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J F van Staden

Publications and source records attributed to J F van Staden.

14 recordsLinked to original sources
PubMed2003

On-line speciation of bromine and bromide using sequential injection analysis with spectrophotometric detection.

An on-line procedure for the simultaneous determination of bromine and total bromine (bromine+bromide oxidised to bromine) is proposed, which lead to the determination of bromide by subtraction. Phenol red was used as chromogenic reagent for bromine and total bromine after bromide was oxidised to bromine by Chloramine T. The linear range found is 1-10 mg L(-1) with a detection limit of 0.6 mg L(-1) for bromine, and a linear range of 0.8-15 mg L(-1) with a detection limit of 0.4 mg L(-1) for total bromine. The calculated RSD for bromine is less than 0.8% and for total bromine less than 0.7%. The system is fully computerised and able to run 30 samples per hour with an automated rinsing step that eliminates sample carry-over. The results for both bromine and bromide from the proposed sequential injection analysis (SIA) system compare favourably with standard manual methods and statistical evaluation proves no significant difference between the results of the proposed SIA system and the standard method at the 95% confidence level. The presence of other halides was found not to interfere.

Journal Article↗
PubMed2002

An on-line potentiometric sequential injection titration process analyser for the determination of acetic acid.

An on-line potentiometric sequential injection titration process analyser for the determination of acetic acid is proposed. A solution of 0.1 mol L(-1) sodium chloride is used as carrier. Titration is achieved by aspirating acetic acid samples between two strong base-zone volumes into a holding coil and by channelling the stack of well-defined zones with flow reversal through a reaction coil to a potentiometric sensor where the peak widths were measured. A linear relationship between peak width and logarithm of the acid concentration was obtained in the range 1-9 g/100 mL. Vinegar samples were analysed without any sample pre-treatment. The method has a relative standard deviation of 0.4% with a sample frequency of 28 samples per hour. The results revealed good agreement between the proposed sequential injection and an automated batch titration method.

Acetic Acid↗
PubMed2002

New horizons in sequential injection kinetic analysis.

The need to measure several quantities rapidly in the same sample has prompted the development of automated methods of analysis that in both the continuous and discontinuous modes offer the possibility of simultaneous determinations. The application of pH gradients and differential kinetic determinations dominate the simultaneous determination of two or more closely related species in mixtures without prior separation. Various options enable use of kinetic-based measurements for the simultaneous determination of different analytes in flow systems. Some possible general reactions are given and discussed. The scope of sequential injection kinetic analysis is illustrated with examples.

Journal Article↗
PubMed2001

Solid-phase reactors in sequential injection analysis. Determination of manganese (II) in tap water and effluent streams using a solid-phase lead(IV) dioxide reactor in a sequential injection system.

The determination of manganese(II) in tap water and effluent streams, using a solid-phase reactor incorporated into a sequential injection system was investigated. Mn2+-ions in samples injected into a carrier stream, were oxidised by solid lead(IV) dioxide suspended on silica gel beads to form MnO4- -ions which were detected spectrophotometrically at 526 nm. The linear range of the system is from 1 to 7 mg L(-1) with a detection limit of 0.62 mg L(-1). The proposed system is suitable for the determination of manganese(II) in tap and effluent streams at a rate of approximately 50 samples per hour with a relative standard deviation of better than 3%. Statistical comparison between the proposed sequential injection system and a standard ICP method revealed that there is no significant difference between the two methods at the 95% confidence level for effluent streams and at 99.9% for tap water.

Journal Article↗
PubMed2001

Maltodextrins as new chiral selectors in the design of potentiometric, enantioselective membrane electrodes.

Maltodextrins (dextrose equivalent (DE) 4.0-7.0, 13.0-17.0, and 16.5-19.5) are proposed as novel chiral selectors for the construction of potentiometric, enantioselective membrane electrodes. The potentiometric, enantioselective membrane electrodes can be used reliably for the assay of S-captopril as raw material and in pharmaceutical formulations such as Novocaptopril tablets, by use of direct potentiometry. The best response was obtained when maltodextrin with higher DE was used for construction of the electrode. The best enantioselectivity and time-stability was achieved for the lower DE maltodextrin. L-proline was found to be the main interferent for all the proposed electrodes. The surface of the electrodes can be regenerated by simply polishing; this furnishes a fresh surface ready for use in a new assay.

Captopril↗
PubMed2001

Spectrophotometric determination of chloride in mineral and drinking waters using sequential injection analysis.

An on-line sequential injection system has been developed for spectrophotometric determination of chloride in drinking mineral, natural, and ground waters. Samples containing different concentrations of chloride were analyzed. The analysis is based on detection of the red iron(III) thiocyanate complex. The complex was monitored spectrophotometrically at 480 nm using de-ionized water as the carrier stream at a flow rate of 3.21 mL min(-1). The method was found to be linear within the range 0-50 mg L(-1) chloride; the detection limit was 3.01 mg L(-1). The fully automated method can be used to analyze 37 samples per hour with a relative standard deviation (RSD) better than 2.50%.

Chlorides↗
PubMed2000

Amperometric biosensor based on D-aminoacid oxidase for the R-perindopril assay.

