Determination of chromium in human milk, serum and urine by electrothermal atomic absorption spectrometry without preliminary ashing

In the present study a Perkin-Elmer 5000 atomic absorption spectrometer equipped with a tungsten--iodide lamp for improved background correction at the 357.9 nm chromium absorption line and an HGA 500 graphite furnace were employed for the direct determination of chromium in human serum, milk and urine. The method of standard additions was used: 0.25-0.75 ng Cr was added to 1 ml samples. Except for urine samples, a dilution of 1 + 1 to 1 + 2 with H2O was necessary in order to obtain correct calibration curves. The average concentration of chromium in all the samples of normal subjects was less than 0.5 ng Cr ml-1. The day-to-day variation for all of the pooled samples was around 10% (relative standard deviation). For urine, the accuracy of the method was tested by comparing the results of another laboratory for the same two round robin samples. Excellent agreement was found between the present method and those of the other laboratory that had used isotope dilution--mass spectrometry and continuum source wavelength modulated echelle--atomic absorption spectrometry to define the chromium concentration in the samples. The detection limit of the method, 0.05 ng Cr ml-1 for urine and serum and 0.1 ng Cr ml-1 for human milk, was sufficient for the biological fluids analyzed. The method was employed for the determination of chromium in 24-h urine samples of maturity onset diabetics supplemented with 20 or 200 micrograms Cr3+ d-1 for six weeks. It was shown that the 24-h urinary chromium excretion accurately indicates the daily dietary chromium intake of these patients.     

A high-gain 58-GHz box-horn array antenna with suppressed gratinglobes

A low-profile high-gain antenna array of box horns for the frequency band 57.2-58.2 GHz is presented. The antenna consists of 256 radiating elements divided into two subgroups of 128 elements fed by a rectangular waveguide feed network. The radiating elements are fed in parallel and the waveguides are connected with T-junctions. The matching of the T-junctions is improved with a matching pin and a splitter. Because of the waveguide feed network, the element spacing is larger than one wavelength, which causes grating lobes. The grating lobes and sidelobes in the H-plane have been suppressed by the use of a combination of subarrays, a special characteristic of the box horn, and an array amplitude tapering. The measured sidelobe levels in the H-plane are below -30 dB at angles larger than 8° from boresight. A gain higher than 35.7 dBi and a return loss higher than 14.4 dB have been measured for the antenna over the band 57.2-58.2 GHz     

An evaluation of DGT performance using a dynamic numerical model

A numerical model of the transport and dynamics of metal complexes in the resin and gel layers of a DGT (diffusive gradients in thin films) device was developed and used to investigate how the chelating resin and metal-ligand complexes in solution affect metal uptake. Decreasing the stability constant or concentration of the binding resin increases the competition for free metal ions by ligands in solution, lowering the rate of mass uptake. Such effects would be rarely observed for moderately or strongly binding resins (K> 10(12)), including Chelex, which out-compete labile ligands in solution. With weakly binding resins, strongly bound solution complexes can diffuse into the resin layer before a measurable amount of dissociation occurs, such that concentrations of bound metal at the rear and front surfaces of the resin layer are equal. With more strongly binding resins, metal mainly binds to the front surface of the resin. Only complexes with the largest binding constants penetrate the gel layer containing Chelex, buttheir lack of lability means thatthe DGT sensitivity to the complex is, in any case, very low. The slow diffusion of complexes, such as those of fulvic acids, which increases the time required to establish steady state, compromises the use of the simple DGT equation. Errors are negligible for 24 h deployments, when diffusive layer thicknesses are less than 1 mm, but 3 day deployments are required to ensure accuracy with 2.4 mm thick layers. The extent to which the commonly used equation, that accounts for the concentration and diffusion of metal-complex species, overestimates DGT uptake if the rate of dissociation is slow, was estimated.     

