Effect of polyethylene glycols on the sensitivity of the thermal lens determination of cobalt with nitrosonaphthols of various structures (nitroso-R-salt and 2-nitroso-1-naphthol)

The effect of polyethylene glycols (PEGs) with molecular weights of 2000, 6000, 13000, and 20000 on the sensitivity of the thermal lens determination of cobalt(III) using nitroso-R-salt and 2-nitroso-1-naphthol is studied. At the polymer concentration as low as 10%, the sensitivity coefficient significantly increases and the detection limit decreases by a factor of 1.5-2 with respect to the determination in an aqueous medium without PEG. This effect is accompanied by an increase in sensitivity due to an increase in the absorbance of the cobalt complexes in PEG solutions at the operating wavelength. Under optimal conditions, the detection limits for cobalt(III) are 6 and 10 ng/mL with nitroso-R-salt and 2-nitroso-1-naphthol, respectively.