Why do the readings not match the laboratory results?
There are several factors involved when comparing oil and grease results obtained from the InfraCal Analyzers to a laboratory method: 1. Unless the laboratory is using an infrared method for analysis, there can be differences due to the fact that different properties of the oil & grease are measured by each type of analysis, such as gas chromatography or gravimetry. 2. There are also acceptable errors within each method. For example, EPA Method 1664 states in their “Ongoing precision & recovery” (section 17.0) that for a 100 ppm sample the acceptable range is 78 -114. If the test includes the silica gel treatment (SGT), the acceptable range is 64 – 132. 3. Getting identical grab samples is also very difficult as oil is not equally distributed in a water sample and this can add differences. 4. Laboratories do not always agree with one another. This chart shows a comparison of a 5 way oil in water sample split analyzed on 2 InfraCals and at 3 labs.
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