Ultraviolet Absorbance Values Research Articles

Concentrations and characteristics of organic carbon in surface water in Arizona: influence of urbanization

Dissolved (DOC) and total (TOC) organic carbon concentrations and compositions were studied for several river systems in Arizona, USA. DOC composition was characterized by ultraviolet and visible absorption and fluorescence emission (excitation wavelength of 370 nm) spectra characteristics. Ephemeral sites had the highest DOC concentrations, and unregulated perennial sites had lower concentrations than unregulated intermittent sites, regulated sites, and sites downstream from wastewater-treatment plants ( p<0.05). Reservoir outflows and wastewater-treatment plant effluent were higher in DOC concentration ( p<0.05) and exhibited less variability in concentration than inflows to the reservoirs. Specific ultraviolet absorbance values at 254 nm were typically less than 2 m −1(milligram DOC per liter) −1 and lower than values found in most temperate-region rivers, but specific ultraviolet absorbance values increased during runoff events. Fluorescence measurements indicated that DOC in desert streams typically exhibit characteristics of autochthonous sources; however, DOC in unregulated upland rivers and desert streams experienced sudden shifts from autochthonous to allochthonous sources during runoff events. The urban water system (reservoir systems and wastewater-treatment plants) was found to affect temporal variability in DOC concentration and composition.

Changes in olive oil composition due to microwave heating

AbstractThe effects of microwave heating on some components of extra‐virgin olive oil were studied. Traditional parameters, including free acidity, peroxide value and ultraviolet absorbance values at 232 and 268 nm, were determined in six extra‐virgin olive oil samples before and after the microwave treatment. Significant differences (P&lt;0.01) were detected for free acidity, peroxide, and ultraviolet absorbance at 268 nm; also, the absorbances at 232 nm showed significant differences (P&lt;0.05) between treated and untreated samples. The glycerolic fractions, triacylglycerols (TAG), diacylglycerols (DAG), and monoacylglycerols (MAG), were isolated by thin‐layer chromatography. The respective percentage fatty acid (FA) composition and percentage amount were obtained by high‐resolution gas chromatography with an internal standard. For the most abundant TAG fraction, the stereospecific analysis was carried out to obtain the FA percentage compositions of the three sn‐positions. Small but significant modifications were observed regarding the decrease in the TAG percentage and increases in the DAG and MAG percentage amounts. No significant changes were observed for the FA compositions of TAG, DAG, and MAG fractions before and after the treatment. Nevertheless, the results of TAG stereospecific analysis showed losses of unsaturated FA in all sn‐positions. Higher percentage changes in the sn‐1‐ than in sn‐2‐position of TAG were observed. Regarding the volatile fraction, different profiles were obtained after the treatment.

Enhanced softening: factors influencing DBP precursor removal

Bench‐scale tests demonstrate the importance of magnesium hydroxide precipitation and NOM characteristics on precursor removal by softening.Relationships of hardness removal, natural organic matter (NOM) removal, and selected chemical characteristics of NOM were explored, and the implications of the enhanced softening portion of the proposed Disinfectants/Disinfection By‐products Rule were assessed. For most of the nine raw water sources examined, the amount of dissolved organic carbon (DOC) removed (both on an absolute and a percentage basis) correlated strongly with the amount of magnesium precipitated. A semilogarithmic model provided a good fit to the data for six of the nine waters (R2 values &gt;0.8). Greater absolute removal of DOC was achieved for raw waters with higher initial DOC concentrations. DOC removal by softening was most effective for the raw water sources with the highest percentage of hydrophobic organic carbon. Greater specific ultraviolet absorbance values also corresponded to greater DOC removal.

Microspectrophotometry of Phenolic Compounds in Bermudagrass Cell Walls in Relation to Rumen Microbial Digestion

