'The absorbance of curves to D is initially linear with time and t,hen follows a square root dependence of time, excel)t a t longer times when convection contributes significantly to mass transfer. The transition time may be determined from the linear portion of the absorbancy curves. The ease with wh,ich spectral studies can be made using C'GE should aid the elucidation of mechanism and kinetics of wrtain electrode processes, in particular those cases where a chemical reaction may follow the charge transfer step. Other applications of CGE, such
as cells for electron spin resonance work or process stream analyzers may prove advantageouq. The scope and limitations of C G E are under further investigation and will be reported in the near future.
(4) Delahay, P., Stiehl, G. L., J . Phys. Chem. 55, 570 (1951). (5) Kuwana, T., ANAL.CHEM.35, 1398 (1963). (6) Loch, L. ll.,, J . Electrochem. SOC.110, 1081 (1963). (7) Mantell, J., Zaromb, S., Zbid., 109, 992 (1962).
LITERATURE CITED
THEODORE KCWANA R . KEITHDARLINGTON DONALD W. LEEDY
(1) Adams, R. X., in,,"Treatise on An-
algtical Chemistry, I. M. Kolthoff and P. J. Elving, eds. Part 1, Vol. 4, Chap. 47, Interscience, Kew York,
1963. ( 2 ) Alden, J. R., Chambers, J. Q., Adams, It. N., J . Electroanal. Chenz. 5, 152 (1963). (3) Cooper, W., .Vatwe 194, 560 (1962).
Department of Chemistry Cniversity of California Riverside, Calif. RECEIVEDfor review May 25, 1964. Accepted June 26, 1964.
Gas Chr(3 ma tog ra phic Determina ti o n of Isomers of Phenylenediamine SIR. A recently reported method for the quantitative de1,ermination of the isomers of phenylenediamine depends upon measurement by a n electrometric (polarographic) method ( 2 ) . To date the most satisfactorj, qualitative determination is based upon reduction of phoiphomolybdic acid ( I ) . A rapid gas chromatographic method is presented here which permits accurate qualitative
and quantitative determination of mixtures of o-, m- and p-phenylenediamines. EXPERIMENTAL
Apparatus.
T h e i m t r u m e n t used
to obtain the chromatograms was a Model 500 linear programmed temperature gas chromatograph (F Bi h3 Scientific Corp.) equipped with a 1mv. Drown Electronik Recorder (JIinneapolis-Honeywell Co.) wit,h a c h a r t speed of 15 inches per hour. Operating Conditions. Detector cell temperature, 310" C.; detector cell current,, 180 ma.; injection port temperature, 320" C. ; helium flow a t exit, 125 ml. per minute; starting column temperature, 150" C . ; final column temperature, 250" C . ; programmed temperature rate, 5.6" C. per minute. Column Preparation. A 2-foot length of 1/4-inch 0.d. stainless steel tubing was packed with 25% by weight Triton X-305 o n 60- to SO-mesh Chromosorb W. Reagents. T h e isomeric phenyle n d i a m i n e s were purified by distillation in a nitrogen atmosphere. T h e known mistures were prepared and diluted just prior to analysis to minimize errors due t o air osidation.
Table I.
--
w
v)
z
X
00
0
w
a
l-
a
0
a
0
3 Y u a
4
I
.
.
.
.
.
0
2
4
6
(1
. 10
12
14
I6
18
-r
20
T I M E , HIHUTES
Figure 2. Chromatogram from analysis of p-phenylenediamine containing 1 .Oyoortho isomer
Analysis of Synthetic Mixtures
Deviation, Mixture I
T I M E , MlhIUTES
Figure 1 . Chromatogram from analysis of mixture of equal amounts of 0 - , m-, p-phenylenedisamine
II I11
added 33.3% o-Phenylenediamine 33 3% p-Phenylenediamine 33 3(,4 ?,1-Phenyleriediamine 10,05&o-Phenylenediamine OO.O(,", p-Phen.leiiediaiiiiiie 1.Oyoo-Phen\lenedinrnine 9 0 . 0 % p-Phen:vleiiediariiine
Found 34.253 o-Phenylenediamine 32 45i p-Phenylenedianline 3 3 . 3Yc m-PhenI.lenedianiine 0 . 5 5 o-Phenylenediariiine 00 5f,1 p-Phenylenediaflliiie O 87; o-Phenylenediarnine 09.27; p-Phenylenetliamine
VOL. 36, NO. 10, SEPTEMBER 1964
CY /C
+O. 9 - 0 $1 0.0 -0.5 10.5 -0 2 +O. 2
2025
Procedure. With instrument parameters set and equilibrium attained, a portion of t h e sample is dissolved in about 3 times its weight of dimethj-1formaniide (DlIF)--i.e.> 10 grams of sample require about 30 ml. of D M F . 4 0.02-ml. portion of t h e diluted sample is injected into t h e instrument. Quantitative results are obt)ained by total area technique (ratio of t h e individual peak areas to the s u m of the peak areas).
