Table II.
Column No.
c.
Adjusted Retention Volumes, V‘R, of Sulfoxides (in ml.) 1 ~~~
200 250 165 165
2 3 200 250 200 250 200 200 140 110
4 200 143
225 143
5 200 250 165 165
6 200 130
He flow, ml/min. Sulfoxide 11 12 7 16 41 52 Dimethyl 13 18 13 23 54 63 Methvl ethvl 39 66 40 68 99 109 n-Probl “ .~ .25 33 44 43 i-ProI;$ i-pr0;;1 21 36 n-Butyl 100 150 75 155 178 188 49 86 53 87 99 101 i-Butyl 46 47 t-Butyl 6 10 14 19 205 332 153 318 327 331 n-Amvl i-Am;l 110 190 114 227 223 222 n-HeGyl 363 590 295 683 615 603 Tetramethylene 41 60 33 76 173 176 Diphenyl 760 177 1190 320 438 96 1400 468 3130 487 2500 p-Tolyl 2525 380 3370 680 878 153 3600 1010 8300 920 5400 Benzyla a Excessive thermal decomposition at these temperatures. ~~
washed and silanized). Chromosorb, 35- to 80-mesh, silver plated as described by Omerod and Scott (5) gave moderately acceptable results. Untreated Chromosorb and Chromosorb W were unsatisfactory because of tailing of the sulfoxides and of the water sometimes present in the samples.
The sharpest and most symmetrical peaks with the least amount of tailing for a given liquid phase were obtained when Gas-Chrom-Z was used as the solid support and either Carbowax 1500 or 20-11 as the stationary phase. Table I1 shows the results on these systems. Silicone gum rubber generally
gave the smallest retention volumes and Carbowax 1500 gave the largest retention volumes. The retention times, measured from the injection point to the top of the peak, showed a slight dependence on sample size. Figure 4 shows a gas chromatogram of a synthetic mixture of sulfoxides, in approximately equal weight concentrations. It is suggested that a weightper cent standard be prepared when quantitative analysis of a mixture is sought. LITERATURE CITED
(1) Beuerman, D. R., Meloan, C. E., ANAL.CHEM.34, 319 (1962). (2) Crown Zellerbach Corp., Camae, Wash. , Technical Bullet,in on Dimethyl Sulfoxide. ( 3 j Felton, H. R., Buehler, A. A., A i s . 4 ~ . CHEM.30, 1163 (1958). (4) Khrasch, X., “Organic Sulfur Compounds,” Vol. 1, pp. 161 and 163, Pergamon Press, New York, 1961. (5) Omerod, E. C., Scott, R. P. W., J . Chromatog. 2, 65 (1959). (6) Pecsok, R. L., “Principles and Practice of Gas Chromatography,” pp. 137-8, R’iley, New York, 1959. RECEIVED for review December 17, 1962. Accepted March 11, 1963. Study supported by the Kansas State University Bureau of General Research.
Determination of Carbon in Hydrogen Peroxide by Combust ion-Gas Chromatog ra p hy F. M. NELSEN
and SIGURD GROENNINGS
Shell Development Co., Emeryville, Calif.
b Ten microliters of sample in a capillary dipper are flash-evaporated a t 300” C. in an empty portion of a quartz tube and swept by helium through a quartz-rod-packed portion of the tube a t about 900” C. Simultaneous decomposition of peroxide and oxidation of organic materials yield water, oxygen, and carbon dioxide. These are swept through a water absorber and a gas chromatographic column packed with silica gel for separation of oxygen and carbon dioxide. The latter is measured by thermal conductivity, and calculations are made from peak height with the aid of a calibration curve. Estimated relative error is *570 in the 100- to 200-p.p.m. range, and the analysis requires 15 minutes.
