Quantitative Analysis of Organic Nitrogen by Flame Spectroscopy MINORU HONMA’ and C. LOTHROP SMITH2 State University
of lowa, lowa City, lowa
A rapid, quantitative organic nitrogen determination by means of flame spectroscopy has been accomplished by using a modified flame with a Smithells-type flame separator as the excitation source and the Hilger %lode1 E2 spectrograph. Measurements were made on the cyanogen band 3883 A. as the analysis line and the CH band 3890 A. as the internal standard line. The log intensity ratios of these line pairs were plotted against log per cent concentration of nitrogen. The resulting curves have a slope which is suitable for working curves for nitrogen in liquid organic compounds. Satisfactory working curves for liquids and gaseous nitrogen compounds were made, and application of this method to a salt was demonstrated, It is possible to determine gaseous nitrogen compounds and compounds which do not contain carbon. The limit of sensitivity is 0.8 mg. of nitrogen in 3 ml. of solution. Concentration ranges of 0.02 to 34.2% nitrogen were studied, and the optimum working range was found to be 0.1 to 15% nitrogen. Extensions of this method have been applied to the quantitative determinations of sodium, potassium, and chlorine. Perhaps the greatest spectrographic advantage is that determination of organic nitrogen may be made in the presence of atmospheric nitrogen.
Q
UANTITATIPE spectrographic methods of analysis have been developed and used extensively in the analyses of metals, alloys, and inorganic salts in mixtures and solutions. However, very little work has been reported on the quantitative determinations of nonmetals or anions. Pfeilsticker (14) has determined qualitatively the line spectrum of chlorine, bromine, iodine, sulfur, selenium, hydrogen, nitrogen, and oxygen by means of a lowpressure arc chamber and has mentioned the possibility of using them for quantitative determinations of these elements. Band spectra produced in emission spectroscopy have been confined mainly to qualitative work, as their troublesome and complex nature limits their use for quantitative analysis. The determination of nitrogen in its chemical compounds is probably one of the most widely used analyses in existence and one that can a t times involve considerable difficulty. Any spectroscopic method that could be devised for exact and rapid determination of this element would probably be of considerable interest. If carbon or a compound of carbon is burned in air in a high temperature electric arc or spark, carbon and nitrogen combine to form cyanogen molecules in an excited state. These molecules give rise to the well-known “cyanogen bands” in the visible and ultraviolet regions of the spectrum (10). Preliminary investigations (5, 9) have shown that it is possible to exclude atmospheric nitrogen by a stream of carbon dioxide in a simple electrode chamber, and if arcing takes place under these conditions the cyanogen bands do not appear. Furthermore, if graphite electrodes are used and compounds containing nitrogen are placed on their tips by the usual technique, the intensities of the cyanogen bands produced are found to be proportional to the nitrogen content of the compounds. The application of the internal standard microdensitometer methods 1 Present address, Francisco 24, Calif. 2 Deceased.
used in routine quantitative spectrochemical analysis results in “working curves” which approximate straight lines with a slope of nearly 1.0 as the amount of nitrogen compound on the electrode is varied. Barratt (1) has reported that it is possible to observe cyanogen bands in flames of various gaseous mixtures, such as coal gasnitrous oxide or carbon monoxide-air and ammonia. Vaidya (19) has mentioned that aniline, nitrobenzene, and pyridine likewise produce cyanogen bands. Ethyl nitrate and amyl nitrite yield cyanogen bands in the flames as observed by Gaydon (8). All of the above observations have been made on the inner cone of the flame. It thus appears that by use of the flame a s the excitation source quantitative measurements of nitrogen in compounds may be possible under suitable conditions. Lundegardh (11) has shown the value of the acetylene flame in quantitative spectroscopic measurements of many metallic salts. In recent years the use of the flame photometer for the rapid and selective estimation of metals, particularly alkalies, is finding increasing acceptance and is slowly replacing more troublesome methods of analysis. In flame spectroscopy or photometry, the analysis solution is sprayed into the flame and the light emitted is then analyzed photographically or photometrically for the constituent in question, These methods require strict standardization of all controllable variables, and are capable of high accuracy in routine Fork. They have the advantage that the standards with which the samples are compared may be easily and accurately made from pure materials. The purpose of this investigation was to see if the cyanogen spectra is produced in the inner cone of the flame for organic nitrogen compounds and to find out whether these bands may be used for quantitative estimations of nitrogen. APPARATUS AND REAGENTS
Grating Spectrograph. A grating spectrograph ITith a modified Eagle mounting was used to obtain a step sector pattern necessary for the calibration of the photographic emulsion. Prism Spectrograph. The Hilger Model E2 spectrograph with quartz optics was used for all quantitative work. Burner. Since the conventional RIeker burner was unsuitable for this work it was necessary to design a new type of burner. The principle of this burner was based on the flame separation accomplished by Smithells (17,18) with some added improvements. A detailed discussion will be published in the future.
