PHOTOVOLT TECHNICAL NOTE
Sample Requirements For Photovolt Coulometric KF Titrators ·

The 2000 USP (Method 921) states that if coulometric analyses for water are used for pharmaceutical materials, a sample mass of between 0.5 to 5.0 milligrams of water must be present. ·

With the present PHOTOVOLT coulometric equipment, this is 10 times the amount of sample needed to obtain satisfactory quantitative water analysis on a product. ·

With the above in mind, let us consider a theoretical problem where we have a sample containing 200 mg/kg (ppm) water. How much sample is required to obtain the 0.05 milligrams of water needed for an adequate analysis?

0.5 mg water x 100                       
___________________ = 0.2% (200 ppm water)
mg sample required                      

mg sample required = 0.05 x 100/0.02

mg sample required = 250 ·

From the above, it is apparent that about 250 milligrams of sample are required to obtain a 50 microgram count on the display of a PHOTOVOLT KARL FISCHER TITRATOR, providing a sample has 200 mg/kg of water. This equation can be used to estimate the least amount of sample needed to give you a 50 micrograms count if you have some indication of the amount of water probably present in your sample.

EQUIVALENTS
0.05 milligrams = 50 micrograms
0.50 milligrams = 500 micrograms
5.00 milligrams = 5000 micrograms
0.02 percent = 200 mg/kg (ppm)
250 milligrams = 0.25 grams

1998-05-07