Table X. Search Results at 352 Dimensions for M-Xylene and N-Dodecane M-Xylene, mol wt = 106, mol form. = CsHla, ref no. = a. API 0254, struct form.
=
MisRef no. Mol wt Mol form. matches Compound name 106 CsHio 1 0-Xylene API 0253 106 CsHio 1 P-Xylene API 0255 106 CsHio 2 0-Xylene API 0178 106 Cr”o 2 P-Xylene API 0422 106 CsHio 2 M-Xylene API 0179 N-Dodecane, mol wt = 170, mol form. = C12H2(,ref no. = API 0404 156 CllH24 5 N-Undecane API 0403 156 CllHI4 5 5-Methyldecane AST2004 156 ClIH24 5 4-Methyldecane AST 2003 170 CllH16 6 N-Dodecane API 1028 170 CiiHi.5 6 4-Methylundecane AST 2013
tape. Therefore most conventional search systems would require transferral of the data from tape t o memory or disk prior to searching, a process requiring a n appreciable amount
of time given the limited buffer size of small machines. The system reported here uses this otherwise wasted time to actually perform the search. It has been shown that peak height encoded to one bit retains sufficient information to allow useful characterization of mass spectra. The spectra can be further reduced in dimensionality by combining correlating mass positions with minimal loss of important information. Encouraging results were obtained with 48-dimensional spectra requiring only 3 16-bit words to completely encode a reduced mass spectrum, A magnetic tape library of the 6652 mass spectra encoded in this way can be searched in 2 seconds for two unknowns. On the other hand by using the techniques of this study, it would be possible to search a n entire library of loo00 low resolution mass spectra with peak height encoded to 16 intensity levels (4 bits per mass position) in 60 seconds from magnetic tape using minimal memory. Minimum required hardware consists of a moderate speed CPU with 4K words of core memory, one 25 IPS, 9-track tape drive with accumulator I/O, and some means of inputting the unknown spectra and outputting search results. RECEIVED for review April 30,1971. Accepted June 29, 1971. Research supported by the National Science Foundation.
Spectrophotometric Determination of Xanthate and Total Sulfur in Viscose Matiur Rahman Research and Development Department, Tee-Pak, Inc., Danville, Ill. 61832
Sodium trithiocarbonate, one of the major components of viscose, displays a sharp isosbestic point at 363 nm. The absorbance at this wavelength gives a more accurate value for the concentration of the salt than the maximum absorbance at 332 nm. The reaction with oxygen in dilute solutions to form trithiopercarbonate causes a relatively rapid decrease in the maximum absorbance and the development of the isosbestic point. This procedure for trithiocarbonate has been combined with the determination of xanthate sulfur by batch ion exchange and spectrophotometry in a slightly modified form to give the new method for both xanthate and total sulfur. The sum of the xanthate and trithiocarbonate values gives the total sulfur, and this checks closely (&l% relative deviation) with other standard methods for total sulfur such as zincate decomposition or oxidation.
ROUTINEANALYSES of total sulfur and its distribution as sodium cellulose xanthate and by-products are important control operations in the viscose process. Several methods are known (1-10) for these analyses. However, most of (1) Reviewed by T. E. Muller and C. B. Purves in “Methods in Carbohydrate Chemistry,” Vol. 111, Roy L. Whistler, Ed., Academic Press, New York, N. Y.,1963, pp 246-250. (2) J. P. Dux and L. H. Phifer, ANAL.CHEM.,29, 1842 (1957). (3) L. H. Phifer and Joan L. Bell, TAPPI, 43, 622 (1960). (4) L. H. Phifer, ibid., 52, 671 (1969). ( 5 ) D. Tunc, R. F. Bampton, and T. E. Muller, ibid., p 1882. (6) E. Schauenstein and E. Treiber, MeNiand Texfi/ber.,32,43(1951). (7) W. H. Fock, Kunstseide, 17, 117 (1935). (8) D. J. Bridgeford, Tee-Pak, Inc., private communication, 1951. (9) H. L. Barthelemy and L. Williams, ANAL, CHEM.,17, 624 (1945). (10) 0. Samuelson and F. Gartner, Acta Chem. Scand., 5,596(1951). 1614
a
these methods are time-consuming, complex, or require special instrumentation. Among these methods, the determination of xanthate sulfur by anion exchange purification of viscose and spectrophotometry, developed by Phifer and coworkers (2, 3), has gained importance recently because of rapidity and simplicity of the steps involved. On the other hand, the method of total sulfur determination by X-ray fluorescence techniques (4) requires special instrumentation. The purpose of this paper is t o describe a simple and rapid spectrophotometric method for the determination of both xanthate and total sulfur in viscose, and to compare the results obtained in this way with several standard procedures. The validity of a recent objection ( 5 ) to the anion exchange purification of viscose is also discussed. Sodium cellulose xanthate and sodium trithiocarbonate, the two major sulfur containing components of viscose, absorb strongly at 303 and 332 nm, respectively (2). A viscose solution thus appears t o be suitable for spectrophotometric analysis as a typical multicomponent system. Schauenstein and Treiber (6), and more recently Tunc, Bampton, and Muller ( 5 ) have reported on the analysis in this way. HOWever, we find that a serious limitation in this method of multicomponent analysis arises from the instability of trithiocarbonate in dilute alkaline solutions. Figure 1 shows that the transmittance at 332 nm of a dilute viscose solution increases rapidly with time. Sodium trithiocarbonate has several absorption bands in the ultraviolet and visible regions (21). The shoulder at (11) J. Dyer, TAPPI, 49, 447 (1966).
