chain length, accompanied by increasing alkali sensitivity, caused low copper tartrate DP values. The agreement between the values for aldehyde groups per anhydroglucose unit in periodate starch by the chlorite and a variety of other methods, including the acidic hydroxylamine and four alkaline methods, was very good. The agreement with the alkaline methods was contrary to expectations, as the alkali sensitivity of periodate starch is the basis for a method (5) of determining aldehyde groups. Furthermore, periodate cellulose has been found to be very sensitive to alkali (14, 18, 19). A discussion of the failure of other a k a line methods, copper tartrate and hypoiodite, for periodate starch, is intended for future publication. Comparison of chlorite values with those of physical methods showed only limited agreement, as could be expected. The agreement with light-scattering values ranged from fair, for moderately homogeneous fractions of arabans, to no agreement a t all for inhomogeneous native dextrans. The agreement with osmotic pressure values of amylopectins ranged from fair to very poor, the latter probably due to differences in pretreatment of samples. The application of the R values of substances of low molecular weight to high polymers is encouraged not only by these cases of agreement and selfconsistency, but also by rate considerations. The rate curves for the oxidation of the aldehyde groups in benzaldehyde and mono- and disaccharide pentoses and hexoses ( I d ) are indistinguishable in shape from those of the polysaccharides. This can be seen by comparing the behavior with time of the R function of the previous work with the present AC/W, the two being proportional,
AC/W = R X millimoles of aldehyde per gram of polysaccharide. Also, the times required to reach curve maxima were comparable. The aldehyde end groups in more or less hydrolyzed dextrans and in amylopectins were actually oxidized at a more uniform rate than the various aldoses, when the rate differences among the chlorite conditions were taken into account ( I d ) . Periodated products reacted much more rapidly with chlorite than the parent dextran or cornstarch, demonstrating the difference between aldehyde groups at positions 1, 2, 3, and 4, although no difference between the two members of a dialdehyde group was observed. The rate of oxidation of periodate cornstarch decreased a-ith the extent of periodation, indicating a hindrance to the chlorite by unoxidized chain members. The aldehyde groups of the extensively periodated dextran and starch were oxidized at nearly the same rate as in benzaldehyde. ACKNOWLEDGMENT
The authors acknowledge helpful discussions with R. M. McCready, and also the cooperation of Allene Jeanes, I. A. Rolff, A. L. Potter, E. B. Kester, and A. E. Goodban in furnishing samples. LITERATURE CITED
(1) Arond, L. H., Frank, H. P., J . Phys. Chem. 58,953 (1954). (2) Blom, J., Rosted, C. O., dcta Chem. ' Scund. 1,32(1947).'
(3) Davidson, G. F., Nevell, T. P., J . Textile Inst. 46. T407 11955). (4) Goodban, A4.' E., Owens,'H. S., J . Polymer Sci. 23, 825 (1957). (5) Hofreiter, B. T., Alexander, B. H., Wolff. I. A,, ANAL. CHEM.27, 1930 (1955). ' (6) Hofreiter, B.
T.,Wolff, I. A,, Mehltretter, C. L., J . Am. Chem. Soe. 79, 6457 (1957).