N
ONELECTROLYTIC
PROCESSES
ARE
currently producing a substantial amount of the hydrogen peroxide in this country. In these processes organic source materials are employed. A 660
ANALYTICAL CHEMISlRY
rapid, reliable method for determining carbon content in the plant streams is required for warning against build-up of organic materials to explosive limits. Furthermore, a control method for determining carbon in the 0- to 200p . p n range is desirable to ensure product quality. The larger amounts of carbon found in the plant streams can be determined by several methods. But, when techniques such as Liebig-type combustion or controlled oxidation (1, 6) are adjusted to determine small amounts, the methods become tedious and sometimes hazardous. A combustion-gas chromatographic procedure has several advantages. Because the sensitivity is high, small samples can be used, thereby eliminating the explosion hazard; its automatic features decrease tedium, and the time of analysis can be appreciably reduced. Generally applicable combustion-gas chromatographic procedures have been described for determining carbon and hydrogen (2, 6). However, to handle hydrogen peroxide,
modifications are desirable for sample introduction and decomposition. In the present scheme of analysis, four requirements must be met: precise measurement and introduction of as little as 0.01 ml. of sample into the apparatus; rapid vaporization and combustion in the helium carrier stream; separation of carbon dioxide from water and oxygen; and accurate measurement of the separated carbon dioxide. The latter requirement poses no problem, as thermal conductivity detectors of adequate sensitivity are available. Likewise, the removal of nater with Dehydrite and separation of oxygen from carbon dioxide by means of silica gel in a gas chromatographic column are well established techniques. The real problem is sample introduction and combustion without introducing foreign carbon, because the latter must be held below 0.05 pg. if one expects the error to be less than 5 p.p.m. with a 0.01-ml. sample. Satisfactory sample introduction is achieved with a pipet in the shape of a
%"
r
SILICONE RUBBER R I N G aai I A F O R S N U G FIT '3N PIPET
sJ SJ
O-RING,
r THE LATHf, DRAW A 2 x 8 CAPILLARY 1 0 I x 1, A N D BEND SHARPLY 10 OVER 90..
ON
12/5 BOROSILICATE GLASS
'%
QUARTZ OR ' I Y C O R
%I" IA,V,,"
QD
-
IX
( I A O F SJ, MIN. 5.0)
B u l l - S E A L A 1.5 &.(MAX) ROD 10 I l i E BEUD
PURIFIED HELIUM--
'/s"
,
QnCOPPER TUBINGST. STEEL SJ
2Q.ND FLAT
A P P R O X 2 On.
'% -
He + 0 2 + CO2 T O TC M E A S . CELL 3 O'C
.
QIJARTZ TUBE SAMPLE PIPET 3.50.VYCOR R O D WITHCAPILLARY TIP
!Io-,$!
~~
TO
D:*i\i.C'.5
Figure 2.
-
d?.Q
ORLND OFF TH< BRANCH CUT R O D AND CAQILLARY G R I N D TIP, A N D FISt-POLl5H G R O U ~ IURFACEI. D
011:9€0 LENGTHS.
;w--.
How to make sample pipet Vycor glass
C O M B U S T I O N CHAMBER WITH 2 x 3 QUARTZ RODS
- - - - - ---
I N HOTTEST Z O N E
-
PJfl
y///A 1
GC COLUMN COPPER T U B I N G , PACKED
60 MESH. GLASS W O O L WADS AT ENDS.30'C.
SJ
rl
QUARTZ WATER ABSORBER, DEHYDRlTE
SJ 1215 BOROSILICP,TE GMSS
%"
BOROSILICATE GLASS TUBE. GLASS W O O L WADS AT ENDS
SILICONE RUBEER R I N G
%" ut, 7,a" a. GLASS DIMENSIONS IN mm.
Figure 1.