ANALYTICAL CHEMISTRY, VOL. 43, NO. 12, OCTOBER 1971
~ 2 5
Viscose
Interval : 4 min
Wavelength ( n m )
Figure 1. Ultraviolet spectra of a dilute viscose solution at 0 "C taken at 4.5-min intervals showing increase of transmittance at 332 and 226 nm
Wavelength ( n m )
Figure 3. Near ultraviolet spectra of a dilute viscose solution at different time intervals showing the isosbestic point at 363 nm
332-335 nm introduces high uncertainties in its determination at this region. On the other hand, the isosbestic point is a well-defined, fixed point in the spectrum independent of time for at least 30 minutes after dilution. The absorption at this point has, therefore, been used for the determination of trithiocarbonate in viscose. An added advantage is gained from the complete absence of xanthate absorption at this wavelength. The use of isosbestic point for studying various reactions has been reviewed by Cohen and Fischer (12).
75 Q 0
c
0
c .-
5 E
?
I-
50
EXPERIMENTAL
25 1
1
I
I
3 00
325
350
Wavelength
I I 400
(nml
Figure 2. Near ultraviolet spectra of sodium trithiocarbonate in dilute alkali at different time intervals. A sharp isqsbestic point appears at 363 nm and a less sharp point shows at 300 nm
392 nm and the maximum at 332 nm are of particular importance. Repeated spectral scans at 2-3 minute intervals in these regions reveal that the intensity of the former ab. sorption increases and that of the latter decreases with time. As a consequence, a sharp isosbestic point (12) is developed at 363 nm (Figure 2, shown in transmittance curves). The same isosbestic point also appears in viscose spectra (Figure 3). The reaction of trithiocarbonate with oxygen dissolved in the solvent t o form trithiopercarbonate (11, 13) is responsible for this phenomenon. When the alkaline solvent is scrubbed with pure nitrogen before use, the rate of change decreases appreciably. The rapid change in the trithiocarbonate absorbance at (12) M. D. Cohen and E. Fischer, J. Chem. Soc., 1962,3044. (13) G . Ingram and E. A. Toms, ibid., 1957, 4328.
Apparatus. All spectra were recorded on a Beckman DK-2 Spectrophotometer using matched quartz cells of 1.Otm pqthlengths. Reagents. Filtered and deaerated commercial viscose was used in all experiments. Amberlite IRA-400 resin, AR grade, 20-50 mesh (Mallinckrodt) was used in the chloride form for the anion exchange purification of viscose. All dilutions, purifications, and measurements were carried out at room temperature (24 f I "C.) except when literature procedures were repeated without any modificatioq. For instance, the viscose was diluted at ice-bath temperature ( 5 ) for recording the spectra shown i n Figure 1. Sodium trithiocarbonate was prepared from sodium sulfide and carbon disulfide (11, 13) and its concentrated solution was stored under nitrogen in the cold (11). Its molar absorptivity at the isobestic point at 363 nm was determined by diluting in nitrogen-purged, cold 1 % sodium hydroxide solution in the following manner. About 3-ml portions of the caustic solution were taken into each of the two spectrophotometer cells and the instrument was properly adjusted. A small drop of the stock solution of trithiocarbonate was then added t o the sample celi from a drawn out capillary made from a disposable pipet. The solution was quickly mixed and its absorbance at 332 nm was immediately recorded followed by the absorbance at 363 nm. The molar absorptivity was calculated from the relation: faaa =
Assa X tm/Aaaz
Analytical Procedures. METHOD A. The new method for the detetmination of both xanthate and total sulfur in viscose consists of the following sequence of steps: ANALYTICAL CHEMISTRY, VOL. 43, NO. 12, OCTOBER 1971
1615
0.6
Table I. Molar Absorptivity of Sodium Tritbiocarbnateat 363 nma
V i s c o s e solution
/
0.4 0
0
c
0
e ul
s os2
Aaaz
A313
0.717 0.699 0.591 0.662 0.656
0.097 0.094 0.081 0.089 0.086
lea
2.46 2.45 2.50 2.49 2.39
Average c~~~ 2.45 x 103
a Each value of c3(3 was determined from a fresh dilution. Also two different preparations were used as stock solutions.
