ash in a model system

The adsorption of lauric, myristic and stearic acids on rice hull ash (RHA) from isooctane as solvent was studied and conformed to a Langmuir isotherm. Monolayer coverage was determined to be 35.7±2.5, 43.5±2.2 and 36±5 mg/g, respectively. The free energy of adsorption, †G°, for the adsorption was determined to be-6.64,-6.23 and-6.49 kcal mol−1 for the adsorbates, respectively. The equilibrium parameter indicated that RHA is a good adsorbent for the three fatty acids examined.

Determination of Ofloxacin Enantiomers in Pharmaceutical Formulations by Capillary Electrophoresis

Abstract A capillary electrophoretic method for the separation of the enantiomers of ofloxacin using carboxymethyl‐β‐cyclodextrin (CM‐β‐CD) as chiral selector is described. The effect of the type of cyclodextrin and its concentration, buffer concentration, and its pH, as well as instrumental parameters, such as applied voltage and temperature were systematically studied. The highest resolution of ofloxacin enantiomers obtained was around 2.8. This was achieved using Tris‐citrate buffer (pH 4.5) that contained 3 mg mL−1 CM‐β‐CD and using UV detection (254 nm), applied voltage (12 kV), and capillary temperature of 25°C. Acceptable validation criteria for selectivity, precision, linearity, limit of detection, and quantitation were also included. Recoveries between 98.3–103.4% were obtained when the method was used to determine the enantiomers of ofloxacin that were spiked to placebos. The proposed method is fast, sensitive, inexpensive, and its usefulness was demonstrated for the analysis of five pharmaceutical preparations, two of which just contained the S‐ofloxacin while the other three contained both isomers as racemic mixtures.