Evaluation of trihalomethanes in tap water samples of Karachi city [Pakistan]

The chlorination of water containing natural organic matter leads to the formation of disinfection by-products. Trihalomethanes [THM[s]] are the major category of disinfection by-product in chlorinated drinking water. This study aimed to investigate the presence of THM[s] in tap water samples collected from different localities of Karachi city. Liquid-liquid extraction and gas chromatography with an electron capture detector was used for the determination of THM[s]. The concentration of THM[s] in tap water samples of Karachi was found below the WHO guideline values. The mean concentration of chloroform, bromodichloromethane and dibromochloromethane were found as 30.40, 1.04 and 0.09 micro g L[-1] respectively. The relative standard deviations for these THM species were 1.15, 1.61 and 1.81 respectively. Bromoform [CHB[r3]] was not detected. On the basis of the results obtained by principal component analysis [PCA], CHCl[3] was found to be the most significant principal component. The effect of free chlorine residual and pH on the concentration of THM[s] were also assessed

Two-phase effect on amperometric titration of some redox systems

Cerium [IV] sulphate tetrahydrate with iron [II]ammonium sulphate hexahydrate and potassium permanganate with iron [II] ammonium sulphate hexahydrate redox systems were studied at a platinum test electrode and Ag|AgCl reference electrode using amperometry at 1.8V and 1.2V. In the presence of chloroform higher values of diffusion current [I[d initial] and [I[d final] were produced whereas a linear and significant shift in diffusion current was recorded in case of ethyl acetate as compared to standard redox systems. The presence of chloroform and ethyl acetate also shifted the equivalence point to a lower value. The influence of chloroform and ethyl acetate on all these parameters is also confirmed statistically by ANOVA. Spectral study of potassium permanganate and potentiometric titration of these redox systems also confirmed the influence of immiscible solvents on the amperometric titration of these redox systems