Anal. Chem. 1980, 52, 1551-1552
1551
peak approximately a 0.1 to 0.5 mM solution of the material is in the detector, the flow could be stopped and cyclic voltammetry could be carried out on such species. With more selective dialysis membranes, such experiments could be done on even lower mass species. As mentioned above, the cell functions well with aqueous KCl as the external electrolyte contacting the membrane with either water-methanol or acetonitrile as the internal, mobile phase. Of course, the only limitation on the working electrode composition is whether the material can be fabricated in the appropriate shape.
may enhance the response. These subjects will be investigated in the future. If the Nafion were acting as an ion-exchange membrane, complex electrochemical effects might be expected since different solvents each with different solutes (both charged and uncharged) reside on opposite sides of the membrane. The hydrolyzed cellulose is neutral, and it may be surprising that no difference was seen in results using these two types of membrane. However, a simple test suggests the reason. With 2 M NaCl inside the Nafion tube immersed in distilled water, within 15 min osmotic effects caused the volume of the liquid inside to double. At the same time, a significant amount of chloride ion was seen to have flowed out through the Ndion membrane. This was detected by precipitation with Ag+. The Nafon membrane a d s as if it has large (on the molecular level) holes allowing at least a fraction of it to appear as a simple neutral barrier. These osmotic effects will be negligible with the mobile phase flowing through the detector. The total amount of sample lost by diffusion through both types of membrane is small owing to the short periods of relatively high concentrations of solutes that occur a t chromatographic peaks. The effect of this effusion on the current response curve will also be small because the solution a t the electrode surface is being replenished faster than once a second in normal use. When the cellulose acetate membrane is hydrolyzed as described above, it will retain molecules with molecular masses greater than about 300. If chromatography is carried out on larger amounts of a sample such that at the chromatographic
LITERATURE CITED (1) Kissinger, P. T. Anal. Cbem. 1977, 4 9 , 447A-456A. (2) Kissinger, P. T.; Refshange, C.: Dreiling. R.: Adams, R. N. Anal. Lett. 1973. 6 . 465-477. (3) Fleet,' B.; Little, C. J. J. Cbromatogr. Scl. 1974, 12, 747-752. (4) Taylor, L. R.; Johnson, D. C. Anal. Cbem. 1974, 46, 262-263. (5) Daveport, R. J.: Johnson, D. C. Anal. Cbem. 1971, 46, 1971-1972. (6) Lankalma, J.; Poppe, H. J. Cbromatogr. 1976, 725, 375-388. (7) Blaedel, W. J.; Dinwiddie, D. E. Anal. Cbem. 1975, 4 7 , 1070-1075. (8) Blaedel, W. J.; Ylm, 2 . Anal. Cbem. 1978, 50, 1722-1724. (9) Oosterhuis, B.; Brunt, K.; Westerink, B. H. C.; Doornbos, D. A. Anal. Cbem. 1980, 52, 203-205. 1328-1329. J.; Czerwinski, A.; Mark, H. E., Jr. Anal. Cbem. 1979, 57, (10) Caja, (11) Caja, J.; Czerwinski, A,; Rubinson, K. A,; Heineman, W. R.; Mark, H. B., Jr. Anal. Cbem. 1980, 52, 1010-1013. (12) Rubinson, K. A.; Baker. P. F. Roc. R . SOC.London, Ser. B 1979, 205, 323-345.
RECEIVED for review April 7, 1980. Accepted May 16, 1980. The chromatographic equipment used in this work was purchased through NSF Grant No. CHE77-15219 to T.W.G.
Determination of Low Levels of Copper by Atomic Absorption Spectrometry with a Simplified Extraction Technique W. Orville Calhoun' and I?. B. Hurley Badische Corporation, P. 0. Drawer D, Wiiiiamsburg, Virginia 23 185
The sensitivity of atomic absorption spectrophotometry for copper is approximately 90 pg/L for 1% absorption ( I ) . The sensitivity is less for viscous or concentrated salt solutions. Accurate measurement of low levels of copper,
