The acetone liquid filter (UV19) consists of pure acetone. This filter is suited to check the stray light of a spectrophotometer in the spectral range between 250 nm and 330 nm, its cut-off is at about 325 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.
Measurement of acetone (UV19) against air (high-purity acetone is used and not dissolved in water)
Currently, the use of the acetone stray light filter is required only in the United States Pharmacopeia (USP) for the determination of the stray light in the spectral range from 250 nm to 330 nm.
In USP <857> (42nd edition, update Dec. 2019), two possible procedures are described for checking for stray light:
Here the acetone filter (UV19) with a path length of 10 mm is measured against the acetone reference filter (UV19H) 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 acetone filter (UV19) with a path length of 10 mm is measured against air (high-purity acetone is used and not dissolved in water). The measured absorbance value at the recommended wavelength 300 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: 667019 (UV19) Request this article |
USP-Set: 667119H (UV19/UV19H)
|APPLICATION||Checking stray light in the spectral range of 250 - 330 nm according to EP and USP|
|CONTENT||high purity acetone|
|STANDARD MEASUREMENT||Cut-off wavelength: 325 nm |
Slit width: 2 nm; with DAkkS calibration certificate
|POSSIBLE MEASUREMENTS||Cut-off wavelength: fix |
Slit width: 2 to 5 nm