Patent ID: 8605271

Claim:
In a critical-angle refractometer which utilizes an image of light reflected from an optical interface with a vessel containing a sample under test to determine an optical property of the sample, a method for evaluating sample properties to prevent improper testing of the sample, comprising the steps of: establishing reflectance information associating the amount of reflection with locations in the image; and utilizing a plurality of properties of the reflectance information to determine if the vessel contains a proper sample under test, wherein the properties include the point of transition from complete to partial reflection and at least one of the following: a scaled average rate of change of reflectance as a function of position in the image in a predefined range of interest (ROI) about the point of transition; the maximum reflectance in the ROI; the minimum reflectance in the ROI; the range of reflectance in the ROI; and the average reflectance in the ROI; wherein sample properties evaluated include at least one of: the sample being present; the optical interface being clean; and an optical property of the sample being out of range; and wherein a sample is considered to be present when the properties of the reflectance information include: a reflectance range across the ROI which exceeds a predetermined high threshold T 1 ; a maximum reflectance which exceeds a predetermined high threshold T 2 ; and a scaled average rate of change of reflectance which exceeds a predetermined high threshold T 3 .