Evaluation of pH Shift in Glass Vials for Auto-Samplers
Do glass vials affect the pH of valuable samples? The answer is simple: "Yes."
pH has a significant impact on the ionization state of specific analytes. For example, a base with a pKa of 8.5 is 99% ionized at pH 6.5 using the 2 pH unit rule and 99% non-ionized at pH 10.5. When the analyte is close to its own pKa, unstable chromatograms may be observed, so it is necessary to adjust the pH to achieve the appropriate ionization state. Differences in the surface activity of vial glass and the leaching of hydrolysis products that affect the sample pH can be confirmed by monitoring the pH changes of deionized water stored in the vial. To investigate how the quality of glass, represented by the expansion coefficient, affects the pH of the solution, we measured the fluctuations in the pH of 18 MΩ pure water stored in an autosampler vial for a certain period at room temperature and compared the results with those obtained using polypropylene containers as a control.