Table 11. Xanthate Sulfur ( %) in Viscose by Methods B and Ca Method B Method C
0.0 C
Io0
085
1.5
Viscose conc ( g / I
)
Figure 4. Variation of absorbance with concentration of viscose
1. About one gram of accurately weighed viscose is diluted t o 100.0 ml with nitrogen-purged 1 % sodium hydroxide. 2. A 5.0-1111 aliquot is stirred with 1-2 grams of IRA-400 resin for 5-10 minutes. The clear solution is separated from the resin by filtering through cotton directly into a 250-ml volumetric flask. The resin is washed with water, the volume of the solution made up t o mark, and its absorbance measured at 303 nm (A303). 3. Another 5.0-1111 aliquot is directly diluted t o 100.0 ml with water and its absorbance at 363 nm (A3e3)recorded. 4. The xanthate and trithiocarbonate sulfurs in the viscose are calculated from these absorbances using Equations 1 and 2 derived from molar absorptivities, dilution factors, and molecular weights. The sum of xanthate and trithiocarbonate sulfurs gives total sulfur (Equation 3). Xanthate sulfur = (A303/Viscosewt (g)) X Trithiocarbonate sulfur
-
Viscose wt (8) Total sulfur
=
3.2
x
103
z (1)
€X
= Am3
Xanthate3
X
1.92
x
103
€T
z (2)
--
+ Trithiocarbonate-S
(3)
where e x and tT are the molar absorptivities of xanthate and trithiocarbonate, respectively. METHODB. This is a slightly modified method of batch ion exchange purification of viscose and spectrophotometric determination of xanthate (S),the modification consisting of the use of a concentrated viscose solution at the purification step. About one gram of accurately weighed viscose is diluted to 15-20 ml with water in a 100-ml beaker. Two to three grams of I R A 4 0 0 resin are added, stirred for 5-10 min, then the resin is separated through a cotton filter and washed. The filtrate is collected in a 250-1111 volumetric flask, and diluted t o the mark with water. A 5.0-ml aliquot is further diluted to 100 ml, and its absorbance measured at 303 nm. The xanthate sulfur is calculated from Equation 1. METHODC is the Fock method (7) of determination of xanthate sulfur after removal of by-products in acetic acidcalcium carbonate buffer. METHODD. I n this method the total sulfur in viscose is determined by oxidation to sulfate with hydrogen peroxide, filtration t o remove the precipitated cellulose, cation-exchange of the filtrate, and titration of the eluted sulfuric acid with a standard sodium hydroxide (8). METHODE is the zincate decomposition and iodimetric determination of total sulfur according to Barthelemy and Williams (9). 1616
X
6303
1.13 1.11 1.13 1.14 1.14 1.15 1.13 1.08 1.11 1.08 1.08 1.11 Each row represents the analyses of an individual sample. 1.12 1.16 1.12 1.09
Table 111. Stability of Cellulose Xanthate at 24 "C Time," min Absorbance Xanth-S, 0 5 10 15 20
0.529 0.533 0.529 0.525 0.522
1.09 1.10 1.09 1.08 1.08
a Relative time starting from the first scan in the spectrophotometer.
