the intent to present a liydrocarbontype or a gas chromatographic method, but to describe the combined use of the two methods to eliminate costly distillation time. The majority of gasoline saniples analyzed by this laboratory for hydrocarbon types are sufficiently nonvolatile to be charged into the mass spectrometer at ambient temperature, by a constant-volume pipet and a mercury orifice. However, if samples are so volatile that vapor loss occurs when this charging twhnique is used, alternate charging procedures may b r used, provided the liquid volume of the sample charge may be measurrrl or calculoted. ACKNOWLEDGMENT
The authors thank the management of the Union Oil Co. of California for permission to publish this paper. They also express appreciation for the assist-
Table I.
Comparison of the Two Methods
Sample Sample A Sample B _ C_ ~ Chroma- Depentan- Chroma- Depeiitan- Chroma- Depentantography ization tography ization tography ization CS and lighter frac-
tion 1.7 CB+fraction Paraffins 44.9 45.0 35.0 hlononaphthenes 34.7 Dinaphthenes 7.4 7.4 Aromatics 13.0 12.6 Data in liquid volume %.
ance rendered by TV. R. Minks in this research. LITERATURE CITED
( 1 ) Am. Soc. Testing Materials, ASTLI
Committee D-2 Rept., Appendix IV, See. 9 (e), 1956. ( 2 ) Brown, R. A , , Consolidated Engineering Co., Mass Spectrometer Group Rept. 71 (November 1949). (3) Dietz, JV. ii., Intern. Symposium on
. ..
10.4 35.1 3.4 0.4 61.1
26.7 35.9 3.3 0.4 60.4
50.8 35.0 4.0
10.2
52.7 33.5 3.9 9.9
Gas Chromatography, Michigan, Bugust 1957. (4) Ferguson, TT'. C., Horn-ard, H. E., a X - 4 L . CHEAf. 30, 314 (1958). (5) Lichtenfels, D. H., Fleck, S. A., Burow, F. H., Coggeshall, S . D., Ihzd., 28, 1376 (1956). (6) Lumpkin, H. E., Thomas, B. W., Elliott, Annelle, I h i d . , 24, 1398 (1952). RECEIVED for review December 8, 1958. Accepted January 23, 1959.
r
CoIori metric Dete rmi nuti on ot Organic Nitrates and Nitramines MARIO A. LACCETTI, STANLEY SEMEL, and MILTON ROTH Feltman Research and Engineering laborafories, Picatinny Arsenal, Dover, N. J.
b The colorimetric ferrous sulfate method has been modified for the determination of organic nitrates of ordnance interest and has been extended to include aliphatic and cyclic nitramine compounds used in propellant and high explosive compositions. The color produced is stable for about 2 hours and follows Beer's law up to 2.6 meq. of nitric oxide per mole of sample per 100 ml. of solution. The organic nitrates and aliphatic nitramines tested completely liberated their nitrogen as nitric oxide, while the cyclic nitramines liberated only a fractional amount of their nitrogen as nitric oxide. Thus, a common Beer's law curve i s obtained for the compounds liberating their nitrogen completely. The curves for the cyclic nitramines, however, exhibit smaller slopes and are unique for each compound.
T
HE reaction between ferrous salts and nitrates in the presence of sulfuric acid to yield a brown solution was known as early as the 18th century. The color is due to the formation of a ferrous ion-nitric oxide complex ( 2 , 3 ) . The reaction can be represented as follorn:
NO,-
+ 3 Fe" + 4H3 I.'e
F e + +aq. t S O
e
[Fe(KO)]+'aq.
-+
+-
+ S O + 2H20
+ 11,000 cal./mole
Recently, Swann and Adams (4) developed a colorimetric method for nitrocellulose based on the classical brown ring test using a reagent composed of 0.5% ferrous sulfate in 75% sulfuric acid. Subsequently, Bandelin and Pankratz ( I ) improved the method by modifying the time, temperature, volumes, acid concentrations, and n-ave length. I n adapting the original method of Swann and Adams, the concentration of ferrous sulfate n as increased in order to determine greater concentrations of the reacting constituents. At the concentrations used, the red-violet color formed is stable for about 2 hours and has an absorption peak a t 525 mu. Furthermore, the reaction is not specific for the -OXO2 group, as was previously thought, but compounds containing -K - S O * groups, (nitramines) will also give the characteristic color which obeys Beer's law. REAGENTS
Ferrous Sulfate Solution. Transfer 10.50 grams of anhydrous ferrous
sulfate to a 500-ml. borosilicate glass beaker. Add 250 nil. of distilled water, place t h e beaker and contents on a hot plate, and bring t o a rapid boil while stirring. Remove t h e beaker and contents from t h e hot plate, cool to room temperature, and pour the turbid solution into a 1-liter borosilicate glass-stoppered bottle. Place the bottle in a cold water bath and add slowly, with caution, 600 =k 50 ml. of concentrated sulfuric acid. After the acid is added and the solution is a t room temperature, dilute to 1 liter n-ith the acid. ANALYSIS OF SAMPLES
Transfer an accurately weighed portion of approximately 0.2500 gram of sample to a 250-1n1. volumetric flask, dissolve, arid dilute to volume with ACS grade acetone. Transfer a n aliquot portion, containing approximately 2.0 nieq. of the sample (referring to the amount of nitric oxide formed per mole of sample), to a 300-ml. glass-stoppered, borosilicate glass flask. Evaporate the acetone with a stream of dry air and add exactly 50 ml. of concentrated sulfuric acid. Stopper the flask and shake until the sample is dissolved. Add exactly 50 ml. of cold (10' to 15" C.) ferrous sulfate reagent, stopper, and cool the flask under running water. Sn irl the flask occasionally, keeping VOL. 31, NO. 6, JUNE 1 9 5 9
1049
-
where Table I.
