Why it’s a good idea to use self masking cuvettes…
This article explains why it is important to use black walled cells for low volume work. We performed this experiment on a Varian Cary 500 a number of years ago to demonstrate this. The experiment:
- Take a suitable visible and stable chemcal, and make up a solution to give you a peak Absorbance measurement of 3+ Absorbance. In this case I used diluted Starna Green, measured at 428 nm, with a 1.0 nm SBW.
- Call this ‘100’ as a top standard – and serially dilute to produce ’75’, ’50’, and ’25’ respectively.
- Using a VAOBS1 clear wall cell – fill with water, and zero the Cary.
- Re-measure the blank, and then each standard in turn.
- Repeat 3, and 4 using a VAOBM1 black walled cell.
- Plot, and compare the ‘Beer-Lambert’ linear response!
How the Optical characteristics of the cells affect the Chemical measurement
1. Using the VAOBS1 clear wall cell- On this evidence, I don’t think I’d want to use this type of cell (without any masking) to measure more than 0.5 A?
|Clear Walled||Blank Corrected|
2. Using the VAOBM1 black wall cell – what a difference! I’ve restored my faith in my analytical expertise – the series 0 – 75 (2.5 A) is a perfect straight line (linearity = 1). Linearity to 3.3 (100) isn’t bad either at 0.9993, but you are beginning to see the stray light characteristics of the Cary 500 instrument at this point.
|Black Walled||Blank Corrected|
|Black Walled||Clear Walled||Difference||% Difference.|