Why does the ZKF-1A Karl Fischer titrator give high water content readings?
Thread Content
This post was last edited by xwtsq on 2011-5-3 at 19:03. The water content measured using a ZKF-1A Karl Fischer titrator is consistently high, and we cannot identify the reason for this. The actual water content in the product is around 0.3%, but the measurement shows around 0.8%. The reasons I have considered are as follows: 1. The product is slightly soluble in methanol, and it tends to absorb moisture. Therefore, we add 30 milliliters of methanol to the reaction vessel and only 0.5 grams of the product sample; this amount is sufficient for the product to dissolve. By weighing the sample quickly, we can ensure that it does not absorb moisture. 2. The laboratory is on the ground floor, where the humidity is high; humidity meters usually show levels of 60-70%, but the humidity shouldn’t have such a significant impact! Our moisture content is measured as a constant value, not on a ppm scale. We bought it a few days ago, and the manufacturer sent someone to help us with the installation. On-site testing showed that the moisture content of our product was 0.2–0.3%, and we obtained the same result when testing it ourselves the next day. The instrument was left there for a week without being used; we started using it the day before yesterday, and ever since the readings have been high – we can’t find the reason for this. We used a single-component, pyridine-free Karl Fischer reagent, with a titration value of around 3.2 mg/mL.
Has the titrability of the Karl Fischer reagent been measured again? Did you pay attention to the color of the endpoint? Is it the same as the endpoint measured during installation?
Reply to 2# xwtsq: I agree with your view; I personally also think it is the change in titrability
This post was last edited by jackwen on 2011-5-3 20:13. Thank you, moderator. We are fully automatic: automatic measurement and reading, automatic titration to the endpoint, and automatic calculation of the results. The color at the endpoint seems to be similar in all cases. We measure the titrability for each sample we process. I still suspect it’s due to the high humidity on the ground floor; coupled with changes in weather that affect humidity levels, and also because we weigh the samples – the balance room and the testing room are not in the same place, so the samples might absorb moisture. Moreover, when the lids are removed to add samples to the reaction vessels, humid air gets in
Use a dehumidifier indoors to reduce moisture absorption by the process samples; regularly replace the methanol solution and check the properties of the samples to ensure they are not strongly alkaline.
Is it calibrated every day? Use purified water for calibration; taking samples with a micro-syringe and performing the calibration three times to obtain an average value should yield more accurate results.
Reply to 4# jackwen: This kind of situation does occur. Once I was at a factory in Shandong; the moisture level of our products met the standards according to our tests. But it happened to be raining there, and their tests showed that the products did not meet the standards. So I asked them to turn on the dehumidification function in the air conditioning for an hour, and the test results were the same as those we got in our own factory
This post was last edited by qugd on 2011-5-15 at 13:30. After talking so much, no one paid any attention to the author’s analysis steps. The current measurement results provided by the poster essentially represent the water content in methanol, or the water content after mixing methanol with the sample. The poster should determine the water content of the methanol used to dissolve the sample; by deducting the blank value, the results might improve. If the water content in methanol is high, it is recommended not to use methanol as a solvent; instead, measure the sample directly. The solvent in the titration cell or measurement cell can be methanol, and remember to add the sample at the end of the titration process.