requires a total time of 20 minutes per sample, compared to an operator time of 60 to 80 minutes and an elapsed time of 240 minutes for the gravimetric method. This method has wide potential application since i t is based on the absorbance of the sulfonate group and is not concerned with vibrations of the parent molecule. It is relatively insensitive to isomer variations and should be applicable over a wide molecular weight range and, although this has
not been investigated, it should be applicable to sulfonates of multiring aromatic systems.
LITERATURE CITED
(1) Barnard, D., Fabian, J. M., Koch, H. P., J . Chem. SOC.1949, 2442. ( 2 ) Schreiber, K. C., ANAL. CHEM.21,
1168 (1949).
ACKNOWLEDGMENT
K e acknowledge the help of Tom Jackson and E. A. Setzkorn in obtaining the gravimetric active analyses and for helping evaluate the infrared method for active determination under plant conditions.
S. D. KULLBOM H. F. SMITH
Analytical Research Section Research and Development Department Continental Oil Co. Ponca City, Okla. RECEIVEDfor review January 7 , 1963. Accepted April 1, 1963.
Determination of Sodium by Controlled-Potentia I Cou Iometry SIR: While engaged in the development of coulometric methods for the determination of certain rare earth elements, a procedure for the determination of sodium was developed as a check on the proper functioning of our apparatus. Because it could be developed into an accurate method for the determination of several alkali metals, we describe it in this preliminary communication. Kolthoff and Coetzee (3) have shown that sodium yields a polarographic wave in acetonitrile solutions containing tetraethylammonium perchlorate (TEAClOJ as supporting electrolyte. This wave, however, occurs at a rather negative potential. We h a r e found i t difficult to use for analytical polarography because of a slightly-distorted wave form and occasional erratic capillary behavior. Furthermore, the measurement of the solution volume as well as the diffusion current is advisable because an appreciable amount of acetonitrile is swept from the polarographic cell during the deaeration step unless the nitrogen is presaturated with acetonitrile in an allglass system. We found that nitrogen saturated with acetonitrile attacks rubber or plastic tubing, and carries a reducible impurity into the polarographic cell. Since sodium can rather easily be reduced to sodium amalgam a t a merTable 1.
Sample size Equal to integrator reading 1.40 1.36 1.40 1.38 1.41 1.42
914
Sodium Determination by Oxidation = 1.310 Heq. (30.13 f i g . Na) Mi cr oequivalents
Background correction 0.088 0.074 0.067
0.071 0,073 0.083
Found, Na 1.31 1.29 1.33
ANALYTICAL CHEMISTRY
1.31
1.34 1.34
cury cathode, a controlled-potential coulometric method can logically be used to circumvent these difficulties. Individual determinations of sodium on the microequivalent level can be made by this method with a mean error of h0.016 keq., as shown by the data presented in Table I for six consecutive experiments. No difficulty which could prevent the extension of the method to larger or smaller amounts of sodium is known to us. The potentiostat--integrator used in this work is similar to that described by Booman ( I ) and is the same as that’ previously used by us ( 4 ) . Integrator readout is by means of a Fluke Model 801 differential voltmeter. A Varian G-10 recorder was used to monitor the current during the electrolysis. The electrolysis cell is similar to one previously described (4), except for the drain stopcock. which was omitted in the cell used in the present work, and the working counter electrode compartment. A neTv electrode compartment was made which isolated the mercury electrode from the silver wire counter electrode by means of a salt bridge. This n-as necessary to prevent the diffusion and migration of silver ion into the sample solution during electrolysis. Since silver halides are significantly soluble in acetonitrile solutions containing excess halide ions, the electrolyte used in the salt bridge, counter electrode. and the reference electrode was the same ‘1’EiiC1O4 solution used as the supporting electrolyte. The potential of the reference electrode was occasionally compared with a n external aqueous S.C.E. so as to permit all potentials to be referred to this electrode. A dropping mercury electrode in the sample compartment allowed the polarographic determination of a suitable control potential for the controlled pot,ential electrolyses. Any available acetonitrile was used as the solvent follon-ing a purification procedure similar to, and based upon that described by Coetzee, et al. ( 2 ) . The essential features of the
N 2 in
(
I-------I
I cm.
