Coulometric Titration Baseline Drift Calibration Methods
Drift calibration isolates cell background current from true sample moisture, preventing hydrolytic degradation and avoiding false incoming resin lot rejections.
Sample Vial Blank
Meaning
Standard analytical control prepared in an empty sealed vial to measure the moisture contained in the enclosed air. In Karl Fischer headspace analysis of polymers, a sample vial blank is processed under the same heating and flow conditions as the actual resin samples. This measurement determines the background moisture contribution from the vial itself, which is then subtracted from the total sample moisture.
Background Correction
Air trapped inside a vial contains moisture that varies with the relative humidity of the laboratory. Running a sample vial blank measures this atmospheric water so it does not skew the polymer dry-weight results.
Quantification Protocol
Operators place an empty vial in the heating oven and purge it with dry carrier gas. The moisture measured from this run establishes the baseline contribution for the sample vial blank. Subtracting this blank value from the subsequent resin measurements is critical when analyzing very dry materials like PET.
It ensures that the calculated moisture level represents only the water released by the polymer pellets.
Quality Control
Fluctuations in laboratory humidity can change the background moisture level between runs. Analyzing a sample vial blank at regular intervals maintains the precision of the moisture measurements. This control step prevents false failures and holds the test to high standards of accuracy.