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At least 487 records · Page 27Linked to original sources
PubMed2001

Repeatability of in vitro measurements of the ultraviolet protection factor (UPF) by spectrophotometry with automatic sampling.

BACKGROUND/AIMS: Spectrophotometric assessment (in vitro) is the most established method for determining the ultraviolet protection factor (UPF) of textiles. Apart from stringent requirements for measurement precision, practical methods are required for the routine determination of the UPF. We report here spectrophotometric measurements of textiles using a newly developed autosampler. Measurement precision was evaluated under repeatable conditions. METHODS: Fifteen different textiles were spectrophotometrically assessed for the determination of the UPF. Sample handling inside the spectrophotometer was performed with a computer-controlled sampling device, capable of loading and unloading a textile sample from a magazine as well as rotating the sample perpendicular to the spectrometer beam. In order to evaluate the repeatability of measurements, one sample of each textile was assessed eight times under the same conditions in the same laboratory. RESULTS: A mean percentage of the standard error of 1% [E(UPF)] was calculated for the UPF measurements. For UPFs >30, a significantly higher E(UPF) was found (r=0.78; P<0.001). E(UV) (3.9%) of ultraviolet A (UVA) transmission differed significantly from E(UV) (1.1 %) of ultraviolet B (UVB) transmission (P<0.05). CONCLUSIONS: Though a slight decrease of repeatability was observed for UVA transmission measurements and UPFs higher than 30, our data indicate a high measurement precision under repeatable conditions. In conclusion, spectrophotometric measurements of textiles with the aid of the autosampler presented have been shown to be highly practical, time saving and precise.

Automation↗
PubMed1995

Acid-base equilibria of 1,4-benzodiazepine 4-oxides by spectrophotometry.

Chlordiazepoxide (a 1,4-benzodiazepine 4-oxide) is an anxiolytic/hypnotic drug in clinical use. It was reported to be predominantly protonated at the N-oxide oxygen in acidic aqueous solutions at pH << 4.6 (pKa). We have studied the acid-base equilibria of three 1,4-benzodiazepine 4-oxides (chlordiazepoxide, diazepam 4-oxide, and nordiazepam 4-oxide) by ultraviolet-visible spectrophotometry. The results indicate that chlordiazepoxide is not protonated at the N-oxide oxygen, but rather at the nitrogen of an imine bond between C2 carbon and its nitrogen substituent in acidic media.

Chemical Phenomena↗
PubMed1990

Method for the determination of the priority pollutant metals by HPLC.

The United States Environmental Protection Agency (EPA) currently specifies atomic absorption spectrophotometry as the method of analysis for the priority pollutant metals. While the method is very sensitive, it does suffer from limitations. As an alternative, the use of dibenzyldithiocarbamate (DBDC) to complex the priority pollutant metals from the sample, with subsequent separation of the complexes by liquid chromatography and quantification by ultraviolet-visible spectrophotometry, is reported. Of the thirteen priority pollutant metals, ten can be determined with the method (Cd, Cu, Cr, Hg, Ni, Pb, Sb, Se, Tl, and Zn). Of the remaining priority pollutant metals, beryllium was not investigated, while silver and arsenic did not form complexes with DBDC. In addition, one potential interference, manganese, can be determined. Cobalt is added as an internal standard. Separation of the complexes on a C18 column is achieved with a quaternary solvent system consisting of 64% methanol, 12% acetonitrile, 5% tetrahydrofuran, and 19% pH 5 acetate buffer. Detection limits range from a low of 0.1 ppb (ng/mL) for selenium to a high of 1.8 ppb for thallium.

Chelating Agents↗
PubMed2004

Acid-base characteristics of bromophenol blue-citrate buffer systems in the amorphous state.

In this study, we have examined the acid-base characteristics of various citrate buffer systems alone and in the presence of the pH indicator dye, bromophenol blue, in aqueous solution, and after lyophilization to produce amorphous material. Fourier transform Raman and solid-state nuclear magnetic resonance spectroscopy have been used to monitor the ratio of ionized to un-ionized citric acid under various conditions, as a function of initial pH in the range of 2.65-4.28. Ultraviolet-visible spectrophotometry was used to probe the extent of proton transfer of bromophenol blue in the citrate buffer systems in solution and the amorphous state. Spectroscopic studies indicated greater ionization of citric acid and bromophenol blue in solution and the solid state with increasing initial solution pH, as expected. Fourier transform Raman measurements indicated the same ratio of ionized to un-ionized citrate species in solution, frozen solution, and the amorphous state. It is shown that the ratio of species at any particular initial pH is primarily determined by the amount of sodium ion present so as to maintain electroneutrality and not necessarily to the fact that pH and pK(a) remain unchanged during freezing and freeze drying. Indeed, for bromophenol blue, the relative ultraviolet-visible intensities for ionized and un-ionized species in the amorphous sample were different from those in solution indicating that the extent of protonation of bromophenol blue was significantly lower in the solid samples. It is concluded that under certain conditions there can be significant differences in the apparent hydrogen activity of molecules in amorphous systems.

Bromphenol Blue↗
PubMed1978

[The influence of capillary permeability on the extravascular protein quantities as measured in situ (author's transl)].

The extravascular protein contents in the perivascular connective tissue of a rat's mesenterial plate was measured ultramicrospectrophotometrically in situ and in vivo after changing the hydrostatic and colloidosmotic pressures of the blood. We analized the perivascular area of the different microcirculatory vessels, arterioles, capillaries and venules. The perivascular protein contents, which corresponds besides arterioles to 40% and besides venules to 59% in comparison to the intravascular blood plasma, decreased in a comparison group under the osmotic influence of the perfusion liquid on the mesenterial plate. An injection of an isotonic saline solution is followed only by small fluctuations of the perivascular protein contents during one hour. After blood loss a transitional increase of extravascular protein at the perivenular area was observed indicating the mobilisation of protein depots. Around arterioles the extravascular protein contents did not change significantly. An intravenous injection of albumin solution was followed by a short-termed increase of tissue protein around the arterioles. Around the venules after 50 minutes the extravascular protein contents increased significantly. Within one hour after the changes of the permeability conditions the maximal induceable protein movements in the perivascular space were calculated as +/- 1.35 g% plasma protein concentration corresponding to a maximun protein exchange of +/- 3.1 mg ml(-1) tissue.

Animals↗