Laserfiche WebLink
METHOD 9040C C �� <br /> pH ELECTROMETRIC MEASUREMENT <br /> 1.0 SCOPE AND A PLICATION <br /> 1.1 This method is used to measure the pH of aqueous wastes and those multiphase <br /> wastes where theaqueous phase constitutes at least 20% of the total volume of the waste. <br /> 1.2 The co�rosivity of concentrated acids and bases, or of concentrated acids and <br /> bases mixed with inert substances, cannot be measured. The pH measurement requires some <br /> water content. <br /> 2.0 SUMMARY <br /> 2.1 The pH of the sample is determined electrometrically using either a glass electrode <br /> in combination with a reference potential or a combination electrode. The measuring device is <br /> calibrated using a series of standard solutions of known pH. <br /> 3.0 INTERFERENCES <br /> 3.1 The glass electrode, in general, is not subject to solution interferences from color, <br /> turbidity, colloidal matter, oxidants, reductants, or moderate (<0.1 molar solution) salinity. <br /> 3.2 Sodiurr error at pH levels >10 can be reduced or eliminated by using a low- <br /> sodium-error electro e. <br /> 3.3 Coatinc s of oily material or particulate matter can impair electrode response. <br /> These coatings can isually be removed by gentle wiping or detergent washing, followed by <br /> rinsing with distilled tvater. An additional treatment with hydrochloric acid (1:10) may be <br /> necessary to remove any remaining film. <br /> 3.4 Tempe ature effects on the electrometric determination of pH arise from two <br /> sources. The first is,caused by the change in electrode output at various temperatures. This <br /> interference should be controlled with instruments having temperature compensation or by <br /> calibrating the electrode-instrument system at the temperature of the samples. The second <br /> source of temperatu a effects is the change of pH due to changes in the sample as the <br /> temperature changes. This error is sample-dependent and cannot be controlled. It should, <br /> therefore, be noted by reporting both the pH and temperature at the time of analysis. <br /> 4.0 APPARATUS ND MATERIALS <br /> 4.1 pH meter-- Laboratory or field model. Many instruments are commercially <br /> available with various specifications and optional equipment. <br /> 4.2 Glass 6 lectrode. <br /> 4.3 Reference electrode -- A silver-silver chloride or other reference electrode of <br /> constant potential may be used. <br /> 9040C - 1 Revision 3 <br /> November 2004 <br />