When using Method 8007 for phosphonates, why is a 1 mg/L PO4 standard solution reading 10 mg/L PO4?
Accuracy check for phosphonates
In the Accuracy Check section of Method 8007 for the phosphonate determineation, a 1 mg/L phosphate standard solution (Product # 256949) is recommended to check the instrument calibration. Digestion is not necessary for this verification, and the standard does not need to be diluted. Because the standard does not require digesting or diluting, 10 mL of standard should be used. The displayed result will be 10 times higher than the standard concentration because a factor of 10 is programmed into the instrument calibration. This factor allows the range of the test to be extended up to 125 mg/L.