TY G O N CONNECTION
Combustion unit and gas chromatography column
capillary dipper as shown in Figure. 1 and 2. Seating of the pipet so as to force the helium Carrie- gas through the capillary, as described by Tenney and Harris ( 7 ) , is unsatisfactory for, on sliding the pipet thrcugh the silicone rubber ring a t the sample introduction port, a carbonaceous film is deposited which will oxidize to give high results. Instead, the pipet is simply suspended freely in the combustion tube where the sample is flash-evaporated at about 300" C. and swept into a hotter zone for combustion. The oxygen for combustion is supplied by the hydrogen peroxide sample itself, which eliminates the need for oxygen gas or copper oxide. The quartz tube combustion chariber, filled with quartz rods for contacst, is carbon-free and easy to clean if contaminated. EXPERIMENTAL
Apparatus and Materials. These are illustrated and described in Figure 1. T h e system for phrification of the helium carrier gas, however, is not. It consists of approxiiii~tely1 foot of '/r-inch copper tubir g packed with Drierite (anhydrous calcium sulfate)
for removal of moisture. This is followed by approximately 2 feet of l/c-inch stainless steel tubing bent to U-shape for immersion in liquid nitrogen; the immersed portion contains a n 8-inch long bed of Molecular Sieve, Type 5A, 14- to 30-mesh (Linde Air Products Co., Tonawanda, 3.Y. ) for removal of other impurities. The sieve is regenerated after 8 hours of use by back-purging with helium for 15 minutes at room temperature; occasional purging at 300' C. may be necessary. The method of making the Vgcor glass sample pipet is shown in Figure 2 ; several pipets should be on hand. Spherical joints and silicone rubber rings are placed on the pipet stems to seal the sample inlet at the top of the combustion tube. With the small inlet (S.J. 12/5), the flowing-helium carrier gas will prevent or minimize diffusion of atmospheric carbon dioxide into the system during pipet insertion. The 8-mm. i.d. quartz combustion tube contains 2 X 3 mm. quartz rods and is kept a t 850" to 900" C. in the furnace. Maintenance of the optimum temperature, about 300' C., for flash evaporation of the sample is accomplished by placing the tip of the pipet just above the entrance to the furnace and appropriately wrapping the com-
bustion tube with asbesto. tape a t this point. A short, borosilicate glass tulle containing Dehydrite (anhydrouu magnesium perchlorate), which has been preequilibrated with carbon dioxide as a precautionary measure, is connected to the exit of the combuPtion tube for removal of mater from the combustion products. This is followed by the chromatographic column. The column is 2 feet of ','&ch copper tubing packed with Davison'3 Grade 12 silica gel, sieved to 28- to 60-mesh (Davison Chemical Co., Baltimore, Xd.). It is maintained a t 30" C. to separate oxygen from carbon diolide. A thermal conductivity cell with two 8000-ohm thermistors, one for measurement and one for reference, is satisfactory. It is thermostated a t 30" C. and operated a t 8.0-ma. total bridge current. The signal from the thermal conductivity cell circuit is fed into a 0- to 1-mv. range strip chart recording potentiometer. Procedure. Pipet Calibration. Clean the pipets by immersion in hot chromic-sulfuric acid t o within 1 c m . of the rubber gasket, rinsing with distilled water and drying Eith a Mast of clean, dry air; store them by -uspension in 25-m1. graduated cylinders. Determine the volume of each pipet as follows: Keigh a small g1a.s-stoppered Erlenmeyer flask containing a little distilled water. Open thfa flask, touch the tip of the pipet to thi. water surface to fill it by capillary action; th2n touch the pipet tip to a dry inaide surface of the flask, close the latter, and reweigh. Calculate the difference in weight as the pipet volume. Results of three such measurements should not differ by more than 0.3 my. Calibration Standards. Prepare solutions containing 0 to 200 mg. of carbon per liter from glycerine of known purity -that is, known carbon conten-and essentially carbon-free electrolytic hydrogen peroxide, adjusted to about 'io70 HzOz by dilution with boiled distilled water. Calibration Curve. Clean the combustion chamber with hot chroniicsulfuric acid and rinse, finally with diqtilled water. dssemble the combustion unit with a clean, empty pipet VOL. 35, NO. 6, M A Y 1963
661
Table I. Relation Between Carbon Content and Peak Height Carbon added Height of
to HzOz,
mg. /liter" 0 26
1
O X 't G E N CARBON DIOXIDE
COSpeak, mm.b 7 24 79 142
T
0.1 rnv.