Table I. Band OH HCO
U. S. Naval Radiological Defense Laboratory, San
458
Flame Bands Found in Aniline Wave Length, A. 3064 3300 3377 3502 3588 3730
CH
3872 3890 4312
cz
4365 4382 4737 5162
CN
3590 3883 4216 (6 bands)
h”
3360 3370
V O L U M E 2 6 , NO. 3, M A R C H 1 9 5 4 Air Regulator. Air control was accomplished with a Beckman air pressure regulator and indicator. Air purification was achieved with a train consisting of a concentrated potassium hydroxide solution, distilled water, and absorbent cotton. Gas Regulator. An expansion type of gas regulator was connected to the Beckman gas manometer. The gas holder floats in the ~ a t e and r rises or falls, correcting for fluctuations in the gas pressure. Atomizer. DeVilbiss No. 40 nebulizers were used throughout the experiment. Densitometer. Measurements of transmittances were made with a Gaertner visual matching densitometer. Developing Machine. Photographic processing \?as done with an ARL-Dietert developing machine. Photographic Plates. Eastman 103a-0 plates were used for quantitative measurements. Photographic Solutions. The solutions included: Eastman D-19 developer, 0.1% acetic acid stop bath, and Eastman F-5 fixer. Nitrogen Compounds. The nitrogen compounds selected were reagent grade or better. Solvents. Distilled water and C.P. organic solvents were used. Gas. Natural gas was the source of fuel for the flames. PHOTOGRAPHIC MEASUREMEYTS
Preliminary Photographic Measurements. Some preliminary measurements were made on the grating spectrograph using an ordinary Meker burner as the flame source. The exposures were varied from 30 minutes to 6 hours. The air supply of the Meker burner was converted into a closed system leaving only one porthole through which an atomizer was connected. Atomized vapors and air Tyere admitted through this vent. An aqueous solution of acetonitrile gave no identifiable band system in the blue region even after 6 hours of exposure, although the flame was visibly colored. prism instrument was then incorporated for this investigation because of the weak intensity of the light source. Burners by Smithells (17, 18) and Gavdon ( 7 ) Tyere built and tested, but they proved unsatisfactorj hecause there \vas too much difficulty in affecting flame separation. S e w burners were designed to increase the intensity of the inner cone of the flame where the occurrence of cyanogen bands \\-as reported. Aisatisfnrtory atomizer-burner was constructed for this study. A few preliminary photographs were taken with the Hilger spectrograph using the new flame source. The exposure time was reduced to a minimum of 2 minutes with an 80-micron slit; honever, the optimum exposure time was found to be 6 to 8 minutes. This reduced exposure time made spectrographic determinations reasonable from the analytical standpoint. The spectra observed vere sharp and \vel1 defined. The bands observed when aniline v a s atomized are given in Table I. Many other bands also appeared, but because their intensities were too low they were not identified. Because of its great intensity, C S 3883 A. \vas selected as the “analysis line,” although C S 3590 A. appeared in a more suitable region which has less background and less interference from other lines or bands. In the selection of the “internal standard” line to form the line pair, consideration was given to freedom from interfering lines, intensity-concentration relationship to the analysis line, excitation potential, and proximity to the analysis line. d number of inorganic alkaline earth halides showing bands in the region of interest n ere examined; they proved unsatisfactory because of the deposition of fine particles in the burner which interfered with the transmission of light. Of these halides, only lines of magnesium 3838 A . and magnesium 3832 A. 1%-erelocated in the analysis region. A fundamental difference in the origins of the magnesium 3838 A . line and the C S 3883 A. band head is obvious, and the use of the former as the internal standard was questionable. On the other hand, the CH band head at 3890 A,, located very close to the CK 3883 A. analysis line, offered possibilities. The difficulty with the CH 3890 A. band \vas that in very intense C X 3883 A. band spectra the two bands could not be resolved by this spectrograph with the SO-micron slit. Therefore, a comparison betm-een the two internal standard choices and the
