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CATION EXCHANGE CAPACITY <br />Reagents <br />Sodium acetate (NaOAc), 1 N, pH 8.2 <br />Ethanol, 95-percent <br />Ammonium acetate (NH OAC), 1 N, pH 7.0 <br />SrC12 20-percent w/v4in H2O <br />Standards <br />Pipet appropriate volumes of a 1000 ppm stock to prepare 1 <br />and .5 ppm standards in 1 N NH4OAc. The final volume should <br />be 18 SrC12. <br />Procedure <br />1. Weigh Sg samples (60m) and place in centrifuge tubes. <br />2. Add 30 ml NaOAC, stopper the tubes, and shake for <br /> 5 minutes. <br />3. Centrifuge until supernatant liquid is clear and decant <br /> as completely as possible. Repeat step 2 and 3 four <br /> times, discarding the supernatant liquid each time. <br />• <br />4. After the last saturation, wash the stoppers and use <br /> absorbant paper to remove any acetate crystals remaining <br /> on the lip of the Centrifuge tube. <br />5. Add 30 ml ethanol to each tube and shake for 5 minutes. <br />6. Centrifuge and discard the supernatant liquid. Continue <br /> washing until the electrical conductivity of the <br /> supernatant is between 55 and 40 umho/cm. <br />7. Replace the absorbed sodium from the sample as in steps <br />2 and 3 except use three 30 ml portions of NH4OAc. <br />Retain supernat from each extraction. - <br />8. Dilute to 100 ml and determine the sodium concentration <br />by atomic absorption spectrophotometry using H2/air <br />flame and appropriate standards.l <br />Calculations <br />X = concentration of sodium in 100 ml NH4OAc. <br />22.9898 mg = milliequivalent weight Na <br />X mg/1 = .X mg/100m1 = .X mg/22 <br />100 <br />20(.X/22.99) m.e. = 2 (X/22.99) <br />100 g 100 g <br />6-110 <br />.OOmq/me = .X m.e. <br />ml 22.99 20 <br />5 g 20 <br />m.e. _ .087X m.e. <br />100 g <br />