and the t constant for n - 1 degrees of freedom and 0.05 risk. The least-squares tabulation is based upon the individual average NMR peak-to-peak measurements assuming that all the error is in the y direction and that the variance in y is the same at all values of' x (fluoride ion concentration). The calculated equa.tion for the calibration curve based on bx wherein a = the least squares tabulation was = a -8.6 and b = 19.8. The observed (7) us. the calculated (ic) values of the NMR peak-to-peak measurements indicates the variance of values @(y, - y)z/(n - 2) of the line of the calibration curve to be 11.58. The limit of detectable fluoride ion by this procedure was about 2 mg/ml. At lower fluoride content concentrations the signal was very difficu:!t to see because of the poor signal to noise ratio. One obvious advantage of the NMR method is that there is no interference from any non-magnetic impurities. The effect of R F saturation upon the fluoride system was studied and it was found that the plateau region was in the range -60 to -20 db. To balance the effect of NMR signal loss caused by R F satu.:ation cs. the increased electronic noise caused by the need fclr greater amplification at greater at-
+
tenuation settings, the value of -24 db was selected in our work. While our primary efforts were directed toward detecting fluoride ion obtained from aluminum fluoride salts in aqueous solution, wide-line NMR measurements were made on solid aluminum fluoride with radically different line widths. A multiple scan had to be employed in the case of the solid aluminum fluoride ore sample because its line-width taxed the ability of the instrument even at the maximum setting of 20 gauss. Work carried out with calcium fluoride was encouraging for the line-widths of the solid calcium salt are easily within the capabilitites of the instrument. A solid fluorinated hydrocarbon yielded no NMR signal in the solid state (under our experimental conditions) but yielded a strong signal when dissolved in methanol. Work is now in progress to determine fluoride content by wide line NMR on other inorganic and organic fluoride compounds. RECEIVED for review June 28,1966. 1966.
Accepted November 17,
Determination of Nitrogen, Carbon, and Sulfur in Liquid Organic Compounds by Gas Chromatography Sam Pennington and Clifton E. Meloan Department of Chemist..y, Kansas, State University Manhattan, Kan. THE USE OF gas chroniatography in quantitative elemental analysis has been well established (1-6). Typical analysis times for the common elements-carbon, hydrogen, and nitrogen-require only a few minutes and the precision and accuracy compare quite favorably with the older and more time consuming methods. One of the major problems associated with elemental analysis using gas chrornatography is the need for plug injection of the combustion gases. This problem has been generally surmounted previously in two ways-Le., either trapping the combusticn gases in a liquid nitrogen trap or using a high frequency induction furnace which approaches instantaneous combustion. Both of these approaches have certain drawbacks. In the case of the liquid nitrogen trap the analysis time is lenglhened by 10 to 15 minutes because of the time needed for complete combustion and manipulating the trap. The inductioi furnace adds $1200 to $1800 to the cost of the instrument. In this work both the trapping and the induction furnace have been eliminated. However, only liquid samples can be used. Another problem has been that C, N, and S have never been reported to have been determined simultaneously. Our procedure provides for this. (1) D. R. Beuerman and C. E. Meloan, ANAL.CHEM., 34, 1671 (1962). (2) A. D. Duswalt and W. W. Brandt, Ibid., 32, 272 (1960). (3) C. F. Nightingale and .I. M. Walker, Ibid., 34, 1435 (1962). (4)M. L. Parsons, S. N. I'ennington, and J. M. Walker, Ibid., 35, 842 (1963). (5) A. S. Said and M. A Robinson, J . Gas Chromatog., 1, 7-11 (1963). (6) R . 1. Scott. EL A. Price, M. D. Grimes, and B. J. Heinrich, A m l . Chim.Acta 231, 428 (1960). ( 7 ) 0. E. Sundberg and C. Maresh, ANAL.CHEM., 32,274 (1960).
