The potassium chloride liquid filter (UV1) consists of 12g/l potassium chloride dissolved in pure water. This filter is suited to check the stray light of a spectrometer in the spectral range between 190 nm and 210 nm, its cut-off is at about 200 nm.
Two regulations - two measuring methods
Currently there are different methods used in the European Pharmacopoeia (EP) and in the United States Pharmacopeia (USP) to determine the stray light.
When checking for stray light according to European Pharmacopoeia (EP 10), the potassium chloride filter (UV1) is measured against the reference filter (UV12) filled with pure water. The measured absorbance value at the wavelength 198 nm must be ≥ 2.0 Abs.
In USP <857> (42th edition, update Dec. 2019), two possible procedures are described for checking for stray light:
Here the potassium chloride filter (UV1) with a path length of 10 mm is measured against the potassium chloride reference filter (UV1H) with a path length of 5 mm. The stray light value can now be calculated from the absorbance maximum obtained, using the following formula:
Sλ = 0.25 x 10-2Aλ
The following acceptance criteria apply:
Aλ ≥ 0.7 Abs and Sλ ≤ 0.01
Here the potassium chloride filter (UV1) with a path length of 10 mm is measured against the reference filter (UV12) filled with pure water. The measured absorbance value at the recommended wavelength 198 nm should be ≥ 2.0 Abs.
Procedure B of USP 857 corresponds to the procedure of the Ph. Eur.
Experiences from daily practice show that the values determined in this stray light measuring method are instrument-dependent. This means the wavelength of the peak varies depending on the spectrophotometer performance. It is important for the user to know that the measured maximum absorption in the checked range is decisive for this checking method and that it should be higher than 0.7 Abs.
|ARTICLE-NO.||EP-Set: 667100 (UV1/UV12) Request this article |
USP-Set: 667100H (UV1/UV1H)
|APPLICATION||Checking stray light in the spectral range of 190 - 210 nm according to EP and USP|
|CONTENT||Potassium chloride 12 g/l in pure water|
|STANDARD CERTIFICATION||Cut-off wavelength: 200 nm |
Slit width: 2 nm; with DAkkS calibration certificate
|POSSIBLE CERTIFICATION||Cut-off wavelength: fix |
Slit width: 2 to 5 nm