Why Black walled Cells?

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:

1. 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.

2. Call this '100' as a top standard - and serially dilute to produce '75', '50', and '25' respectively.

3. Using a type 18 - 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/B.

6. Plot, and compare the 'Beer-Lambert' linear response!

How the Optical characteristics of the cells affect the Chemical measurement

1. Using the type 18 - 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
	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

2. Using the type 18/B cells - 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
	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


	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

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Why Black walled Cells?