Evaluation of a Thermal Pulse Flowmeter for Quantitative Size Exclusion Chromatography

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Abstract
The objective of this paper is to show an evaluation of the accuracy and precision of mobile phase flow rate measurement for size exclusion chromatography (SEC) using a thermal pulse flowmeter (TPF). The TPF measures flow by generating a pulse of heat in the liquid and determining the time required for it to be transported downstream to a fixed thermistor. The paper emphasizes development of a generally applicable method of assessing the TPF. The first method examined involved attaching a high precision syringe pump to the TPF to control input. Different responses were obtained with different solvents. Also, pulse transport time reproducibility as a function of solvent flow rate was determined and explained using error propagation analysis. However, with the very low values of error variance involved, uncertainties originated from the performance of the syringe pump system and SEC requirements. Therefore, the second method of evaluation selected was to correct actual SEC data using the TPF and to compare molecular weight averages to the known values. One calculation option was chosen and showed that, for this, particular rather noisy high temperature SEC system, the flow rate correction significantly improved accuracy of Mn but slightly worsened accuracy of Mw as well as precision of the averages. This second evaluation method, use of SEC data, is recommended over off-line approaches.