Fiber optic sensors using novel substrates for hydrogen sulfide determination by solid surface fluorescence.

Two different fiber optic sensors were developed for the determination of hydrogen sulfide at ppb concentration levels; a probe-type fiber optic sensor coated with polyethylene oxide containing 0.5 M CdCl(2) and a fiber optic sensor utilizing 0.5 M CdCl(2)-pretreated filter paper as solid substrate. In the first type, CdCl(2)-polyethyleneoxide (PEO) mixture was coated onto the tip of a fiber optic probe and the probe was exposed to H(2)S. The methodology is based on the measurement of CdS fluorescence on the surface. Detection limit (3s) of the PEO-coated fiber optic system was 36.0 ppb for H(2)S and precision at the 0.552 ppm level was 29% R.S.D. For the fiber optic system utilizing CdCl(2)-pretreated filter paper, two different configurations were devised and evaluated; a bifurcated fiber optic sensor and a single fiber optic sensor. Similar figures were obtained with these two systems; the detection limit (3s) was 4.0 ppb for the bifurcated fiber optic sensor and 4.3 ppb for the single fiber optic sensor, and both sensors had linear responses in the range 0.032-1.0 ppm. Their precisions at 0.299 ppm level were also very similar, 10 and 11% R.S.D., respectively, for the bifurcated and single fiber systems. In addition to the fiber optic sensors developed, various surfactants (sodiumdodecylsulfate (SDS), Aerosol OT, Aerosol A102, Aerosol 501), some cellulosic substances (sodium carboxymethylcellulose (CMC), ethylcellulose, hydroxypropylmethylcellulose, ethylhydroxyethylcellulose, alpha-cellulose) and several water-soluble polymers (polyacrylicacid polyethleneoxide (PEO), polyvinylalcohol (PVA)) were dissolved in proper solvents and after mixing with 0.5 M CdCl(2), were spread over glass slides. These novel solid substrates were exposed to H(2)S and fluorescence signal on the surfaces of the glass slides was measured with a luminescence spectrometer. The new substrates were shown to be good alternatives to filter paper for the determination of H(2)S by room temperature solid surface fluorescence spectrometry.

A novel sorbent tube for ambient hydrogen sulfide determination.

A novel tubular device has been developed for hydrogen sulfide determination in air. Several substrates such as commercial silica gel and alumina TLC plates, silica gel powder, alumina, CaSO(4), CaCO(3), BaSO(4), MgO, chalk, alpha-cellulose and ethyl cellulose were tested as solid substrates. 30-70-mesh silica gel was finally employed in glass tubes of 4.0 mm internal diameter. Silica gel is treated with 0.5 M aqueous CdCl(2) solution, dried, filled into the glass tube and sample gas is passed through the device using nitrogen as the carrier gas where 70% relative humidity is employed. The analyte reacts with the solid substrate to form a luminescent spot whose length in the tube is measured and correlated to concentration. The flow rate was 68 ml min(-1). The analytical system is linear in the range of 0.2-1.3 ppm H(2)S for the specified conditions. The prepared devices are stable at least for 3 months prior to sampling; and after sampling, the luminescing spot is stable also at least for 3 months.

Selenium status of healthy Turkish children.

Selenium concentrations, in blood plasma, red blood cells, hair of 61 healthy children, ages 0-14 yr, were determined using hydride generation atomic absorption spectrometry. Starting from late lactation period, selenium concentrations in all these matrices were found to be increasing with age. A good correlation was found between erythrocyte and plasma, hair and plasma, and hair and erythrocyte selenium concentrations. Although plasma, erythrocyte, and hair selenium concentrations of girls seemed to be higher than that of boys (only in erythrocytes), selenium concentrations of girls were found to be significantly (p < 0.002) higher than that of boys, 71 +/- 9 ng/mL, vs 65 +/- 10 ng/mL, respectively. Selenium status of Turkish children is found to be lower than that found in the literature; marginal selenium deficiency could be important in the development of some selenium deficiency related diseases. There is a need for extension of this study to healthy children from different regions in Turkey and to different disease states.

Hydrogen sulfide determination by solid surface luminescence.

In the analytical system suggested, atmospheric hydrogen sulfide reacts with the surface of a filter paper treated with aqueous cadmium chloride and yields a luminescent species whose intensity can be correlated with the analyte concentration in ambient air. It was shown that the luminescent species are CdS solid particles which were formed in a well defined size. The paper luminescence was also tried on polymeric surfaces; polyethyleneoxide, polyvinyl alcohol, ethylcellulose and carboxymethylcellulose were found to give a similar luminescence signal. The system can be used on the tip of an optical fiber for an irreversible, cumulative type of analytical device for hydrogen sulfide determination. The 3s detection limit for the paper luminescence detection system was 7.8 ppb H(2)S.

Determination of germanium by AAS in chloride-containing matrices.

Interference effects of NaCl on the ET-AAS determination of Ge have been studied. The use of several matrix modifiers to alleviate this problem such as Ni and Zn perchlorates and nitrates, nitric acid, ammonium nitrate are reported. The stabilizing effect of Zn and Ni perchlorates allows the use of high pretreatment temperatures. NaCl is thus thermally volatilized from the atomizer by employing pretreatment temperatures higher than 1500 degrees C resulting in an improved sensitivity. Germanium levels in zinc plant slag samples, have been determined and compared to those obtained for the same samples spiked with NaCl with platform and wall atomization using nickel perchlorate as a matrix modifier. The results were compared with those from a hydride generation system equipped with a liquid nitrogen trap. The recoveries for germanium have been almost complete and amount to 99% for the original slag samples and 80% for 15% (w/w) NaCl containing spiked samples.

Determination and speciation of mercury in a dental work-place by cold vapour atomic absorption spectrometry and gas-liquid chromatography.

Cold Vapour Atomic Absorption Spectrometry (CVAAS) and Gas-Liquid Chromatography (GLC) have been used for determination and speciation of mercury. Total mercury, methylmercury, ethylmercury and phenylmercury concentrations in urine samples taken from students and staff of a dental work-place were investigated. Air samples were also analyzed. Detection limits, as three times the standard deviation, and in units of ng analyte per ml urine were found to be 1.7, 12, 2.4 and 21 for total mercury, methylmercury chloride, ethylmercury chloride and phenylmercury chloride, respectively.