Ala'ddin M. Almuaibed

Flow-injection study of inhibition and reactivation of immobilized acetylcholinesterase : determination of the pesticides paraoxon and carbamoylcholine

Abstract The inhibitory effects of paraxon and carbamoylcholine as examples of organophosphorus and carbamate pesticides, respectively, on the activity of acetylcholinesterase (AChE) immobilized on controlled pore glass have been investigated, using a dual injection flow system and spectrophotometric detection. Reactivation of the inhibited immobilized AChE by pyridine-2-aldoxime methochloride (2-PAM), magnesium or fluoride ions has also been studied. 2 × 10 −5 M 2-PAM restores almost 100% of the activity of the immobilized enzyme. Methods for determination of paraoxon and carbamoylcholine are presented, based on the inhibition and reactivation of immobilized AChE as monitored by its catalyzed hydrolysis of acetylthiocholine iodide and the subsequent reaction of the thiocholine produced with 5,5′-dithiobis(2-nitrobenzoic acid). The calibration graphs are linear up to 8 × 10 −4 M and 6 × 10 −4 M, respectively, with relative standard deviations ( n = 5) of 5 %, and 3σ limits of detection of 5 × 10 −5 M and 6 × 10 −5 M, respectively.

Flow spectrophotometric method for determination of hydrogen peroxide using a cation exchanger for preconcentration

A flow spectrophotometric method for the preconcentration and determination of hydrogen peroxide is developed. It is based on the formation of the titanium(IV) peroxo complex and its retention on a minicolumn cation exchanger, elution with sulphuric acid and spectrophotometric detection at 410 nm. The calibration graph is linear over the range 4 × 10−6−6 × 10−5 M. The 2σ detection limit is 1 × 10−6 M (34 ng ml−1 and the exchange capacity is 1.1 mmol H2O2 g−1 dry weight.

Determination of acetaldehyde by flow injection analysis with soluble or immobilized aldehyde dehydrogenase

Abstract Acetaldehyde (0.18–7.7 × 10 −4 M) in water is determined by using a double injection technique with the soluble enzyme or with a mini-column of aldehyde dehydrogenase immobilized on cyanogen-activated Sepharose 4B. The NADH produced is monitored spectrophotometrically. The sample throughput is ca. 40 h −1 , and the immobilized enzyme is stable for at least a month. Ethanol up to 5% (v/v) does not interfere.

Flow injection amperometric and chemiluminescence individual and simultaneous determination of lysine and glucose with immobilized lysine oxidase and glucose oxidase

Abstract Flow injection amperometric and chemiluminescence methods for the individual and simultaneous determination of lysine and glucose by using lysine oxidase and glucose oxidase are described in this paper. The calibration graphs for lysine are linear over the range 1 × 10 −5 − 1.6 × 10 −4 and 2.05 × 10 −7 − 2.75 × 10 −5 M for amperometric and chemiluminescence detection respectively. The detection limits (3σ) for lysine are 5 × 10 −6 M with amperometric and 4.0 × 10 −8 M with chemiluminescence detection. The sample throughput rates are 80 and 100 h −1 , respectively. Lysine and glucose concentrations can be monitored simultaneously in the range 1.5 − 9 × 10 −5 M and 7 × 10 −7 −8 × 10 −6 M with amperometric and chemiluminescence detection respectively. The interference effects of some amino acids and metal ions are examined. An on-line cation-exchange minicolumn is inserted into the chemiluminescence manifold to remove the interference effect of Fe 2+ and Cu 2+ .

Flow-injection amperometric determination of oxalate with immobilized oxalate oxidase

Abstract Oxalate is immobilized on controlled-pore glass and is used on-line in a glass minicolumn (2.5×25 mm). The hydrogen peroxide formed is detected amperometrically. Oxalate (6×10−6−9×10−4 M) is determined in a flowing stream of pH 3.5 citrate (or succinate) buffer. As little as 20 ng (in 40 μl; 5.7×10−6 M) of oxalate can be detected. Copper inhibition can be removed either by adding EDTA to the carrier stream or incorporating a chelating-resin minicolumn into the flow system prior to the enzyme column.

