ANALYTICAL CHEMISTRY
1704 Table I. Aniline Point Results with Small Scale Test for Pure Compounds Results on Substances Literature Used in Study Compound Value (9), ’ C. ASTM 1012-49T Small scale test n-Decanea 77.5 76.4 77.9 n-Heptaneb 69.7 69.4 69.5 Methylcyclohexane b 39.5 40.0 40.4 hlethylcyclopentaneb 33 .O 33.8 33.7 l-octene’l 32.5 32.6 32.7 -4verage deviatjon from theoretical i0.48 Average deviation from ASTh‘f method zk0 44 a Humphrey-Wilkinson, Inc.: minimum purity. 95%. b Phillips Petroleum Co.; minimum purity, 99%.
Table 11. Reproducibility of Aniline Point Results with Small Scale Test Using Methylcyclohexane and a Refinery Sample Determination No: 1 2 3 4 Methylcyclohexane 40.3 40.0 40.4 Refinery sample 2410 76 9 7 7 . 5 7 7 . 1 7 6 : 9
Aiv.,A”, ~
oc.
40.2 77.1
0
~
c.
~
*0.2 zto.2
\V.C. Jones for advice and assistance with the experimental arrangement. LITERATURE CITED
Table I1 illustrates the repeatability of the test (same opwatoi and apparatus) for aniline point determinations on methylcyclohexane and on a refinery sample. These results indicate a repeatability similar t o that of the ASTLI method (I)-namely, A 0 . 2 ”c. ACKNOWLEDGMENT
The author wishes t o express her appreciation t o the Humble Oil and Refining Co. for permission to publish this paper and to
( 1 ) .lm. Soc. Testing Materials, “ASTM Standards on Petroleum
Products and Lubricants,” Methods D 611 and D 1012, 235-40, 43i-9 (1950). ( 2 ) Ibtd.. Method D 101249T. ( 3 ) Ball, J. S., U.9. Bur. Mines, Rept. Invest. 3721, 3147 (1943). (4) Leeds & Korthrup, Philadelphia, “Standard Conversion Table 21031 for Thermocouples.” (5) Tiaard, H. T., and Marshall, A. G., J . Soc. Chen. Ind., 40, 20-5T (1921). R L C E ~ EMarch D 31, 1951.
Mineral Analysis with the Flame Photometer SAMUEL B. KNIGHT, W. C. MATHIS, AND J. R. GRAHAM Venable Chemical Laboratory, Cniversity of .\-orth Carolina, Chapel Hill,4. C . E C E S T L Y Biffen ( 1 ) reported the determination of sodium and potassium in refractory materials by means of the flame photometer. The samples were rendered soluble by a calcium carbonate fusion. Blanks were run to correct for the large amount of calcium introduced, and excellent results were obtained. The Bureau of Standards samples reported in this paper were dissolved by fuming down with hydrofluoric and perchloric acids and then diluting to the desired volume, using a modified version of the method of Marvin and Woolaver (6). This method should be faster than the fusion method, and has the advantage of not introducing large amounts of calcium. However, certain silicates are difficult to dissolve in hydrofluoric-perchloric mixtures and the fusion method ( 1 ) is probably of more general application. Of the five samples reported in this paper, only one (opal glass) is r? duplicate of those reported by BifYen (1 ). FLAME PHOTOMETER MEASUREMENTS
ness using overhead heat and a stream of air directed over the surface of the platinum dish. The overhead heating greatly reduced spattering and the air stream saved time. Some samples re uired two or three evaporations for complete solution, and, if Righ in calcium, a final evaporation with perchloric acid only to ensure complete removal of fluoride. Finally, the sample was transferred to a 100-ml. volumetric flask and diluted to the mark. Aliquots of this same 100-ml. portion were diluted to volumes, so that the final sodium or potassium concentrations were about 15 p.p,m., and the calcium concentration was about 30 p.p.m. Dilution to these optimum concentrations often requires a preliminary dilution and rough reading on the flame photometer. In order to prepare the known solution necessary for reading the instrument according to