I
100 193 a Added as glycerine. Averages of several tests.
I 0
inserted but without the water absorber. With helium flowing through the system, heat the furnace to evaporate the residual water, and finally adjust the furnace temperature to 850" to 900" C. Connect the water absorber and chromatographic column. Set the helium flow a t 60 cc. per minute; adjust the detector current, cell block and column temperature (30" C.), and turn on the recorder. Cool the standard sample to icewater temperature. Touch the tip of the pipet to the cold liquid for filling by capillary action; then touch the tip to a clean watchglass to remove any adhering liquid. If the pipet is not completely filled, cleaning with hot acid must be repeated. Replace the empty pipet in the combustion tube by the filled one without touching its tip to the spherical joint, and clamp the latter a t once, to prevent sample loss. Observe the combustion tube just above the pipet tip. Satisfactory sample introduction is indicated when only a little fog is formed due to a trace of flash-back of original sample, and an air peak of l/rminute maximum duration appears in the chromatogram. When the latter shows a level baseline after the carbon dioxide peak, the apparatus is ready for the next charge. The pipets are reused without cleaning as long as they permit complete filling of sample by capillary action. A typical chromatogram is reproduced in Figure 3. [The positioning of the pipet tip in the combustion tube is quite critical as too high a temperature will cause the sample to flash-vaporize into the upper portion of the tube, where it may react with the rubber gasket and cause high results. The position is adjusted by moving the rubber gasket on the stem. If the Dehydrite has not been preequilibrated with carbon dioxide, first results may be low. Satisfactory equilibration is obtained by injection of one or two samples containing about 100 p.p.m. of carbon. Apparatus contamination is indicated when high or inconsistent results are obtained with the base electrolytic hydrogen peroxide. If the contamination is not eliminated by injection of a few samples of this hydrogen peroxide, the apparatus should again be cleaned with hot acid.] Repeat the procedure with several calibration standards and with the base hydrogen peroxide. Measure the carbon dioxide peak heights or areas on the chromatogram and multiply these by
662
ANALYTICAL CHEMISTRY
1
5 MINUTES
I
IO
Figure 3. Chromatogram for hydrogen peroxide sample 110 mg. carbon per liter
the factor, O.Ol/pipet volume, to correct the results to a common 0.01-ml. sample. Plot milligrams of carbon per liter us. peak heights to obtain a calibration curve. Sample Analysis. Proceed according to the above directions for establishment of the calibration curve, and read the results from the latter. RESULTS
A calibration curve was obtained from tests with three known blends of glycerine and essentially carbon-free hydrogen peroxide and from tests with the hydrogen peroxide itself. Peak heights were used rather than peak areas because they were slightly more repeatable and, of course, easier to measure. The values for plotting were averages of several determinations, and are presented in Table I. The table shows that a carbon dioxide peak was obtained with electrolytic hydrogen peroxide alone. The data for the other samples gave an essentially linear curve, and extrapolation to a zero carbon dioxide peak indicated that the electrolytic hydrogen peroxide contained 10 mg. of carbon per liter. To ascertain the precision of the method and the small effect of variations in pipets, the data from the calibration tests were calculated back from the calibration curve with results as given in Table 11. Thirteen additional results with the 110-mg.-carbon-per-liter sample varied from 105 to 113. An estimate of precision indicated that, a t this level, duplicate results should not differ by more than 8 and, at the 200-mg.-per-liter level, by not more than 23 (95% probability). These figures probably also represent accuracy. This method has replaced the more tedious Liebig-type combustion method where 15 ml. of hydrogen peroxide sample was slowly added dropwise onto silver gauze, contained in the combustion tube, and swept by oxygen through
