Qualitative and Semiquantitative Tests for Amine Hy drochlo rides on Paper Chromatograms STEPHEN DAL NOGARE Research Division, Polychemicals Department,
E. 1.
d o Pont d e Nemours
SE>.IIQUA\-TITATIVE T E S T
Two simple tests based on reaction of chloride ion with silver ion were devised in order to locate and obtain a semiquantitative estimate of amine hydrochloridespots on paper chromatograms. Spots which contain as little as 3 y of chloride ion can be located by the qualitative test. The semiquantitative test, based on titration of the chloride ion, showed 885% recovery with good precision. The tests require only that the amines he in the h j drochlorideform; they apparently are not dependent upon the amine structure.
The mnine hydrochloride spots are cut out of the paper chromatogram, using the silver spot test on a duplicate chromatogram as a guide. R , values mal- he used as guides, although they do not give information concerning the area or shape of the spot t o be excised. The paper cutout is placed in a 20-ml. beaker containing 5 ml. of 0.1.11 potassium nit’rate which is stirred by a slow standard aqueous st,ream of nitrogen. .4pproximately 5 X silver nitrate is used to titrate the chloride ion from the paper. The potentiometric technique of Kolthoff and Buroda (Z), nsing the silver-silver chloride indicator electrode and the saturated calomel electrode as reference, is used to follow the titration. .4 paper blank of nearly identical area is anal>-zedin the same manner. The hlank cutout is taken from an area of the chromatogram which contains no solutes hut nhich a a s exposed to the developing solvent.
A
LTHOCGH mixtures of mono- and diamine hydrochlorides can be readily separated by paper Chromatography, there is 110 generally applicahle test for the qualitative and semiquantitative drtermination of these materials. The colorimetric tests summarized by Block and others ( 1 ) and Lederer and Lederer (9)lvere found not entirely suitahle, because they were either time-corisriming or did not give a satisfactory test for hoth the mono- and diamines. The tests described here are based on the detection of chloride ion I)>. reaction with silver ion. Qualitatively, the amine hydrochloride spots are detected by the red u c t i o ~of~ silver chloride to metdlic silver. The chloride content of the spots from a separate chromatogram may he titrated by the sensitive potentiometric procedure of Bolthoff and Ruroda (a).
RESULTS
QUALIT4TIVE T E S T
After the paper chromatogram has been developed to give the desired separation of amine hydrochlorides, the solvent is allowed t o evaporate either spontaneously or with gentle heating. When the paper appears dry, it is uniformly and lightly sprayed v-ith a 1% ammoniacal silver nitrate solution. Care should be taken to keep the reagent from running; otherwise the amine spots will blur, The wet paper is first dipped in 10% aqueous acetic acid and then in fresh distilled water. Black metallic silver is deposited in the amine hydrochloride spots upon exposing the wet paper t o ultraviolet light.
Tahle I. Known,
Analysis of Pyrrolidine-Ethylenediamine llixtures Pyrrolidine in Sample .4dded,
Found,
7
Y
6%
64.6 118.5 164.1 203.1 266.8 355 5 546.9
48.8 84.8 145.6 176.8 242.0 321.7 487.7
78 5 74 4 92.2 90 5 94.4
‘V
7.6 14.1 39.7 24 7 33 0 1 tJ.2
Table 11.
-
Recoi-ery,
Some data from the determination of pyrrolidine in synthetic mistures of pyrrolidine (llathcsoni and Pt hylenedianiine ( l h s t man Iiodak) hj-drochlorides are given helow to i1lustr:tte the application of these procedures. The qualitative spot test \vas used to establish that srparation of these salts could he made a t 25” C. on strips of TVhntinan S o . 1 paper with n-ater-satur:itrd butanol :ts the developing solvent. TVith the ascending technique, complete separation rrsulted after the solvent travelrd 13 cin. I n this system the liydrochlorides of pyrrolidine and ethylenediamine eshihited R , v:ilucs of 0.30 and 0.01, respectively. A series of knoxn mixtures \viis analyzed by the serniquantitative technique, with the results shown in Table I. Between -i o 0 and 850 y of the various mixtures in IO p l . of solution ~ a s spotted on the paper for each analysis. An average recovery of 88,170 with a standard deviation of 8.2% was obtained for the mixtures in Tahle I . S o effort was made to correct the cause of inc.oniplrte recovery other than to apply a calibration rorrc~rtioiifor the 10-pI. micropipet. .-i series of samples containing snidler amounts of pyrrolidine was also nnalyeed. T h r w results P h o w d that as little as 3 -y of chloride ion could he detected t)y the qualitative and semiquaiititative tests. In the above case. this n-odd represent 0.4 mole 70 pyrrolidine in 15 MI. of a 1 .II amine solution. The reproducibility of the semiquantitative test was found to be surprisingly good, as shown in Table 11. These data represent eight analyses for one component in a single u n k n o w ~ amine mixture. A total of 1610 y of the amine hydrochloride mixture in 10 PI. of solution was applied to each paper strip. The first column in Table I1 lists the blank values which \\’?re used to correct the titration results. A standard deviatioii of 0.7% was calculated from these data.
94.1 YP 7
Precision of Semiquantitative Test
~- Silver S i t r a t e ” , 111. Paper Psrrolidine. HCi blank spot (iincorr.) 0.28 6.73 6.78 0.28 6 75 0 31 0 .‘31 6.61 6.65 0 81 0.25 578 i 17 0 25 6.61 0.23 Silver nitrate, 5 13 X 10-4s.
Pyrrolidine. HCl Found, Found in Y sarnde, % 22.1 356 22.2 358 22.0 355 21.6 347 21.7 350 22.4 3 60 23.7 382 351 21 8
& Co., Inc., Wilmington, D e l .
ACKNOW LEDGMEVT
The author is indebted to P. R. Cross, who performed inn\t of the experiments reported here, and to L. \V.Safranski for 111s enthusiastic interest in the work. LITERATCRE CITED
(1) Block. R. J., LeStrange, R., Zweig, F., “Paper Chromatography.”
1 s t ed., Academic Pres- Sew York, 1952. (2) Kolthoff, I. AI., Kuroda, P. K., AXAL.CHEM.23, 1304 (1951) (3) Lederer, E., Lederer, N., ”(‘hromatography,” 1st ed., El
