By Jane L. Stevens, Product Manager, Thermo Fisher Scientific
There has long been verification testing between lab and online instrumentation for water quality measurements, especially for Drinking Water and Wastewater (DW//WW). The lab methods have a historical edge and generally are considered more accurate, but time consuming and required skilled chemist o technician. Lab methods are often to definitive technique due to their long use since the inception of Clean Water Act in the early 1970s. Online analyzers are newer and therefore have usually been compared against the lab methods during their engineering development process. The November 10, 2009 Federal Register publication of EPA Method 334.0 for reporting data from online monitors for residual chlorine is the first has created exuberance for those companies offering online instrumentation as part of their water quality product lines. This new method addresses the criteria for use of online residual chlorine measurement data being used for regulatory reporting. Following this new method, we will show a strong accuracy correlation between measurements taken from the online analyzers and portable colorimeters. These colorimeter methods are currently approved for use in reporting free chlorine levels to EPA. Typically, these colorimeters use a DPD (N,N- diethyl-p-phenylenediamine) method which is an EPA approved method for Drinking Water testing.