RESULTS AND DISCUSSION The molar absorptivity of sodium trithiocarbonate at 332 nm is 18,200 (11). By using this value to determine the instantaneous concentration of trithiocarbonate, the molar absorptivity at the isosbestic point at 363 nm was found to be 2,450 26 (average deviation). This was an average of five determinations (Table I). Beer's law is obeyed at 363 nm by viscose solutions at the analytical concentration range of 0.5 to 1.5 g/l. (Figure 4). Table I1 shows the result of a number of xanthate sulfur determinations by Method B. These were calculated using 16,000 as the value of the molar absorptivity of cellulose xanthate at 303 nm (2). The Table also contains the results of xanthate sulfur determined by Method C simultaneously on the same samples of viscose (analyzed independently by Mrs. M. Cox, Tee-Pak, Inc.). The general agreement between these two different methods proves the correctness of the molar absorptivity of xanthate. The modification introduced into the batch ion exchange procedure, namely the purification of a more concentrated solution of viscose than used by Phifer and Bell (3), enabled us to work at room temperature instead of 0 "C, and thus avoid extra steps of cooling and recalibrating volumetric glasswares at low temperatures. The threshold amount of resin is also lowered (2-3 grams instead of 7 grams), making it cheaper t o throw it away. The stability of a purified xanthate at room temperature is shown against time in Table 111. From the time of the first spectral scan to about 20 min, the xanthate level remains within 1 relative deviation. Therefore, this should serve as a satisfactory method for xanthate determination. Combining this procedure with the direct determination of trithiocarbonate from its absorbance at 363 nm gives Method A. Typical results of xanthate, trithiocarbonate, and total
ANALYTICAL CHEMISTRY, VOL. 43, NO. 12, OCTOBER 1971
*
z
sulfur analyses by this method are presented in Table IV. The xanthate sulfur values are now compared with those determined simultaneously by Method B (analyzed independently by J. A. Lynch, Tee-Pak, Inc.), and the total sulfur is compared with Method D. Overall agreement is again found t o be quite satisfactory. A laboratory ripening of the viscose for 2-3 hr can be easily detected (3) in the form of lower xanthate and higher trithiocarbonate while the total sulfur remains constant. The accuracy of the total sulfur analysis by this new procedure was further tested by a third independent method, namely by zincate decomposition and iodimetry (9). Table V shows the results of duplicate analyses (starting from separate weighing in step 1) of three viscose samples by Methods A, D, and E. The excellent agreement between all three methods proves conclusively the validity of adding up xanthate and trithiocarbonate t o give total sulfur in viscose. While small amounts of sulfur (0.01 t o 0.02%) may exist as sulfide in the ripened viscose and lie within our experimental error, lack of a simple and unequivocal method precludes its detection and determination in the presence of relatively large amounts of cellulose xanthate and trithiocarbonate. It is, therefore, concluded from the present results that most of the sulfide sulfur exists in combination with carbon disulfide, formed from the ripening of viscose, as the total trithiocarbonate: ROCSz-
Table IV. Xanthate, Trithiocarbonate, and Total Sulfur in Viscose by Methods A, B, and Da Method A Trithio-S, Method B Method D Xanth-S, Total-S, Xanth-S, Total-S, % 1.14 1.15 1.11* 1.14 1 .47e
2.21 2.22 2.23 2.16 2.38
1.13 1.13 1.15 1.15 . . .d
2.16 2.18 2.23 2.18 2.40
,. Each row represents an individual sample. * Aged in the laboratory for 2.5 hr in a closed container. A special kind of viscose. Not determined.
Sarnple No. 1 2 3 a
+ HzO ROH + CSz + OHs2- + cs2 CS32-
1.07 1.07 1.12 1.02 0.91
Table V. Comparison of Total Sulfur in Viscose by Methods A, D, and E Method A Method D Method E Xanth-S, Trithio-S, Total-S, Total-S, Total-S, % Y3
z
z
z
1.16 1,17 1.16 1.17 1.15 1.14
1.03 1.02 1.02 1.02 1.05 1.06
2.19 2.19 2.18 2.19 2.20 2.20
2.20 2.20 2.18 2.18 2.19 2.19
2. 18 2.18 2.17 ... 2.20 2.20
Not determined.
