Column Overloading Research Articles

Application of Azulene as Visual Aid to Monitor Column Chromatographic Fractionation of Samples for Pesticide and Polychlorinated Biphenyl Determination

Abstract Environmental samples are cleaned up by Florisil column chromatography, using azulene as a visual aid to monitor column performance. Azulene migrates as a blue band in the 6% ethyl ether-hexane fraction, and the gas chromatograph electron capture detector (GC-ECD) is nonresponsive at the use concentration. This method complements the standardization of Florisil columns by weight adjustment based on adsorption of lauric acid. Spiking of sample with azulene provides a convenient real-time monitor for column channeling, mistakes in polarity of mobile phases, particular sample composition, column overloading, and dynamic changes in the adsorptivity of the stationary phase between lauric acid calibration and use. Using this visual aid, the analyst is alerted to unexpected column behaviors. Normally, polychlorinated biphenyls (PCBs) elute in the 6% fraction, in front of the blue indicator. Experiences with azulene and industrial effluent samples demonstrated that PCBs can elute in the 100% hexane fraction. GC-ECD analysis of the hexane eluate revealed a PCB characteristic chromatogram, not observed with the original extract. Thus, monitoring column performance avoided reporting a false negative result, i.e., no PCBs in the 6% ethyl ether-hexane fraction.

Cross-Correlation Chromatography Applied to Gas-Solid Adsorption Studies

Abstract : The use of cross correlation techniques on multiple injection gas chromatography as a means to describe gas-solid interactions has been demonstrated. A deconvolution technique using the Fourier transform of both the cross correlation of the output and the auto correlation of the input series has been developed. The deconvolution allows the differentiation between correlation noise due to an imperfectly random input series and actual correlation peaks due to column interaction. The relationship between sample size and the resulting column overloading and the size of secondary correlation peaks is discussed. (Author)

Polymer reactors and molecular weight distribution. Part III. Gel permeation chromatography, methods of correcting for imperfect resolution

AbstractThis paper reports a preliminary evaluation of four methods of correcting for imperfect resolution in gel permeation chromatography. These are methods of Tung, Smith, Hess and Kratz, and Pickett. To evaluate the methods over a range of resolutions, many broad‐ and narrow‐distribution polystyrene samples covering the molecular weight range 1000–500,000 were analyzed with three different column combinations having residence times from 20 to 150 min. The results show the increasing importance of the resolution correction with increasing molecular weight and decreasing residence times. For Tung's method the correction to molecular weight averages ranged from about 4% for 150 min. of residence time to about 12% for 20 min. Residence times as short as 10 or 15 min. should be possible without serious loss of accuracy. Inconsistencies in the high molecular weight results for the methods of Tung and Smith indicate inadequacies in the assumed chromatogram shapes for single molecular species, due to effects of column overloading and species interaction. These effects can be reduced by decreasing the sample concentration. When these effects are not prominent, the methods of Tung and Smith appear to be adequate. Smith's modified method permits the use of various chromatogram shapes for single species to account for overloading and interaction. Computational difficulties at present limit the use of the method of Hess and Kratz. Pickett's method looks promising, especially if concentration dependence can be included in the chromatograms representing the single species. Further evaluation needs to be done to determine which method best handles the region where overloading and species interaction occur.