methods 3 and 4 above, it is necessary to make first a reading of the unknown by method 1 or 2. This gives the ap rovimate percentages of sodium, potassium, and calcium, Otger analytical data are necessary in order t o add the proper amount of aluminum, magnesium, and other metals that might be present. All reasonable precautions were taken to ensure contaminationfree samples. Reagents were tested for contamination and appropriate corrections made when necessary. Borosilicate glass volumetric flasks were used, and standard solutions were made up frequently. Calibration curves were checked before each set of readings. Calibration curves were made using the best reagent grade obtainable of potassium chloride, sodium chloride, lithium nitrate, and calcium carbonate. I n addition, the synthetic knowns
The flame photometer used in this work was a Perkin-Elmer, Model 52A, which can be read by using the internal standard principle or the direct (or absolute) method. Readings were made on most samples by (1) direct reading; (2) the internal standard method after lithium had been introduced uhtil its concentration in the finaldilutedsamplewas100p.p.m.; (3) direct reading after the instrument had been “zeroed” with a synthetic Table 1. Determination of Sodium known of approximately the same com% Kat0 Found and Percentage Error, Flame Photometer position as that of the unknown, except Data that the substance to be determined was Direct Internal Bureau of Standards Data with standard with omitted; and (4) the internal standard XaD, Direct Internal synthetic synthetic Sample R Reading standard knoan known method after the instrument had been set with a synt>heticknown. 1. Soda feldspar 99 10 73 1 0 . 2 7 i 0 . 1 2 1 0 . 7 1 z t 0 . 1 3 10.57 & 0 . 0 3 1 0 . 8 6 z t 0 . 0 4 2.
Soda-lime glass 128
3.
.4rgillaceous limestone 1-a
EXPERIMENTAL PROCEDURE
One-gram samples were placed in flat bottomed platinum dishes and treated with 15 ml. of 700/, perchloric acid and 10 ml. of 47% hydrofluoric acid. The samples were evaporated t o near dry-
Opal glass 91
(-4.3%) (-0.2%) (-1.5%) (+1.2%) 1 6 . 8 3 15.37 z t O . 3 1 1 6 . 4 9 z t O . 1 3 1 5 . 4 3 3z 0 . 3 6 16.67 i: 0 . 0 8 (-8.7%) (-2.0%) (-8.3%) (-1.5%) 0 . 3 9 0 . 3 8 i 0 . 0 1 0 . 4 1 i: 0 . 0 1 0 . 3 8 i: 0 . 0 1 0 . 3 9 3z 0 . 0 1 (3%) (5%) (3%) (0%) 8 . 4 8 7 . 6 9 z k 0 . 1 0 8 . 3 O i O . 0 5 8.70=kOo.03 8 . 7 6 z k 0 . 0 4 (-9.3%) (-2.1%) (+2.6%) (+3.3%)
.
.
i
~
~
i
V O L U M E 2 3 , N O . 11, N O V E M B E R 1 9 5 1 required the use of aluminum chloride and magnesium chloride solutions. The latter was prepared from the oxide. Stock solutions were prepared by weighing enough of each pure compound to make 1 liter of solution containing 1000 p.p.m. of the desired ion. Calcium carbonate and magnesium oxide were made soluble by adding 10 ml. of concentrated hydrochloric acid Proper aliquots of these solutions were used t o prepare the more dilute stock solutions necessary for known curves and for analyzing the unknowns. Results for sodium are shown in Table I, potassium in Table 11, and calcium in Table 111. All results represent a t least three samples in which the checks were good t o 1% unless the amount of constituent was very small. At least three photometer readings were made on each sample and the average was chosen as the reading for that sample
1705
Table 11. Determination of Potassium yo K20 Found a n d Percentage Error, Flame Photometer Data
1.
Bureau of Standards D a t a Kg0, Sample % Soda-feldspar 99 0.41
2.
Soda-lime glass 128
0 99
3.
Argillaceous limestone 1-a
0 71
4.
Opal glass 91
3 25
Direct reading 0 . 4 8 i. 0 . 0 3 (+17%) 1.10 i 0 . 0 4 (+11%) 0.68 = 0.01 (-4.2%) 3 . 2 6 i 0.07 1+0 3 % )
2.
