were used and no effort was made to control rigidly their quantitative composition. The fractions separated on the 2nitrobiphenyl column were collected individually in 2,4-dinitrophenylhydrazine reagent and the derivatives were chromatographed on paper by the method of Meigh ( 4 ) . The extent of migration of each spot in terms of the carbon number of the saturated aldehyde series is shown in Figure 2 . Thus, a combination of gas liquid chromatography and paper chromatography of the derivatives of the eluted fractions greatly increases the ease and certainty of identification of these low molecular weight carbonyl compounds. h number of other stationary phases were investigated and found unsatisfactory because of incomplete separation. Carbowax 600 gave five peaks with propionaldehyde: acetone and acrolein : isobutyraldehyde forming
two inseparable pairs. Dinonylphthalate and Craig’s polyester gave only five peaks, also with propionaldehyde and acetone and acrolein appearing together with the former while acetone, acrolein, and isobutyraldehyde were eluted as a single peak with the latter. In addition, tri-o-tolylphosphate, ‘Tcon,” “Glycowax 5-932,’’ 2,4-dinitrotoluene, and o-nitroaniline also gave only five peaks with the seven-component mixture. Silicone, propylene glycol, Tween 60, benzophenone, 2-phenoxyethanol, and caprinoin resolved the mixture into six peaks with propionaldehyde and acetone appearing together. Triphenylphosphite and 2,5-hexanedione gave complete resolution of the mixture, but the former proved t o be too unstable, while the latter was too volatile and interfered with further identification of the collected fractions.
LITERATURE CITED
(1) Gaddis, A. &I.,Ellis, R., ANAL.CHEM. 31, 870 (1959). (2) Kyryacos, G., Menapace, H. R., Boord, C . E., I b i d . , p. 222. (3) Lynn, W. S., Jr., Steele, L. A., Staple, E., Ibid., 28, 132 (1956). (4) Meigh, 1).F., .\-atwe 170, 579 (1952). (5) Schmitt, W. J., Moriconi, E. J., O’Connor, R. F., ANAL.CHEM.2 8 , 249 (1966). (6) Schwartz, D. P., Parka, 0. W., Keeney, M.,I b i d . , 34, 669 (1962). (7) Seligman, R. B., Edmonds, 31. D., Chem. I n d . ( L o n d o n ) 1955, p. 1406. GEORGEM I Z ~ N O EVELYX LIChfEANS J. R. CHIPAULT
The Hormel Institute University of Minnesota Austin, Minn.
WORK supported in part by the U. S. Army Natick Laboratories, Katick, Mass. Fish and Wildlife Service of the U. S. Department of the Interior; and The Hormel Foundation.
Determination of Trace Nitrogen in Petroleum by a Microcombustion Technique SIR: The importance of the determination of trace quantities of nitrogen in petroleum fractions is amply demonstrated by the frequency with which such methods appear in the literature U , S , 519,101. Generally, the methods described are modifications of either the Dumas, or the Kjeldahl technique, which are either too insensitive or too time consuming to meet the authors’ requirement of being able to determine nitrogen down to 1 p,p.m, in less than one hour. Reitsema and Xllphin (12) have shown that organic nitrogen can be quantitatively converted to SOuand determined by gas chromatography. The present authors did not feel, however, that the gas chromatographic equipment available would be sensitive enough to meet the requirements mentioned above. I t was decided to attempt conversion of the organic nitrogen to KO2 over a platinized asbestos catalyst in a n oxygen atmosphere. The NOz produced would then be measured using the GriessIlosvay reaction previously described (a, 4, 6-8, 1 1 , I S ) as a method of detecting nitrite ion in solution or SO2 n the atmosphere. The reactions assumed to occur are as follows:
+ 02+ combustion by-products
R-IY NOu
152
ANALYTICAL CHEMISTRY
(1)
NO;
+ S O I H-a N H 2
t
Sulfanilic acid
d2 --t
1-Naphthylamine
“ I2
(3)
Red dye The intensity of the color produced by the dye from reaction 3 was then measured a t 535 mw and related to nitrogen content of the sample through a calibration curve prepared from known potassium nitrite solutions. EXPERIMENTAL
Reagent and Solutions. Reagent grade materials are used throughout. Sulfanilic Acid and 1-Naphthylamine Solutions. The solutions d t scribed by Telcher (14) are used. Platinized Asbestos. The platinized aqbestos catalyst is prepared by
