811
V O L U M E 22, NO. 6, J U N E 1 9 5 0 7. Nickel Dimethylglyoxime Reagent (2). A 0.1 solution of nickel sulfate is saturated with dimethylglyoxime and the supernatant liquid is used as the streak reagent. It is useful for very basic substances. The zone is red on a colorless column. 8. Iodide-Starch-Bromate Reagent. The reagent is prepared by mixing equal volumes of 1% potassium bromate, 1% potassium iodide, and 5% starch solutions just before using. It is useful as test for acids. A dark blue zone is a positive indication. 9. Negative Nessler’s Test. Nessler’s reagent is streaked on the column and then overstreaked with 1 M ammonia. The inhibition of the orange color due to the reaction of the Nessler’s reagent and the ammonia indicates a zone of acetone or nitromethane. 10. Azide-Starch-Iodide Reagent (2). This is prepared by mixing equal volumes of saturated solution of iodine in 1% p o t s sium iodide and a solution of 10% sodium azide in 1% starch. A bleaching of the blue color indicates a zone of carbon disulfide. 11. SchB’s and Nessler’s Reagent. The column is first streaked with Schiff’s reagent and after 2 minutes is overstreaked with Nessler’s reagent. A blue zone indicates some aliphatic amines. 12. Cupric Sulfate and Bromine Fumes. The column is streaked with the 0.1 M cupric sulfate solution, then exposed to fumes from a dilute solution of bromine in carbon tetrachloride passed over the column in a medicine dropper. The blank portions of the column alon the cupric sulfate streak turn brown while the zone remains byue. This test is useful for di- and triarylaniines. 13. Formaldehyde and Plumbite Test (2). The column is first streaked with a 40% solution of formaldehyde and followed by a streak of 0.1 M sodium plumbite; a brown zone indicates carbon disulfide. 14. Special Filtrol. A suspension of special Filtrol in petroleum ether or benzene is prepared. This suspension is streaked on the column so that there is a streak of the special Filtrol powder deposited. This powder will form a green or blue zone with many amines.
15. Nessler’s-Potassium Hydroxide-Carbon Disulfide Reagent. The column is streaked with carbon disulfide and overstreaked with 10% potassium hydroxide, which in turn is overstreaked with Nessler’s reagent. The formation of a vellow zone indicates an alcohol. 16. 2,4-Dinitrophenylhydrazinein Hydrochloric Acid (3). A saturated solution of 2,4dinitrophenylhydrazine in 2 M hydrochloric acid gives a strong yellow zone on a pale yellow background with ketones and aldehydes. On overstreaking with 6 M sodium hydroxide a transient dark color develops. The following reagents have not been found in the literature and are apparently new in their application as streak tests: 2, 3, 4,8, 9,11, 12, 14, 15, and 16. LITERATURE CITED
Brockmann, H., and Volpers, F., Ber;, 80, 77 (1947). Feigl, F., “Spot Tests,” 3rd ed., New York, Elsevier Publishing Co., 1946. Iddles, H. A., Low, A. W., Rosen, B. D., and Hart, R. I., IND. ENG.CHEM.,ANAL.ED., 11, 102 (1939). Karrer, P.,and Schopp, K., Helu. Chim. Acta, 17, 693 (1943). Sease, G. W., J. Am. Chem. SOC., 69, 2242 (1947); 70, 3630 (1948).
Strain, H. H.,“Chromatographic Adsorption Analysis,” New York, Interscience Publishers, 1942. Trueblood, K. N., Sohroeder, W., and co-workers, OSRD Rept. 5952 (1946).
Winterstein, A., and Schon, K., 2. physiol. Chem., 230, 139 (1934).
Zechmeister, L., and Cholnoky, L.,“Principles and Practices of Chromatography,” 2nd ed., New York, John Wiley & Sons, 1944. RECEIVEDMarch 9. 1949. Presented a t the Southwest Regional Meeting of the AMERICANCHEMICAL SOCIETY,Shreveport, La., December 1948. Work done under Contract N7onr-356, T.O. I V between the Office of Naval Research and Louisiana State University.
Characterization of Some Chromatographic Adsorbents PATRICK H. MONAGHAN, HANS A. SUTER, AND ARTHUR L. LEROSEN Louisiana State University, Baton Rouge, La. Data a r e presented here for the characterization of a number of chromatographic adsorbents. The relation between T,, and Yois derived and confirmed by experimental data.
