Browsing by Subject "Colorimetric analysis"
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Item Development of a rapid method for the determination of fiber content in polyester/cotton blends(Texas Tech University, 1983-08) Sours, Ellen LouiseMethods were developed to accurately and quickly determine the polyester fiber proportions present in polyester/ cotton blends. The results of the developed techniques were compared to those obtained using the American Association of Textile Chemists and Colorists (AATCC) Test Method 20A, a sulfuric acid dissolution technique. Six fabric blend levels and eleven fiber blend levels were used to develop the methodology. The samples were dyed using sublimation techniques and disperse dyes. Reflectance data were utilized in developing simple linear regression equations to predict polyester content. In some cases, the polyester contents of blends as determined by the newly developed methods showed no significant differences (a<^.05) when compared with the polyester contents of the same samples as determined by the AATCC Test Method. Blend levels predicted by the sublimation techniques had standard errors of the mean that fell within the accepted + 3% range as required by the Federal Trade Commission for truth in labeling. The developed methods provide rapid and easily executed tests for determining polyester fiber blend proportions in polyester/cotton blends.Item Flow-based automatic analysis systems(Texas Tech University, 2000-05) Galanis, SofiaPolyurethane foam is utilized by furniture, automotive, construction, insulation and footwear industries at a growing rate. A dominant prepolymer for polyurethane foam is polyether polyol. The current technique for analyzing potassium hydroxide (KOH) in polyol involves a laborious wet chemical method, in which a significant time lag exists between sample collection and availability of the analytical result. An on-line, near real time KOH analyzer to monitor the polyol is desirable. An automated flow analysis system utilizing conductivity detection was investigated. If KOH is the principal electrolyte contaminant, it will be the dominant current carrier. By mixing the polyol with an acid solution at different ratios, the neutralization point was successfully indicated by a minimum in conductivity in initial experiments. The suitability of acid introduction by permeation tubes, gaseous acids and alcohol solution injections was tested. However, the presence of significant background conductivity suggested that the method will not be feasible at low parts per million (ppm) levels of KOH. Therefore, an alternative approach was required. An automated reverse flow injection (Fl) based continuous analyzer with a fiber-optic based optical absorbance detector was fabricated and various schemes were tested. The most successful of these involved the injections of a solution of bromocresol green (BCG) in 2-propanol, with or without added mineral acid, into the sample polyol stream in a single-line Fl manifold maintained at 110°C (dispersion factor of 50-25 for a dilute aqueous stream at room temperature with 10 and 30 ^iL of solution injected). Measurements could be made In the present system every 4 minutes. Deliberate alteration of water content of the polyol stream in the range of interest was found to have no discernible effect on the measurement.Item Measurement of hexavalent chromium in leather by colorimetric methods(Texas Tech University, 2000-05) Jambunathan, SivakumarColorimetric methods of measurement forms an important basis for analysis of a variety of compounds and metallic species. Some of the more important advantages of using colorimetric methods include low cost, limited need for sophisticated instruments or personnel. Determination of hexavalent chromium (Cr(yi)) by diphenylcarbazide(DPC) is a very common method. Chromium (VI) is carcinogenic and its determination is very important. Chromium (VI) occurs in chromiimi-tanned leather samples and there are regulations on permissible limits. The current official procedure (called the IUC-18 procedure) is based on DPC and is generally inapplicable to leather samples that produce a colored extract. The customary DPC method as well as several modifications thereof have been studied in a variety of leather samples with a view to improve sensitivity of the procedure. A pre-bleaching procedure was developed. This allowed reliable analysis of a majority (but not all) of the samples studied as compared to results obtained with ICPOES of cation exchanged samples as the reference method. Also, the sensitivity of the DPC method has been greatly improved upon by use of a liquid core waveguide based flow through absorbance detector. As a necessary component to the above efforts, the development of an optical fiber coupled Light Emitting Diode (LED) light source based flow-through optical absorbance detector was carried out. The LED source is readily changeable. Optical fibers are used to carry light from the electronics/display unit to a reflective flow-through cell and back. The cell can thus be located remotely from the electronics unit and the umbilical connection is not susceptible to electrical noise. The noise level of this detector with LEDs of different emission maxima were observed to be in the range of 3-20 µAU under actual use conditions, with a maximum short term drift of 4 µAU/min after the initial warm up period. When the analyte absorbance is well matched with the source emission characteristics, the detector response is linear with concentration over at least two orders of magnitude. The liquid flow path through the cell is linear with a large exit aperture such that bubbles are not trapped in the optical path. The optical arrangement is such that the incident light crosses the liquid flow orthogonally, and is reflected back by a rear mirror to the receiver fiber. This arrangement reduces the refractive index sensitivity by an order of magnitude relative to conventional Z-path flow cells.Item Microdetermination of sulfate in environmental samples(Texas Tech University, 1983-12) Hwang, HoonA new indicator, 2-(8-hydroxy-3,6-disulfo-l-naphthylazo)-l,8- dihydroxynaphthalene-3,6-disulfonic acid (which is called Beryllon II or DSNADNS) has been discovered and is proposed for microtitrimetric determination of sulfate with barium. The procedure is an order of magnitude more sensitive (limit of detection is 0.25 ppm) and less interference prone compared to previously used indicators. The color change is sharper and faster compared to thorin. The optimum conditions involve titration in 80% isopropanol at an apparent pH of 3.5. The superiority of the indicator is attributed to the lower solubility of the barium-dye salt. Results are presented for environmental samples and compared to values obtained by Ion Chromatography. Also, the use of beryllon II in its form of the barium salt for colorimetric determination of sulfate provides a promising result.Item Screening pesticides with a colorimetric phage induction essay(Texas Tech University, 1981-05) Hume, Sharlene HelenNot available