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 560 nm 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  µg 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 µg mL−1 of Mn(II). The precision (as relative standar...