EIiminuti on
of PreIimina ry Depe ntu nizati o n of Gasoline Prior to Hydrocarbon-Type Analysis by Mass Spectrometry H. E. HOWARD and W. C. FERGUSON Research Deparfmenf, Union Oil Co. o f California, Brea, Calif.
b The usual mass spectrometric procedure for the determination of hydrocarbon types in nonolefinic gasolines containing Cg and lighter hydrocarbons is encumbered by a preliminary distillation to remove the cs and lighter hydrocarbons. Now, however, the need for preliminary depentanization can be eliminated by the use of gas chromatography in conjunction with the mass spectrometric analysis. Cb and lighter hydrocarbons are determined by any gas chromatographic method which expresses results in liquid volume per cent. On the basis of these data, the mass spectrum of the total gasoline is mathematically corrected for the presence of Cg and lighter hydrocarbons. No loss of accuracy is experienced, and costly distillation time, 2 to 4 hours, is eliminated. of nonolefinic hydrocarbons containing six to 11 carbon atoms are readily resolved by mass spectrometry into types including iso- and n-paraffins, mono- and dinaphthenes, and aromatics. Several procedures have been reported-e.g., Brown ( 2 ) ,Lumpkin (6), Ferguson and Howard (4), ASTM (1). A. shortcoming common to each of these methods is that none can be directly applied to mixtures containing Cj and lighter compounds. Such samples require preliminary distillation to remove these light hydrocarbons. The time, 2 to 4 hours, required for this depentanization is considerably greater than the analytical time requirement for the mass spectrometric type analysis. h routine gas chromatographic procedure similar to those described in the literature ( 3 , 5 ) is used in this laboratory to determine the individual Cg and lighter hydrocarbons in nonolefinic gasoline. These results are expressed in liquid volume per cent of the total sample. On the basis of these chromatographic data, the mass spectrum of the total gasoline is mathematically corrected for the presence of Cg and lighter hydrocarbons to eliminate the need for a preliminary distillation of these lighter components. The total IXTURES
1048
ANALYTICAL CHEMISTRY
time required for the gas chromatographic analysis and the correction of the mass spectrum is less than 30 minutes as compared to 2 to 4 hours required for depentanization by distillation. PRINCIPLES OF METHOD
Liquid volume sensitivities are determined for n-pentane, isopentane, nbutane, isobutane, and n-propane a t each mass unit where they interfere with peaks selected for the hydrocarbontype analysis. Sensitivity here is defined as divisions of peak height per liquid volume of sample charged to the mass spectrometer. Each of these sensitivities n-hen multiplied by its respective liquid volume percentage (gas chromatographic analysis) will numerically equal the value of the peak heights caused by each Cs and lighter hydrocarbon in the mass spectrum of the total gasoline. Hence, by subtraction of these values from their respective peak heights in the total gasoline spectrum, the residual spectrum will be the same as if the sample had been depentanized prior to obtaining the mass spectrum. APPARATUS AND REAGENTS
A Consolidated Electrodynamics Co. mass spectrometer Model 21-102 modified to 21-103C, with a high speed amplifier, was used. The magnet current was 0.750 ampere, and the isatron temperature was 270" C. -4constant volume pipet (0.001 ml.) and a mercury orifice system were used to introduce samples into the mass spectrometer. A Burrell Kromotog Model K-2 was used for the chromatographic analyses. The columns were 8 feet long. The column packing consisted of benzyl ether on 40 to 60-mesh firebrick, Kith a ratio of 40 ml. of benzyl ether to 100 grams of firebrick. The columns were operated at room temperature, with a helium flow rate of about 50 ml. per minute. Calibration. Obtain spectra of npentane and isopentane, using a constant-volume pipet and a mercury orifice introduction system. Calculate t h e sensitivities for each com-
pound a t the desired mass m i t s by diyiding each peak height by 100. Obtain spectra of n-butane, isobutane, and n-propane. Because these components are charged as gases, the corresponding liquid volumes are obtained using the gas law relation: Liquid volume nhere P
=
V
= = = =
T
IllW d
P
v
760
22,400
= - X __
2773
JlW
sample pressure, mm. of mercury gas volume, ml. temperature, "Kelvin molecular n-eight density
Calculate the liquid volume sensitivities as described for the pentanes. These liquid volume sensitivities must be based on the same liquid volume that is charged to the mass spectrometer for the hydrocarbon type analysis. Procedure. Determine the liquid volume per cent of each C5 and lighter hydrocarbon in t h e sample, by gas chromatography. Obtain the mass spectrum of t h e total sample, using the same liquid volume charge on n hich t h e sensithities of t h e pentanes, butanes, and propane are based. Measure the peak heights normally used in t h e hydrocarbon-type analysis. Correct the peaks where the pentanes, butanes, and propane interfere viith the following equation: Corrected peak
= a
- bc
(2)
where n = gross peak height b = sensitivity c = liquid volume per cent Accuracy. Comparative results of t h e proposed method and depentanization prior t o the hydrocarbon type analysis are shown in Table I. The excellent agreement illustrates t h a t t h e accuracy is equal t o t h a t obtained by t h e preliminary distillation of the sample. DISCUSSION
The authors assume that those who use the proposed method will hare already calibrated for one of the various mass spectrometric type analyses and that they will have a gas chromatographic method similar to the one described in the introduction. It is not
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
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