refluxing for 3 hours 5 grams of asbestos fibers with concentrated nitric acid. The fibers are washed free of acid and dried. Chloroplatinic acid (0.9975 gram) is dissolved in 10 ml. of water, cooled to 32’ F., and 8 ml. of 37% formaldehyde are added. A4cid treated asbestos (3.5 grams) are added to this solution, followed by 8 grains of KOH in 10 inl. of water added slowly with stirring. The temperature is kept’ below 41’ F. while the mixture is stirred for an additional 15 minutes. The temperature is then raised to 140’ F. and held for 15 minutes more. After water washing three times by decantation, followed by one wash with 56 ml. of 1lY acetic acid, the mass is transferred to a Buchner funnel and washed with hot water until free from chloride and alkali. The catalyst is dried in an oven a t 212’ F. until uniformly gray in color. Potassium Nitrite Solution. A standard potassium nitrite solut>ion, for uRe in calibrating the spectrophotometer, is prepared by dissolving 0.6234 =k 0.0001 gram of KKO? in distilled water and diluting t o a liter. Carrier Gas. Oxygen is fed directly to the combustion tube from a twostage reducing valve. Low pressure oxygen is supplied a t about 10 p.s.i.g. although this may vary as the asbestos packing settles in the combustion tube. Apparatus. COMBVSTIOKTRAIX. The combustion unit consist,s of a stationary heater of about 19.5 r m . in length and a movable heater about
4.5 em. long. The movable heater should have a traverse of a t least 13 cm., and is preferably of the automatic type with a variable rate of travel. Each heater must he capable of sustained operation in the 500' to 600O C. range. The movable heater should be of the split type to enable the operator to remove it from the combustion tube while charging the sample. COMBUSTION TUBE. An 11.25- X 525-mm. Vycor microcomhustion tube with 10/30 3 joints is used. A 3-mm. plug of ignited asbestos fibers is used in the nose end to retain a 18Cmm. length of platinized mbestos filling. ABSORBER.Helical borosilicate a b sorber constructed of 7-mm. o.d. tubing woundinto twenty- three9-cm. 0.d. coils. The entrance end of the coil is fitted with a 10/30 3 glass joint for attachment to the combustion tube. A soap bubble flow meter is connected to the exit end through a cork stopper. SPECTROPHOTOMETER. A Beckman DU spectrophotometer fitted to handle IO-cm. cells was used to make all absorbance measurements. Procedure. Both the stationary and movable heaters are turned on and adjusted to about 700' C. T h e combustion tube is purged with oxygen a t a Aow rate of about 10 ml. per minute for 30 minutes to remove traces of nitrogenous material from the combustion zone. After completion of the preheat, the fixed furnace temperature is lowered to 550' C. and the movable heater temperature to about 600" C. Fifteen milliliters of the snlfadilic acid solution are poured into the coil from the exit end and allowed to drain to the entrance end. Care must be taken not to wet the standard taper joint at this time. A 6- to 14mg. sample is introduced into the combustion tube, in either a platinum boat or a glass capillary, and p o i tioned about 1.5 inches from the st* tionary heater. The movable heater is then brought up about the tube and moved to within 1.5 inches of the sample. The heater temperature is adjusted to 600' C. and the furnace drive is turned on and set for 1 cm. per minute advance. Upon completion of the first burn-through, the procedure is repeated with the rate of heater advance set for 3 em. per minute. Total combustion time is ahout 25 minutes. Upon completion of the combustion, the coil is disconnected and drained into a clean, dry 50-ml. volumetric flask. Ten ml. of sulfanilic acid solution, followed by 25 ml. of 1-naphthylamine solution are added to the coil as a rinse. The washings are added to the volumetric flask and the volume is made up to the mark with 1-naphthylamine solution. The red color is allowed to develop for 5 minutes a t room temperature, and the absorbance is measured at 535 mp in a 10-cm. cell. An empty boat is run as a blank and the absorbance is subtracted from the sample abnorbanee. Blanks are normally run first thing in the morning and then with every fourth sample during the day. Our experience is that the blank value is about 0.05 absorbance unit in a 10-cm. cell.
Figure I . Apparatus used for determino tion of t r w e nitrogen by combustion
Micrograms of nitrogen are calculated from a calibration curve made up using known amounts of the standard KKO? solution. In preparing t,he calihration curve, it must be remembered that the observed absorbances are to be corrected by a factor of 0.5 to account for the fact that only half the nitrogen in the sample is observed as
ACKNOWLEDGMENT
The authors are indebted to F. R. Hampe and K. Gordon for the Kjeldahl analyses used in this investigation.
lome
I.