The amount and location of phenolic compounds within plant cell walls are important factors in limiting forage digestibility. The present study was undertaken to evaluate phenolic compounds within plant cell wall types that differed in digestibility in leaf blades of ‘Coastal’ (CB) and ‘Coastcross‐1’ (CX) bermudagrasses [Cynodon dactylon (L.) Pers]. The ultraviolet (UV) spectra of the cell wall types in bermudagrass leaf blades were obtained by microspectrophotometry and the results related to their digestibilities (measured by microscopy after in vitro incubation in rumen fluid) and to their histochemical reactions for phenolic compounds. Cell walls of all tissues gave three absorption peaks in the ranges of 317 to 324, 285 to 293, and 244 to 254 nm. Indigestible cell walls (sclerenchyma and mestomc sheath) had high UV absorbance (ca. 1.8 at 320 nm) and had positive tests with histochemical reagents for phenolics. In contrast, totally digestible cell walls (mesophyll and phloem) had low UV absorbance (ca. 0.2 at 320 nm) and had negative or weak reactions for phenolics. Partially digestible cell walls (parenchyma bundle sheath and epidermis) had intermediate UV absorbance (ca. 0.45 at 320 nm) and were positive for phenolics with chlorine‐sulfite and diazotized sulfanilic acid reagents. Comparison of cell wall types in leaf blades of CB and the more highly digestible CX showed that corresponding tissues of the two cultivars had similar UV absorbance values, with the exception of parenchyma bundle sheath; the parenchyma bundle sheath cell walls of CX had approximately two‐thirds the UV absorbance values of those of CB and were more digestible. Hence, improved digestibility of CX leaf blades appears to result from a lower concentration of phenolic compounds within cell walls of parenchyma bundle sheaths.

Measurement of wastewater treatment efficiency by fluorescence and UV absorbance

The degree of chemical treatment in terms of removal of organic matter from different wastewaters has been investigated by employing potassium ferrate (K2FeO4) and ozone in various combinations. The study was performed in both the batch and the continuous flow systems. The treatment efficiency was determined through three different methods, i.e., chemical oxygen demand (COD), fluorescence and ultraviolet (UV) absorption. Fluorescence and UV absorption techniques were employed due to their specificity in measurement of humic substances, aromatic compounds and heterocyclic systems, whereas COD is a general parameter for the estimation of total organic matter. Fluorescence and UV absorbance values were correlated with respective COD values.

Effect of Maleic Acid on the Ultraviolet Absorption of Some Antihistamine Maleate Salts

Abstract Several official compendial monographs contain assay procedures which compare the ultraviolet (UV) absorbance of a sample solution of a mineral acid salt of an antihistamine with that of a standard solution of the antihistamine maleate salt. The recovery data, UV absorbance values, and UV spectra presented show that erroneously low assay results are obtained when UV absorptions (below 280 nm) of antihistamine maleate sample solutions previously extracted from alkaline aqueous media into organic solvents are compared with antihistamine maleate standard sample solutions diluted directly in the same acid medium. Such errors are shown to be caused by the UV absorption properties of the maleic acid moiety.

Computer-oriented analysis of human chromosomes. I. Photometric estimation of DNA content.

The potential value of DNA content as a parameter for karyotype analysis is presented, and a method is developed based on optical density measurements of gallocyanin-chrome alum stained chromosomes. The optical information is obtained automatically in digital form by CYDAC, a special purpose cytophotometer. A partly automated computer analysis of the data then provides the relative stain content of individual chromosomes and chromosome arms. Experience with three metaphases from the same human female indicates stable clustering of the results, with sufficient discrimination among clusters to identify eleven discrete chromosome classes. It would appear from the values obtained that gallocyanin-chrome alum stain content of individual chromosome arms correlates closely with length and ultraviolet absorbance values given in the literature. It is not yet clear whether stain content represents DNA content alone, or includes other constituents of the chromosome that tend to be proportional to DNA content. Judging from the analysis of errors, improvement in the resolution of the photometric method can be expected. This approach has promising applications in the automation of karyotype analysis and as an additional and powerful parameter in cytogenetic study.

Ronnel (0,0-Dimethyl 0-(2,4,5-trichlorophenyl) phosphorothioate) in Feeds

Abstract An ultraviolet spectrophotometric method for ronnel (at levels of 0.04 to 0.3%) in complete feed mixtures was developed during the year and studied by two collaborators. Ronnel is extracted with methanol and hydrolyzed to 2,4,5-trichlorophenate. After evaporation of the methanol, the residue is dissolved in water, acidified, and steam distilled. The 2,4,5-trichlorophenol is extracted from the steam distillate with iso-octane, and its ultraviolet absorbance values are determined. Results showed satisfactory recoveries of the added ronnel with good agreement between replicates and laboratories. Blank values on the unfortified feeds were extremely low. It is recommended that this method be subjected to collaborative study, and that the first action method (adopted October 1961) for ronnel in mineral-base mixtures be adopted as official, final action.