Determination of beryllium by electrothermal atomic absorption spectrometry using tungsten surfaces and zirconium modifier.

Electrothermal atomization of beryllium from graphite and tungsten surfaces was compared with and without the use of various chemical modifiers. Tungsten proved to be the best substrate, giving the more sensitive integrated atomic absorption signals of beryllium. Tungsten platform atomization with zirconium as a chemical modifier was used for the determination of beryllium in several NIST SRM certified reference samples, with good agreement obtained between the results found and the certified values. The precision of the measurements (at 10 microgL(-1)), the limit of detection (3sigma), and the characteristic mass of beryllium were 2.50%, 0.009 microgL(-1) and 0.42 pg, respectively.

Low level radioactivity measurements with phoswich detectors using coincident techniques and digital pulse processing analysis.

A new system has been developed for the detection of low radioactivity levels of fission products and actinides using coincidence techniques. The device combines a phoswich detector for alpha/beta/gamma-ray recognition with a fast digital card for electronic pulse analysis. The phoswich can be used in a coincident mode by identifying the composed signal produced by the simultaneous detection of alpha/beta particles and X-rays/gamma particles. The technique of coincidences with phoswich detectors was proposed recently to verify the Nuclear Test Ban Treaty (NTBT) which established the necessity of monitoring low levels of gaseous fission products produced by underground nuclear explosions. With the device proposed here it is possible to identify the coincidence events and determine the energy and type of coincident particles. The sensitivity of the system has been improved by employing liquid scintillators and a high resolution low energy germanium detector. In this case it is possible to identify simultaneously by alpha/gamma coincidence transuranic nuclides present in environmental samples without necessity of performing radiochemical separation. The minimum detectable activity was estimated to be 0.01 Bq kg(-1) for 0.1 kg of soil and 1000 min counting.

Nickel as a chemical modifier for sensitivity enhancement and fast atomization processes in electrothermal atomic absorption spectrometric determination of cadmium in biological and environmental samples.

A systematic study of the efficiency of protons, Ni, Pd and Th as chemical modifiers for the determination of cadmium by electrothermal atomic absorption spectrometry (ETAAS) using fast temperature programs was made for platform atomization. A comparison was made in terms of the salt type, absorbance-time profiles and elimination of the sodium chloride interference. The results were adapted to develop a method for the ETAAS determination of cadmium in biological and environmental samples. The highest sensitivity to determine cadmium in biological and environmental samples was obtained using nickel (together with protons) as a chemical modifier. The accuracy of the method was tested by the determination of cadmium in different certified reference materials. The best detection limit and the characteristic mass of Cd were found to be 0.03 ng mL(-1) and 0.35 pg, respectively.

Speciation of selenite and selenate using living bacteria.

In this work, a reliable method is described for speciation of soluble inorganic selenium ions, Se(IV) and Se(VI), which combines an uptake process by using living bacterial cells and electrothermal atomic absorption spectrometry (ETAAS). A selective retention of either Se(IV) or Se(IV) plus Se(VI) can be carried out by using the uptake system made up of either Pseudomonas putida or Escherichia coli strains cultivated in a culture medium based on glucose (P. putida) and glucose plus dipotassium phosphate (E. coli) mixed together with the original sample solution containing the selenium species. Discrimination between inorganic selenium species is possible by combining the optimization of the bacterial cell, the growth conditions and the relative rates of their retention from the sample. In the general procedure, an equilibrium between the analyte in the solution and the uptake system is allowed to be established, and then the concentration of selenium is determined directly in the biomass by slurry sampling ETAAS. Nonetheless, a theoretical model is proposed to describe the retention process by the living bacterial cells, which also provides a feasible quantification of the extraction process before the adsorption equilibrium is reached and whenever the agitation conditions and the sampling time are under control. The detection limits for the inorganic selenium species at the best retention conditions are of 5.7 ng Se(IV) ml(-1) for P. putida and 6.1 ng Se(IV) ml(-1) and 6.3 ng Se(VI) ml(-1) for E. coli. The relative standard deviations of the adsorption/determination process are 2.9-6.3%.

A thermodynamic approach to the binding mechanisms of cefotaxime to serum albumins.

The interaction between cefotaxime and the serum albumin of several mammalian species (swine, rabbits, and sheep) at the albumin concentration of 5 x 10(-5) M was studied. Ultrafiltration and spectrophotometric determination of the free antibiotic in the filtrate were used. Binding percentages were determined, and the binding constants and number of sites at various temperatures were calculated. An increase in binding constants, especially in sheep albumin, and an increase in the number of sites from two to three were observed when compared to the results obtained at the physiological albumin concentration. The thermodynamic parameters of interaction varied between the following values: change in Gibbs energy, between -5.7 and -6.4 kcal.mol-1; change in enthalpy, between -6.7 and -9.6 kcal.mol-1; and change in entropy, between -3.1 and -11.2 entropy units. The binding constants increased considerably as the ionic strength of the solution decreased although the number of binding sites remained unchanged. These results indicate the existence of ionic and hydrogen bonds. The possibility of a small contribution from hydrophobic bonds cannot be ruled out.

Possible biotransformation mechanism of 3-aminopropionitrile by means of free radicals.

The possible role of free radicals in the transformation of 3-aminopropionitrile giving rise to the liberation of cyanide was studied. Rat liver homogenates were cellularly fractionated. It was confirmed that the transformation occurred mainly in the microsomal fraction. The different isozyme forms of cytochrome P-450 were then partially purified and their velocity and affinity constants determined. It could be deduced that the cyanide-forming activity was mainly due to the LM3C cytochrome form. Dimethylsulfoxide was a potent competitive transformation inhibitor while mannitol was a moderate one. An OH radical generator inorganic system was also shown to liberate cyanide from 3-aminopropionitrile. In view of these results, a transformation mechanism of 3-aminopropionitrile by means of OH free radicals is suggested with the formation of cyanide anion in a cell-free organic system as well as in the microsomal fraction of rat liver.

The interaction of cefotaxime with the serum albumin of several mammalian species.

1. The interaction of cefotaxime with the serum albumin of several mammalian species; horses, swine, sheep, dogs and rabbits, was studied comparatively. The technique of ultrafiltration and spectrophotometric determination of the free antibiotic in the filtrate was used. 2. Binding percentages, which vary according to the species studied, were found to be higher in swine and rabbit albumins (between 92 and 81%) and lower for sheep, dog and horse albumins (between 67 and 52%). 3. The number of binding sites is usually close to 2; in the case of the horse it is 2.43. The apparent binding constants are: swine, 1.61 x 10(4) M-1; rabbit, 1.19 x 10(4) M-1; sheep, 2.33 x 10(3) M-1; dog, 2.00 x 10(3) M-1; horse, 1.42 x 10(3) M-1. The Scatchard model was used for data analysis. 4. Possible consequences of this interaction regarding clinical use of cefotaxime on different species are discussed.

[Production of cyanide in the rat liver from 3-aminopropionitrile]. / Production de cyanure dans le foie de rat à partir de 3-aminopropionitrile.

CN- Production was investigated from a saturated mononitrile, 3-aminopropionitrile, in small liver pieces and liver homogenates. Results show that CN- production is a function of time and of the concentration of active ingredient, with a trend to saturation in both cases. Similarly, cell integrity is not required for the biotransformation of 3-aminopropionitrile to occur. Cofactors such as NADPH must be present to reach high level activities. The effect of free radicals scavengers such as mannitol and DMSO was also studied.