Takashi Korenaga

A process monitoring/controlling system for the treatment of wastewater containing chromium(VI)

An advanced monitoring system for controlling the treatment process of wastewater containing chromium(VI) was developed using a flow method as a chemical sensing probe. In this system, the acquisition of monitoring information and the control of the treatment process is computer-controllable. By application of the system to control the end-point of redox-treatment, an accuracy and precision better than ±0.9% (n = 5) and a relative standard deviation smaller than 0.5% (n = 5) were found; furthermore, safe discharge of wastewater can be ensured without the addition of any coprecipitation reagents.

Determination of chemical oxygen demand by a flow-injection method using cerium(IV) sulphate as oxidizing agent

Abstract A method based on flow injection was developed for the automated determination of chemical oxygen demand (COD) that provided a number of possibilities for improvement of the limitations of the standard manual methods. The strong oxidizing agent used is cerium(IV) sulphate, which resulted in a high degree of sample oxidation under mild operating conditions. The reaction between samples and cerium(IV) ion produced a sensitive and reproducible signal, i.e., a decrease in absorbance. The detection limit and relative standard deviation of the method were 0.5 mg l −1 and 0.6% ( n = 10), respectively, for a standard sample consisting of l -glutamic acid and lactose in a ratio of 5:1. When 50-μl samples were injected at a frequency of 20 h −1 , the determination range was 0.5–130 mg l −1 COD. Chloride was tolerated up to a concentration of 30 g l −1 without any masking agents. COD values for various types of wastewater samples correlated well with those obtained by standard manual methods.

The determination of chemical oxygen demand in waste-waters with dichromate by flow injection analysis

Abstract A simple method is described for the continuous determination of chemical oxygen demand (COD) in wastewater samples by flow injection analysis. Samples are injected into a water stream which merges with an acidic dichromate carrier solution. After reaction in a PTFE coil at 120°C, absorbances are measured at 445 nm. D-Glucose is satisfactory as a standard substance for COD in a variety of wastewaters. A sampling rate of 15 samples per hour can be achieved, and the detection limit and precision are 5 mg l-1 as COD and 0.4%, respectively. Chloride concentrations of ⩾ 100 mg l-1 interfere slightly unless silver and/or mercury salts are added. COD values for various wastewater samples correlate well with those obtained by standard methods using dichromate or permanganate.

Continuous-flow injection analysis of aqueous environmental samples for chemical oxygen demand

A method is described for the continuous, rapid determination of chemical oxygen demand (COD). The method is based on flow injection analysis (FIA) and uses acidic potassium permanganate solution as both an oxidant and a spectrophotometric reagent, and glucose as a standard. COD values for aqueous environmental samples, such as industrial wastewaters, are compared with those obtained using the Japanese Industrial Standard (JIS) method and are found to be within an error range of ±30%. The method is comparable to other manual and automatic methods and has several advantages. A sampling rate of 20 samples per hour can be achieved, and the detection limit and precision are 5 mg l–1 as COD and 0.6%, respectively. Chloride ion up to levels of 6000 mg l–1 does not interfere, even in the absence of silver salts.

Fully automated system for the continuous monitoring of ammonium ion in fish farming plant sea water by flow-injection analysis

Abstract An automated system for the continuous monitoring of ammonium ion in fish farming plant sea water is described. The sample is introduced into a carrier stream by an automated sample injector and merged with a reagent solution containing sodium salicylate and sodium nitroprusside. The sample stream is then mixed with a second reagent solution containing sodium hypochlorite and heated at 50°C. The absorbance of the resulting solution is monitored at 660 nm. The calibration graph was linear up to at least 3.0 mg 1 −1 NH+4-N. The relative standard deviation for 20 injections of samples containing 1.0 mg 1−1 NH+4-N was 0.35%. The interference from Ca2+ and Mg2+ was masked with potassium sodium tartrate. The interference due to amino acids and proteins present in fish foods and wastes was eliminated by adjusting the pH to 6–7 when the sample merged with the first reagent solution.

Flow Injection Analysis Using Potassium Permanganate: An Approach for Measuring Chemical Oxygen Demand in Organic Wastes and Waters

Abstract A rapid and continuous analytical method based on flow injection analysis was developed for the determination of chemical oxygen demand due to organic substances in water pollution. Potassium permanganate and sulfuric acid solutions were individually pumped up as an oxidizing agent and glucose was used as a standard substance. The results for filtered organic waste and water samples were as reasonable as compared to those measured by the manual acidic permanganate method.