( 7 ) Jeanes, A., Haynes, W.C., Wilham C. A., Rankin, J. C., Jfelvin, E . H., Austin, M. J., Cluskey, J. E., Fisher, B. E., Tsuchiva, H. M., Rist, C. E., Ibid., 76, 504i (i954). (8) . , Jeanes. A.. Schieltz. N. C.. Wilham.' C. A., J : B i d . Chem. 176, Slf(1948). (9) Jeanes, A,, Wilham, C. A., J . Am. Chem. SOC.72, 2655 (1950). (10) Jeanes, A,, Wilham, C. A,, Irliers, J. C., J . Biol. Chem. 176, 603 (1948). (11) Launer, H. F., Tomimatsu, Y . ,ANAL. CHEM.26, 382 (1954). (12) Ibid., 31, 1385(1959). (13'1 Launer. H. F.. Tomimatsu. Y..' ' J . A m . ChemrSoc.26, 2591 (1954): (14) Meller, A,, Tappi 34, 171 (1951). (15) Potter, rl. L.,Hassid, W. Z., J . Am. Chem. SOC.76.3488. 3774(1948). (16) Potter, A,' L., 'Silveira, V., McCready, R. M.,Owens, H. S., Ibid., 75, 1335 (1953). (17) Rankin, J . C., Mehltretter, C. L., ANAL.CHEM.28, 1012 (1956). (18) Reeves, R. E., Ind. Eng. Chem. 35, 1281 (1943). (19) Rutherford, H. A., Minor, F. W., Martin, A. R., Harris, iM.,J . Research Xatl. Bur. Standards 29, 131 (1942). (20) Schoch, T. J., Advances in Carbohydrate Chem. 1 , 247-77 (1945). (21) Sloan, J. W., Alexander, B. H., Lohmar, R. L., Wolff, I. A,, Rist, C. E., J . Am. Chem. SOC.76, 4429 (1954). (22) Sloan, J. W., Hofreiter, B. T., hfellies, R. L., Wolff, I. A., Ind. Eng. Chem. 48, 1165 (1956). (23) Tomimatsu, Y . ,Palmer, K. J., Goodban, A. E., Ward, W. H., J . Polymer Sci. 36,129 (1959). (24) Van Cleve, J . W., Schaefer, W. C., Rist, C. E., J . Am. Chem. SOC.78, 4435 (1956). (25) Wilham, C. A., Alexander, B. H., Jeanes, Allene, Arch. Biochem. Biophys. 59, 61 (1955). (26) Wilham, C. A., Jeanes, Allene, un-
published results.
(27) Wilson, W. K., Padget, A. A., Tappi 38, 292 (1955). (28) Wolff, 1. A., blehltretter, C. L.,
Mellies, R. L., Watson, P. R., Hofreiter, B. T., Patrick, P. L., Rist, C. E., Ind. Eng. Chem. 46, 370 (1954).
RECEIVEDfor review March 20, 1959. Accepted April 27, 1959.
Rapid Determination of Organically Bound Fluorine E. Z. SENKOWSKI, E. G. WOLLISH, and E. G. E. SHAFER Analytical Research Laboratory, Hoffmann-la Roche hc., Nufley, ,An uncomplicated method for the determination of organically bound fluorine was desired. The procedure described is rapid and simple and requires minimum equipment. The sample is burned in the presence of a small quantity of sodium peroxide in an atmosphere of oxygen, in a Schoniger borosilicate glass flask. In the resulting solution fluorine is determined photometrically by Megregian's procedure. Small quantities of phos-
1574
ANALYTICAL CHEMISTRY
N. 1.
phates do not interfere, but larger proportions require a Willard-Winter distillation. The method is applicable to a variety of organic fluorine compounds and can b e carried out with satisfactory accuracy and precision in less than 1 hour.
T
determination of organically bound fluorine has presented a problem for a considerable number of years. The fact that many methods HE
have been published indicates that the need for a simple and rapid routine procedure has not been satisfied. The literature pertaining to fluorine determinations in organic microanalysis has recently been reviewed in detail by M a (4, 6). Most of the investigators have decomposed the sample by oxidative fusion in a peroxide bomb or by reduction using sodium, potassium (4), or sodium biphenyl ( 1 ) . However, dissolution and
.
