operating a t such low solvent/support ratios require nonadsorptive supports and very small sample injections. Another advantage of the AgN03 columns comes from the ability one has to change V, without affecting a or v d by changing the partial pressure of water in the carrier gas. In cases where the ratio Vd/Vr is not negligible, Equation 1shows that the value of Nreq decreases as V, is increased. This provides an additional parameter for the analyst to use to achieve desirable separations. For example, the relative retention time for the AgN03 column at 25 "C is equal to 1.07 for the difficult m-xylenelp -xylene separation. Under these conditions, with a flow rate of 60 ml/min, m-xylene was eluted in 5.7 min with a partial separation from p-xylene. Lowering the temperature of the water-saturator from 18 to 13 "C doubled the elution time and reduced the number of theoretical plates required for separation from 10 100 to 9 000. Increasing the flow rate to 150 ml/min effected a complete separation of p-xylene from m-xylene in 4 min. This may be compared to the studies of Desty, Goldup, and Swanton ( 5 ) . They separated the two compounds in 17 min using a capillary column coated with 7,8-benzoquinoline a t 78 "C.
CONCLUSIONS The AgNO3-glass bead columns are desirable columns for aromatic hydrocarbon analysis. Because of their low operating
temperatures, the full advantage of the complexing ability of AgN03 can be gained. This can lead to large values of the relative retention time for various solute pairs. T h e mechanism of aromatic hydrocarbon separation is obscure. Apparently, solid AgNO3 must complex with unsaturated hydrocarbons in the same manner as silver ion complexes with unsaturated hydrocarbons in solution (6).The effect can be large because aromatic hydrocarbons are not eluted by dry carrier gas. Water vapor in the carrier must compete with the hydrocarbons for the active sites on the solid silver nitrate. Higher partial pressures of water result in fewer available sites for the hydrocarbons and lead to smaller elution times.
LITERATURE CITED (1) C. S. G. Phillips, "Progress in Gas Chromatography", J. H. Purnell, Ed., Interscience Publishers, New York, N.Y., 1968, p 121. (2) C. C. Scott, J. lnst. Petrol., 45, 118 (1959). (3) I. Halasz, E. Hartman, and E. Heine, "Gas Chromatography 1964 Brighton", J. J. Kirkland, Ed., John Wiley, New York, N.Y., 1971, p 325. (4) J. H. Purnell, "Gas Chromatography", John Wiley and Sons, New York, N.Y., 1962. (5) D. H. A. Desty, A. Goldup, and W. T. Swanton, Nature (London), 183, 107 (1959). (6) L. G. Sillen and A. E. Martell, "Stability Constants", Special Publication No. 17, The Chemical Society, London, 1964.
RECEIVEDfor review December 19, 1975. Accepted August 19, 1976.
Determination of Arsenic, Tungsten, and Antimony in Natural Waters by Neutron Activation and Inorganic Ion Exchange Ernest S. Gladney" and James W. Owens
Los Alamos Scientific Laboratory, P.O. Box 1663, Los Alamos, N.M. 87545
Ion exchange on Al2O3columns has been used to quantltatlvely measure As, Sb, and W in water. Thls procedure requires short thermal neutron irradiations; rrapid ion exchange wlthout chemical manipulations,and short y-ray counts on a Ge( Li) detector. Precisions of f 5 % can be routinely obtained and the following detection limits have been achieved: As, 0.05 ppb; Sb, 0.03 ppb; and W, 0.05 ppb.
Inorganic ion exchange procedures have not been widely exploited for trace element determinations by neutron activation. One of the best known appiications is the use of hydrated antimony pentoxide (HAP) for the removal of radioactive 24Na from irradiated sample solutions (1-3). The properties of hydrated manganese dioxide (HMD) have been explored ( 4 ) and it has been used as a gas phase trap for the separation of I from CI and Br ( 5 ) .A number of other inorganic compounds have also been tested for selective retention of numerous cations and anions (6, 7). Among these exchangers, acidic A1203(chromatographic grade) is probably the most widely available. Girardi et al. (7) and Kuhn (8) have studied the retention characteristics of various elements from differing acid solutions on A1203 columns. Among the elements showing either complete or partial retention (P, As, Sb, Ge, Sn, Mo, W, Ta, Nb, Au, Th, Pa, and U) most have anionic complexes which are thought to be the active species (6, 7). Aluminium oxide separations have been applied to the production of carrier-free 2220
radioisotopes ( 6 ) ,to the separation of molybdates and tungstates from geologic samples (9),to the determination of T h and U in minerals and ores (IO),to the isolation of Mo from fission products ( 1 1 ) ,and to the measurement of P in biological materials by neutron activation (12). The application of A1203separations to quantitative trace element measurements in natural waters will be explored in this paper. The U.S. Public Health Service has established a recommended acceptable As concentration of 10 ppb in drinking water (13).Arsenic may be measured a t these levels by a number of procedures: colorimetry (as the Ag-diethyldithiocarbamate complex) (14), polarography ( 1 5 ) , neutron activation (16, 17) atomic emission spectroscopy (18),and flameless atomic absorption (19,20). The technique reported in this paper was developed as a quality control supplement to flameless atomic absorption determination of As. Antimony and tungsten have received considerably less attention in natural waters. Russian scientists have characterized Sb in ground waters in vast regions of the Soviet Union during hydrogeochemical prospecting for more valuable elements (21, ZZ), although the reported sensitivities for their analyses are only 30 ppb. Tungsten has been occasionally measured in ground water (23), rainwater (24),and geothermal waters (25) by neutron activation or x-ray fluorescence, but this determination has required evaporation of large volumes of water to obtain sufficient analyte. Both S b and W may prove to be useful tracers in geothermal systems and adjoining watersheds, and a more efficient analytical procedure is needed to exploit this potentiality.
ANALYTICAL CHEMISTRY, VOL. 48, NO. 14, DECEMBER 1 9 7 6
Table I. Arsenic, Antimony, and Tungsten Concentrations in Natural Waters from Northern N e w Mexico, ppb As Sample No.
Neutron activation
Atomic absorption 165 f 7 155 f 7 162 f 7 164 f 7 163 f 7 63 f 3 36 f 1 36 f 1 37 f 2 62 f 3 3.1 f 0.5 3.3 f 0.5 4.1 f 0.5 3.2 f 0.5 4.0 f 0.5 180 f 15 25 f 2 91 & 3 89 f 3 93 f 3 51 f 3 45 f 8 11f 3 22 f 2 2.4 f 0.4 4.5 f 0.4 0.55 f 0.05
169 f 8 165 f 8 177 f 9 170 f 8 167 f 5 63 f 4 38 f 3 37 f 3 38 f 3 61 f 4 11 3.3 f 0.5 12 3.0 f 0.5 13 3.6 f 0.5 14 3.1 f 0.5 15 4.1 f 0.5 16 192 f 19 17 22 f 2 18 91 f 9 19 95 f 9 20 91f9 21 52 f 3 22 39 f 2 23 9.8 f 0.9 24 20 f 2 25 2.6 f 0.3 26 4.2 f 0.4 27 0.60 f 0.06 Not detected due to As interference. 1
2 3 4 5 6 7 8 9 10
Table 11. Standard Addition of As, Sb, and W to New Mexico Water, Sample No. 11
Element As
Sb
W
Amount added, ng/ml 0 20 40 60 80 0 1.0 2.0 5.0 10.0 0 10.0 20.0 30.0 40.0
Amount found, ng/ml 3 24 43 64 85