KO2-.
KeSUlrS u D I a i n e a on Dienos of Known Compounds
AV.
RESULTS
Comparison of the results obtained using the new method with those obtained by Kjeldahl analysis shows an average deviation of f 1 . 4 p.p.m. in the 0- to 40-p.p.m. range, +4 p.p.rn. in the 40- to 100-p.p.m. range and a n overall deviation of +8 p.p.m. from 100 to 800 p,p.m, Tables I and I1 give some of the values obtained from known blends and a comparison of some results, on samples which were run by both the new method and the Kjeldahl procedure. To oht,ain optimum accuracy and precision, glassware and reagents must be scrupulously protected from contamination. Periodic analysis of a known nample, similar in properties to those being run, is recommended as a check on the method. Applicability. A number of pure, nitrogen containing compounds of different structure have been analyzed by this method. A summary of these appears in Table I. Moreover, 8. wide variety of petroleum fractions have been analyzed successfully by this procedure. These include light gas oils, kerosine, motor oil blends, greases, and polymers. In addition to trace nitrogen analysis, the method has heen used to determine nitrogen in the 1 to 10% range in cases where only microgram amounts of sample have been available.
' N N added, found, detns. p.p.m. p.p.m. NO. of
Compound m-Nitrophenol Acetanilide Cyanoaeet,ic acid
Piperidine Piperidine 1-Octylamine 1-Oetylamine 1-Octylamine 1-Octylamine COetylamine GOetylamine Ar Ni Gr
1 1
234
1
3
22s 12 31 4
1
70
2 2 9
27 6 43 2 24 11
5 7
4
Ta
kn,
...._-,,-..,--I
-, ..,-."-... -..-
C Sample Light cycle gas nil No. 1 No. 2 No. 3 No. 4 No. 6 No. 7 No. 8
No. 9 No. 10 No. 11 Kerosine Grease (eon mercid) Luhe oil icomArcid)
VOL. 37, NO, I , JANUARY 1965
153
LITERATURE CITED
(1) Bond, G. R., Jr., Harriz, C. G., ANAL. CHEM.30, 1882 (1958). (2) Campbell, A. D., Munro, M. H. G., Anal. Chim. Acta 28, 574 (1963).
(3) Farley, L. L., Guffy, J. C., Winkler, R. A., ANAL.CHEM.36, 1061 (1964). (4) Glover, C. A., Sloan, C. H., Anderson, R., 138th Meeting, ACS, New York, N. Y., September 1960. (5) Gouverneur, P., Anal. Chim. Acta 26, 212 (1962).
(6) Griess, P., Ber. Deut. Chem. Ges. 12, 426 11879). (7) Haslam,’J., Hamilton, J. B., Squirrell, D. C. M.,Analyst 86, 293 (1961). (8) Ilosvay, M. L., Bull. SOC.Chim. Parzs 2,347 (188s) _ ”,. (9) Milner, (1.I., “Analysis of Petroleum for Trace Elements,” p. 74, Macmillan, New York. 1963. f 10) Milner, ’ 0 . I., Zahner, R. J., ANAL. CHEM.32. 294 11960). (11) Nelson: J. L., Kurtz, L. J., Bray, R. H., Ibzd., 26, 1081 (1964). (12) Reitsema, R. H., Allphin, N. L., Zbzd., 33, 355 (1961).
(13) Sawicki, E., Stanley, T. W., Elbert, W. C., Zbid., 32, 297 (1962). (14) Relcher, F. J., “3rganic Analytical Reagents,” Vol. 11, p. 405, Van Nostrand, New York, 1948. T. A. SORRIS J. E. FLYBN Texaco Research Center Texaco, Inc. Beacon, N. Y. Division of Analytical Chemistry, 147th Meeting, ACS, Philadelphia, Pa., April 1964.