neutralization of the fusion mixture and the presence of decomposition products from the sample often interfered with the direct determination of fluorine in the resulting solution. I n most of the methods, therefore, a separation procedure was required following decomposition of the sample. Separations have used ion exchange (8) or the more conventional Willard-Winter (11) distillation of fluosilicic acid, usually performed prior t o the final quantitative determination. These purification steps not only render the methods rather complicated and time-consuming, but also contribute t o the hazard of loss of fluorine. I n 1955, Schoniger (9) first described a simple and ingenious method for the rapid combustion of organic compounds, particularly those containing sulfur or halides. EXPERIMENTAL
When Schoniger's procedure was applied to organic fluorine compounds, the resulting solution contained a sufficiently low concentration of decomposition products and inorganic salts to permit direct application of the colorimetric method described by hfegregian (8). The recoveries, however, were only about 93 to 94%) of theory, which suggested incomplete combustion, although their consistent reproducibility was rather surprising. Attempts were made to modify the combustion procedure in order to drive the oxidation to completion. Addition of a small quantity of sodium peroxide to the sample prior to its combustion in an atmosphere of oxygen nil1 accomplish this objective. This is directly followed by colorimetry using zirconylEriochrome Cyanine R complex. The details and limitations of the photometric procedure have been described by Megregian (8). Khile this colorimetric method is preferred for its simplicity, the final determination of fluorine after decomposition of the sample is by no means limited to this procedure: Steyermark (10) has applied direct photometric titration t o the burned sample solution without prior distillation, in the absence of arsenic or phosphorus, using thorium nitrate according t o >fa and Gwirtsman (6). Water, rather khan sodium hydroxide, was used to absorb the fluoride. to minimize ionic interference. For detection of the end point he used the photoelectric filter photometer of Mavrodineau and Gwirtsman ( 7 ) . It was necessary to steam-distill fluosilicic acid only if the sample contained arsenic or phosphorus. METHOD
Apparatus. Thomas-Schoniger combustion flask, borosilicate glass,
Table I.
Accuracy and Precision of Results ~~
F! V io
2
Compound Research cpd. Research cpd.
Formula C4HqK2F02 CsHnNZFO,
3 4
Research cpd. Research cpd. with
CgHnN,F06
7.25 22.62
5
1,3,5-Trifluoroaniline p,p'-Difluorodiphenyl Kel-F Teflon
C~H~NF, C12H8F* (-CF,-CFCI-), (-CFr-)=
SO.
1
s o . of
_.
Theory Found 14 61 14 62 7 73 7 79
s
Detns.
+O 1 1 1 0 08
11 26
7.20 22.94
50.05 f0.04
2 4
35.38 35 15 19.98 20.39 48.98 49.47 75.98 77.28
kO.17 f0.07 10.76 f0.34
2 2 3 2
Av . Dev.
-4F. ProuD -
6 7
8
0
-
1
45' angle. When the combustion has 500-ml. size, including specially cut been completed, shake the flask vigorWhatman Xo. 42 filter paper (Catalog ously for 1 minute. Place 10 to 15 ml. No. 6470 E, Arthur H. Thomas & Co., of water in the well around the stopper Philadelphia, Pa.). and allow the flask to stand for 15 Reagents. Eriochrome Cyanine R minutes, to permit complete absorption Solution. Dissolve 0.18 gram of Erioof the combustion products by the chrome Cyanine R (Geigy Chemical liquid. Then warm the flask slightly on Corp., Saw Mill Road, Ardsley, N. Y.) a steam bath so as to permit easy rein 100 ml. of water. moval of the stopper. Wash the stopper Zirconyl Chloride Solution. Dissolve and platinum holder with water, collect0.265 gram of zirconyl chloride octaing the water in the flask. Add two hydrate, basic (Fisher Scientific Co.), in drops of phenolphthalein 1% in alcohol 50 ml. of water, add 700 ml. of concenand neutralize the solution to colorless trated hydrochloric acid, and dilute to by dropn-ise addition of 10% nitric acid lo00 ml. with water. Cool to room (approximately 1.6N), then again add temperature and adjust to volume. 0.1N sodium hydroxide dropwise to the Standard Sodium Fluoride Solution appearance of a slight pink color. Trans(Prepare fresh!). Dry sodium fluoride, fer the solution quantitatil-ely to a 1OOOreagent grade, for 2 hours a t 120" C. ml. volumetric flask and bring .to volume Dissolve 211.0 mg., weighed exactly, in vith water. Into a 50-ml. volumetric sufficient water to make lo00 ml. Subflask pipet a sufficient quantity of this dilute 20.00 ml. of this solution with water to make lo00 ml. (Concentrasolution to provide 30 to 35 y of fluorine, and proceed as follon s: tion 2.00 y of F-/ml.) Procedure. SAFETY PRECAUTIONS Carry out t h e combustion inside a Blank, Sam 16, safety hood or behind a safety shield. Ml. 1 8 PREPARATION OF SAMPLE. The sam25 Sample Water ple should be in form of a fine dry powaliquot der. Polymers may be poffdered in a water TT'iley mill, in presence of dry ice, if t o make necessary. Dry all samples in vacuo t o 25 eliminate moisture. Eriochrome CyaOn a combustion paper weigh accunine R solution 5 5 rately a sample of from 10 t o 35 mg. Hydrochloric acid, wt. depending upon its expected fluorine 8.4-V 5 .. content. For compounds with more Zirconyl chloride than 30% fluorine, use a 10-mg. sample. 