Why it's a good idea to use self masking cuvettes
black walled cuvettes micro scope slide holder
for low volume work. I performed this experiment a few years ago, and have been dying to try it for the last three years on a Cary 500! Well - at long last I got a spare few moments and here are the results. The experiment:
1. Take a suitable visible dyestuff, and make up a solution to give you a peak Absorbance measurement of 3+ Absorbance. In this case I used Sap Green, measured at 428 nm, with a 1.0 nm SBW.
2. Call this '100' as a top standard - and serially dilute to produce '75', '50', and '25' respectively.
3. Using a type 18/B - fill with water, and zero the Cary.
4. Re-measure the blank, and then each standard in turn.
5. Repeat 3, and 4 using a type 18.
6. Plot, and compare the 'Beer-Lambert' linear response!
Physical and Chemical Characteristics
1. Using the type 18/B cells, I've restored my faith in my analytical expertise, in the fact that the series 0 -75 (2.5 A) is a perfect (linearity = 1) straight line. 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 at this point Black Walled Blank Corrected
0 0.0004 0 0.0000
25 0.8508 25 0.8505
50 1.7149 50 1.7145
75 2.5611 75 2.5607
100 3.3106 100 3.3103

2. Using the type 18 - boy what a difference! 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? Black Walled Blank Corrected
0 0.0004 0 0.0000
25 0.8177 25 0.8173
50 1.4730 50 1.4726
75 1.8064 75 1.8060
100 1.8999 100 1.8995
Clear Walled
Linear Black Walled
Black Walled
Black Walled Clear Walled   Difference % Difference.
0.0000 0.0000 0 0 0
0.8505 0.8173 25 0.0331 3.9
1.7145 1.4726 50 0.2420 14.1
2.5607 1.8060 75 0.7547 29.5
3.3103 1.8995 100 1.4108 42.6