459 analysis line was made. For 12 successive runs of the same solution on one plate, the average deviation from the mean was 5.37% for the log (IcN/IM~) and 6.71% for log (IcN/IcH). Although magnesium was a superior internal standard in this respect, disadvantages such as the deposition of salt in the burner offset this advantage; therefore the C H band head of 3890 A. was chosen for the internal standard line in all of the quantitative nitrogen determinations. Qualitative Nitrogen Determinations. If any type of analysis is to be of spectrographic importance, the method should be capable of determining a specific element among all types of compounds. Thus, in the determination of nitrogen, the method would be ideal if the spectrographic procedure could be applied unchanged to all types of nitrogen linkages, except molecular nitrogen. If flame excitation is to be useful in qualitative determinations, the analysis line of CN 3883 4 . should then be present in all types of nitrogen compounds. Therefore, a great many nitrogen compounds 7%ere atomized in different solvents, among the former were solids, liquids, and gaseous nitrogen compounds. Aqueous solutions of some of the rompounds determined are shown in Table 11. Some of the alcoholic solutions of nitrogen compounds are shown in Table 111.
Table 11. Aqueous Solutions of Nitrogen C o m p o u n d s Compound Hexamethylene diamine Glutamic acid Hydroxylamine hydrochloride Succinimide Ammonium acetate Urea Picric acid 8emicarbazide hydro chloride Hydrazine sulfate Acetamide Ammonia Acetonitrile Methylamine Ethvlamine Potassium cyanide Sodium nitrite Sodium nitrate
C y 3883 (Relative Intensity) Strong Weak Weak Trace Weak Strong Weal, FYeal, \Teak Moderate Strong Strong Strone StronL: Moderate Moderate
Table 111. Alcoholic Solutions of Nitrogen C o m p o u p d s Compound Aniline 1Iethylaniline Dimethrlaniline Azobeniene Azoxybeneene p-Nitroaniline Phenylhydrazine Pyridine Benzonitrile .V-n-Butylbenzamide Ammonium nitrate p-Toluidine p-Sitrophenol Nitromethane 2-Xitrobutanol Piperidine C hloroacetonitrile Formamide Sulfanilic acid S-hIethylformanilide
CK 3883 (Relative Intensity) Xoderate Weal, Weal, Weal, Keah \Teak 1Ioderate Strong Strong Strong Strong Weak Weak Strong Strone Strong Strong Strong Trace Moderate
The cyanogen band spectra of 4216 A,, 3883 A , , and 3590 A. were found in varying intensity in each of the compounds determined. The blanks run on the solvent showed very few interferences in the analysis region of 3883 A. Qualitative Nitrogen Determinations. In the quantitative determinations a systematic study was made of liquid nitrogen compounds with various bond types. GESERALPROCEDURE. The procedure adopted for a single compound is the same as that for acetonitrile. Synthetic standards were prepared by taking pure acetonitrile and diluting r\ ith denatured ethyl alcohol. A series of 11 solutions was prepared with varying concentrations of acetonitrile and thus different percentages of nitrogen in each solution prepared. These solutions
460 were then used to obtain points on the working curve for this compound. The slit of the Hilger spectrograph was set a t 80 microns and the reducer wedge on the slit was adjusted so that the spectrum was 2.5 mm. high, which corresponded to the height of the slit opening in the densitometer. The gas was then turned on and regulated to 25 mm. pressure on the Beckman manometer. The burner was then lit, the entire flame burning a t the top of the outer tube. Primary air was turned on and controlled until the Beckman pressure gage registered 15 pounds per square inch on a closed system. This was done by pinching the air hose until the required pressure was reached. An atomizer filled with a few milliliters of ethyl alcohol was connected to the vapor inlet tube of the burner. Kext the air hose was connected to the atomizer and the regulator turned until 1 pound per square inch was indicated on the register. The auxiliary air was gradually turned on until separation of the inner cone from the outer cone was accomplished. The outer cone remained on top of the outer tube and burned nTith an invisible flame. The inner cone dropped down t o the top of the inner tube and was colored bluish green. The air hose was then disconnected, the atomizer removed, and the excess alcohol drained out until dry. When the primary air was disconnected, the inner cone jumped up and combined with the outer cone burning a t the top of the outer tube. The gas and air were left burning a t these regulated pressures. Three milliliters of denatured alcohol were pipetted into the atomizer which was then connected to the burner. The