Neutral electrolyzed water (NEW), chlorine dioxide,organic acid based product,and ultraviolet‐C for inactivation of microbes in fresh‐cut vegetable washing waters

The effect of decontamination methods on fresh‐cut vegetable washing waters was evaluated. NEW, ClO₂, organic acid‐based product FPW, and UV‐C were tested with and without an interfering carrot juice of 1% (IS), on Yersinia enterocolitica and Yersinia pseudotuberculosis, Escherichia coli, and yeast Candida lambica. The use of ClO₂ (50 ppm active chlorine) resulted in >4 log reduction of Y. enterocolitica, Y. pseudotuberculosis, E. coli and >3 log reduction of C. lambica. The antibacterial effect of NEW was less effective in the presence of IS when compared with ClO_2. The inactivation of C. lambica by FPW reached a maximum of 2.8 log cfu/mL (concentration 0.125%), but the antimicrobial effect was delayed by the IS. The effect of FPW on E. coli was significantly reduced by 1% IS. The inactivation of E. coli and C. lambica with UV‐C IS decreased the inactivation and lengthened its time. Filtration improved the effect of UV‐C inactivation.

Practical applications

When chemical decontamination methods were used in fresh‐cut vegetable processing, the presence of organic matter in process water increased the reaction times and the need for higher concentrations of the chemical decontamination and the time of physical decontamination. Yersinia required longer inactivation times than E. coli. When UV‐C is used for decontamination of process waters, waters should be filtered to enhance the disinfection efficacy.     

Photodegradation of Selected Aromatic Constituents of Creosote in Organic Solvents

Polycyclic aromatic hydrocarbons (PAHs), naphthalene, phenanthrene, anthracene, and pyrene were irradiated in acetonitrile (CH₃CN) and in dichloromethane (CH₂Cl₂) on individual PAH compounds and in the presence of other compounds. The observed photodegradation of PAHs was dependent on the structure of the compound. Anthracene and pyrene were the most photoreactive in dichloromethane: with total degradation after 0.5 h irradiation for anthracene and 1.5 h for pyrene. The decomposition of PAHs was faster in dichloromethane than in acetonitrile.     

Test results of 310 GHz hologram compact antenna test range

The quiet-zone field test results of a submillimetre-wave compact antenna test range (CATR) based on a 60 cm diameter hologram are presented. The instrumentation setup based on a dedicated millimetre-wave vector network analyser is also briefly described. The presented test results at 310 GHz show the potential of the hologram CATR for submillimetre-wave antenna testing     

Passivation of nanostructured silicon optical devices by thermal carbonization

Nanostructured silicon interference filters have been thermally carbonized by acetylene decomposition at different temperatures in order to passivate their high internal surface area. Stability has been studied by periodically measuring the optical spectrum of treated and untreated porous silicon filters stored in oxidizing environments. Experimental results show that thermal carbonization stabilizes the structures against oxidation, since treated samples show no significant shift of their optical spectra after storage in either ambient air or ethanol for up to two months. Moreover, the thermal carbonization process has no significant effect on the optical performance of the filters. Results show that thermal carbonization by acetylene decomposition provides an effective way to produce chemically stable porous silicon optical devices for biological and chemical sensing.     

Effects of ethanol to water ratio in feed solution on the crystallinity of spray-dried lactose

In the present study, the effects of ethanol to water ratio in feed solution on the physical properties of spray-dried alpha-lactose monohydrate were evaluated. Crystallinity of the spray-dried lactose was determined by isothermal microcalorimetry (IMC) and by differential scanning calorimetry (DSC). Water content of the spray-dried lactose was determined by thermogravimetric analysis and the surface area was evaluated by Brunauer, Emmett, and Teller (BET) method. The crystallinity of spray-dried lactose varied from 0% to 100%, depending on the ratio of ethanol to water in the feed solution. Lactose spray dried from pure ethanol was 100% crystalline and contained hydrate water. Lactose spray dried from pure water was 100% amorphous. The feed solution substantially affected the ratio of surface water to hydrate water, as the content of surface water increased and hydrate water decreased, while the crystallinity of spray-dried lactose decreased. Surface area of the spray-dried lactose increased as a function of amorphous content.