5 solution These quantities are optimal, as they permit complete combustion (specks of carbon do not interfere) and convenient Dilute the solutions to 60 ml. x i t h dilutions. n-ater, mix, and measure the absorbance Add atmroximatelv 20 me. of sodium of the sample solution after setting the peroxide'io the sample con&ning up to Beckman Model B spectrophotometer 30% fluorine and 30 mg. of sodium peror equivalent instrument a t 527.5 mk t o oxide to samples with higher fluorine zero absorbance n ith the reagent blank. content and carefully fold the paper. Prepare a standard graph, using the Place the folded paper in the platinum standard sodium fluoride solution a t holder attached to the stopper of the concentrations of 20, 30, and 40 y of Schoniger flask and gently press the fluoride per 50 ml., and carry out the holder together to secure the paper and procedure as outlined for the sample. .ample in place. The plot of concentration against abIn the 500-ml. Schoniger flask place sorbance is linear within this range. 50 ml. of 0.1N sodium hydroxide and Determine the fluonne content of the saturate the solution by bubbling oxygen sample aliquot from the standard graph. through it from an oxygen cylinder. Although the reagents were rather K h e n the air in the flask has been restable, it is a d h a b l e t o rim a threeplaced by oxygen, ignite the extended point standard graph with sodium tab of the filter paper attached t o the fluoride a t the same time as the sample. glass stopper. insert the stopper quickly The color developed in the solution into the flask after rapidly removing the to be measured i3 .table for a t least oxygen delivery tube, and invert the 1hour. tightly stoppered flask, holding it at a
+
VOL. 31, NO. 9, SEPTEMBER 1959
1575
Table II.
Effects of Phosphates
Sample Fluorine Solution Found, y 35.2 y F-/50 ml. 35.2 400 y P 0 4 35.0 800 y POr 39.0 2000 y PO1 Bleaching of complex
+ + +
Interference None About 10% Complete
RESULTS A N D DISCUSSION
A number of fluorine-containing organic compounds, all of which had given satisfactory values for carbon, hydrogen, and nitrogen [Nos. 1 to 4 analyzed by Steyermark (10) and Nos. 5 t o 8 b y Francis (S)], were subjected to fluorine determinations (Table I). The precision obtainable is evident from the standard deviation, s = 0.11, arrived a t from 11 determinations of compound 1, and s = 0.08 calculated from the results of 26 determinations of compound 2 . The estimated overall accuracy of the method is *2%. Compound 4 contained a -CF3 group. It had been feared that on combustion, CFs might be at least partially volatilized, with a concomitant
loss of fluorine. This is not the case, as fluorine was completely recovered. I n another experiment the effect of phosphates on the absorbance of the fluoride-zirconyl complex was studied. As can be seen from Table 11, 400 y of phosphate per 50 ml. of final solution appeared t o be without effect on the absorbance. However, when 800 y were added, a positive error of about 10% resulted; 2000 y completely interfered with the determination. If the combustion of an organic fluorine compound, having up to two phosphorus atoms or phosphate groups per fluorine atom, is followed by hlegregian’s (8)photometric method, no interference need be expected. The presence of larger quantities of phosphates, however, necessitates a Willard-Winter (11) distillation. The method is very rapid, requiring less than 1 hour per determination. ACKNOWLEDGMENT
The authors are indebted to F. P. Mahn for valuable assistance, to J. A. Napoli for helpful suggestions, to A1 Steyermark, Hoffman-La Roche Inc., for the carbon, hydrogen, and nitrogen determinations of compounds 1 to 4,
and to Howard Francis, Jr., Pennsalt Chemicals Corp., for furnishing compounds 5 to 8, together with carbon, hydrogen, and nitrogen values. LITERATURE CITED
(1) Bennett, C. E., Debbrecht, F. J., Division of Analytical Chemistry, 131st
Meeting, ACS, Miami, Fla., A ril 1957. (2) Eger, C., Yarden, A., ANAL. 28, 512 (1956). (3) Francis, H., Jr., Pennsalt Chemicals Corp., Philadelphia, Pa., private communication. (4) Ma, T. S., ANAL. CHEM.30, 1557 (1958). (5) Ma, T. S., Microchem. J. 2, 91 (1958). (6) Ma, T. S., Gwirtsman, J., ANAL. CHEM.29, 140 (1957). (7) Mavrodineau, R., Gwirtsman, J.,
S HEX.