copper oxide a t 850" C. The effluent carbon dioxide was collected in absorbers containing aqueous barium chloride and a known amount of standard sodium hydroxide solution. Titration of the excess of the latter provided a means for measuring the absorbed carbon dioxide. During the replacement period, results by the two methods were compared. The precision of the present combustion-gas chromatographic method was slightly better than that of the combustion-volumetric method. The averages of several results by each method with 10 different samples are shown in Table 111. The data in Tables I1 and I11 demonstrate the applicability of the method for determining 0 to 200 mg. of carbon per liter in hydrogen peroxide, but it has also been applied successfully to samples containing as much as 0.5% by weight of carbon. Normal amounts of inorganic inhibitors (phosphates, stannates and nitrates) do not interfere. The method has even been used to determine carbon in river water mixed with an equal amount of base hydrogen
Table II. Carbon Contents of Glycerine and Hydrogen Peroxide Blends Computed from Peak Heights
Carbon, mg./lit'er Found Present Pipet A Pipet B 10" 9 7 12 11 36
203
32
33
10 33
33 37
199
193 201 204 208 200 214 190 a Amount ascribed t o the base hydrogen peroxide. 208
201
Table 111. Comparison of Results by the Combustion-Gas Chromatographic and the Combustion-Volumetric (Leibig) Methods
Carbon, mg./liter CombustionCombustion-GC volumetric method method 79 75 74 67 84 79 90 94 92 93 90 92 97 97 96 94 90 92 96 94
peroxide; however, as organic material and hydrogen peroxide form detonable mixtures, this source of oxygen should not be resorted to indiscriminately (3, 4). The method has bl2en in routine use more than three years. It is fast (15 minutes), and the equipment is relatively free of maintenance problems. ACKNOW LEIIGMENT
The authors are indebted to s. z. Perry and E. D. Peters for valuable
counsel and encouragement, and to the personnel of Shell Chemical Co. a t Norco, La., for contribution of the data in Table I11 and for practical evaluation of the method. LITERATURE CITED
(1) Brooks, F. R., A w z i , E. J., Shell Development C0.j Private COmmunic@tion, 1959. (2) Duswalt, A. A., Brandt, W. W., ANAL. CKEM.32, 272 (1960). (3) Monger, J. M., Sello, H., Lehwalder, D. C., J. Chem. Eng. Data 6, 23 (1961).
(4) Shell Chemical Corp., New York,
~ ; ~ ~ g , B , " ~ e ~ ~
search Data on Safety Limitations.~, (5) Streim, H. G., Boyce, E. A., U. S. Naval Air Rocket Test Station, Lake Denmark, Dover, N. Y., private communication, 1957. (6) Sundberg, 0. E., Maresh, C., ANAL. CREM. 32, 274 (1960). (7) Tenney, H. M., Harris, R. J., Zbid., 29, 317 (1957). RECEIVED for review November 26, 1962. Accepted March 15, 1963.
S pect rop(7 otome t ric Determination of 1,4-Naphthoquinone in Phthalic Anhydride C. E. GONTER and JOHN J. PETTY Pittsburgh Chemical Co., Research and Development Department, Neville Island, Pittsburgh 25, Pa.
b The reaction of qLiinones with compounds containing active hydrogen to form intensely colored compounds is used as the basis for a method to determine microgram quantities of 1,4naphthoquinone in refined phthalic anhydride. When 1,4naphthoquinone i s reacted with malononitrile in aqueous or alcoholic solution followed b y the addition of ammoniiim hydroxide or other alkali, the solution becomes blue. The intensity of the color is dependent upon pH, the solvent, and the anion concentration. Maximum absorption occurs at 583 mH, Beer's law i s obeyed, and the color i s stable for 24 hours. 1,4-Naphthoquinone can be determined in refined phthialic anhydride in concentrations as low as 0.5 p.p.m., with a standard deviation of *0.12. Furthermore, the method has been adapted to crude phthalic anhydride.
