TM05-01 Change in method for determination of potassium from flame atomic absorption (FAA) to inductively coupled plasma-optical emission spectrometry (ICP-OES)

This technical memorandum documents replacement of USGS direct flame atomic absorption (FAA) spectrophotometric methods (Fishman and Friedman, 1989) for determining filtered and whole water recoverable potassium with inductively coupled plasma-optical emission spectrometry methods (ICP-OES) (Clesceri and others, 1998). To stay current with modern cost-saving technologies and improve data quality, the NWQL replaced aging FAA instruments with modern ICP-OES instruments. ICP-OES technology has changed substantially in recent years, thus expanding the capability of the instrument to determine potassium. The new lab codes and method codes are listed below. The sample bottle type and the nitric acid preservation requirements did not change. These new codes are available in the Laboratory Information Management System (LIMS) per the dates mentioned above. The low-level potassium is available for samples with specific conductance of 100 microsiemens or less and is generally appropriate for precipitation and other pristine samples. If the low-level lab code (2774) is requested and the specific conductance exceeds 100 microsiemens or the concentration exceeds 1 mg/L -- the upper range for reporting potassium with lab code 2774 -- then the laboratory will switch to analysis by the regular lab code (2773) and results will be reported with lab code 2773.