Um método de análise por injeção em fluxo para determinação de Zn2+ em colírios foi descrito. Neste trabalho, o íon Zn2+ foi complexado com vermelho de Alizarina S em tampão borato (pH 9,0) e o cromóforo formado foi monitorado espectrofotometricamente em 520 nm. A curva analítica foi linear no intervalo de concentração de Zn2+ de 6,05 x 10-6 a 1,50 x 10-4 mol L-1, com um limite de detecção de 3,60 x 10-6 mol L-1. As recuperações variaram de 96,3 a 105% e o desvio padrão relativo foi de 1,2 % (n = 10) para uma solução padrão de Zn2+ de 5,5x10-5 mol L-1. A freqüência analítica de 60 h-1 foi obtida. Os resultados obtidos para determinação de Zn2+ em colírios empregando-se o procedimento proposto estão em concordância com os resultados obtidos empregando-se um procedimento comparativo a um nível de confiança de 95%.

A spectrophotometric flow injection method for the determination of Zn(II) in ophthalmic formulations was developed. In this work, Zn(II) ion was complexed with Alizarin red S in borate buffer solution (pH 9.0) and the chromophore produced was monitored at 520 nm. The analytical curve was linear in the Zn(II) concentration range from 6.05 x 10-6 to 1.50 x 10-4 mol L-1 with a detection limit of 3.60 x 10-6 mol L-1. Recoveries ranged from 96.3 to 105 % and a relative standard deviation of 1.2 % (n = 10) for 5.5x10-5 mol L-1 Zn(II) reference solution were obtained. The sampling rate was 60 h-1 and the results obtained of Zn(II) in ophthalmic products using this procedure are in close agreement with those obtained using a comparative spectrophotometric procedure at 95 % confidence level.

An indirect flow injection spectrophotometric procedure is proposed for the determination of N-acetyl-L-cysteine in pharmaceutical formulations. In this system, ferroin ([Fe(II)-(fen)2]2+) in excess, with a strong absorption at 500 nm, is oxidized by cerium(IV) yielding cerium(III) and [Fe(III)-(fen)2]3+ (colorless), thus producing a baseline. When N-acetyl-L-cysteine solution is introduced into the flow injection system, it reacts with cerium(IV) increasing the analytical signal in proportion to the drug concentration. Under optimal experimental conditions, the linearity of the analytical curve for N-acetyl-L-cysteine ranged from 6.5x10-6 to 1.3x10-4 mol L-1. The detection limit was 5.0x10-6 mol L-1and recoveries between 98.0 and 106% were obtained. The sampling frequency was 60 determinations per hour and the RSD was smaller than 1.4% for 2.2x10-5 mol L-1 N-acetyl-L-cysteine.