A flow injection spectrophotometric procedure is proposed for the determination of paracetamol (acetaminophen) in pharmaceutical formulations. Powdered and liquid samples were previously dissolved/diluted in 0.05 mol L-1 hydrochloric acid solution and a volume of 250 µL was injected directly into a carrier stream of this same acid solution, flowing at 2.5 mL min-1. Paracetamol reacts with sodium hypochlorite forming N-acetyl-p-benzoquinoneimine which then reacts with sodium salicylate in sodium hydroxide solution yielding a blue indophenol dye which was measured at 640 nm in the pH range of 9.5-10.0. Paracetamol was determined in pharmaceutical products in the 1.0 to 100.0 mg L-1 (3.3x10-6 a 6.6x10-4 mol L-1) concentration range, with a detection limit of 0.5 mg L-1 (1.6x10-6 mol L-1). The recovery of this analyte in five samples ranged from 98.0 to 103.6 %. The analytical frequency was 80 determinations per hour and the RSDs were less than 1% for paracetamol concentrations of 25.0, 50.0 and 75.0 mg L-1 (n=10). A paired t-test showed that all results obtained for paracetamol in commercial formulations using the proposed flow injection procedure and a spectrophotometric batch procedure agree at the 95% confidence level.

A flow injection spectrophotometric procedure exploiting merging zones is proposed for determining vitamin B2 (riboflavin) in pharmaceutical preparations. The determination is based on the red-colored complex formation between vitamin B2 and silver(I) which was measured at 520 nm. Vitamin B2 was determined in four pharmaceutical preparations in the 1.0 to 50.0 mg L-1 concentration range, with a detection limit of 0.5 mg L-1. The recovery from three samples ranged from 98.0 to 104.0 %. The analytical frequency was 42 h-1 and r.s.d. were lower than 1% for solutions containing 10.0, 30.0 and 50.0 mg L-1 vitamin B2 (n= 10). The results obtained in commercial formulations using the FIA procedure were in good agreement with those obtained by using a conventional fluorimetric procedure (r=0.9998) and also with the label values (r= 0.9997).

A flow injection (FI) spectrophotometric procedure is proposed for the determination of vitamin B6 (pyridoxine hydrochloride) in pharmaceutical preparations. Powdered samples containing from 2.5 to 4.5 mg, were previously dissolved in 0.1 mol L-1 phosphate buffer solution (pH 7.0) and a volume of 500 muL was injected directly into a carrier stream consisting of this same phosphate buffer solution, flowing at 4.4 mL min-1. The stable blue indophenol dye produced in the oxidation of pyridoxine hydrochloride by potassium hexacyanoferrate(III) and N,N-diethyl-p-phenylenediamine solution was directly measured at 684 nm. Vitamin B6 was determined in five pharmaceutical preparations in the 0.5 to 6.0 mg L-1 concentration range (calibration graph: A= -0.00499 + 0.11963 C; r= 0.9991, where A is the absorbance and C is the vitamin B6 concentration in mg L-1), with a detection limit of 0.02 mg L-1 (3 Sblank/slope). The recovery of this vitamin from three samples ranged from 97.5 to 103.3 %. The analytical frequency was 62 h-1 and r.s.d. were less than 2% for solutions containing 1.0 and 3.0 mg L-1 vitamin B6 (n= 10). The results obtained for the determination of vitamin B6 in commercial formulations were in good agreement with those obtained by a spectrophotometric procedure (r=0.9997) and also with the label values (r= 0.9998).

Construiu-se um eletrodo íon-seletivo de grafite-epoxi recoberto para Fe(III), baseado no par-iônico formado entre o ânion [Fe(citrato)2]3- e o cátion tricaprililmetilamônio (Aliquat 336) incorporado em uma matriz de PVC (cloreto de polivinila). Uma membrana fina foi preparada pela incorporação deste par-iônico, ftalato de dibutila (DBPh) em PVC e aplicados diretamente em um tubo Perspex® contendo o condutor de grafite-epoxi. A solução de recobrimento foi preparada pela dissolução de 30% (m/m) de PVC em 10 mL de tetraidrofurano seguido da adição de 65% (m/m) de plastificante DBPh e 5% (m/m) do par-iônico. Investigou-se o efeito do pH, concentração de citrato e de alguns cátions sobre a resposta do eletrodo. O eletrodo apresentou uma resposta linear para E(mV) vs. log[Fe(citrato)2]3- no intervalo de concentração de ferro(III) de 1,0 x 10-3 a 1,0 x 10-1 mol/L em meio de citrato 1,0 mol/L, uma inclinação de 19,3 ± 0,5 mV/década e um tempo de vida de pelos menos 6 meses (mais de 800 determinações por cada membrana polimérica usada). O limite de detecção foi 7,5 x 10-4 mol/L e o desvio padrão relativo foi menor de 3% para solução contendo 5,0 x 10-3 mol/L de Fe(III) (n = 10). A aplicação deste eletrodo na determinação de ferro em amostras de vitamina é descrito. Os resultados obtidos com esse procedimento estão em concordância com aqueles obtidos usando espectrofotometria de absorção atômica (r = 0,9999).

A coated graphite-epoxy ion-selective electrode for iron(III), based on the ion-pair formed between [Fe(citrate)2]3- and the tricaprylylmethylammonium cation (Aliquat 336) in a poly(vinylchloride) (PVC) matrix has been constructed. A thin membrane film of this ion-pair, dibutylphthalate (DBPh) in PVC was deposited directly onto a Perspex® tube, which contained a graphite-epoxy conductor substrate. The coating solution was prepared by dissolving 30% (w/w) of PVC in 10 mL of tetrahydrofuran following addition of 65% (w/w) DBPh and 5% (w/w) of the ionic pair. The effect of pH, citrate concentration and some cations on the electrode response has been investigated. The E(mV) vs. log [Fe(citrate)2]3- electrode response was linear for iron(III) concentration from 1.0 x 10-3 mol/L to 1.0 x 10-1 mol/L in 1.0 mol/L citrate medium, with a slope of 19.3 ± 0.5 mV/decade and a useful lifetime of at least six months (more than 800 determinations for each polymeric membrane used). The detection limit was 7.5 x 10-4 mol/L and the relative standard deviation was less than 3% for a solution containing 5.0 x 10-3 mol/L of iron(III) (n = 10). The application of this electrode for iron(III) determination in samples of vitamin formulations is described. The results obtained with this procedure are in close agreement with those obtained using AA spectrophotometry (r = 0.9999).