The sodium nitrite liquid filter (UV11) consists of 50 g/l sodium nitrite in pure water. This filter is suited to check the stray light of a spectrometer in the spectral range between 300 nm and 400 nm, its cut off is at about 388 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 Ph. Eur., the sodium nitrite filter (UV11) is measured against the reference filter (UV12) filled with pure water. The measured absorbance value at the wavelengths 340 and 370 nm must be ≥ 3.0 Abs.
In USP <857> (update Dec. 2022), two possible procedures are described for checking for stray light:
Here the sodium nitrite filter (UV11) with a path length of 10 mm is measured against the sodium nitrite reference filter (UV11H) 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 10-2∆A
The following acceptance criteria apply:
∆A ≥ 0.7 Abs and Sλ ≤ 0.01
Here the sodium nitrite filter (UV11) 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 340 nm should be ≥ 2.0 Abs.
Procedure B of USP 857 corresponds to the procedure of the European Pharmacopoeia
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: 667102 (UV11/UV12) Request this article |
USP-Set: 667102H (UV11/UV11H)
|APPLICATION||Checking stray light in the spectral range of 300 - 400 nm according to EP and USP|
|CONTENT||Sodium nitrite 50 g/l in pure water|
|STANDARD MEASUREMENT||Cut-off wavelength: 388 nm (EP) / 385 nm (USP) |
Slit width: 2 nm; with DAkkS calibration certificate
|POSSIBLE MEASUREMENTS||Cut-off wavelength: fix |
Slit width: 1 and 2 nm