The possibility of using thiocyanate to determine iron(II) and/or iron(III) in water-acetone mixturehas been re-examined as part of a systematic and comparative study involving metallic complexes ofpseudohalide ligands. Some parameters that affect the complete oxidation of the ferrous cations, theirsubsequent complexation and the system stability have been studied to optimize the experimental conditions.Our results show the viability and potentiality of this simply methodology as an alternative analytical procedureto determine iron cations with high sensitivity, precision and accuracy. Studies on the calibration, stability,precision, and effect of various different ions have been carried out by using absorbance values measured at480 nm. The analytical curve for the total iron determination obeys Beer’s law (r = 0.9993), showing a highersensitivity (molar absorptivity of 2.10x10 4 L cm -1 mol -1 ) when compared with other traditional systems (ligands)or even with the “similar” azide ion [1.53x10 4 L cm -1 mol -1 , for iron–III/azide complexes, in 70% (v/v)tetrahydrofuran/water, at 396 nm]. Under such optimized experimental conditions, it is possible to determineiron in the concentration range from 0.5 to 2 ppm (15-65% T for older equipments, quartz cells of 1.00 cm).

Neste estudo, procurou-se desenvolver e avaliar filmes para a captação e quantificação de vapores de amônia no ar, através de um sensor piezelétrico de quartzo. Muitas substâncias e suas misturas, em diferentes proporções, foram investigadas como possíveis filmes captores. Em etapas seguintes, verificaram-se alguns parâmetros importantes como o efeito da vazão do poluente, da temperatura de trabalho e da massa da película, otimizando-se as condições experimentais para a montagem do método. Concluiu-se que o filme mais promissor, sob as condições ajustadas, seria uma mistura 2:1 (v/v) de solução comercial (A) de ácido glicólico (70% m/m) em água, adicionada a tetrakis(hidroxietil)etilenodiamina - THEED (3:4 v/v), com uma solução saturada (B) de ácido tânico em acetona. Estudos de repetibilidade, do tempo de contacto (poluente-sensor) e de alguns possíveis interferentes completaram os trabalhos. As curvas analíticas resultantes mostraram faixas lineares na região de trabalho (2,0 a 11 ppmv ou 1,4 a 7,7 mg/m3 de NH3), para quatro diferentes tempos de exposição (0,5; 1; 2 e 3 min), com coeficientes de correlação (r) variando entre 0,9994 e 0,9980, e respectivas sensibilidades de 13,5 a 42,0 Hz/ppmv.

Carbon monoxide was detected and determined by a piezoelectric quartz crystal sensor coated with nickel(II)-phthalocyanine 50 % (v/v) solution in glycerine. Studies on the effect of temperature, flow rate, and some possible interferents were carried out. Calibration curves, sensor stability (lifetime) and the precision of measurements were also verified. The resulting selectivity is probably due to the coordinative binding between the electronically unsatured metal complexes and the analyte. The analytical curve is linear in the concentration range 0.10 to 1.0 % (v/v).

A sensitive and alternative method for the spectrophotometric determination ofchromium(III) based on the formation of chromium(III)/azide complexes was established byinvestigating a new band in the ultraviolet region. The best experimental conditions for the analyticaldetermination of this metallic ion were: ligand and perchloric acid analytical concentration = 493 and12.0 mmol L -1 , respectively; aqueous medium; T = 25.0 oC; contact time = 1 hour. The maximummolar absorptivity coefficient occurred at 287 nm (average 1.481 ± 0.008 × 10 4 L mol -1 cm -1 ), leadingto the determination of metal ion concentrations one hundred times lower than the ones formerlydetermined in the visible region. The system obeys Beer’s Law and is suitable for chromiumdetermination in the 0.702-2.81 mg L -1 concentration range (15-65% T, 1.00 cm-width quartz cells).Analytical applications of the current method were tested with a nutritional supplement containingchromium. Results were compared with those obtained with atomic absorption spectrometry.