V O L U M E 2 7 , NO. 1 1 , N O V E M B E R 1 9 5 5
1815
I*:thylenediamine-wat,er proved superior for t,itrations of salts Iioth in rate of dissolution of sample and in sharpness of end points. Although no part'icular effort was made to refine the ])i~oc*edural details, such as temperature corrections in the volume measurement,s, purification of solvents, repurification of iwmpounds, and increasing sample size for larger tit.ration volunies to decrease the buret reading error, the titrations as made 1 v e w rssentially stoichiomet,ric, with the exceptions indicated. Titration volumes ranged from 2.5 t o 9 ml., being limited b y : ~ ~ ~ : i i l d ) iof l i tcompounds. y Tlie relative strengths of acids, as exhibited in the acidic and 1i:isic solvents here used, were not differentiated potentiometi~ic~:illy tlvcn where there spread in pK, values from 12.40 f'iri, 1 -iiit.thyl-~-nitroffu:rnidineto 8.10 for 1-benzoyl-3-nitroguanidinr. Of part,icular interest were the unusually good titrations obtained for nitroguanidine and thiourea in trifluoroacetic acid. 'rhrse materials are not titratable in glacial acetic acid. Trifluoro:icetic acid has t h w proved extremely promising as a solvr~ntfor a new systrm of acids and bases in these preliniinary
experiments. The neutralizations are apparently facilitated by the removal of perchloric ai4d salts, which are only slightly soluhle in this medium of low dielectric constant. 4CKVOW LEDGMEYT
This paper has been released for puhliration by W.B. lIcI,can, technicd director of the S a v a l Ordnance Test Station. LITERATURE CITED
(1) De Tries, J. E., and Gants, E. 9. C . , J . A m . Chem. Soc., 76, 1008
(1954).
S.,ASAL. CHEZI.,24, 306 (1952). Ibid.,p. 674. (4) Fritz, J. S., and Keen, 11. T.. Ibid.. 24, 308 (1952). ( 5 ) Henry, R. A , , De Vries, J. E., and Bosrhan, R . , to be published in J . A m . Chem. SOC. (6) AIoss. AI. L., Elliott, J. H.. and Hall, 11, T.. Ax.4~.CHEY..20, 784 (1948). ( 2 ) Fritz, J.
(:3)
RhCEIvEn for review J u n e 14, 1955. .iccepted August 8, 1955. Diviuion of Analyticul Chemistry, 127th Aleetinp, ACS, Cincinnati, Ohio, Marcli-.ipril 10*55.
Flame Photometry of Organic Phosphorus D. W. BRlTE Hanford Atomic Products Operation, General Electric Co., Richland, Wash.
4 rapid method for determining phosphorus based upon flame emission measurement at 540 mp was deteloped, and ten rcpresentatite organic phosphorus compounds in alcoholic solution were determined in the range 0.01 to 0.03.M with an average error of 0.0006.W. Sodium and calcium cause positive errors because of interfering emission. Sitrogen, sulfur, iodine, and chlorine do not interfere at concentrations equi\alent LO that of the phosphorus.
T
HE recent expansion of the flame photometric field of annl\-sis to include the tletrrmination of elements ot,her t,han the, :ilkdies and the itlkaliiie eart,hs has been welcomed by costvonscious analytical chrmists, owing to t,he savings often reali z e d in time and expense upon adoption of a flame photometric inet,hod. Gilbert (3) has reported quantitative measurements of 16 elements by use of the flame photometer. The effect of iioiimetals on the emission spectrum of metallic elements in some cit'ies niakes possible the det,erminat,ion of the nonmetal by flame photometry. An example is t o be found in a report by Dippel, Bricker, and Furnian ( 2 ) of det,ermination of phoPphorus
Table I.
Ilioctyl benzene phosphonate
Butyl octyl phenyl phosphate Dibutyl ethoxyethyl phosiihate T r i (8-ch1oro)ethyl phosphate
E t h y l di(chloropheny1) phospliinate Tricresyl phosphate Dibutyl phosphate Phosphoric acid Benzene phosphonic acid
Phosphorus .4dded, M 0 0147 0 0 0 0 0 0
o n
0220 0097 0145 0115 0172 0141 0210 0192
n 0284 0 0126 0 0191 0 0119 0 0178 0 0191 0 0281 0 0172
n
0285 0 0253
Phosphorus Found, '1.i 0 0 0 0 0 0 0
0146 0222 0100 0146 0112
n
0169 0137 0217
0 0 0 0 0 0 0 0
0189 0115 0169 0183 0267 0176 0279 0254
n ozoj 0 0304 o 0118
(4). invwtigation has been made of the continuous emission of phosphorus from solutions of organophosphorus compounds in alcohol or kerosine. I t has lieen found that t'he emission of phosphorus is suitable for the determination of these compounds over a wide range of concentrations in t,hrse solvents with :id(,quate sensitivity for many npp~ications. APPARATUS
h Beckman Model D U spectrophotometer equipped with Beckman S o . 9200 flame photometq attachment, hydrogen burner, and Beckman KO, -1300 photoniiiltiplier attachment was used for making the measurements reported. PROCEDURE
Prepare standard solutions of a stable organophosphate compound, such as tributyl phosphate, in eth>-lalcohol in the range 0.005 t o 0.04X. Prepare solutions of the samples in ethyl alcohol such that they fall in this same range with respect t o phosphorus concentration. Measure the emission at 540 mp of the standards and the sam les relative t o t,he emission of the 0.04X phosphorus a calibration curve by plotting phosphorus standard. concentration us. per cent relative emission. Obtain the phosphorus content of the sample aliquots from the calibration curve.
construct
Determination of Organic Phosphorus
Compound Analyzed Tributyl phosphite
A continuous or Iimd spect,rum may be used advant,:igeously in certain cases to allow the direct determination of a nonmetallic element, as in the de~ and Smith termination of organic nitrogen described l i Honma by its effect on the eniis3ion of' calcium.
