Laboratory Performance of Spectrophotometers: Results of a National Survey

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Abstract
Absorbance readings of acid dichromate, alkaline potassium chromate, and Thomson’s solutions at various wavelengths on narrow half-bandwidth spectrophotometers by 132 participant and seven reference laboratories taking part in the 1973 Survey of the College of American Pathologists are presented and discussed from the point of view of interlaboratory and interreference variability, accuracy, and probable causes of error. Interlaboratory variability for readings in the ultraviolet region of the spectrum ranged from less than 5 to about 30%. Much of the variability is predictable from the stated manufacturers’ tolerances. It is greatest for low concentrations in the ultraviolet region of the spectrum. Refined means of participants’ readings provide a useful estimate of the correct values. There appears to be significant bias among instruments from different manufacturers.

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