R.E. Taljaard

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.

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 calcium in water, urine and pharmaceutical samples by sequential injection analysis

A sequential injection analysis system for the determination of calcium in water, urine and pharmaceutical samples is proposed. The method is based on the fast complexation reaction between cresolphthalein complexone and calcium with spectrophotometric detection. Baseline shift due to a background originating from coloured free reagent species, was eliminated by an optimised sequence of samples and reagents. The proposed system is fully computerised and is able to monitor calcium in samples at a frequency of 43 samples per hour with a relative standard deviation of < 1.4%. The calibration graph is linear between 0 and 20 mg l−1. The detection limit is 0.05 mg l−1.

Simultaneous determination of cobalt(II) and Ni(II) in water and soil samples with sequential injection analysis

The discontinuous nature of the sequential injection technique makes it ideally suitable for kinetic determinations. One of the advantages of kinetic analysis over equilibrium methods is the possibility of carrying out simultaneous determinations based on the different rates of their reactions with a common reagent. The different rates of the pseudo-first order dissociation of the citrate complexes of cobalt(II) and nickel(II) at pH 8.00 are used as a basis for the kinetic determination of these ions at trace levels in water and soil extracts. The reactions are followed by measuring the absorbance of complexes of the metal ions with 4-(2-pyridylazo)resorcinol (PAR) which are formed in a subsequent rapid reaction. EDTA is added to mask the major interferences. The proposed system is fully computerised and is able to monitor Co(II) and Ni(II) in samples at a frequency of 11 samples per hour with a relative standard deviation better than 1.2%. The detection limits are 0.14 and 0.20 mg/l for Ni(II) and Co(II) respectively.

Application of sequential-injection analysis as process analyzers

The development of sequential-injection analysis (SIA) from its mother technique flow-injection analysis (FIA) is reviewed. A short historical background is given as well as discussions on the basic principles and operational parameters governing the design of an SIA system. Single-, double-, and multizone systems are described together with more complicated systems including calibration, dilution, extraction, dialysis, titrations, separation, preconcentration, and systems incorporating mixing chambers.

On-line monitoring of phosphate in natural water and effluent streams using sequential injection analysis

Automation of the molybdenum blue method by sequential injection (SIA) for the on-line monitoring of phosphate in natural waters is presented. Although sequential injection analysis runs at one fifth the speed of conventional FIA, it presents many advantages such as simplicity of the manifold, robustness and computer compatibility. A reduction in reagent and sample consumption is also observed. Flow detector fouling does not occur in SIA manifolds as the detector is in contact with water between analysis. The proposed SIA analyser is able to monitor phosphate in the range 0–70 mg l−1 with a standard deviation of 0.9%. The detection limit is 0.5 mg l−1 PO43−.

On-line dilution with sequential injection analysis: a system for monitoring sulphate in industrial effluents

Abstract On-line dilution with sequential injection analysis has been evaluated for sulphate monitoring in industrial effluents using a dilution coil in the conduits of the manifold system and a dilution step as part of the timing sequence. The manifold of the SIA system with the dilution coil is more complex than the system including the dilution step. The former method needs more complicated programming as well. Shorter analysis time favoured the dilution with the dilution step, but the limited linear range of this method is a large drawback. The large linear range of the SIA system with dilution coil makes it very suitable to be used as a process analyser. The proposed SIA system is suitable to monitor sulphate in industrial effluents in the range 50–5000 mg/L with a dilution coil, in the range 50–1000 mg/L with a timing sequence of 6.5 s and in the range 750–5000 mg/L with a timing sequence of 15 s using a dilution step; all three ranges with a RSD <4.5%.

Influence of different volume ratios on the isodispersion point in sequential injection analysis

Abstract The importance of zone penetration can be ascribed to the fact that this influence has a dramatic effect on the surface area over which a concentration gradient exists and therefore over which axial mixing takes place. In this study different volume ratios were used to illustrate the shift of the isodispersion point due to the difference in concentration gradients in sequential injection analysis (SIA). The position of penetration and the sequence of introduction of samples and reagents for different sample and reagent volume ratios in a total constant volume has a major influence on the response of the final peak profile. The response of the final peak profile depends largely on the kinetics involved in both the ascending and tailing parts of the sample and reagent zones at the isodispersion point.

Non-linearity with metal-metal ligand complex reactions in flow injection systems. Metal-thiocyanate reactions

Abstract The linearity of the standard calibration graph for the spectrophotometric flow injection determination of chloride, based on its displacement of thiocyanate from mercury(II) thiocyanate and the subsequent reaction of the thiocyanate with iron(III), was extended by the addition of nickel(II) and copper(II) to the standard reagent solution. This was done after a theoretical study of the relationship between the amount of metal ion and thiocyanate as ligand in the metal-thiocyanate complex reaction systems. The calibration graph was linear between 0 and 1200 mg l −1 for standard chloride solutions with r = 0.982 ( n = 12) as opposed to 0–80 mg l −1 in the normal procedure.

Determination of reaction stoichiometries by using the sequential injection analysis technique

Abstract A simple and reliable sequential injection analysis system is proposed to determine the reaction stoichiometries of different complexes. In this study, the Fe(III)/Tiron complex as 1:1 complex and the Fe(II)/1,10-phenanthroline complex as 1:3 complex were evaluated. The importance of the correct reagent order, as well as the need for thorough mixing, is highlighted.