Hello,
I have unsuccessfully tried to determine ultraviolet protection factor (UPF) for fabric samples as described in standard EN 13758-1. To calculate UPF, I have measured absorbance spectra of the fabrics with a spectrophotometer with an integrating sphere, as told in the standard. However, my calculations produced way too low UPF values for each sample, including reference samples with known UPF. After double-checking the calculations and absorbance data with my professors, we noticed that at 290 - 340 nm even the most opaque samples did not exceed certain absorbance threshold. In fact, almost all my samples had some kind of an "absorbance plateau" there.
My questions:
1) What could have gone wrong with my measurements?
2) Is it common for the absorbance data to plateau like that?
3) Is the data unusable? If yes, how can I get correct absorbance data when doing re-measurements?
All the best and thank you for your answers.
Hello Juha,
The fact with the "absorbance plateau" you mentioned sounds interesting.
It seems that the limit of the dynamic range of the detector is reached in this case, i.e. the detector cannot differentiate anymore if, e.g., 0.01 % or 0.001 % light are transmitted. That is potentially causing that a certain absorbance threshold is not exceeded even for very opaque samples.
In the case of a strongly absorbing solution that would cause a similar effect, one would simply dilute the solution to be compatible with the absorbance range that is accessible with the spectrophotometer. Unfortunately, that method will not work with solid samples like your fabrics.
Not sure if that would help, but potentially you could try to measure in reflectance mode (not absorbance) and then determine absorbance data from these measurements?
Best regards,
Kay
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