Karl Fischer (KF) titration has become a universally accepted analytical technique used in labs analyzing wide range of samples from any industry. Independent of the application, one aspect of Karl Fischer titration remains unchanged – the need to standardize or calibrate the instrumentation. It is good analytical practice to check the titer of KF titrating agents prior to performing new titrations, especially if the reagent bottle has been previously opened.
Calibration, validation and inspection of analytical instruments and reagents is performed with a specific amount of water, either pure water or water standards. The challenge with pure water is the low amount required (10-50 mg for volumetry, and 0.1-1 mg for coulometry), which is difficult to handle and weigh.
The next choice might be sodium tartrate dihydrate. As a solid standard containing 15.66% water, it does not suffer sample size concerns like water. As a primary standard, sodium tartrate dihydrate exhibits several desirable characteristics: is stable under normal laboratory conditions, does not effloresce, and is not hygroscopic even in high humidity conditions. However it has one drawback - solubility. The solubility of sodium tartrate dihydrate in methanol is limited. It may require a 3-10 minute stir time to completely dissolve, depending upon conditions in the lab.
Due to the solubility concerns raised by sodium tartrate dihydrate, many analysts began looking into liquid standards. Starting from liquid standards in bottles, improvements led to an individual single-use pre-notched glass ampoules, which insure the integrity of the standard until it is opened. Liquid Hydranal Water Standards consist of a solvent mixture with specific composition and precisely determined water content of 10 000 ppm, 1 000 ppm, 100 ppm or even around 10 ppm (for standard based on mineral oil).
With the dual ISO accreditation in 2014 (ISO 17025 and ISO Guide 34), Hydranal has introduced the Certified Reference Materials (CRM) Water Standards to the portfolio along with the new improved 0.1 PC Water Standard, which offers higher stability than the already existing 0.1 Water Standard.
All of Hydranal-Water Standards are verified against NIST SRM 2890 and some additionally against NMIJ CRM4222-a. They are supplied with detailed instruction for use and depending on their quality level either with Report of Analysis (RoA) or Certificate of Analysis (CoA) showing the exact water content.
We therefore recommend Hydranal-Water Standards with an exactly confirmed water content for:
- Titer determination
- Monitoring precision and accuracy
- Validation and inspection of Karl Fischer titrators according to ISO, GMP, GLP and FDA guidelines
Thanks to Hydranal’s liquid standards packaged in glass ampoules, analysts have accurate and reliable standards available. Solubility and appropriate sample sizes are not an issue. Water is no longer the only choice available.
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