Contribs. Boyce Thompson Inst. 18, 181
(1955).
(8) Megregian, S., ASAL. CHEW 26, 1161 i1954). ( 9 j Schoniger, W., Mikrochim. Acta 1955,
123; 1956, 869. (10) Steyermark, Al, Hoffmann-La Roche Inc., Nutley, N. J., private communication. (11) Willard, H. H., Winter, 0. B., IND. ESG. CHEW,ANAL.ED. 5, 7 (1933). RECEIVED for review November 17, 1958. Accepted March 18, 1959. Meeting-inMiniature, North Jersey Section, ACS, January 26, 1959.
Trace Analysis for Total Nitrogen in Petroleum Fractions Adsorption-ter Meulen Method EUGENE C. SCHLUTER, Jr. Research Deportment, Union Oil Co. o f California, Brea, Calif.
b Trace amounts of organic nitrogen compounds in petroleum fractions poison conversion catalysts. The determination of total nitrogen in petroleum fractions a t very low concentrations presents a serious analytical problem. By the method presented here the nitrogen compounds are concentrated from a relatively large volume of hydrocarbon by adsorption on a silica gel column. This column is then placed in a ter Meulen apparatus where the nitrogen compounds and the hydrocarbons wetting the gel are desorbed b y hydrogen and heat. The vapors pass through the ter Meulen catalyst with very little pyrolysis of hydrocarbons. The nitrogen compounds are converted to ammonia, which is collected in an absorber and determined by standard methods. The procedure may b e used to determine as little as 0.1 p.p.m. of nitrogen.
1576
ANALYTICAL‘ CHEMISTRY
T
petroleum industry is becoming increasingly aware of the deleterious effects of organic nitrogen compounds in various phases of petroleum refining. Nitrogen compounds reduce stability of refined products by gum formation and impart undesirable odor and color (6, IS). They also adversely affect the activity of cracking and other type catalysts (3, 7, 9, 1.2, 14). Nitrogen is particularly deleterious to the activity of platinum-type catalysts used in present day reforming operations. The charge stocks to reformers using platinum-type catalysts usually contain less than 20 pap.m. of nitrogen, the determination of which creates an analytical problem. The conventional (Kjeldahl, Dumas, and ter Meulen) methods available for the determination of total nitrogen are intended for the determination of nitrogen a t levels above 100 p.p.m., HE
and they are not directly applicable for the determination of trace amounts. Except for the Dumas, these methods have been modified to allow the detection of as little as 1 p.p.m. of total nitrogen. Because the ultimate sensitivity of the conventional Kjeldahl method is limited by a relatively large and variable blank, efforts to increase sensitivity have been aimed a t minimizing the effect of the blank. One solution is to increase the sample size. Bond and Harriz (1) concentrate the organic nitrogen compounds from a large sample by adsorption on a small silica gel column, which is then broken up into sections and digested by the conventional Kjeldahl method. Results with an accuracy of i.5% at the 1- to 10p.p.m. level are claimed. Bumping of the Kjeldahl flask during the digestion
