J. F. van Staden

A coated tubular solid-state chloride-selective electrode in flow-injection analysis

Abstract The construction, suitability and behaviour of a coated tubular solid-state chloride ion-selective electrode in continuous flow analysis are discussed. The flow-through cell is constructed easily from Tygon tubing and silver foil, which is treated to give a silver/silver chloride electrode. The optimum contact area is obtained with a tube 5 mm long and of 2 mm internal diameter, for a total flow rate of 4.7 cm 3 min −1 ; the carrier streams are 1.0 mol dm 3 potassium nitrate. Response times are fast (3–4 s for 95% response). With 30-μl samples, the working range covers 5–5000 mg dm 3 chloride with a reproducibility better than 1.7% (relative standard deviation); the stability of the system is excellent. Interferences are similar to those found in batch analysis with Ag/AgCl electrodes, but are less severe in the flow system; pH has no effect in the range 2–12. Results obtained for chloride in waters at a sample throughput rate of about 120 h −1 agree well with results by a standard spectrophotometric automated method.

Spectrophotometric determination of thiocyanate by sequential injection analysis

A sequential injection analysis (SIA) system was developed for the spectrophotometric determination of thiocyanate as Fe(SCN) 2C . The physical parameters (flow rate, sample and reagent volumes, holding coil and reaction coil internal diameter and length) which influence dispersion in a SIA system were optimized. The effect of the reagent concentration and nitric acid concentration (in the reagent solution and carrier stream, respectively), were also studied. Reagent consumption was effectively reduced by introducing the reagent as a zone into the nitric acid carrier stream, compared to flow injection analysis where the reagent itself is the carrier stream. The system is fully computerized and able to monitor thiocyanate in samples at 24 samples per hour with a relative standard deviation of <1.20% for samples and standards with thiocyanate concentrations above 10.0 mg l 1 . The calibration graph is linear from 2.0 to 150.0 mg l 1 with a 3 detection limit of 1.1 mg l 1 . The system has been applied to the determination of thiocyanate in process solutions and waste waters. ©2000 Elsevier Science B.V. All rights reserved.

Determination of ammonia in water and industrial effluent streams with the indophenol blue method using sequential injection analysis

Abstract A suitable sequential injection analysis (SIA) analyser to monitor water quality in terms of the ammonia content in water and industrial effluent streams was developed. The system is fully computerised and is able to monitor ammonia in samples at a frequency of ca. 16 samples per hour with a relative standard deviation better than 1.8%. The calibration curve is linear between 0 and 50 mg l−1 which falls within the required analyte range. The levels of possible interferants in the water and industrial effluent streams were negligible to cause any interference on the proposed system.

Spectrophotometric determination of Cu(II) with sequential injection analysis.

A sequential injection system, based on the reaction of Cu(II) with diethyldithiocarbamate (DDTC), was developed for the determination of Cu(II) in plant food and water samples. The extraction procedure, generally used to extract the Cu(II)-DDTC complex for subsequent analysis was eliminated in this procedure. The complex was detected spectrophotometrically in aqueous solutions at 460 nm. The physical and chemical parameters depicting the system were studied to obtain optimum conditions for sample analysis. The system developed is fully computerized and able to monitor Cu(II) in samples at seven samples per hour with a relative standard deviation of <4.50%. The calibration curve is linear from 0.5-5.0 mg/l with a detection limit of 0.2 mg/l. Interferences were reduced by introducing multiple flow reversals, to increase mixing between the reagent and sample zones, and subsequently enhance working of the masking agents (EDTA/citrate).

Determination of sulphate in natural waters and industrial effluents by sequential injection analysis

A sequential injection analysis system for the determination of sulphate in natural waters and industrial effluents has been developed. The method is based on the turbidimetric determination of sulphate using barium chloride as reagent and measuring the absorbance of the formed suspension spectrophotometrically at 540 nm. The proposed system is fully computerised and is able to monitor sulphate in samples at a frequency of 26 samples per hour with a relative standard deviation of better than 3.9%. The calibration graph is linear between 10 and 200 mg l−1.

Determination of paracetamol in pharmaceutical formulations using a sequential injection system

A simple method for the rapid determination of paracetamol in pharmaceutical formulations is described. The method involves oxidation of paracetamol by potassium hexacyanoferrate(III) and a subsequent reaction with phenol in the presence of ammonia. The blue complex formed is measured at 630 nm. The system has a sample frequency of 27 samples per h with a detection limit of 0.2 mg l(-1). The calibration curve is linear up to 60 mg l(-1) with a relative standard deviation of 1.2% (n=10).

Membrane separation in flow injection systems

A critical review of membranes for on-line separations in flow-through dialysers is given. Historical perspectives are briefly outlined. The fundamental aspects of dialysis as the selective separation of species through a semi-permeable membrane are discussed. Work done on theoretical principles by a number of authors is described and a simplified model is given. The basic components, locations thereof and the influence of various parameters on dialysis efficiency are highlighted. The value of dialysis as sampling preparation system for chromatography and reactor systems is outlined and the suitability of dialyser/flow injection systems in dilution, preconcentration and multicomponent analysis is evaluated. The review is concluded with a brief look at the use of dialysis in proteinligand binding studies and microdialysis.

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.

Simultaneous determination of chloride and sulphate in natural waters by flow-injection analysis

Abstract An automatic method for the simultaneous determination of chloride and sulphate in natural waters, based on the concept of flow-injection analysis is described. The sampling rate is 200 samples h −1 . The method is suitable for the analysis of chloride with a coefficient of variation of better than 1.3% and sulphate with a coefficient of variation of better than 20%.

Chemical speciation by sequential injection analysis: an overview

The simplicity of the sequential injection (SIA) manifold and its low need for maintenance makes it an ideal tool in speciation. As miniaturization and reduction of reagent consumption are also ultimate goals in chemical sensing, it is useful to review the use of combined injection and programmed flow as a central issue in designing SIA systems with chemical sensors and structurally simplified chemical analysers. This overview gives an insight into the current state, analytical scope and performance characteristics of sequential injection systems as analytical tools for speciation. The suitability of SIA for speciation analysis is illustrated by the methods used in the conduits of sequential injection systems for the chemical conversion of different chemical forms into detectable chemical species. Configurations of the basic sequential injection speciation analysis systems were designed around a multi-syringe-time-based-injection system with one detector, direct and indirect speciation of different forms using a single detector including diode array detection and direct speciation of different forms using multiple detection. Examples showing the use of SIA for the simultaneous determination or speciation of metal ions, inorganic anions and organic compounds are given with some recent results from our research groups.