A spectrophotometric method for manganese determination in water samples based on ion pair formation and dispersive liquid-liquid microextraction

In this work, a simple, inexpensive, and environmentally friendly extractive spectrophotometric method for the determination of manganese is suggested. The method is based on the formation and dispersive liquid-liquid microextraction (DLLME) of a violet-coloured ion pair of Mn(II) with 1,3,3-trimethyl-2-[3-(3-methyl-3H-benzothiazol-2-ylidene)-propenyl]-3H-indolium (BTIC) in the presence of 1-nitroso-2-naphthol (HL) as ligand, and subsequent UV-VIS spectrophotometric detection at 560nm of the ion pair formed. The appropriate experimental conditions for the DLLME procedure were found to be: a pH of 9.5; 0.12 mmol L-1 of BTIC; extraction solvent - toluene containing 1.75 mmol L-1 of HL; disperser solvent - methanol; auxiliary solvent - tetrachloromethane. Beer's law is obeyed in the range 0.055-0.88 mu g mL(-1) of Mn(II). The limit of detection (LOD), calculated based on three times of the standard deviation of the blank test (n = 10), was found to be 0.004 mu g mL(-1) of Mn(II). The precision (as relative standard deviation, RSD%) and accuracy (as recovery percentage, R%) of the method were examined by performing five replicate determinations at four concentration levels over two days and varied between 1.2 and 3.8, and 97.7 and 104.5, respectively. The suggested method was successfully applied to the analysis of various water samples (mineral water, spring water and drinking water).