Colorimetric Data for Compounds Reacting with Ferrous Sulfate Reagent
Bbsorbancy Index, Mg./100 Ml., 1.000-Cm. Cell 36.2
Compound Potassium nitrate Nitroglycerin (N.G.) PentGrythritol tetranitrate (PETN) Triethyleneglycol dinitrate ITEGN) N-‘Methyl:hT-nitro-2,4,6-trinitroaniline (Tetryl) Hexahydro-1,3,5-trinitro-s-triazine (RDX) Octahydro-l,3,5,7--tetranitros-tetrazine (HMX) Nitroguanidine (N/Q)
31.2
Molecular Extinction, E x lo-* 2.79 7.28
31.6
10.00
4~. 9 . -5
4.85
110.0
2.61
42.0
5.29
81.2 35.4
3.65 2.94
the temperature of the flask between 25’ and 30 O C. Allow the color to develop for 45 minutes and read the absorbance on a spectrophotometer at 525 mp. Use the ferrous sulfate reagent, diluted with a n equal volume of concentrated sulfuric acid, as a blank. Prepare standard curves on the instrument to be used for analysis. DISCUSSION
The 8 compounds listed in Table I were analyzed by this method. I n plotting absorbance vs. milliequivalents of nitric oxide formed for each of the 8 coinpounds, it was found that all b u t R D X and HRIX gave the same straight line. This is interpreted to mean t h a t a complete release of nitric oxide has taken place in all cases except for R D X and
HMX. The curves for RDX and H M X , which $\-ere also straight lines, had smaller slopes than the other compounds. The slopes were found to be 0.76 and 0.34% of the general nitrate slope for R D X and HhIIX, respectively. Apparently, the cyclic attachment of the nitramine group hindered complete liberation of nitric oxide in these compounds. The unique slopes of the curves for RDX and HMX indicate that a method of analysis for mixtures of these compounds is feasible. I n the case of the six compounds that exhibit equivalent liberation of nitric oxide, any one is identified b y substituting in and solving the following equation. M = - NS 0.413A
M = molecular weight of sampie S = sample weight, mg./100 ml. of solution N = moles of nitric oxide released per mole of sample A = absorbance of sample at 525 m p with 1-cm. cell
This equation assumes that all the absorbance is due to the color reaction in which the nitric oxide liberated is the controlling factor. I n addition to identifying a sample by its molecular weight, the equation may be solved for any of the other variables. Thus, the equation is applicable to qualitative as well as quantitative determination of nitrates and nitramines which liberate nitric oxide completely. LITERATURE CITED
(1) Bandelin, F. J., Pankratz, R. E. ANAL.CHEM.30, 1435 (1958).
(2) Feigl, F., “Qualitative Analysis by Spot Test,” 2nd ed., p. 210, Nordemann, New York, 1939. (3) Sirotkin, G. D., Starostin, V. V., J . A p p l . C k m . U.S.S.R., 29, 1081 (1954) (English trans.) (4) Swann, M. H., Adams, M. L., ANAL. CHEM.28, 1630 (1956). RECEIVEDfor review August 12, 1958. Accepted December 29, 1958. Analytical Division, Meetin in Miniature, North Jersey Section, A(%, Seton Hall University, South Orange, N. J., January 27, 1958.
Colorimetric Determination of Hexahydro-1,3,5trinitro-s-triazine and Octahydro-l,3,5,7tetranitro-s-tetrazine in Admixtures STANLEY SEMEL, MARIO A. LACCETTI, and MILTON ROTH Feltman Research and Engineering laboratories, Picatinny Arsenal, Dover, Both hexahydro-lI3,5-trinitro-s-triazine (RDX) and octahydro-l,3,5,7tetranitro-s-tetrazine (HMX), when dissolved in concentrated sulfuric acid, produce a red-violet color in the presence of ferrous ions. With each compound, the intensity of the color is proportional to the concentration, with the maximum absorbance occurring a t 525 mp. However, the slopes of the curves for RDX and HMX differ significantly so that it is possible to analyze mixtures of the two compounds without prior separation.
D
of hexahydro-1,3,5-trinitro-s-triazine (RDX) and octahydro - 1,3,5,7 - tetranitro - s ETERMINATIONS
1050
ANALYTICAL CHEMISTRY
N. 1.
tetrazine (HMX) have been difficult because of their close structural similarity, Because the manufacturing process for one compound usually produces some of the other as a contaminating by-product, an analytical method is needed that is specific for each compound and independent of the presence of the contaminant. Several methods have been used for the determination of HXX and/or RDX. A colorimetric method for R D X developed by Wright (12) is based on a reaction with sodium nitroprusside in an alkaline medium. Maximum absorbance for this color occurs at a wave length of 625 mp. Howerer, this method is applicable over a range
of only 2 to 200 p.p.m. of sample, and the R D X color complex is stable for only 4 minutes. HAIX does not react. For the analysis of mixtures of R D X and H M X , three procedures are in general use. One is a hydrolytic method developed at Vanderbilt University ( 2 ) which is designed to separate R D X b y selective hydrolysis. This method is accurate to &0.5% for samples containing less than 60% H M X and to &2% for greater amounts of H M X . The accuracy is less if the particle size of the R D X is not uniform. bwause this adversely affects the rate of hydrolysis. The second is an ultraviolet spectrophotometric method (9) in which
