Sequential injection analysis (SIA) that was developed in 1990 is a simple, versatile and automated technique based on precise aspiration of small volumes of reagents and samples into a single channel. It is economical in terms of reagent consumption and waste generation. SIA is applied to food, environmental and pharmaceutical samples. SIA parameters and the chemical variables are optimized and figures of merit are reported. Spectrophotometer has been used as a detector in the analysis of formaldehyde (HCHO), ascorbic acid and ferric iron (Fe (III)). A stopped flow method was adapted to SIA spectrophometric technique. Enhanced sensitivity was obtained using a stopped flow method as compared to a non-stopped flow method. The SIA spectrophotometric determination of Fe (III) through complex formation with the thiocyanate and the Tiron reagents has been studied in chapter 3. The two methods were compared based on convenience, sensitivity, simplicity, reliability and on general application. Both methods are simple, employ readily available reagents and have lower detection limits and shorter analysis time of 72 samples per hour. The thiocyanate method enabled the determination of Fe (III) in the linear range of 2 to 50 mg/ℓ with a detection limit of 0,2 mg/ℓ whereas the Tiron method provided a linear range of 1 to 50 mg/ℓ with a detection limit of 0,1 mg/ℓ. Chapter 4 presents the application of SIA spectrophotometric method for the determination of formaldehyde in wastewater. The method is based on the inhibition of brilliant green-sulfite reaction by formaldehyde. The kinetic method was implemented by stopping the flow when the complex reaches the detector and the measurements were taken as the reaction proceeds. The SIA method was compared with the chromotropic acid method and the paired t-test was used to determine whether the results obtained by the two methods differ significantly. Good sensitivity with a detection limit of 0,06 mg/ℓ and a wider linear range of 1-3 mg/ℓ was achieved. Chapter 5 describes the indirect determination of ascorbic acid in pharmaceutical samples, sweets and beverage (orange juice). This method is based on reduction of Fe (III) to ferrous iron (Fe (II)) by ascorbic acid under UV-light irradiation and the reaction of generated Fe (II) with 1,10-phenanthroline. The flow was stopped in the holding coil for a defined time to ensure that complete reduction process take place under irradiation. Photochemical reaction methods improved the sensitivity with detection limit of 0,06 mg/ℓ. Good precision was obtained with relative standard deviation of 1,3 %. The method compared well with the N-bromosuccinimide titration method. The versatility and simplicity of SIA technique makes it suitable to different requirements of various analytical problems.
Dissertation (MSc (Chemistry))--University of Pretoria, 2007.