Study on the spectrophotometric determination of silver with bromopyrogallol red in presence of cetylperidinium chloride

This paper describes a simple, rapid, selective and sensitive method for the determination of silver( Ag), based on the formation of a coloured complex of silver with bromopyrogallol red (BPR) in the presence of surfactant cationic cetylpyridinium chloride (CPC). The formation of the ternary complex is accompagnied by a marked increase in the absorbance and a bathochromic shift in the maximal absorption of the complex from 438 to 622.5 nm, hence, there is a difference (Delta lambda = lambda(Ag BPR CPC) - lambda(Ag BPR) = 184.5 nm) and large hyperchromic shift in lambda(max) (Delta A = A(Ag BPR CPC) - A(ag BPR) = 0.493), and the ternary complex is stable for at least 8 hr. In the absence and presence of cetylpyridinium chloride, 1:1 binary and 1:2:3 ternary complexes having molar absorptivities of 3.2 x 10(3) and 1.3 x 10(4) 1.mol.(-1)cm(-1) at 438 and 622.5 nm, and stability constants of 8.3 x 10(6) and 2.3 x 10(10), respectively. The optimum pH range for the reaction is 5 - 6 and Beer's law is obeyed over the concentration range 2.15 - 8.60 mu g/ml of silver(I). The interference of various ions has been studied and the method has been successfully applied to the determination of silver in silver standard amalgam, used in dental prosthesis, where excellent agreement between reported and obtained results were achieved. The relative standard deviation was better than 2% in all cases.