T
HE work reported here is part of a program of study of the specificity of chromatographic adsorbents. It was necessary to know the characteristics of the common adsorbents in order to select those suitable for use. ks a by-product of this investigation some interesting relations have been shown between the adsorbent and its properties. The methods used are described elsewhere ( 8 ) ; they consisted essentially of determining for each adsorbent the characteristic and measuring adsorption affinity. Other values of V,, and TKO, terms such as k and K could be calculated from these data.
A
= driving pressure, mm. mercury
a
= column interstitial volume, ml. per mm. = viscosity of solvent, centipoises = column length, cm. = a packing measure defhed as the ratio of the length of packed column required to hold a unit volume of solvent to the length of unpacked tube required to contain the same volume of solvent = distance of a point on an adsorptive zone from the top of the column (usually the leadmg or trailing edge of the zone) = distance the front edge of the developing solvent has moved in the packed column, measured from the top of the column = ratio of the movement of an adsorbed zone to the movement of the solvent defhed mathematically as dz/dD. The rate for the leading edge is Rz and for the trailing edge is Rt. For this determination the initial volume of solution was i r l ml. of 0.01 M solution ( r is radius of tube used)
?
L
s z
D
DEFINITION OF TERMS
V , = rate of flow of the developing solvent through the chromatographic column measured in mm. per minute a t constant flow. The values given are for columns 75 * 2 mm.’ long packed under vacuum alone. The driving presmre was about 700 mm. of mercury. The vacuum waa supplied by a water pump. The packing is aided only by tapping the glass tube with the stamper until no more settlin is observed T~= o time in second% required for the solvent to penetrate 50 mm. into an initially dry column 75 * 2 mm. long under a driving force of a pressure of about 700 mm. of mercury (the full vacuum supplied by a water pump). I n the present work benzene was used as the solvent = permeability of column in darcys k K = a constant formed by the grou ing of constants ( k A / 760a). This constant is usefur in estimatin the flow rates through other types of column (V, = f?P/rlL)
= cross-sectional area of the column, sq. cm.
P
R
The experimental data are shown in Table I ; blanks indicate that the data were not obtained because of difficulty in measurement. On prewashed columns TSO could not be obtained and in general calculations were not made for k and K . On some adsorbents the o-nitroaniline zone could not be detected because of the dark color of the adsorbent, etc. Attempts to use fluorescent substances for the R determination on these adsorbents were not successful because the fluorescent zone could not be observed.
ANALYTICAL CHEMISTRY
812
Some adsorbents did not adsorb +nitroaniline appreciably from benzene and consequentiy crin only be considered as weaker adsorbents than the others in regard to the standard substance used here. For ordinary work it is generally desirable that the values of V,, k, K , and RI be in the following ranges: V , = 10 to 50 mm. per minute (using benzene as a solvent) = 3 to 1 7 darcys R1 = 0.10 to 0.30 for substance to be chromatographed K = 0.06t00.32
k
Variations in S are of minor importance. A large amount of data is made available here for a comparison between Tsc and V,. The relationship between these two quantities was derived, assuming constant pressure throughout the determination, which is approximately true. The result of this calculation was the equation: V e = 1000/Tw. A comparison between the values found experimentally and the line given by plotting this equation is shown in Figure 1. The agreement is enough to justify the assumption that the relation is true, and therefore V. values may be calculated from TU determinations. The derivation of the relation is shown below : 00
h
7-mh
00
0
0000
w
o m o h
The term V. has been shown t o be inversely proportional to the column length a t constant solvent viscosity
0
0000
(1).
N?
m
Y 00
-N-,?
4??0
N .
U
9 : 3
V,
5
blLor l/Vo
-
Llb
(1)
m 0
-.