Figure 1. ratus
Sample preparation appa-
purification method are extraction of acidic impurities with saturated sodium hydroxide solution, removal of unsaturated nitriles by the cyanoethylation reaction, and removal of basic impurities
and 11 atci 11 ith phoqhorus pentoxide. 'L'EAC10, can be eatily prepared b j adding perchloric acid to a solution of tetraethylammonium bromide or hydroxide, mashing the precipitate free of bromide ion, and recrystallizing from water. The material used in our work was dried at 50' C. and stored in a desiccator over P205. The tenth-molar supporting electrolyte is prepared b y adding 2.30 grams of TEACIOl to 100 i d . of the purified xetonitrile in a \ olumetric flask. Sptxial precautions to exclude atmospheric mater are unnecessary, but solutions should not be left exposed to the air for longer than the time required for ,ransfer from one container to another. The samples mere prepaied from aqueous stock solutions of sodium rhloride or nitrate. Usually 1000 h of a 10-2L11solution v a s evaporated to dryness on a water b:rth using the apparatus shown in Figure 1. The salt was then converted to sodium perchlorate by addition of a 'ew drops of 60% perchloric acid, and the excess acid iemoved by heating 011 a n oil bath a t about 200' to 250' C. A stream of nitrogen 'lias used to SI! eep out the gase-
ous products in both steps. The dry, acid-free sodium perchlorate was then transferred to a 10-ml. volumetric flask using small portions of the purified acetonitrile delivered from a micro transfer pipet. A 1000-h aliquot was then taken for each determination. Five milliliters of the supporting electrolyte solution and the sample aliquot were placed in the cathode compartment of the electrolysis cell and deaerated for five minutes with a stream of nitrogen. The sodium was then reduced into 3 to 5 ml. of mercury at a potential of -2.3 volts us. an external aqueous S.C.E. ilbout 5 minutes were required for the reduction. ljpon completion of the reduction, the control potential was reset to -0.1 volt and codometric oxidation performed in 5 to 7 minutes. The only background corrcction significant a t the 1-peq. level is that for a small, continuous, faradaic current of about 0.008 peq. per 100 seconds. This background correction rvas determined by continuing the electrolysis until the electrolysis current decayed to a constant value, and it was optimally low a t an oxidation control potential or -0.1
volt. l3lanLs carried through the entire procedure were negligible. The remaining alkali perchlorates art' also soluble in acetonitrile to some extent and can probably be determined by an estension of this method. A complete report on coulometric anaiysis of alkali metal mixtures will be made a t a later date. LITERATURE CITED
(1) Booman, G. L., ANAL. CHEM.29,
213 (1957).
( 2 ) Coetzee, J. F., Cunningham, G. P., McGuire, D. K., Padmanabhan, G. R., Zbid., 34, 1139 (1962). (3) Kolthoff, I. M., Coetzee, J. F., J . Am. Chem. SOC.79, 870 (1957). (4) tWise, E. X., Cokal, E. J., ANAI..
CHIN. 32, 1417 (1960).
E. J. COKAI. E. s.wrss
Chemistry Department University of Arizona Tucson, Ariz. RECEIVEDfor review hlarch 7 , 1963. Accepted April 12, 1063. Research supported, in part, by the U. S. Atomic Energy Commission under Contract AT( 11-1)-553.
New Adsorbents for Gas Chromatography SIR: Our preliminary experiments indicate t h a t i t is possible to create adsorbents useful in gas chromatography by careful elimination of volatile substances from a crystal ,so as to avoid collapse of the crystal framework into a very fine powder. When powdering can be avoided, the resulting solid should have a rather uniform porosity in addition to having a much higher specific surface area compared to the crystals of the starting material. Although many earlier investigators (1, 2 ) have dehydrated a variety of compounds and determined the surface areas of the products, relatively few cf these products have been used as adsorbents because of their relatively small specific surface areas. Furthermore, we have demonstrated that compo[ nds other than \later can be driven off, thereby producing adsorbents hav n g different characteristics. Duffield and Rogers ( 3 ) have shown t h a t a chemically reactive solid which has a very lorn capacity, could be used for gas chromatography by combining a very small sample size and a very sensitive detector. T o date, we have successfully prepared six adsorbents from the first six compounds selected for study. This indicates t h a t collapse 0 ' the crystals into fine pori-ders will not be so serious a fac-
tor in limiting the choice of compounds for study as anticipated. The folloa-ing adsorbents have been prepared by heating in a n oven a t the indicated temperature: Cu(Py)dN03)2 from Cu(Py)?(XO3)*( f J (Py = pyridine) at 80 C. Cu(NH3)2(N03)2from Cu(NH3),(XO3)2( 7 ) at 150" C. Cu(Py)SO, from Cu(Py),S04 (4)a t 100" C. CuSOa .H20 from CuS04.5H20(9)a t 125" C. CdSOc from 3CdS04.8H20 (8) a t 165' C. MgClz.2H20from MgC12.6H20( 5 ) a t 100" C. EXPERIMENTAL
Apparatus and Conditions. .In AIrrographHy-FI 600 flame ionization gas chromatograph was operated a t maximum sensitivity using 6-foot columns of '/*-inch 0.d. copper tubing. Linde high-purity nitrogen was used a? the carrier gas at a flow rate of about 25 cc. per minute. The plunger of a 50-pl. syringe containing the sampl(1 was pumped with air two or more times until a 1-p1. portion of the air in the syringe contained only enough sample to give a peak height of approximateljhalf the width of the chart paper of a Leeds &. n'orthrup Speedomas H strip-
chart rccoi der ha1 iiig a full-scale response of 1 mv. -411 of the retention d a t a are for a column temperature of 38" C. unless otherwise specified. Upon increasing the column temperature above 38" C , the normal decrease in retention times ivas observed. Some of the compounds that did not come off these adsorbents in less than 1 hour at 38" C. sometimes appeared a t higher column temperatures. Preparation and Packing of the Adsorbents. Adsorbents were prepared b y placing t h e starting material (50- t o 60-mesh) into a n oven a t a specified temperature (4-9). Usually after about 4 hours, the required number of molecules had been volatilized from the starting material I n some cases a definite color change occurred in the starting material when the desired adsorbent had been produced. Once the adsorbent had been produced, it could be stored indefinitely in a desiccator over calcium sulfate or calcium chloride. I n packing a column with one of thrse adsorbents, one cannot use an ordinary vibrator because the adsorbents crumble into a fine powder. K i t h such a fine powder in the column, virtually no carrier gas will flow a t ordinary pressures. However, by tapping the column tubing gently with the wooden handle of a spatula, packing of the columns proceeded very satisVOL. 35, NO.
7,JUNE 1963
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