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METHOD 9040 <br /> r <br /> pH ELECTROMETRIC MEASUREMENT <br /> 1.0 SCOPE AND APPLICATION <br /> 1.1 Method 9040 is used to measure the pH of aqueous wastes and those <br /> multiphase wastes where Ithe aqueous phase constitutes at <br /> total volume of the waste. -aeast 20% -of the <br /> 2.0 SUMMARY <br /> 2.1 The pH of the sample is determined electrometrically using either a <br /> glass electrode in combination with a reference potential or a combination <br /> electrode. The measuring device is calibrated using a series of standard <br /> solutions of known pH. <br /> 3.0 INTERFERENCES <br /> 3.1 The glass electrode, in general , is not subject to solution <br /> interferences from color, turbidity, colloidal matter, oxidants, reductants, <br /> or high salinity. <br /> 3.2 Sodium error at pH levels >10 can be reduced or eliminated by using . <br /> a low-sodium-error electrode. <br /> 3.3 Coatings of oily material or particulate matter can impair electrode <br /> response. These coatings can usually be removed b <br /> gentle wipinor deteent <br /> washing, followed by rinsing with distilled watee <br /> r. Anadditional treatment <br /> with hydrochloric acid (1:9) may be necessary to remove any remaining film. <br /> 3.4 Temperature effects on the electrometric determination of pH arise <br /> from two sources. The first is caused by the change in electrode output at <br /> various temperatures. This interference can be controlled with instruments <br /> having temperature compensation or by calibrating the electrode-instrument <br /> system at the temperature of the samples. The second source of temperature <br /> effects is the change of pH due to changes in the sample as the temperature <br /> changes. This error is sample-depen <br /> therefore, be noted by reporting botdent and cannot be controlled. It should <br /> h the pH and temperature at the time of <br /> anaiysis. <br /> y:u APP': oTUS AND MATERIALS <br /> pt ter: laboratory or sieI model . Many instruments are co�aier- <br /> c?a: ab a with various spec4ications and optional equipment. <br /> 9040 — 1 <br /> Revision O <br /> Date September 1986 <br />