Spectrophotometric determination of boron in natural waters by solvent extraction with chromotropic acid and removal of the excess of reagent

A method of removing the excess of reagent extracted into an organic phase in the solvent extraction of metal complex anions with quaternary ammonium salts was applied to the solvent extraction of the boron complex anion formed with chromotropic acid (1,8-dihydroxynaphthalene-3,6-disulphonic acid) by using zephiramine (tetradecyldimethylbenzylammonium chloride). EDTA, chromotropic acid, zephiramine and buffer (pH 3.5) are added to the sample solution, which is then shaken with 1,2-dichloroethane. The organic phase is washed twice with a back-washing solution (0.6 M in sodium chloride, pH 9.2) and the absorbance of the organic phase measured in a quartz cell. The boron complex is extracted quantitatively into the 1,2-dichloroethane and its apparent molar absorptivity in 1,2-dichloroethane is 1.4 × 104 l mol–1 cm–1 at 351 nm. Micro and trace amounts of boron in natural waters are determined spectrophotometrically.

Aspects of sample dispersion for optimizing flow-injection analysis systems

Abstract Solute dispersion of an injected sample plug was studied by using an experimental apparatus with ideal laminar flow in order to develop a hydrodynamic model for the design of sensitive and precise flow-injection analysis systems. The dispersion behaviour of the sample slug under different manifold conditions was first studied in detail to evaluate the effects of various operating conditions such as tube radius, tube length, flow-rate and molecular diffusion coefficient of sample solute. The capillary flow properties were also examined for some commercial micropumps to select the most suitable pumping method. Mixing profiles and baseline stability in short, straight tubes were investigated. A double-plunger micropump having a linear can mechanism and a fast, short reciprocation time was proposed to obtain smoother mixing and more stable pumping with good reproducibility. Complete mixing and low flow-rate pumping are strongly desired for reliable flow-injection methods for industrial process use; biosensing devices for protein and enzyme bioassays require lower consumption of valuable reagents.

Extraction-spectrophotometric determination of aluminium in river water with pyrocatechol violet and a quaternary ammonium salt

The simple removal of excess of co-extracted reagent in the solvent extraction of anionic metal complexes with a quaternary ammonium salt greatly improves the determination of aluminium with Pyrocatechol Violet (PV) and zephiramine (tetradecyldimethylbenzylammonium chloride). The exchange equilibrium constants for PV reagent and aluminium complex with four univalent anions (halides and nitrate) were determined when chloroform and 1,2-dichloroethane were used as extracting solvents. The constants were compared with those obtained with Pyrogallol Red. The method with PV and chloroform is suitable for the determination of micro-amounts of aluminium in river water. The apparent molar absorptivity of the aluminium complex in chloroform is 8.9 x 10(4) 1 mol(-1) cm(-1) at 587 nm. The limit of detection and precision achieved with the method are 3 mug l(-1) and within 4% respectively. A large excess of reagent can be used, and the ternary complex can be completely extracted over the pH range 5.5-10. Masking agents allow most interferences to be suppressed.

Nitrosophenol and nitrosonaphthol derivatives as reagents for the spectrophotometric determination of iron and determination of micro-amounts in waters with 2-nitroso-5-dimethylaminophenol

Twenty-five nitroso compounds have been examined for suitability as organic analytical reagents for the spectrophotometric determination of iron(II) ion. The complexes formed by 2-nitroso-5-dimethylaminophenol (nitroso-DMAP) and 2-nitroso-5-diethylaminophenol (nitroso-DEAP) with iron(II) are shown to have a 1:4 composition and the other iron(II) complexes a 1:3 composition. Nitroso-DMAP and nitroso-DEAP were found to be very sensitive reagents for iron(II) ion, the molar absorptivities of their complexes being about 4 × 104 at about 750 nm in aqueous solution. The colour of the nitroso-DMAP-iron(II) complex is very stable in aqueous solution at about pH 8, while that of the nitroso-DEAP complex is less stable. Nitroso-DMAP is more useful for the determination of micro-amounts of iron than nitroso-DEAP, because of the greater stability of the reagent and the complex formed and the solubility of the latter in aqueous solution.Diverse ions, which are generally present in city and river waters did not interfere in the direct spectrophotometric determination of micro-amounts of iron in these waters with nitroso-DMAP.