Mohammad Yaqoob

Flow‐injection determination of cysteine in pharmaceuticals based on luminol–persulphate chemiluminescence detection

A flow injection (FI) method is reported for the determination of l-cysteine, based on its enhancement on chemiluminescence (CL) emission of luminol oxidized by sodium persulphate in alkaline solution. The calibration graph was linear over the range 1.0 x 10(-9)-5.0 x 10(-7) mol/L (r(2) = 0.9992), with relative standard deviations (RSDs) in the range 1.1-2.3% (n = 4). The limit of detection (3 sigma blank) was 5.0 x 10(-10) mol/L with a sample throughput of 120/h. The method was applied to pharmaceuticals and the results obtained were in reasonable agreement with the amount labelled. The proposed method was also applied to cysteine in synthetic amino acid mixtures. Calibration graphs of N-acetylcysteine and glutathione over the range 1.0-50 x 10(-8) and 0.5-7.5 x 10(-7) mol/L were also established (r(2) = 0.998 and 0.9986) with RSDs in the range 1.0-2.0% (n = 4), and the limits of detection (3 sigma blank) were 5.0 x 10(-9) and 1.0 x 10(-8) mol/L, respectively.

Determination of thiram in natural waters using flow-injection with cerium(IV)-quinine chemiluminescence system.

A simple and rapid flow-injection chemiluminescence method has been developed for the determination of dithiocarbamate fungicide thiram based on the chemiluminescence reaction of thiram with ceric sulfate and quinine in aqueous sulfuric acid. The present method allowed the determination of thiram in the concentration range of 7.5-2500 ng/mL and the detection limit (signal-to-noise ratio = 3) was 7.5 ng/mL with sample throughput of 120/h. The relative standard deviation was 2.5% for 10 replicate analyses of 500 ng/mL thiram. The effects of foreign species including various anions and cations present in water at environmentally relevant concentrations and some pesticides were also investigated. The proposed method was applied to determine thiram in spiked natural waters using octadecyl bonded phase silica (C(18)) cartridges for solid-phase extraction. The recoveries were in the range 99 +/- 1 to 104 +/- 1%.

Determination of nitrate and nitrite in freshwaters using flow-injection with luminol chemiluminescence detection

A simple and sensitive flow-injection (FI) method for the determination of nitrate and nitrite in natural waters, based on luminol chemiluminescence (CL) detection, is reported. Nitrate was reduced online to nitrite via a copperized cadmium (Cu-Cd) column and then reacted with acidic hydrogen peroxide to form peroxynitrous acid. CL emission was observed from the oxidation of luminol in an alkaline medium in the presence of the peroxynitrite anion. The limits of detection (S:N = 3) were 0.02 and 0.01 µg N/L, with sample throughputs of 40 and 90 /h for nitrate and nitrite, respectively. Calibration graphs were linear over the range 0.02-50 and 0.01-50 µg N/L [R2  = 0.9984 (n = 8) and R2  = 0.9965 (n = 7)] for nitrate and nitrite, respectively, with relative standard deviations (RSDs; n = 3) in the range 1.8-4.6%. The key chemical and physical variables (reagent concentrations, buffer pH, flow rates, sample volume, Cu-Cd reductor column length) were optimized and potential interferences investigated. The effect of cations [Ca(II), Mg(II), Co(II), Fe(II) and Cu(II)] was masked online with EDTA. Common anions (PO4(3-) , SO4(2-) and HCO3-) did not interfere at their maximum admissible concentrations in freshwaters. The effect of salinity on the luminol CL reaction with and without nitrate and nitrite (2 and 0.5 µg N/L, respectively) was also investigated. The method was successfully applied to freshwaters and the results obtained were in good agreement with those obtained by an automated segmented flow analyser reference method.

Flow injection determination of thyroxine in pharmaceutical preparations using tris(2,2'-bipyridyl)ruthenium(III)-NADH chemiluminescence detection.

A flow injection (FI) method is reported for the determination of thyroxine based on its enhancement of chemiluminescence (CL) from the Ru(bpy)(3)(3+)-NADH system. The calibration graph was linear over the range 2.0-10x10(-8)mol L(-1) (r(2)=0.9989) with relative standard deviations (R.S.D.) in the range 2.0-4.5% (n=4). The limit of detection (3sigma blank) was 1.0x10(-9)mol L(-1) with sample throughput of 120h(-1). The effect of some organic compounds, anions and cations were studied for l-thyroxine determination. The method was applied to pharmaceutical preparations and the results obtained were in reasonable agreement with the amount labeled. The method was statistically compared with the results obtained by RIA; no significant disagreement at 95% confidence limit was observed. A calibration graph of NADH over the range 1.3x10(-8)-1.3x10(-6)mol L(-1) was also established (r(2)=0.9992) with R.S.D. in the range1.0-3.5% (n=4). The limit of detection (3sigma) was 1.0x10(-10)mol L(-1) NADH.

Determination of total iron in fresh waters using flow injection with potassium permanganate chemiluminescence detection

A flow injection method is described for the determination of iron in fresh water based on potassium permanganate chemiluminescence detection via oxidation of formaldehyde in aqueous hydrochloric acid. Total iron concentrations are determined after reducing Fe(III) to Fe(II) using hydroxylamine hydrochloride. The detection limit (three standard deviations of blank) is 1.0 nM, with a sample throughput of 120 h−1. The calibration graph was linear over the range (2–10) × 10−7 M (r2 = 0.9985) with relative standard deviations (n = 5) in the range 1.0–2.3%. The effect of interfering cations (Ca(II), Mg(II), Zn(II), Ni(II), Co(II), Fe(III), Mn(II), Pb(II), and Cu(II)) and common anions (Cl−, SO42−, PO43−, NO3−, NO2−, I−, F−, and SO32−) was studied at their maximum admissible concentrations in fresh water. The method was applied to fresh-water samples from the Quetta Valley, and the results obtained (0.04 ± 0.001–0.11 ± 0.01 mg/L Fe(II)) were in reasonable agreement with those obtained using the spectrophotometric reference method (0.05 ± 0.01–0.12 ± 0.02 mg/L Fe(II)).