A new amperometric biosensor based on D-aminoacid oxidase is described for the assay of R-perindopril. R-perindopril can be determined in the 400-20 nmol/L concentration range; the detection limit is 10 nmol/L. The selectivity was checked with S-perindopril, D- and L-proline, and polyvinylpyrrolidone. The main interfering species was D-proline. An automated system for the assay of R-perindopril based on the concept of flow injection with an amperometric biosensor (based on D-aminoacid oxidase) as detector is also described. The system is suitable for the on-line monitoring of R-perindopril at a sampling rate of 72 samples/h, in the linear range: 100 nmol/L -20 nmol/L with an RSD better than 0.09% (n = 10).

Angiotensin-Converting Enzyme Inhibitors↗
PubMed1993

Cervical intervertebral disc prolapse associated with traumatic facet dislocations.

Closed reduction of dislocated facet joints is considered safe by most authors. We report the occurrence of traumatic cervical disc prolapse associated with these injuries in four patients. Without adequate radiological exclusion of this pathology, reduction may have catastrophic consequences as illustrated by two of our cases. Anterior discectomy and open reduction and fixation provide safe and successful avenues of treatment.

Adult↗
PubMed1991

Improvement on the microdiffusion technique for the determination of ionic and ionizable fluoride in cows' milk.

Different microdiffusion techniques for the determination of ionic and ionizable fluoride in milk have been evaluated for measurement with a fluoride-selective sensor. This work culminated in a modified version of the hexamethyldisiloxane-acid diffusion technique where an increased amount of perchloric acid and sodium hydroxide seemed to be a prerequisite for accurate and precise results. The configuration of the fluoride-selective electrode was also modified by using an adapted microanalytical procedure to determine fluoride in small volumes (50 microliters each) and to avoid contamination between successive milk samples. The resultant procedure is free of interferences and is capable of measuring fluoride in milk at concentrations from 0.02 to 10.00 mg dm-3 with improved accuracy and precision compared with earlier work.

Animals↗
PubMed1990

Simultaneous determination of total and free calcium in milk by flow injection.

A fast and reliable procedure for the determination of total and free calcium in milk is described. The method is based on the flow injection (Fl) technique. Total calcium is determined by atomic absorption spectrometry (AAS) (422.7 nm) and free calcium by spectrophotometry (580 nm). Interference in the determination of free calcium is eliminated by using a dialyser, which also separates the total and free calcium. Interference from phosphates in milk in the determination of total calcium by AAS is overcome by using a dinitrogen oxide-acetylene flame with the necessary suppression with K+. With 30-microliters samples the Fl system covers a standard working range of 100-1500 mg dm-3 of Ca2+. The system is suitable for the simultaneous determination of total calcium (relative standard deviation less than 1.30% for 1300-1500 mg dm-3 of total calcium) and free calcium (relative standard deviation less than 0.85% for 120-170 mg dm-3 of free calcium) in milk at a sampling frequency of about 60 samples h-1. The results obtained agree reasonably well with results from the AAS method.

Animals↗
PubMed1990

Experimental evaluation of commercially available semi-permeable membranes for use with parallel-plate dialysers in flow injection systems.

Mass transfer in on-line analytical parallel-plate dialysers was studied in the continuous and flow injection (FI) modes in order to characterise the nature of the dialysis process and its dependence on experimental variables. A number of different semi-permeable membrane surfaces were evaluated in the laminar-flow and plug-flow configurations. The fraction of analyte transferred from the donor to the acceptor stream depends on parameters such as type of membrane used, membrane surface, membrane line-length, membrane porosity, concentration of analyte in the donor stream, the use of concurrent and countercurrent flow between the donor and acceptor streams, and flow-rates of the donor and acceptor streams. The dialysis of calcium and chloride ions, in the absence of protein, was studied with different membrane types and dialysers with different dimensions in continuous flow and FI, and the influence of the above mentioned parameters on the dynamic dialysis process of these ions is described.

Anions↗
PubMed1983

Simultaneous determination of protein (nitrogen), phosphorus, and calcium in animal feedstuffs by multichannel flow-injection analysis.

A 3-channel flow-injection procedure was developed, which enables the simultaneous determination of protein, phosphorus, and calcium in a wide range of animal feeds from a single digestion. Samples are digested with a block digestor, diluted, and analyzed at a rate of 82 samples/h. Protein (nitrogen) as ammonia is determined colorimetrically by the indophenol method. Phosphorus and calcium are determined by measuring the absorbances of the molybdenum blue and calcium-cresolphthalein complexes at 660 and 580 nm, respectively. Protein is determined in the range from 0 to 75%, phosphorus in the range from 0 to 6%, and calcium in the range from 0 to 6%. The results obtained do not differ significantly from those obtained by proven manual methods, and considerable time, space, and reagents are saved.

Animal Feed↗
PubMedDate not supplied

Immunosensors in clinical analysis.

Clinical analysis requires methods of high reliability. The importance of immunosensors in clinical analysis is discussed. Due to the fact that the construction of immunosensors plays a very important role in their response characteristics, different types of immunosensor designs are highlighted. The performances of immunosensors are discussed taking into account the type of transducer utilized for construction.

Animals↗