Reason for Difference between Absorbance Readings from Two Different Spectrophotometers

Question

There is a significant difference between the absorbance readings from two different spectrophotometers (One is Cary 60) but with sample type and concentration. May I ask what could be the possible source of this error? Reading from Cary 60 is around 2.5 while the other equipment is only around 1.1 au.

Mike Picollelli · Accepted Answer

Hello: 
 
 Power cycle both spectrophotometers, and let them warm up for an hour. Run the instrument self-tests. 
 If the samples are liquid, are you using a plastic or quartz cuvette? If they are plastic, place a cuvette in each spec and zero or baseline correct. Transfer the sample from the cuvette in Spec A and transfer to Spec B. Once the cuvette is in place, don't remove it. Are they the correct cuvette for the instrument beam height. (e.g., The Cary 60 is 20 mm, & the Cary 8454 is 15 mm.) 
 Adjust your concentration to an OD of 1.0. A serial dilution of the sample might reveal something. 
 (I have never seen the case where two spectrophotometers differed in result in 15 years as a bench scientist.)

Reason for Difference between Absorbance Readings from Two Different Spectrophotometers

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