B
1,4naphthoquinone (1,P NQ) and/or its adducts and decomposition products lire highly colored, their presence in refined phthalic anhydride (PAA) is part cularly objectionable. Numerous methods have been proposed for analyzing for 1 , 4 N Q ; however, most are limited by either sensitivity or specific ty. The polarographic procedure brtsed on the reduction of 1,PNQ to 1,4-dihydroxynaphthalene at a dropping mercury electrode is satisfacto1.y when the concentration of 1,PNQ is above 0.1% and it is the only quinone present. The ultraviolet spectrophotometric method of Peters (6) lacks sensitivity when the concentrati'sn of 1 , 4 N Q in PAA is below 1%. The colorimetric method proposed by Johnson and CritcMeld ( 1 ) employing the reaction of ECAUSE
2,Pdinitrophenylhydrazine with quinones is sufficiently sensitive. However, no practical way has been found to hydrolyze PAA to phthalic acid, which is necessary because the hydrazine reacts preferentially with the anhydride. Condensation reactions of quinones with amines to form colored compounds have been described by Lacoste, Covington, and Frisone (6). Of the amines tested with 1 , 4 N Q in the presence of PAA, propylamine, isopropylamine, and cyclohexyl amine gave stable, yellowcolored solutions. The limit of detectability of 1 , 4 N Q in 3 grams of PAA was between 1.2 and 1.3 p.p.m. Investigations described by Kesting (2-4) indicate that compounds which have one or two negative groups attached to a methylene group react with quinones to form colored compounds. The color and its intensity were dependent upon the type of quinone, the pH, the solvent, and the negative groups attached to the methylene groups. Kesting used the reaction between malononitrile and 1 , P N Q as a pH indicator. The following method for the determination of 1,4-KQ is an adaptation of this reaction. EXPERIMENTAL
Apparatus and Reagents. Malononitrile, 1% solution in methanol. Reagent solution for crude PAA or liquors, 80 grams of quinone-free PAA, 96 ml. of concentrated ammonium hydroxide, and 304 ml. of water diluted to 1 liter with methanol. 1,4-Naphthoquinone, purified by steam distillation and sublimation. 1,4-Kaphthoquinone standard solution, 0.01 gram of purified 1,4-NQ in 100 ml. of methanol. Store in a dark bottle. Phthalic anhydride, recrystallized from chloroform.
Soectroohotometer. Beckman Model DK12. Absorption cells, silica, 1.0- and 10.0-cm. Calibration Procedure for Refined PAA. Dilute 5.0 ml. of 1,4-?uTQstandard t o 100 ml. with methanol. Pipet 0.0 (blank), 2.0, 4.0, 6.0, and 10.0 ml. of the dilute solution into 50-ml. volumetric flasks, each containing 5.0 grams of recrystallized PXA and 25 ml. of methanol. Add 2 ml. of malononitrile solution. Heat on a steam bath until all of the PAA is dissolved. Cool the solutions, and add 10 ml. of 9N ammonium hydroxide. Cool the solutions to room temperature. Dilute to volume with methanol. Determine the absorbance of the solutions a t 583 mp in matched, 10.0-cm., silica absorption cells. Use water as a reference and use a slit width of 0.043 mm. Refined PAA Samples. Accurately weigh 5 grams of sample into a 50-ml. volumetric flask. Add 25 ml. of methanol and 2 ml. of malononitrile solution. Treat according to the procedure for calibration. Calibration Procedure for Crude PAA. Dilute 25.0 ml. of 1,4-N& standard solution t o 100 ml. with methanol. Pipet 0.0 (blank), 3.0, 5.0, 10.0, and 15.0 ml. of the dilute solution into 50-ml. volumetric flasks. Add 2 ml. of malononitrile solution and 25 ml. of reagent solution. Heat from 5 to 10 minutes on a steam bath. Cool the solutions to room temperature. Dilute to volume with methanol. Determine the absorbance of the solutions a t 583 mp in matched, 1.0-cm., silica absorption cells. Use water as a reference, and use a slit width of 0.043 mm. Samples of Crude PAA. Accurately weigh 0.5 gram of sample into a 100ml. volumetric flask. Add 50 ml. of methanol. If the sample does not dissolve, heat on a steam bath. Dilute t o volume with methanol. Pipet A
VOL 35, NO. 6, MAY 1963
663