shutter of the plate holder was next opened. (The plate was previously exposed for a calibration pattern on the grating spectrograph employing a 10-second Spectrosource iron arc and a rotating step sector.) The air hose u as then connected to the atomizer. Immediately the inner cone separated from the outer cone and burned a t the top of the inner tube. The stop watch was started, and the exposure begun. The height of the inner cone of the flame was controlled by the auxiliary air supply. Decreasing the air caused the height to increase, and increasing the air supply caused a decrease in the inner cone flame height. The height of the inner cone was watched continuously during the exposure, since occasional changes in the flame characteristics were noted especially when viscous liquids were being atomized. The air pressure in this arrangement was calibrated with the atomizer so that exactly 7 minutes elapsed before the ethyl alcohol was completely atomized. At the end of 7 minutes as observed on the stop watch the plate holder shutter was closed. The air hose was disconnected, and the atomizer \\as removed and dried, Three milliliters of analysis solution were pipetted into the atomizer. The above procedure was then repeated. After this run, the atomizer was thoroughly R ashed with ethyl alcohol and dried before the next run. Subsequent runs were repetitions of the above procedure. The exposed plate \yas then developed, fixed, and washed in the usual manner. WORKISGCURVES.The working curves Rere prepared from the standard plates in the customary manner using the internal standard techniques from the readings of CN 3883 A. and CH 3890 A. Each plate used for this study was calibrated for response characteristics. The working curve drawn had a definite ‘‘toe” in the lower concentration ranges of nitrogen, This was due mostly to flame background. The corrections for the residuum were based on the procedure described by Pierce and Sachtrieb (15). The only departure from this procedure was that a blank on the solvent was run and the estimated amount of residuum was known. Thus, a point was established between the log intensity ratio of the residuum and the internal standard and the concentration axis when a straight line was drawn through the points of higher concentrations and extrapolated to lower concentrations of nitrogen. This quantity was then added to each one of the nitrogen concentrations and the points replotted. The corrected working curve gave a nearly ideal line and so further corrections for residuum were unnecessary. The entire procedure described above was repeated for each nitrogen compound analyzed. The length of exposure, the time of development, reading of the plates, calibration, and other variables in procedure were carried out as identically as possible. The rate of atomization for each compound was different, and in order to atomize 3 ml. of solution air pressure to the atomizer had to be increased considerably for the more viscous compounds. Atomizer air pressure ranged from nearly 0 to 11 pounds per square inch. Each atomizer was calibrated for atomization rate a t constant pressure for a given solution. It was also calibrated for pounds per square inch air pressure us. time required for atomization of a given volume of solution. Thus, in the case of ethyl alcohol, 1 pound per square inch of air pressure mould atomize 3 ml. in 7
ANALYTICAL CHEMISTRY minutes A8 seconds. The time was maintained from pure alcohol solvent to about 20% solute in alcohol, then the characteristics of atomization gradually changed to that of the solute. A study of the atomization rate us. density, surface tension, viscosity, and boiling point indicated that the boiling point of the major substance (usually the solvent) gave an approximate measure of the time and pressure necessary for atomization (except water). The amount of solution used was found to be critical to about 5%. The time involved was also critical to 5%. Thirty seconds increased exposure resulted in lowered intensity ratios. Too short an atomization period was not as serious because the flame was left burning for the required time even though the solution had been completely atomized. 1.8 1.6