Sample Soda-lime glass 128
CaO, 7, 4.76
Direct reading 4.34i0.17 (-8.8%) 4 0 . 3 5 i0 . 4 1
3.
Argillaceoiis limestone 1-a
41.32
4.
Opal glaw 91
1 0 . 4 8 10.03 i 0 . 1 3 (-4.37,) 49.62 5 0 . 0 5 i 0 . 3 6 (+0.9%)
(-2.3%)
Table IV.
S a , 20 K a , 10 Na, 20 S a , 10 S a , 20
K , 10 K , 20
K. 10 K , 20 K , 10 K , 20
Li, 10
S a , 100 S a , 300 Na, 500 N a , 100
7 7
ran of K~~~~~ Concentration, P.p.m. Li, 20
;
4
Li, 10
4
1
Li, 20
2 1
1 2a 2a
18 33 11 21 9 11 12 5 7 8 0 1 1
'2 2 0
Li, 10 Li, 20
1
8 18 6 14
C a , 10 C a , 20 Ca, 10 C a , 20
la
3a
C a , 10
3" 3
2 1 1
Percentage Error, Flame Photometer D a t a Direct Internal with standard with Internal synthetic synthetic standard known known 4.67i0.05 4.41i0.09 4.80i0.05 (-1.9%) (-7.3%) (+0.8%,) 4 1 . 2 2 i 0 . 2 3 40.90 i 0 26 4 1 . 2 5 0 16 (-0.2%) (-1%) ( - 0 2%) 1 0 . 8 3 + 0 . 0 3 1 0 . 4 8 i 0 . 1 4 10.10 & 0 . 0 7 (+3.3%',) (0%) (-3.6%) 47.65 i 0 . 1 8 49.01 i 0 . 2 0 4 9 . 3 8 i 0 . 1 4 (-4%) (1.2%) (-0.5%)
mineral analysis. I n no case did it give completely unreliable results. Finally, in examining the percentage error columns in Tables I, I1 and 111,the actual per cent of the constituent should be considered. When the per cent of constituent is small, the results may be very good but still make a poor showing in the percentage error column. Sumerous interference curves were prepared t o determine the effect of several alkalies and alkaline earths on each other. A number of investigators ( 2 , 6) have shown that the presence of a foreign ion may cause a high reading (enhancement) in the flame photometric determination of a given substance, 1% hile another foreign ion may cause loir readings (repression). iittempts, to employ interference curves t o correct for the presence of foreign ions met n ith little success when more than one
2 3
(+le%)
0.70 I 0 . 0 1 (-1.4%) 3 32 i 0 . 0 5 1t2.27,)
Percentage Error Caused by Foreign Ions
E r r o r in Reading Ion of Known Concentration, % Direct Internal standard 9 10
(+15%) 1 15 =z 0 01
So CaO Found and Bureau of Standards D a t a
Tables I, 11, a n d I11 show that the 5 . Phosphate rock 120 direct reading method is not so reliable in most cases as the internal standard reading. The direct reading gave very poor results in several instances, but only in one case (calcium oxide in phosphate rock 120) was the internal standard reading completely unreliable. Marvin and Koolaver ( 5 ) report that phosphates interfere x i t h sodium and potassium. Sample 120 had too little sodium and potassium for accurate a n a l y s i ~by this method, but the very high phosphate content may interfere t o some small extent with the calcium analysis. The direct reading method employing the s) nthetic knov n was better than the direct reading emploling a \later blank in all but one case, and only once were the results completely unreliable (sodium oxide in soda-lime glass 128). Although it would be erroneous t o state that the internal standard method employing a synthetic known is the most reliable in every case, this method is probably best for the average
Foreign Ion Added, P.p.m. K . 100 K . 200 K , 100 K. 200 Li, 100 Li, 200 Li, 100 Li. 200 Ca, 100 C a , 200 C a , 100 Ca, 200 S a . 100 N a , 300 N a , 100 N a , 300 Li, 100 Li, 300 Li, 500 Li, 100 Li, 300 Li, 500 C a , 100 C a , 300 C a , 500 C a , 100 C a , 300 Ca. 500
Internal standard with synthetic known 0.40 i O . 0 1 (-2.5%) 1.00 i0 . 0 2 (-5%) (+I%) 0 . 7 3 i 0 . 0 2 0 . 7 3 f 0 01 (+2.8%) (+2.8%) 3 . 3 3 i 0 . 0 3 3 . 4 3 i 0 03 ( $ 2 4%) (+5.5%)
Table 111. Determination of Calcium
DISCUSSION OF RESULTS
Ion of Known Concentration, P.p.m. N a , 10
Direct with synthetic known 0.43 1 0 . 0 1 (f4.991,) 0.94 i 0.03
Internal standard 0.47 & 0.02
C a , 20 a
Repression.
