A novel hydrodynamic sequential injection (HSI) spectrophotometric system for determination of manganese was developed. It is based on the complexation of Mn(II) with formaldoxime in basic solution (pH ! 10) to produce product that could be monitored spectrophotometrically at 450 nm. Based on the HSI concept, both sample and reagents were aspirated through solenoid valves to fill a defined volumes conduit between 3-way connectors connected in series, forming stacked zones of solutions similar to those in normal SI. The concept was successfully demonstrated for manganese determination. A linear calibration graph over a range of 0.5 to 30 mg L À1 Mn(II) with a detection limit of 0.2 mg L À1 was obtained. Relative standard deviations for 11 replicated injections of 5 and 20 mg Mn L À1 were 5.6% and 2.4%, respectively. A sample throughput of 45 h À1 was achieved. The results from investigation of exchangeable manganese in soil samples by the developed method were found to be in good agreement with the results obtained by a batch spectrophotometric method, despite the proposed system employed simpler and more cost-effective devices=instruments, had higher degrees of automation with full microcontroller control of the operation, and consumed smaller amounts of chemicals (250 mL each of hydroxylamine, sample, and formaldoxime solutions and 2.5 mL of buffer carrier solution per operation cycle).

An automated hydrodynamic sequential injection (HSI) system with spectrophotometric detection was developed. Thanks to the hydrodynamic injection principle, simple devices can be used for introducing reproducible microliter volumes of both sample and reagent into the flow channel to form stacked zones in a similar fashion to those in a sequential injection system. The zones were then pushed to the detector and a peak profile was recorded. The determination of nitrite and nitrate in water samples by employing the Griess reaction was chosen as a model. Calibration graphs with linearity in the range of 0.7 -40 mM were obtained for both nitrite and nitrate. Detection limits were found to be 0.3 mM NO2 -and 0.4 mM NO3 -, respectively, with a sample throughput of 20 h -1 for consecutive determination of both the species. The developed system was successfully applied to the analysis of water samples, employing simple and cost-effective instrumentation and offering higher degrees of automation and low chemical consumption.

We propose the creation of reusable indicator-sorbed-solids, using anion-exchange resins or kaolin as supports, with the aim to reduce chemical use towards green analytical chemistry. Indicators (phenolphthalein, thymol blue and butterfly pea flower extract as a natural indicator) sorbed on a solid support, were employed in acid-base titration, in both homogenous aqueous and heterogenous aqueous organic phases. Applications of the developed techniques to some real samples, such as vinegar, colored fruit juice and vegetable oil, have been demonstrated.

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The method for iron determination by using the microvolume of chemicals coupled with employing natural reagent was proposed towards green analytical chemistry. A simple, portable, and economic digital microscope was used to magnify the drop of 30 μL of product, that was mixed between sample and guava leaf extract reagent, to monitor the analytical signal as primitive color, red/ green/blue or RGB. The optimum conditions for the reagent extraction and the RGB detection were investigated. The calibration graph with linearity in the range of 40-120 mg L-1 Fe(III) was obtained with the detection limit at 10.8 mg L-1. High precision was achieved with %RSD less than 1.8%. The developed method was successfully applied to the assay of iron in supplement samples and found to be in good agreement with the results obtained by the FAAS method at the 95% confidence level.