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To study the further applicability of this method, solid and gaseous nitrogen compounds were investigated. Ethyl alcohol was used as the solvent and the procedure was carried out as before. Because of their insolubility in ethyl alcohol, a minimum amount of water was used to dissolve some compounds and ethyl alcohol was then added to the required volume. Of the 10 solid compounds tried, urea, ammonium acetate, and acetamide gave results comparable to liquid nitrogen compounds. The gaseous compounds gave good results. Other Quantitative Determinations. Observations of the various spectra showed that other elements could be determined by this procedure. When chloroacetonitrile was analyzed, profuse band systems of cuprous chloride were found which increased in intensity with increasing concentrations of chloroacetonitrile. The copper came from part of the burner equipment used in the arrangement. 44 satisfactory working curve was prepared by using cuprous chloride 4354 A. as the analysis line and Cz 4737 A. as the internal standard line and plotting this ratio against the concentration of chlorine. Examination of the flame spectra of sodium nitrate revealed an intense line of sodium 5890 A. and an intensity gradient. Using this sodium line and the Cz5162 A. band as the internal standard, a aorking curve was prepared for sodium. In the potassium cyanide spectra, an intense line of potassium a t 4044 9.was present. With this line and the CH band 4312 A. as the internal standard, a working curve for potassium was prepared. The working curves for sodium, potassium, and chlorine are shown in Figure 1. The chloroacetonitrile flame spectra produced in the inner cone of the flame are shown in Figure 2. DISCUSSION
Ainumber of problems had to be resolved in order to obtain satisfactory results for this investigation. The choice of a suitable atomizer to be used in conjunction with the burner designed was very important. Some attempts were made to construct a new type of atomizer, but the results were not gratifying. DeVilbiss
V O L U M E 26, NO. 3, M A R C H 1 9 5 4
461
No. 40 and No. 44 atomizers were used next and the former proved to give the better performance. It is a reflux type and so a fractionation process occurs; the more volatile component, usually the solvent, atomizes first. There is also a considerable cooling effect due to the absorption of heat required t o atomize the solution, and this is very noticeable when the atomizer is run for any length of time. Moreover, in a concentrated solution of solid solute, crystallization takes place which plugs the cadllary of the atomizer. These dissd""...LI"Y.." Y" 1"
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nique in the operations to obtain reproducible results. In the selection of a proper solvent for the quantitative determinations some of the considerations are: vapor pressure, viscosity, surfaee tension, flrtme stability, chemical reactivity, flame propagation, solubility of solute, production of the proper spectrum, and nebulosity of the spray when atomized. Each solvent selected far this study was tttomized, burned, and photographed; atomieation rates of equal volumes were cheeked. Solvents studied included: chloroform, carbon tetrachloride, benzene, cyclohexane, cyclohexene, water, methyl alcohol, ethyl alcohol, isopropyl alcohol, ethyl acetate, ether, and acetone.
CVCl 4354 CN 4216
CN
3883
CN 3590
NH
3360
OH 3064
Figure 2.
nitrogen. Pearse and Gaydon (IS) reported that most hydrocarbon flames do not possess energies beyond 5 electron volts. The dissociation energy for molecular nitrogen is reported to be between 7 and 12 electron volts, whieh excludes its excitation by the flame in most cases. Gaydon (8) showed that some cyanogen was formed in the combustion of butane and acetylene. Xatural gas which is essentially methane and nitrogen (16) was selected for the nitrogen determinations mainly because it was readily available. Blanks run with each uhotomauhic d a t e revealed t h a t
Flame Spectra of Chlnroacetonitrilc
Carbon tetrachloride and chloroform were discarded because the chlorine present gave rise to many interfering band spectra and toxic gases were formed in the oxidation products. Benzene and cyclohexane were eliminated because they froze in the atamiaer. Water gave a very slaw rate of atomization. Ethyl acetate, ether, cyclohexene, and acetone were too volatile with this type of atomizer. Of the remaining solvents, ethyl alcohol wa.6 selected because more information was available concerning the solvent properties of this compound. The majar portion of the quantitative nitrogen determinations was made using ethyl alcohol as the solvent. The selection of gas for use in the determinations was important io that the gas determined the amount of background present in the analysis region. Desirable properties of the gas are the posression of sufficient energy to excite dl types of nitrogen compounds and the formation of cyanogen without exciting air
