How are Gelex secondary standards used?
Using Gelex secondary standards
Gelex standards are secondary standards in solid or gel form that require no dilution or mixing. They provide a quick and convenient way to check if the calibration of laboratory and portable turbidimeters has changed on a daily basis. To use, place the Gelex standard in the sample cell compartment in a defined orientation right after the turbidimeter has been calibrated with a primary standard, and record the displayed value. Then periodically (daily or weekly, for instance) place the standard back in the instrument in the same orientation to verify that the calibration has not changed significantly. When the value of the Gelex standard differs by more than 5% from the value right after the turbidimeter was last calibrated, the turbidimeter should be calibrated again with a primary formazin or Stablcal® standard. Both formazin and Stablcal® are accepted primary standards for turbidimeter calibration. Gelex standards should never be used to calibrate a turbidimeter, only to check the calibration after the turbidimeter has been calibrated with a primary standard.