Error -0
+o
ooni
0002
+ O 0003
+o -0 -0 -0
on01 0003 0003 0004
+n o o o i +n no13
+o -0
-0 -0 -0 -0 -0
+O
-n
+o
0020 0008 0002 0004 0009 0008 0014 0004 0006 0001
EXPERIME\TAL RESULTS
h straight-line plot was obtained by f o l l o ~ing the above procedure. The range may be extended down to the limit of detection, which was found to be about 10-4.11 phosphorus. Before ethyl alcohol was selected as a solvent because of its ability to dissolve a large number of organic compounds, several calibration curves were constructed for tributyl phosphate in kerosine covering the entire range of 0 to 100% tributyl phosphate. Figures 1 and 2 show the manner in which the standard curves vary with range. These curves demonstrate the wide choice of phosphorus concentration ranges possible in standardizing the method and shoLv that the curves are no longer linear in higher
ANALYTICAL CHEMISTRY
1816
d
y
0
!
Figure 1.
I
I
1
I
IO 20 30 40 PER C E N T TRIBUTYL
50
60
PHOSPHATE
70
BO
90
0
IO0
CENT
I
TRIBUTYL
PHOSPHATE
High Range Slit w i d t h mm.
Curve A B
0.06 0.02 0.01
in Table 11. Of the elements studied, xhich include calcium, sodium, nitrogen, sulfur, chlorine, and iodine in several forms, only calcium and sodium cause interference with the method a t the concentrations chosen. The reproducibility of the flame photometric measurements was estimated using hydrocarbon solutions of tributyl phosphate.
Table 111.
Reproducibility of Measurement Tributyl Phosphate Found. % Solution 1 Solution 2
Mean Standard deliation of mean
Effect of Various Compounds on Determination of 0.0184M Phosphorus
lfaterials Added
Molarity
Pyridine Chloroacetic acid m-Nitrobenzoic acid Urea Thiourea Iodoform Thioglycolic acid Calcium ricinoleate Sodium benzoate
0.063 0.053 0.030 0,083 0.066 0.013 0.054 0.018 0.008
Phosphorus Found, M 0.0186 0.0183 0.0183 0.0187 0.0185 0.0187 0.0188 >0.04 >0.04
3
0.14 0.10 0.10 0.08
46.3 44.3 46 6 45 8 46 6 46.0 4~. 5 2 45.4 44 4 47 0 45.8 +0.88 ~
Table 11.
15 KEROSINE
Low Range Slit width, mni.
C D
concentrations of phosphorus, because of changes in the physical properties of the mixture. The qualitative observation was made that approximately equal intensities of radiation resulted from solutions of identical concentrations of tributyl phosphate in ethyl alcohol and in kerosine A study was made of the effect of the state of chemical combination of the phosphorus on the flame emission. Ten different phosphorus compounds were obtained and alcoholic solutions were prepared in the range 0.01 t o 0.04.V. Upon analyzing the solutions flame photometrically by the procedure given above, an average error of 0.0006Jf resulted. The compounds analyzed, named in conformance with the scheme of nomenclature presented by Daasch and Smith (I), are listed in Table I, together with the phosphorus concentrations of the solutions used for analysis, the phosphorus concentration found, and the absolute error.
IN
Figure 2. Emission at 540 mp 2's. tributyl phosphate concentration in kerosine
Emission at 540 mM us. tributyl phosphate concentration in kerosine
Curve A B C
05 PER
IN K E R O S I N E
1.71 1.69 1.68 1.72 1.71 1.68 1.70 1.68 1.72 1.70 1.70
10.015
Error +0.0002
- 0.0001 +o ,0001 +0.0003
+o .OOOI
+0.0003 +0.0004
>0.02 >0.02
Some of the compounds were commercial preparations of unknown purity, and the deviations listed in Table I reflect any lack of purity of the compounds tested. The effect of the presence of other elements frequently found in organic molecules was also investigated. A solution of tributyl phosphate in ethyl alcohol was prepared such that 20-ml. aliquots diluted to 50 ml. resulted in a phosphorus concentration of 0.0184M. Known amounts of the materials tested for interference were added to the solutions, which were then analyzed by the above procedure for phosphorus. The compounds tested and their effect on the determination of phosphorus are shown
Ten measurements were made alternately on each of a 45 and 1.70% tributyl phosphate solution. Before each measurement it was necessary to reset the slit width and sensitivity of the instrument to give a reading of 100% relative emission for a reference standard. The precision figures found in this manner should therefore include any error for nonreproducibility in setting the slit width or in standardizing the instrument. The resulting dial reading was converted to per cent tributyl phosphate from a previously prepared standard curve. The results of this study are shown in Table 111. LITERATURE CITED
Daasch, L. W., and Smith, D. C., Naval Research Laboratory, Report 3657 (April 1950). (2) Dippel, W7. A , , Bricker, C. E., and Furman, N. H., A N ~ LCHEM., . 26, 553 (1954). (3) Gilbert, Paul F., Jr., Ind. Labs., 3, 41 (1952). (4) Honma, 31..a n d Smith, C. L., A 4 CHEM., ~ ~ ~26, . 458 (1954). (1)
R E C E I V Efor D review r e b r u a r y 3 , 1 9 5 5 , Accepted July 11, 1955.