Here b is a constant and L is the length of the column in millimeters The term Tu may be represented aa follows:
m :
N '
w :
2 : 3 00
2s
[L*/2b]:0=
(:)($)
-
50/2VL, (2)
I n this step constant pressure was sssumed; although this is not strictly true, the results indicate that it is a reasonable approximation. The V , differs from V, which is the value reported ex rimentally. f%srnuch as V c is determined for a 75-mm. column, it is neceasary to convert V,, into terms of V,,,. Because V. is inversely proportional to the column length, it ollows:
V,, = (75/50) V,
= (3/2)Vc,,
(3)
813
V O L U M E 22, NO. 6, J U N E 1 9 5 0 200
v,
100
0
0.10
0
0.20
Figure 1. Theoretical and Experimental Values of Relation between V , and 1/Tw
Vc is given in minutes and value for V, IS:
7‘60
is given in seconds, so the final
I t is interesting to compare some of the adsorbents in regard to their adsorption of the standard substance, enitroaniline, aa shown in Table I. Many factors other than the surface structure of the adsorbent &ect the adsorption abity-via., surface area, particle size, purity, adsorbed moisture, etc. It is evident that the order of decreasing adsorption &ity is roughly: acid silicates, silica gel, silicic acid, alkaline oxides, alkaline hydroxidea. Magnesium-containing adsorbents apparently are stronger than the corresponding calcium compounds with reference to o-nitroaniline. Data for lot numbers of the batches of adsorbents used here are not given, as it would be practically impossible to obtain these particular lots of adsorbent for future use. In general, it haa been the authors’ experience that the various brands of adsorbenta show only minor variations in properties, whereas the only variations of major importsnce in the choice of an adsorbent are in order of mapitude; thus an adsorbent may show a flow rata which is too fast, too slow, or satisfactory for a given operation. In the authors’ experience, Merck reagent silicic acid over a period of about 6 years has always shown nearly the eame properties, regardless of the lot used; two lots are included in the present survey as an indication of the extent of variation which may occur from lot to lot. The cmes used represent approximataly the maximum variation noted for this particular adsorbent. Numerous other cmes of thii same kind might be cited. The data presented here have been found very useful in the selection of adsorbents. It is hoped that the publication of this kind of data will stimulate the characterization of commercial adsorbenta and thereby aid in making available better adsorbenta. LITERATURE CITED
(1) LeRosen,A. L.,ANAL.CEEM.,19,189 (1947). (2) LeRosen,A. L.,Ibid., 22,809 (1950). RECEIVED March 9, 1949. Presented at the AMEaICAN CHEMICAL Soam Meeting-in-Miniature at New Orleans, La., May 1948. The work denoribed in this paper was done under Contraot N7onr-866, T.O. IV, between the O5oe of Naval Research and Louiaians State University.
where the last V , is V-,.
Critical Examination of Platinum Sulfide Precipitation D. S. JACKSON AND F. E. BEAMISH University of Toronto, Toronto, Ontario, Canada A detailed investigation has been made of the conditions affecting the sulfide precipitation of platinum, in particular the effect of various proportions of sodium chloride and of hydrochloric acid. The efficiency of different concentrations of ammonium chloride and of hydrochloric acid used to wash and leach the precipitate has been evaluated. A procedure for the accurate microdetermination of platinum in the presence of sodium chloride has been developed.
T
HE precipitation of a platinic salt with hydrogen sulfide was recorded by Berzelius in 1826 ( 4 ) . Many early workers were of the opinion that the precipitated material was complex in nature. Antony and Lucchesi ( 1 ) stated that a t temperatures below 90”C. sulfoplatinates were formed. However, von Meyer (II ) considered that the precipitate was a looae compound of platinum disulfide and hydrogen sulfide. These two concepts have been discussed by recent investigators (8, 6, 8, 13) in the light of modern theories of structure, but no completely satisfactory picture has been evolved. DETERMINATION OF PLATINUM BY STANDARD PROCEDURES
Three generally accepted recipes for the determination of platinum by means of the sulfide precipitation have been re-
ported (7, 8, IS). Them procedures differ significantly in detail. I t has long been accepted in the authors’ laboratory that all these procedures produced high reaults and that there was an apparent discrepancy in the results obtained from different procedures. The hydrogen sulfide precipitation of platinum is preceded by a separation from interfering elements. Sodium chloride is therefore a probable constituent of the precipitation medium. This condition was anticipated in the preparation of the standard platinum solution. A weighed quantity of reagent platinum was dissolved in aqua regia, sodium chloride waa added, and the solution was evaporated repeatedly in the presence of concentrated hydrochloric acid. Each aliquot used contained 0.10 gram of sodium chloride, giving, before precipitation, a solution 0.034 molar in sodium chloride. The platinum in