and most of this baud originated from the gas burned, i t was imperative to regulate its flow. Fluctuations of the gas prensure were quite noticeable on the manometer so a regulator had to be constructed and adjusted for a constant gas pressure. This pressure was regulated to +l ml. a t a 25-mi. height of isopropyl alcohol over a period of 10 minutes. Oxygen-nitrogen ratio was found to be quite critical in the production of cyanogen bands by Barratt (i), Liveing and Dewar (IO), and by Garner and Saunders (6). Fowlcr and Shaw (4) reported that oxygen quenched the cyanogen produred by the carbon arc. Hence, the amount of oxygen present in the flame had some bearing on the amount of cyanogen produced. The formation of CH bands was also dependent on the oxygen eoncentration; thus the amount of air entering the flame was important. After purification and stabiliastion with a Beckman regulator the air pressure variations were checked by atomizing known amounts of ethyl alcohol. Excellent stabilization was achieved for the air pressure. Alkali nitrates, nitrites, and cyanides gave rather unsatisfactory performances. A thin white film was deposited on the inner walls of the outer tube of the flame separator causing decreased spectral transmission because of the filtering effect of this coating. Although the cyanogen spectra were formed in all cases, the intensitv ratios obtained deviated considernblv more than
cyanogen band head 3883 A. wa8 observed, some more intense than others. Qualitatively, the appearance of the cyanogen bands in the inner cone of the gas Bane could be used 8s a method of detection of nitrogen although the sensitivity was not very high, about 1 mg. of nitrogen being necessary for definite indications. The intensitp of the cyanogen spectra observed in all of the flames was in general proportional to the concentration of the nitrogen present in the solution atomized into the inner cone of the gas flame, provided the carbon concentrat,ion was maintained the same. This intensity gradient observed on the photographic plate indicated that quantitative determinations of nitrogen by means of the cyanogen spectra. could be achieved much in the same manner as the determination of metallic elements. In general, most of the amines gave working curves with idealized slopes. The working curves of the 12 amines tested gave points in the same region within spectrochemical accuracy. I n these cases, a single generalized curve could be drawn through all the points. The nitro compounds investigated each gave straight line working curves with a slope of 1.0 except in two cases, o-nitroanisole and 2-nitrobutanol where the slope was 0.7. Furthermore, there was also a positive shift in the working curve compared to the amine curves. In Figure 3 the working curves for a-picoline and Znitropropane are presented. The nitriles, quite unlike the amines or nitro compounds, gave working curves of varying slopes. Some explanation of the difference in slopes could be accounted for by volatility differences of the solutes. Isobutyronitrile and acetonitrile, the most volatile compounds in this series, gave the steepest C U F Y ~ Swhile cetyl nitrile and a-tolunitrile, cornpounds of high boiling points, had a
ANALYTICAL CHEMISTRY
462
slope of 0.6 in their working curves. Other nitrogen compounds determined gave varying slopes, 0.4 for urea and 1.0 for ammonia. The working curves of malonitrile and ammonia are shown in Figure 4. In the analysis of a mixture, such as a solution of amines, this method would work well, but for unknown mixtures the method would not apply without further refinements in the procedure or separation of the mixtures into known types of compounds. 18
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.6
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1.0 1.2 1.4 1.6 1.8
L O G PER C E N T N I T R O G E N
Figure 4.
-1.0-.8
-6
m.4 -2
0
.2
.4
.6
.8
1.0 1.2 1.4 1.6
Working Curves for Ammonia and Malonitrile
The greatest singular advantage from the standpoint of emission spectroscopy is that determination of organic nitrogen can be made in the presence of atmospheric nitrogen. The procedure demonstrated that by a proper selection of an excitation source, selective excitation of molecules or atoms can be achieved.
L O G PER C E N T NITROGEN
Figure 3.