+
+
This also agrees with the observation made above on the laboratory ripening of viscose (Table IV, third row of data). Muller and coworkers (5) have raised objections t o the use of ion exchange resins for the purification of viscose for xanthate determination. According t o these authors, a part of the xanthate is lost in the resin, and thus the molar absorptivity obtained in this way ( 2 ) is subject t o inaccuracy. Therefore, a new method of multicomponent analysis of viscose has been suggested (9, based on the determination of trithiocarbonate from its maximum absorbance at 336 nm (Figure l), subtraction of the trithiocarbonate spectrum from the total viscose spectrum, and treatment of the remainder as due t o a mixture of cellulose xanthate and cellulose dixanthogen. In this way a higher value of molar absorptivity for cellulose xanthate was found. Samuelson and Gartner (10) proposed the anion exchange purification of viscose o n the basis of “mechanical exclusion by sieve action” (14) of the large organic ion, cellulose xanthate from the small inorganic ion, trithiocarbonate. Quantitative separations by similar sieve action have been achieved in other systems, e.g., organic dyes from inorganic electrolytes (14, 1 9 , and pectin from electrolytes (16, 17). In the case of viscose the separation of cellulose xanthate from inorganic anions was shown t o be quantitative by Samuelson and Gartner (10) as well as by Phifer and coworkers (2, 3) who made independent determinations of cellulose and sulfur contents before and after ion exchange. Our present ob~~
(14) F. HelfFerich, “Ion Exchange,” McGraw-Hill, New York, N. Y., 1962, pp 160-161. (15) R. W. Richardson, Nature, 164, 916 (1949); J. Chem. Soc., 1951, 910. (16) K. T. Williams and C. M. Johnson, IND.ENG.CHEM.,ANAL. ED., 16,23 (1944). (17) 0. Sarnuelson, “Ion Exchangers in Analytical Chemistry,” Wlley, New York, N. Y. 1953, pp 187-188.
SamDle Nd. 1
2
3
Table VI. Effect of Quantity of Resin on Xanthate Sulfur Values Method A Method B Resin. Xanth-S. Sarnde Resin. X a n t h x grams % NO: grams’
z
1.5 2.5 4.0 6.0 1 .o 2.0 3.5 6.0 1.0 2.0 3.5 5.0
1.13 1.13 1.12 1.11 1.15 1.14 1.13 1.11 1.13 1.13 1.11 1.10
4
1.7 2.7 4.0 6.0
1.15 1.16 1.16 1.16
servation of the effect of increasing amounts of ion exchange resin on the xanthate sulfur values obtained by both Methods A and B is shown in Table VI. In Method B, 2 to 6 grams of resin d o not affect the result at all, and when a more dilute solution is used in Method A, 1 to 3 grams of resin show similar results. Rough calculations indicate that 2 to 3 grams of resin in Method B and 1 t o 2 grams in Method A represent about 10 t o 100 times the equivalent exchange capacity of the inorganic ions present in these solutions. These amounts should, therefore, be sufficient to bring the exchange equilibrium t o completion. The small decrease of xanthate sulfur in Method A when large amounts of resin have been used may be attributed to surface absorption. CONCLUSIONS
The combination of precision, reliability, and speed of the new spectrophotometric determination of xanthate and total sulfur in viscose (Method A) makes it superior to existing
ANALYTICAL CHEMISTRY, VOL. 43, NO. 12, OCTOBER 1971
a
1617
procedures. It is also ideally adaptable to routine quality control in viscose plants. The method depends On the finding Of this work that the by-product sulfur in undiluted viscose is almost entirely in the form of trithiocarbonate. Other postulated sulfur-containing by-products, namely sodium sulfide (18) or cellulose dixanthogen ( 5 ) are present in negligible amounts, if at all. -.
(18) E. Kline in “Cellulose and Cellulose Derivatives,” E. Ott, H. M. Spurlin, and M. W. Grafflin, Ed., 2nd ed., Part 11, Interscience, New York, N. Y . 1954, p 991.
ACKNOWLEDGMENT
I thank Messrs. A. F. Turbak, M. N. O’Brien, and D. J. Bridgeford for stimulating discussions during this work. Technical assistance of Mrs. M, E. coxand Mr. J, A. Lynch is gratefully acknowledged. RECEIVED for review April 22, 1971. Accepted June 29, 1971. Presented before the Cellulose, Wood, and Fiber Chemistry Division at the 160th National Meeting of the American Chemical Society, Chicago, Ill., September, 1970. Acknowledgment is due to the Management of Tee-Pak, Inc. for permission to publish this work.
