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<br />pH <br />Metbod 150.1 (Electrometric) <br />STOREY NO. <br />Determined on site 00400 <br />Laboratory 00403 <br />1. Scope and Application <br />1. I This method is applicable to drinking, surface, and saline waters, domestic and industrial <br />wastes. <br />2. Summary of Method <br />2.1 The pH of a sample is determined electrometrically using either a glass electrode in <br />combination with a reference potential or a combination electrode. <br />3. Sample Handling and Preservation <br />3.1 Samples should be analyzed as soon as possible preferably in the field at the time of <br />sampling. <br />3.2 High-purity waters and waters not at equilibrium with the atmosphere are subject to <br />changes when exposed to the atmosphere, therefore the sample containers should be <br />filled completely and kept sealed prior to analysis. <br />4. Interferences <br />4.1 The glass electrode, in general, is not subject to solution interferences from color, <br />turbidity, colloidal matter, oxidants, reductants or high salinity. <br />4.2 Sodium error at pH levels greater than 10 can be reduced or eliminated by using a "low <br />sodium ercor" electrode. <br />4.3 Coatings of oily material or particulate matter can impair electrode response. These <br />coatings can usually be removed by gentle wiping or detergent washing, followed by <br />distilled water rinsing. An additional treatment with hydrochloric acid (1 + 9) may be <br />necessary to remove any remaining film. <br />4.4 Temperature effects on the electrometric measurement of pH arise from two sources. <br />The first is caused by •the change in electrode output at various temperatures. This <br />interference can be controlled with instruments having temperature compensation or by <br />calibrating the electrode-instrument system at the temperature of the samples. The <br />second source is the change of pH inherent in the sample at various temperatures. This <br />error is sample dependent and cannot be controlled, it should therefore be noted by <br />reporting both the pH and temperature at the time of analysis. <br />5. Apparatus <br />5.1 pH Meter-laboratory or field model. A wide variety of instruments are commercially <br />available with various specifications and optional equipment. <br />Approved for NPDES <br />Issued 1971 <br />Editorial revision 197E <br />150.1-1 <br />