EXPERIMENTAL
Chemicals. All chemicals used were reagent grade unless stated otherwise. Commercial helium was scrubbed to remove HZOand COZby passing it through anhydrone and Ascarite towers. Apparatus. A Sargent automatic microcombustion apparatus was used for the combustion furnaces. The separation of the combustion gases was carried out using an Aerograph Model A-90-P chromatograph equipped with a Bausch and Lomb VOM-5 recorder. All samples were injected with a Hamilton syringe equipped with a Chaney adapter set to deliver 2 pl. The following procedure was used to introduce a reproducible volume of sample into the system. The syringe was filled by pulling back the plunger and the excess volume was expelled by pressing the plunger forward till the Chaney adapter struck the stop flange. The resting point of the adapter on the stop flange was found to be extremely important. A point as close to the front edge of the stop flange as possible that still gave full support to the adapter was chosen, and this exact point was used for each injection. Procedure. The two furnaces (Figure 1) were allowed to equilibrate at their operating temperatures for 12 hours before runs were made. Conditions were as described in the legend for Figure 1. To make an analysis, a 2 - 4 sample was injected at Point C, after which the recorder drive was turned on. Enough time exists between the elution of the COz and SOZ peaks to allow attenuator adjustment if this is required because of the low sulfur content of the sample. The area of each peak was calculated according to the equation (5) : Area
=
peak height
x 'iZ
height width X 1.065
An overall area/mg of C, N, or S for all samples examined was used as a standard for each element. VOL. 39, NO. 1, JANUARY 1967
119
I
I
I
I
I
I
I ,
A
C
E
F
G
I Figure 1. Combustion apparatus A. Helium carrier gas; flow rate 60 ml/min B. Scrubber containing anhydrone and Ascarite
c. Injection port-840" C D. Combustion tube-40 cm long, '/&ch 0.d. 304 stainless steel E. Long furnace, 18-cm; tube packed with CuO; 850" f 25" C F. S-cm space G. Short furnace, 10-cm; tube packed with Cu wire; 500" f 25" C H. Column; l/d-inch 0.d. copper tubing, 12 feet long packed with 33% silicone oil 550 on Chromasorb P 60-80 mesh, col. temp. -40" C I . Detector-T.C. 40" C, 150 ma The short furnace is operated at a cooler temperature than the long furnace. If this were not done, S could not be obtained in some samples because it apparently forms COS, which reacts with copper at the higher temperature. RESULTS AND DISCUSSION
The stainless-steel tubing and operating temperaturesabout 100" higher than that normally used for C, N analysisprovides a sufficient reserve of heat for complete quantitative combustion of the sample in a very short time, thus eliminating the trap and the induction furnace. Temperatures above 800" C are necessary for quantitative conversion of S to SO2 (1). Figure 2 shows the results of this combustion procedure. A total of 3.5 minutes is required from the time the sample is injected. The results of the analysis of 10 compounds are presented in terms of mean error in Table I ; they represent an average of at least 3 determinations. It is obvious that all of these samples are volatile liquids of
Figure 2.
Chromatogram of combustion products Chart speed 2 inches/minute
30r
ON
TO 860'
Table I. Analysis Results Mean error '79 Compound
C
S
N 221
Acetonitrile Carbon disulfide o-Chloroaniline o-Dichlorobenzene Diethylsulfite Dimethylformamide Methyl ethyl sulfonate Nitroethane Pyridine Dimethylsulfide Std dev
-0.01 +O. 14 f0.13
0.16 -0.24 +0.02
20
-0.02
18
,/' reL 8..
-
+0.08 +O. 23
+0.32 -0.15 +O. 36 -0.10 -0.85 +0.03
-0.27 -0.03 1-0.06 +0.20 0.32
0.27
0.07
I
1
1
1
1
1
TEMP. *C*
Figure 3. Combustion tube temperature vs peak area
-with MnOz - - - - without MnOz
-0-0- approximate SO2 curve Table 11. Comparison of Chromatographic Methods Standard deviation Pennington and Meloan Beuerman and Meloan (1) Parson (4) Duswalt and Brandt (2) Sundberg and Maresh (7) Nightingale and Walker (3) F/M Instrument
120
0
ANALYTICAL CHEMISTRY
C
S
N
0.27
0.32 0.21
0.07 0.11
0.38 0.53 0.52 0.27
0.58 0.18
low molecular weight. At the present time it appears that our system is limited to this type of compound. The water formed during the combustion was not trapped and did not affect the chromatogram in a manner that could be detected. It was apparently adsorbed by the support material and eluted over a long period of time. No reaction between the HzOand SOzwas observed. In an effort to improve the combustion, a mixture of MnOa and CuO was used. This gives excellent results for C and N but S as SOz did not pass through the tube.
However, C and N analysis could be carried out in 90 seconds (see Figure 3). Table I1 is a comparison of this procedure with others reported in the literature. Certainly a standa-d deviation of 1.0.17 for N is not realistic based on the results of only a few samples, but it does indicate that the procedure works and is not out of line with previous work. The next step in the overall procedure is to add halogens to the system.
RECEIVEDfor review November 18, 1965. Resubmitted August 15, 1966. Accepted August 15, 1966. Work supported by the National Aeronautics and Space Administration through operating funds to carry out this project, and by the National Science Foundation through funds to purchase the chromatograph and the recorder. Presented at the 1st Midwest Regional ACS Meeting, Kansas City, Mo., November 1965. This study represents partial fulfillment (S.P.) of the requirements for the Ph.D. degree in chemistry.
