Why it's a good idea to use black walled self masking cuvettes

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!

Results & Conclusions

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?	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


	Clear Walled
	Linear Black Walled
	Black Walled

Black Walled	Clear Walled		Difference	% Difference.
0.0000	0.0000	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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