Working Curves for a-Picoline and 2- Nitropropane
The range of the nitrogen percentages studied was 0.02% for diluted cetyl nitrile to 34.2% for pure acetonitrile. The optimum working range of this method was 0.1 to 15% nitrogen. For working curves uncorrected for residuum, the lower limit for quantitative analysis was about 2 mg. The corrected working curve showed that 0.8 mg. of nitrogen could be determined with fair accuracy for any liquid amine solution. Reproducibility data from a series of 11 spectra of the same compound gave a standard deviation of 2.23% of the mean. Another series of 10 determinations gave a standard deviation of 1.62% of the mean. Table IV shows the log intensity ratios obtained for acetonitrile in ethyl alcohol used for this study. Several workers (2, 3, 12) have reported the effects of certain extraneous substances in the quantitative determinations of elements by flame photometry. The interferences noted were enhancement or inhibition of the line spectra of elements such as aodium or potassium caused by the presence of other ions in the flame. In molecular spectra, the possibilities of interferences from other molecules and atoms which enhance or inhibit the radiations from the internal standard and analysis bands would be much greater. In two cases, benzylamine and o-nitroanisole, there was an increase in the CH intensity a t higher concentration ranges of 4 to 11% nitrogen. Semicarbaxide hydrochloride gave the opposite effect in that there was a decrease in the CH intensity in the concentration ranges of 0.3 to 6% nitrogen. All other nitrogeneous compounds tested by the described procedure gave predicted CH intensities. Solvent effect studies in which acetonitrile was used as the solute showed measurable differences. The working curves of ether, ethyl alcohol, or cyclohexene as solvents could be superimposed on one another, but the curves of acetone, methanol, benzene, or ethyl acetate showed slight positive shifts from the ethyl alcohol curve although the slopes were the same. Only water, which has a very high surface tension, gave erratic behavior which was reflected in the working curve. Some 65 nitrogenous compounds were determined in this study and each one yielded a definite cyanogen spectrum in the inner cone of the flame when performed under a uniform procedure.
Table IV.
Reproducibility Data on Acetonitrile in Ethyl Alcohol Log
Log (IC&& b 1.26 1.17 1.02 1.26 1.24 1.04 1.26 1.25 1.29 1.17 1.16 1 20 1.21 1.16 1.26 1.23 1.22 1.18 1.22 1.07 1.18 a 5 , l 2 % nitrogen: mean, 1.15; standard deviation of mean, 2.23% b 6 31% nitrogen; mean 1.24; standard deviation of mean, 1.62%. (ICK/ICR)U
LITERATURE CITED (1) Barratt, S.,Proc. Roy. SOC.(London),98A,40-9 (1921). (2) Berry, J., Chappell, D., and Barnes, C., IND.ENG.CHEM.,ANAL. ED.,18, 19-24 (1946). (3) Bills, C., McDonald, F., and Niedermeier, W., ANAL.CHEM.,21, 1076-80 (1949). (4) Fowler, A,,and Shaw, H., Proc. Roy. SOC.(London),86A,118-30 (1911). (5) Frederickson, L., and Smith, L., ASAL. CHEY.,23, 742-44 (1951). (6) Garner, W., and Saunders, S.,J . Chem. Soc., 127,76 (1925). ’ (7) Gaydon, A , , Proc. Roy. SOC.(London), 179A, 439-50 (1942). (8) Gaydon, A., “Spectroscopy and Combustion Theory,” London, Chapman and Hall, Ltd., 1942. (9) Honma, AT., unpublished work. (10) Liveing, G., and Dewar, J., “Collected Papers on Spectroscopy,” London, Cambridge University Press, 1915. (11) Lundegardh, H., “Die Quantitative Spektralanalyse der Elemente,” Vol. I, 11, Jena, Verlag von Gustav Fischer, 1929. (12) Parks, T., Johnson, H., and Lykken, L., ANAL.CHEW,20,8225 (1946). (13) Pearse, R., and Gaydon, A, “Identification of XZolecular Spectra,” New York, John Wiley & Sons, 1941. (14) Pfeilsticker, K., Spectrochim. Acta, 1, 424-36 (1941). (15) Pierce, W., and Xachtrieb, N., IND. ENG.CHEM.,AUAL.ED.,13, 774-81 (1941). (16) Shreve, R. N., “Chemical Process Industries,” New York, McGraw-Hill Book Co., 1945. (17) Smithells, 8 . ,Trans. Chem. Soc., 61, 204-16 (1892). (18) Smithells, il.,and Dent, F., Ibid., 65, 603-10 (1894). (19) Vaidya, W,, Proc. Indian Acad. Sci., 2A, 352-7 (1935).
RECEIVED for review September 8, 1953. Accepted November 30, 1953.