Isolation and Analysis of Carbonyl Compounds as Oximes James W . Vogh Bartiesoilie Energy Research Center, Bureau of Mines, U . S. Department of the Interior, Bartlesoille, Okla. 74003
Analysis of carbonyls in complex mixtures, such as automotive exhaust, is seriously hampered by interference problems. Methods for isolating carbonyls from interfering components exist but render mixtures that are not readily analyzable. In the present study, procedures were developed for collectinq and isolating carbonyls from complex mixtures as oximes, and for subsequent chromatographic analysis of the oxime mixture. The isolation procedure was based on the weak-acid properties of oximes, which permit separation from hydrocarbons and other neutral materials by extraction with pentane. Retention of oximes in the basic phase was improved by addition of alcohols and by extraction at low temperatures. Chromatographic analysis of oximes was accomplished using an all-glass system. Oximes were decomposed to nitriles by hot metal surfaces but were stable in glass equipment that had been cleaned to remove heavy metal oxides. The most satisfactory chromatographic column had a glass tube filled with glassbead support that was coated with a polyglycol liquid phase. In chromatograms, most aliphatic aldoximes showed double chromatographic peaks that were due to the ryn and anti isomers. These were identified, and the isomer peak ratio was shown to be affected by steric interference. Phenols were recovered in the isolation procedure and could be analyzed in the same chromatographic system. Applications in diesel- and gasoline-engine exhaust are discussed. THERE ARE numerous procedures for collection, isolation, and analysis of mixtures of aldehydes and ketones. However, the choice of method may be limited when experiments involve dilute sample and complex mixtures. In these cases, isolation of the carbonyl compounds or their derivatives from interfering components is the most critical part of the procedure. These problems are found in engine exhaust gas analysis because the aldehydes and ketones are quite complex but are only a minor part of the organic components. Hydrocarbons in the engine exhaust interfere seriously in direct gas chromatographic analysis and generally prevent determination of the higher-molecular-weight carbonyls. These problems led to a review of carbonyl analysis methods and to the development of new procedures for isolation and detailed determination of the aldehydes and ketones present in engine exhaust gases. The best known methods that serve both collection and isolation of the carbonyl compounds are based on the solid 1618
dinitrophenylhydrazone derivative (1) and the soluble ionic bisulfite (2, 3) and Girard (4) derivatives. The Girard reagents provide the best available procedure for the collection and isolation steps. These reagents react quite generally and readily with carbonyls, although some sterically hindered ketones react poorly.(5). The isolation is usually based on extraction of a water solution of the derivative by a nonpolar solvent, and the separation is specific and complete. The Girard derivative of some carbonyls decomposes to a considerable extent during ordinary extraction procedures, but a method for extraction under anhydrous conditions has been developed to prevent this (6). This method may not be useful if the original sample contains water. Other problems in the Girard procedure are incomplete recovery of some carbonyl derivatives (4) and the need to regenerate and recover the carbonyls for gas chromatographic analysis. Conversion to oxime derivatives is a particularly useful technique for collecting and isolating carbonyls. The derivative-forming reaction is quite rapid for most carbonyls and occurs in all carbonyl classes, including the sterically hindered ketones. The high reaction speed is particularly helpful in sample collection from gas streams by high-speed scrubbers. Further, oximes are weak acids (pK 10-12) (7)-a property that could be used to isolate them for analytical purposes. Because oximes are stable in basic solution (8) and may be recovered without apparent loss, they can be separated from hydrocarbons and most other neutral compounds by extraction from a paraffinic solvent by dilute base. Detailed analysis of the carbonyls may be carried out either directly on the oximes or o n the carbonyls regenerated from the oximes. Although several methods have been developed (1) R. J. Soukup, R. J. Scarpellino, and E. Danielczik, ANAL. CHEM., 36, 2255 (1964). (2) D. A. Levaggi and M. Feldstein, J . Air Pollut. Control Ass., 20, 312 (1970). (3) . . C . F. Ellis, R. F. Kendall, and B. H. Eccleston, ANAL.CHEM., 37, 511 (1965). (4) . , D. F. Gadbois, J. M. Mendelsohn, and L. J. Ronsivalli, ibid., p 1776. ( 5 ) 0. H. Wheeler, Chem. Reu., 62, 205 (1962). 39, 530 (1967). (6) S. F. Osman and J. L. Barson, ANAL.CHEM., (7) E. F. Degering, “An Outline of Organic Nitrogen Compounds,” University Lithoprinters, Ypsilanti, Mich., 1945, Chap. 13, p 180. (8) Ibid., p 194.
ANALYTICAL CHEMISTRY, VOL. 43, NO. 12, OCTOBER 1971