Determination of carbaryl by flow injection with luminol chemiluminescence inhibition detection

A flow-injection procedure is described for the determination of carbaryl based on its inhibition effect on luminol-cobalt(II) chemiluminescence reaction in alkaline medium in the presence of hydrogen peroxide. The calibration data over the range 5.0 × 10−7 to 20 × 10−6 M give a correlation coefficient (r 2) of 0.9972 with relative standard deviations (RSD; n = 4) in the range of 1.0–2.1% with a limit of detection (3 × blank noise) of 2.37 × 10−7 M for carbaryl. The sample throughput was 120 h−1. The effects of some carbamates, anions, and cations were studied on luminol CL system for carbaryl determination. The proposed method has been applied to determine carbaryl in natural waters.

The effect of mycophenolate mofetil and azathioprine dose on renal allograft outcome in the United kingdom.

Background. Mycophenolate mofetil (MMF) therapy compared with azathioprine has not led to improved long-term renal allograft outcomes perhaps as MMF dose is limited by tolerability and dose reduction is associated with inferior graft outcome. The consequences, however, of dose reduction of mycophenolate mofetil relative to azathioprine have not been reported. Method. We studied dosing patterns of MMF and azathioprine in the first year after transplantation and their impact on graft outcome after renal transplantation between 1999 and 2002 in the United Kingdom. Results. Sixty-two percent of patients were found to be taking less than 2 g of MMF and 45% were taking less than 100 mg of azathioprine at 1 year after transplantation. Graft outcome was comparable in patients receiving 2 g or more of MMF (n=209), 1 to 2 g of MMF (n=267), and 100 mg or more of azathioprine (n=504) at 1 year after transplantation. Less than 1 g of MMF (n=71) and less than 100 mg of azathioprine (n=413) was associated with a 3-fold and 2-fold increased 4.5 year risk-adjusted hazard ratio (HR) of graft failure, respectively, with reduced graft function. Finally, less than 1 g of MMF was not superior to less than 100 mg of azathioprine. Conclusion. Azathioprine levels are not routinely measured and long-term results of concentration controlled MMF studies are awaited. Currently, dose is a useful measure of drug exposure. This study suggests that less than 1 g of MMF and less than 100 mg of azathioprine are associated with inferior graft outcome.

Determination of Thyroxine Using Tris(2,2′‐Bipyridyl)Ruthenium(III)‐NADH Enhanced Electrochemiluminescence Detection

Abstract A low cost, single channel portable flow injection electrogenerated chemiluminescence (ECL) system is reported for the determination of l‐thyroxine based on its enhancement effect on Ru(bpy)3 3+‐NADH‐ECL intensity. The calibration graph was linear over the range 5.0×10−8–1.0×10−6 mol l−1 (R 2=0.9981) with relative standard deviations (RSD, n=4) in the range 0.11–1.5%. The limit of detection (3σ blank) was 5.0×10−8 mol l−1 with a sample throughput of 60 h−1. The method was applied to pharmaceutical preparations and the results obtained (51.2±1.23–52±1.14 µg l‐thyroxine per tablet) were in good agreement with the amount labeled (50 µg l‐thyroxine per tablet, sodium salt) and RIA method (50.2±1.25 µg l‐thyroxine per tablet) as the reference method. NADH calibration graph (in the range 5.0×10−8–1.8×10−6 mol l−1, R 2=0.9989) was also established with RSD (n=4) in the range 0.25–2.1% with a limit of detection (3σ blank) 5.0×10−8 mol l−1.

Chemiluminescent Determination of Cholesterol by Flow Injection Analysis with Immobilized Cholesterol Oxidase.

Abstract A rapid and sensitive chemiluminescent assay for the determination of cholesterol in blood serum is described. The procedure is based on the measurement of chemiluminescence emission resulting from the oxidation of Luminol with hydrogen peroxide in the presence of catalyst, cobalt(II). Hydrogen peroxide was produced by passing cholesterol samples through an immobilized cholesterol oxidase column. The limit of detection was 0.01 mg/dl and the relative standard deviation over the range of 10–60 mg/dl was less than 5%. Results agreed well with those obtained with a spectrophotometric method for the determination of cholesterol in serum.

Determination of arsenic(V) in freshwaters by flow injection with luminol chemiluminescence detection

A simple and rapid flow injection (FI) method is reported for the determination of arsenic(V) based on luminol chemiluminescence (CL) detection. The molybdoarsenic heteropoly acid formed by arsenic and ammonium molybdate in the presence of ammonium vanadate in acidic conditions generated chemiluminescence emission via the oxidation of luminol. The limit of detection was 0.15 μg L−1, with a sample throughput 120 h−1. A linear calibration graph was obtained over the range 0.15 to 7.5 μg L−1 (r 2 = 0.9989; n = 9) with relative standard deviation (n = 4) in the range 0.8 to 2.5%. Interfering cations were removed by passing the sample through an in-line iminodiacetate chelating column and phosphate (at 0.6 mg L−1) was removed off-line by magnesium-induced coprecipitation (MAGIC) method. The method was applied to freshwater samples and the results obtained were in reasonable agreement with the results obtained using HGAAS as the reference method.