When following the Accuracy Check procedure for phosphonates, why should my result be 10 times higher than the displayed value?

Document ID

Document ID TE362

Version

Version 2.0

Status

Status Published

Published Date

Published Date 27/05/2017
Question
When following the Accuracy Check procedure for phosphonates, why should my result be 10 times higher than the displayed value?
Summary
Accuracy check for phosphonates
Answer
In the Accuracy Check section of the Phosphonate procedure (Hach Method 8007), a 1 mg/L phosphate standard solution is used to check the instrument calibration. Digestion is not necessary for this verification, and the standard does not need to be diluted.

Because you are not digesting or diluting the standard, you can equivalently begin with 10 mL of sample, add the PhosVer3, and read the result. 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 go to 125 mg/L.

This factor assumes that a 10-fold dilution was made (5 mL in 50 mL). Note that if a 5 mL volume is used from Table 1, no multiplication factor is needed from Table 2 (factor=1). You could alternatively follow the procedure using 50 mL of standard (using the volume suggested in Table 1 for a 1 mg/L concentration). From Table 2, for 50 mL you will multiply the displayed reading by 0.1. This adjusts for the factor of 10 programmed in the instrument calibration.