RESULTS A N D DISCUSSION
Figure 1 shows a chromatogram obtained froin the analysis of a mixture containing equal amounts of the three phenylenediamine isomers. Figure 2 shows a chromatogram obtained from the analysis of a mixture containing 1% by weight of o-phenylenediamine in p-phenylenediamine. Table I summarizes the results ob-
tained from the analysis of synthetic mixtures.
t,hree
LITERATURE CITED
( I ) Frieser, It. G., Scardaville, P. A,, ANAL.CHEM.32, 196 (1960). (2) Mark, H. B., Jr., Ibid., 36,940 (1964). WILLIAMH. BRYAN Southern Dyestuff Co. hlart,in-bIarietta Corp. Charlotte, K . C. RECEIVEDfor review May 11, 1964. Accepted June 29, 1964.
Determination of Silica in the Presence of Phosphate and Fluoride SIR: A rapid and precise wet analytical method was developed for the determination of small amounts of silica in t h e presence of phosphate, fluoride, and calcium. The classical method of Berzelius ( I ) , based on three types of silica separation, was unsatisfactory for small amounts of silica or in the presence of calcium and phosphate (11). The method was modified by Hoffman and Lundell (7') and by Shell and Craig ( I I), but neither modification gave satisfactory separations in the presence of calcium and phosphate. Schrenk and Ode (9) developed a method using perchloric-boric acid dehydration and Shell (10) reported that addition of aluininuni prior to hydrochloric acid dehydration improved recovery of silica. Hazel (6) suggested the use of a sodium tetraborate-sodium carbonate flus for decomposition of silicate minerals, and cautioned against
Table I.
possible contamination of the silica with boron, which had to be removed. Brabson, Duncan, and Murphy ( 2 ) described a n iniproved gravimetric quinolinium molybdosilicate method, but only reported results of tests up to a P205to SiO, ratio of 7 to 1. Cronkite (3) suggested a rapid method using gelatin as a coagulant. However, the method requires a minimum of 100 mg. of SiO,. Harel, Herman, and Jalmi (6) suggested a method which is based on removal of fluoride by addition of sodium silicate, but the method does not give the required precision for low levels. Two recent reviews on the general subject are noteworthy (4, S). EXPERIMENTAL
Procedure. X weighed sample (up to 8 grams) containing t h e equivalent of less t h a n 2 gram.; of P 2 0 5a n d 0 25 gram of F 13 neutralized 111th t h e fusion mixture (3 parts N a 2 C 0 3 and
SiO, Recoveries from H3POd-H&FrCaO
Systems
(NazC03-Na2B40? Fusions)
SiOn, ing. Calcd. Founda 109 3 82 1 107 4 106 8 0 0
0 5
124 3 101 7 115 4
92 2 94 5 110 7
0 0
0 5
123 0 128 7
Recovery,
72
75 99
74 93 96
Fusionb mix, g. 5. 5
7 7 7 7 8
59 3 48 8 122 0 94 8 122 2 122 7 100 8 133 3 83 2 62 a Based on single HC10, dehydratlon 3 parts Sa2C03 to 1 part Sa?B40i Solution containing 3OC; H3PO4,4 5 CaO
20 26 *
ANALYTICAL CHEMISTRY
&Pod,CaO nux, g.c
10 10 15 15 15 15 8 8 8 8 8
Remarks ... 2 Al/F
Blank det. , . .
2 Al/F 2 Al/F 2 A1 blank det.
2 . 5 Al/F 2 . 5 Al/F
2 . 5 Al/F, no borate
1 part S a 2 B 4 0 7in ) a platinum dish. An e\cess of 15 grams of fusion mixture and a quantity of aluminum hydrolide equivalent to 1.89 grams of A1~03are added. hfter fusion, the cooled melt is leached with water in a beaker and 65 ml. of i2Y0 perchloric acid are added. The solution is evaporated, strongly fumed for 15 minutes, and boiled with a watch glass cover on the beaker for an additional 25 minutes. ( S o t e : observe safety precautions for use of perchloric acid.) ;ifter partial cooling, 300 ml. of hat water are added and the solution is boiled for a few minutes, filtered through a niedium porosity paper, and washed thoroughly with 1% hydrochloric acid. The filtrate is evaporated again to perchloric acid fumes and the above procedure is repeated. The filter papers from the two filtrations are combined, ignited, and the silica is determined by the H F volatilization procedure. RESULTS, DISCUSSIONS, A N D CONCLUSIONS
Synthetic mistures of phosphoric acid, fluosilicic acid, and calcium oside were analyzed by the boric-perchloric acid digestion method (9). The amounts of Si02 introduced were from.87 to 140 mg. The recoveries varied from 47 t o 7870. Sodium hydroxide treatment a t room temperature prior to the acid digestion failed to improve the recoveries. Apparently fluosilicic acid is too stable for these decomposition conditions. Similar synthetic mixtures were subjected to the boras-sodium carbonate fusion procedure (6))followed by perchloric acid dehydration. Results in Table I show substantial improvement in recovery of silica, especially in tests in which aluminum was added prior t o fusion. The last experiment show-
