“Coulometric CO2 Titration for the Determination of H20+in Rocks.” Technical paper presented at the 42nd Southwest Regional American Chemical Society Meeting. November 19-21. 1986.
Tweedy. S. W., T. L. Pinkston, and D. W. Koppenaal
PROGRAM AND ABSTRACTS
NOVEMBER 19-21, 1986
COULOMETRIC CO2 TITRATION FOR THE DETERMINATION OF H2O+ IN ROCKS. S.W. Tweedy, T.L. Pinkston, D. W. Koppenaal, Bureau of Economic Gerology, The University of Texas at Austin, University Station, Box X, Austin, Texas 78713
A coulometric titration method has been adapted for the determination of H2O+ (bound water) in rocks. The method involves pyrolysis of the dried sample and quantitative conversion of the liberated water to carbon dioxide by reaction with 1,1 -carbonyldiimidazole. The carbon dioxide is then absorbed in solution and titrated coulometrically. The method appears to be superior in precision and accuracy when compared with an established Karl Fischer titration procedure for H2O+ determination and has the following advantages over other methods used in similar analyses: (1) high temperature pyrolysis insures total liberation of water, (2) standardization of the titrant is precluded, (3) large (~200 mg) samples can be accommodated, (4) condensation problems existent in the Penfield method are avoided. Accuracy of +4% with precision of 3% is achieved at H2O+ concentration levels of one weight percent. Description of the system used, along with comparative data for performance on standard reference rock samples will be presented.
SOME COMMONG THERMOANALYTICAL CHARACTERISTICS OF DURABLE PRESS RESINS BASED ON CYCLIC UREA, Brenda J. Trask and B. A. Kottes Andrews, Southern Regional Research Center, 1100 Robert E. Lee Blvd., P.O. Box 19687, New Orleans, LA 70179
Thermal analyses, including Differential Scanning Calorimetry (DSC), Thermogravimetry (TG), and Differential Thermogravimetry (DTG), were performed on a series of derivatives of cyclic urea. Such compounds are used extensively for durable press finishing of cotton textiles. Two common features were discovered after more than 12 resins were analyzed under nitrogen. These features related to the presence of an oxygen-containing substituent on the ring carbons or the ring nitrogens. The former substitution was expresses as an exothermic response between 200o-300oC and the latter as an endotherm between 300o-400oC. Specific substituent modifications that changed these responses are described.
DIGITAL SIMULATION AND PEAK RESOLUTION IN DIFFERENTIAL SCANNING CALORIMETRY. Guang-Way Jang and Krishman Rajeshwar, Department of Chemistry, The University of Texas at Arlington, Arlington, Texas 76019-0065
An equivalent-circuit model is presented for a commercial heat-flux differential scanning calorimetry (DSC) cell. This model is developed in a form which permits direct comparison with experimental data. The various thermal resistance factors in the cell are computed via this model. In particular, the influence of variables such as the heating rate and the thermal characteristics of sample and the purge gas atmosphere, is critically examined. A digital simulation method is finally used to test the influence of these variables on peak shape and resolution. The simulated and experimental thermograms demonstrate for the first time that better peak resolution and sensitivity can be achieved in DSC by using a high conductivity purge gas such as helium.
GoIGO (Good in Garbage Out)
Shyam S. Shukla, Department of Chemistry, Lamar University, Beaumont, TX 77710
Access to powerful computing ability in the laboratory has contributed to an increasing use of sophisticated computational techniques by chemists. Generally, the results of a computation are considered to be correct. However, even when the data is correct, the results of a computation can be grossly incorrect. This is because of the fact that most computing machines have limitations which basically arise from the finite representation of the numbers, leading to round-off and truncation errors. On the first glance the magnitude of these errors appears to be small but their effect can be amplified because of accumulation, ill-conditioning of algorithm, cancellation, and instability. In this paper we will discuss such computational errors, as well as strategies to minimize them.