Determination of the Carbohydrate Composition of Wood Pulps by Gas Chromatography of the Alditol Acetates Edwin P. Crowell and Bruce B. Burnett Research and Developntent Dicision, Union Camp Corp., P.O. Box 412, Princeton, N. J. THERE IS A NEED in the ield of wood and wood pulp chemistry for a rapid and more accurate method for the determination of the five sugars normally obtained by the hydrolysis of wood products. The traditional paper chromatographic method is very time consuming, cumbersome and tedious to apply ( I ) . Gas chromatographic analysis of monosaccharides has received much attention of late as a result of the pioneer work of Sweeley and coworkers with trimethylsilyl derivatives (2). Other workers have followed the silyl ether derivative approach to the quanatitative analysis of sugar samples ( 3 - 3 , Three reports have appeared which utilize the silyl ether derivatization in the analysis of pulp hydrolyzates (6-8). The trimethylsilyl derivatization is simple and rapid, but it does have shortcomings. Because water reacts with the reagents, it is necessary to employ extensive drying procedures. The chromatography is difficult to interpret because each of the five sugars produces several anomers which result in chromatograms with 14 components. Complete resolution has not yet been achieved for this system. Consequently, the chromatographic conditions must be rigidly controlled to maintain analytical precision, and the data reduction is cumbersome. It has been our experience that silanization of simple sugars is not always quantitative and sometimes requires extended reaction times. In addition. the literature also indicates that there have been problems with lack of reproducibility in the conversion of steroids to trimet iylsilyl ethers for gas chromatography (9).
It appeared to us thai the successful development of a gas chromatographic method for pulp sugars capable of routine
(1) J. F. Saeman, W. E. Moore, R. L. Mitchell, and M. A. Millet, Tuppi, 37, 336 (1954).
(2) C. C. Sweeley, R. Bentley, M. Makita, and W. W. Wells, J. Am. Chem. Soc., 85, 2497 (15163). (3) R. J. Alexander and J. T. Garbutt, ANAL.CHEM., 37, 303 (1965). (4) J. Kagan and T. J. Malxy, ANAL.CHEM., 37, 288 (1965). (5) J. S. Sawardeker and J . H. Sloneker, ANAL.CHEM.,37, 945 (1965). (6) 0. Bethge, C. Holmstrom, and S. Juhlin, Scensk Pupperstidn 68, 60 (1965). (7) H. E. Brower, J. E. Jeffery, and M. W. Folsom, ANAL.CHEM., 38, 362 (1966). (8) D. W. Clayton and M. E. MacMillan, American Chemical Society Meeting, Phoenix, Ariz., January 1966. (9) H. L. Lou, J. Gus Chromatog., 4, 136 (1966).
application depended on a derivatization scheme that gave one volatile product for each sugar. Gunner, Jones, and Perry (IO)showed that single peaks are obtained for the alditol acetates of the sugars of interest in our work. Sawardeker, Sloneker, and Jeanes (11) extended this observation and obtained preliminary quantitative data which appeared encouraging. Their column consisted of a 37, liquid phase of an organosilicone polyester of ethylene glycol succinate chemically combined with a silicone of the cyanoethyl type. The purpose of this work was to investigate the alditol acetate approach to the gas chromatographic analysis of sugar mixtures resulting from the hydrolysis of southern pine wood pulps. Derivatization and chromatographic conditions were investigated and optimized. In the final procedure the sugar mixture in aqueous solution is reduced with sodium borohydride to form the alditols, which in turn are acetylated with acetic anhydride-pyridine. The acetates are isolated, dissolved in methylene chloride, and chromatographed. With the chromatographic conditions employed, excellent resolution of the five pulp components and the internal standard is obtained in 40 minutes. EXPERIMENTAL
Apparatus. The gas chromatograph used in this work was a dual column F & M Model 700 instrument equipped with a flame ionization detector. Chromatographic peak area measurements were made with an Infotronics Model l l H S electronic integrator connected directly to the electrometer. A 6' X 1/4''-o.d.column packed with 3z ECNSS-M on Gas Chrom Q (Applied Science Laboratories) was employed at a helium flow rate of 90 cc/min. The iiijection port of the instrument was modified to reduce the dead volume of the vaporizer assembly and to allow on-column injection. The column was operated isothermally at 180" C with an injection port temperature of 250" C and a detector temperature of 290" C. Standards. The monosaccharides employed as standards (D-glucose, D-galactose, D-mannose, D-xylose, D-arabinose, L-rhamnose) were obtained from Mann Research Labora-
(10) S. W. Gunner, J. K. N. Jones, and M. B. Perry, Can. J. Ckem., 39, 1892 (1961). (11) J. S. Sawardeker, J. H. Sloneker, and A. Jeanes, ANAL.CHEM., 37, 1602 (1965). VOL. 39,
NO. 1, JANUARY 1967
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