Spectrophotometric Determination of Phosphorus in Alloy Steel SIR: Fogg and Wilkinson (1) reported success in determining phosphorus in boiler water effluents and salt deposits by reducing the phosphorusmolybdenum complex in dilute sulfuric acid medium with ascorbic acid. Evidence is available in the literature of extraction of this complex from dilute sulfuric acid with normal butyl alcohol ( 9 ) . These two approaches were combined and modified for application to phosphorus analysis of alloy steels. Fogg and Wilkinson use sulfuric acid as the reaction medium in their reported procedure. However, it was decided to adapt their method for use with perchloric acid because of the larger volume of acid permissible for complete extraction and the formation of easily dissolved perchlorates, rather than the slightly soluble sulfates obtained when high alloy steels in acid solution are fumed in sulfuric acid to remove the more volatile mineral acids. I n a final volume of 100 ml., 15 to 17 ml. of perchloric acid were required for complete extraction of complexed phosphorus; when sulfuric was used, only 2.5 ml. could be tolerated. If members of the earth acids are present, as they are in many of the modern, complex alloys, they will, of course, be precipitated by this treatment. However, this should cause no concern because solvent extraction apparently eliminates the posTable I.
Sample N.B.S. 8h X.B.S. 123a N.B.S. 123b N.B.S. 167 N.B.S. 1%8 S.B.S. 349 18-8 Stainless
sibility of loss by occlusion. Filtration would obviously enhance this possibility. Removal of arsenic is effected by the addition of 10 ml. of a 5 to 1 hydrochloric acid to hydrobromic acid mixture to the cooled sample solution after it has been fumed in perchloric acid. The sample solution is then evaporated again to perchloric acid fumes to volatilize arsenic and remove excess halogen acids. As in other phosphorus procedures, the solution containing the reducing agent must be heated to develop the characteristic molybdenum blue. However, the normal butyl alcohol used as extractant was not a very good solvent for ascorbic acid and did not boil evenly. This spasmodic boiling often brought about splashing of the solution and loss of sample. Nevertheless, full color does not develop a t room temperature even after hours of standing; maximum color developed after 1 minute of boiling. It was decided, therefore, to try to reextract the complex from the organic phase back into the aqueous phase. Because extraction occurred in acidic medium, it was believed that reextraction should occur in a basic medium. Trials of this idea showed that it did, indeed, occur and most effectively when a 2.5y0 solution of sodium hydroxide
Phosphorus Recoveries on Steel Samples PhosDhorus. %
Certificate 0.094 0.035 0.024 0.010 0.008 0.002 0 . ll7b
Experimental Range Average 0.093 0.090-0.097 0.035 0.033-0.036 0.024 0.022-0.026 0.010-0.011 0.011 0.006-0.008 0.007 0 , 0 0 1 7 4 0023 0,0020 0.1194.120 0.119
Precisiona f0.006 f O , 003 f O , 003 f 0,001 f O . 002 f0.0005 ...
( ,7570 Xb)
Xi base alloy 0.003b 0.0049-0.0056 0,0053 (5% Xb) Reproducibility at 95% confidence limits (two sigma). * Analyzed by classical procedures.
0
154
ANALYTICAL CHEMISTRY
...
was used. Making the solution basic a t this point has the additional advantage of facilitating acidity adjustment prior to reduction and color development. The basic solution containing the oxidized phosphorus-molybdenum complex was adjusted to neutral to litmus with dilute sulfuric acid as reconimended. But recoveries of known amounts of phosphorus were erratic, suggesting, among other possibilities, that a pH of 7 was not the best for reduction to molybdenum blue in this system. Aliquots of a pure phosphate solution, adjusted to pH neutrality and given definite known excesses of dilute sulfuric acid and dilute sodium hydroxide, were color-developed and showed that maximum, reproducible color was obtained when 5 to 7 drops of the acid beyond the neutral point were added. That a range of 3 drops is satisfactory precludes the necessity of determining this pH with each test, although it was 1.3 0.1 p H units. Analyses of standard steel samples gave recoveries of phosphorus dependent on the amount of iron present-Le., the higher the iron content, the lower the phosphorus recovery. Although Fogg and Wilkinson suggest iron interference, they did not encounter this element to the degree found in ferrous alloys. Pure phosphate solutions containing varying amounts of an iron compound were analyzed and verified this observation. The simple expedients, however, of doubling the amount of ammonium molybdate solution (5y0w./v.) from 5 to 10 ml. and adding 0.5 to 1.0 gram of solid sodium sulfate to the solution prior to extraction both served to remove this interference and resulted in cxcellent phosphorus recoveries independent of the amount of iron in the original sample. The use of a procedure of extractionreextraction of phosphate complexed with molybdate and subsequent reduction to molybdenum blue with ascorbic acid gave recoveries of phosphorus in
*