Foreign Ion Added, P.p.m. h-a, 300 N a , 500 K , 100 K , 300 K , 500 K . 100 K , 300 K , 500 C a , 100 C a , 300 C a , 500 Ca. 100 C a 300 Ca: 500 N a , 100 N a , 300 N a , 500 N a , 100 K a , 300 K a , 500 K , 100 K , 300 K 500 K: 100 K , 300 K , 500 Li, 100 Li, 300 Li, 500 Li, 100 Li, 300 Li. 500
Error in Reading Ion of Known Concentration, % Direct Internal standard 0 la
4 4
4 3 2 2 0 1 2 la
1-
..
2 15 28 36 6 12 15 9 20 28 6 10 12
15 22 2 7 11
24 32 4 8
.. .. .. ..
11
10
, .
12 28 39 7 14 18 4
..
1106
ANALYTICAL CHEMISTRY
foreign ion w~ present, as in working with natural samples. For esaniple, potassium and calcium separately may enhance a given bodium determination, but if these two foreign ions are mixed, the sodium correction is not predictable as determined from the separate correction curves. h-evertheless, some results from interference curves studies are report.ed in Table IV. Table 11’ may be summarized as follows: Keither sodium, potassium, nor calcium has much effect on lithium readings. Lithium and sodium affect pot,assium readings markedly in the direct method and appreciably in the internal standard method. Berry et al. ,(2), Bills et al. (3), and Inman et al. ( 4 ) report that sodium causes depression of potassium readings. The results of t,he present, investigation, however, show enhancement of potassium readings by sodium. The authors have no adequate explanation for thip effect, and therefore must att,ribute it to the indxumrnt used. A11 t’healkalies have a marked enhancing effect on both 10 and 20 p.p.m. of calcium. Potassium has a considerable enhancing effect on sodium, but lithium and calcium seem to have little effec,t on potassium readings. All ions have a large effect on calcium. The errors caused by foreign ions appear to be due to photochemical effects and not. to light leakage through the instrument, as blanks were run in each instance and proper corrections were made when leakage was observed-when a solution was cont,aminat,ed with a foreign ion, any reading that this foreign ion alone might give was subtracted from the reading obtained when the substance to be determined was introduced. Interference curves made by t.he internal standard method usually resulted in less enhancement or repression bhan those by the direct reading method. In spite of the slight effect of sodium, potassium, and calcium on direct lithium readings, and the marked effect of potassium on direct sodium readings, lithium used as a n internal standard resulta in appreciably better data than would be expected if the internal standard method corrected only for atomizer and burner variations. N o explanation can be offered for this.
The large error when the sodium-potassium ratio is high may be seen in the determination of sodium in samples 1 and 2. Sodium has a large enhancing effect on potassium, and the relatively large error for potassium in these two samples may be the result of this ratio. Hovever, the internal standard method employing the synthetic known gives good results for potassium in these two samples. Finally, the optimum concentrations of sodmm and potassium for final readings of the concentration of either were found to be between 10 and 20 p.p.m. The percentage error caused by a fixed concentration of foreign ion is about the same between these limitq The calcium concentration should be twice as great. ACKNOWLEDGMENT
This work is part of a project in flame photometry being carried out at this laboratory, and was supported in part by the Atomic Energy Commission. The authors’ thanks are due Lewis H Rogers, Carbide and Carbon Chemicals Corp., Oak Ridge, Tenn., for his help and advice. LITERATURE CITED
(1) Biffcn,
F.hI., .-lsa~.CHEM.,22, 1014-17
(1950).