Flow-injection spectrophotometric determination of chloride with an on-line solid mercury(II) thiocyanate minicolumn and bromide with a silver thiocyanate minicolumn

Abstract Flow-injection spectrophotometric procedures are described for the determination of chloride and bromide using on-line solid mercury(II) thiocyanate and silver thiocyanate minicolumns, respectively. The linear response ranges for chloride and bromide are 0.28 × 10 −4 −8.5 × 10 −4 M and 0.38 × 10 −4 −2.4 × 10 −4 M, respectively. The sample throughput for both systems is 100 h −1 . The lifetime of the minicolumns is 50 and 200 injections, respectively.

Individual and simultaneous determination of uric acid and ascorbic acid by flow injection analysis

Flow injection methods for the individual and simultaneous determination of ascorbic acid and uric acid are proposed. A spectrophotometer and a miniamperometric detector are connected in sequence. The calibration graphs for uric acid obtained by measuring its absorbance at 293 nm and its current at +0.6 V are linear up to at least 80 and 70 mug/ml, respectively, with an rsd (n = 10) of 1 % for both methods at mid-range concentrations. The calibration graph for ascorbic acid with amperometric detection is linear up to 80 mg/l. with an rsd (n = 10) of 0.8% at 30 mg/l. The simultaneous determination of uric acid and ascorbic acid is based on measurement of the absorbance of uric acid at 393 nm and amperometric determination of both analytes at +0.6 V. The average relative errors of the analysis of binary mixtures of uric acid and ascorbic acid are 2.2 and 4.2%, respectively.

Enzymatic methods for the determination of ethanol based on linear and cyclif flow-injection systems

Linear and cyclic systems are described for the determination of ethanol (ca. 0.17–30×10−3 M). In the linear system, the solution passes either through a minicolumn of yeast alcohol dehydrogenase (YADH) immobilized on controlled-pore glass or through minicolumns of the immobilized YADH and of yeast aldehyde dehydrogenase immobilized on cyanogen bromide-activated Sepharose-4B. The NADH formed is monitored either spectrophotometrically or spectrofluorimetrically. In the cyclic system, the solution passes through the same enzyme columns, and the NADH produced is monitored similarly before reconversion to NAD+ in a minicolumn of glutamate dehydrogenase immobilized on cyanogen bromie-activated Sepharose-4B in the presence of α-ketoglutarate and ammonium ions also present in the flow system. the sample throughout for both systems is ca. 40 h−1 and 50 h−1 for spectrophotometric and spectrofluorimetric detection, respectively. An on-line double-injection technique is described as an alternative to the cyclic system for limiting the consumption of NAD+.

Individual and sequential flow injection spectrophotometric determination of vanadium(V) and titanium(IV)

SummaryMethods for the individual and sequential flow injection spectrophotometric determination of vanadium(V) and titanium(IV) are proposed, based on the formation of peroxo complexes. The detection limits are 1.0 × 10−5 mol/l V (120 μl) and 2.5 × 10−6 mol/l Ti (80 μl). A cation exchange resin mini-column is incorporated on-line into the vanadium manifold to remove the titanium complex and allow the vanadium to be determined selectively. A normal injection valve is used for the individual determinations, but it is modified for determination of V(V)/−Ti(IV) mixtures in order to introduce two samples sequentially into the reagent stream. One passes through a cation exchanger minicolumn, the other through an empty column, before reaching the detector. The former allows V alone to be measured, the latter V+Ti.

Flow procedure for ion-exchange preconcentration and on-line spectrophotometric determination of iron(III) as its thiocyanate complex

On-line ion-exchange preconcentration of iron(III) on a conventional cation exchange resin with spectrophotometric detection based on thiocyanate complexation is described. The calibration graph is linear over the range 0.01–0.2 μg ml−1 and the detection limit (3 σ) is 6 ng ml−1 for a 6-ml sample. No interference effects were detected. The recovery of iron from the resin is 95%. 12 samples h−1 can be analysed.