(2) Berry, J. R., Chappell, D. C., and Barnes, R. B., IND.ENG. C H E h f . , -4NAL. E D . , 18, 19-24 (1946). (3) Bills,C. E., RlcDonaId, F. G., Niederrnier, W., and Schwartm, h.1. C., ANAL.CHEM.,21, 1076-80 (1949). (4) Inman, W. It., Rogers, R. A., and Fouvnier, J. A , , Ibid., 23, 482 (1951).
( 5 ) Marvin, G. C., and Woolaver, L. B., IND.ENG.CHEX.,ANAL. ED.,17, 554-6 (1945). (6) Parks. T. D., Johnson, H. O., and Lykken, L.. ANAL. C H E M . , 20, 822-5 (1948).
RECEIYED Deceriiber 18, 1950.
Rapid Control Method for Amines in Hydrocarbon Polymerization Feed ROBERT T. KEEN‘,Keystone Oil Refining Co., Detroit, Mich. N T H E operation of commercial hydrocarbon polymerization plants using phosphoric acid catalyst, control of nitrogen bases is essential for prevention of rapid catalyst deactivation. In 1946 Donn and Levin ( 4 ) publighed a method for determining these bases in hydrocarbon feed stocks. This method requires a rather elaborate and difficultly portable apparatus, and it requires 3 to 4 hours to complete an analysis, although accurate results are obtainable. The purpose of the present investigation was to develop a very rapid but simple and fairly accurate method for control of bases in polymerization feed stocks. Such a method would be particularly useful for rapid control work by relatively unskilled personnel. Several titrants utilizing different acids have been recommended for nitrogen bases in nonaqueous media. A number of solvents for the acids have been used. hlCOhOh weaken the basicity of bases but have been used ( 6 , 8 , 9 , 1 2 ) . Several workers propose perchloric acid in acetic acid as titrant (1, 5, 7 , IO). Fritz (6)suggests perchloric acid in dioxane. Both diovane and acetic acid were unsuitable because of freezing a t low temperatures. As diethyl Cellosolve (ethylene glycol diethyl ether) dissolved perchloric acid easily, was not too volatile, and did not freeze a t the low temperature required, this solvent was used in development of the described method. Perchloric acid in diethyl Cellosolve reacts rapidly with amines in nonaqueous solvents a t low temperatures. When samples of amines likely to be present in hydrocarbons were titrated, sharp end points were obtained regardless of the amine present.
’
Present address, Oak Ridge, Tenn.
A satisfactory procedure was developed using very simple a p paratus.
A cyclone sampling device, such as that used in refineries, was used for taking liquid gas samples. This device is a metal cone with a pipe of small diameter entering a t the top outer edge of the cone. The end of this pipe is threaded and the device is screwed into a sampling line. When the valve is opened, the entering gas is given a swirling motion as it turns toward the lower end; hence the name “cyclone” sampler. The gas cools the sampler by evaporation until a point is reached where the sampler becomes cold enough to act as a condenser. Gases such as propylene, propane, and higher are readily liquefied in this manner. A 250-ml. Erlenmeyer flask, a reflux digestion head as devised by Smith and Getz (11),and a dry iceacetone cooling bath are also required. The cyclone device and the reflux head are shown in Figure 1. The problem was attacked using a strictly nonaqueous solvent approach, because the standard acid added must be in a solvent miscible with the hydrocarbon a t low temperatures and sharper end points are usually obtained in titration of amine in solvents of lower dielectric constant, owing to less ionization, etc.
To the flask are added 5 ml. of 0.02 N perchloric acid in diethyl Cellosolve. The sample is added and refluxed away and the excess aid is titrated. Diphenylguanidine in diethyl Cellosolve is used as the titrant. REAGENTS
Diethyl Cellosolve. A commercial product obtainable from Carbide and Carbon is refluxed over sodium to remove all the
