LITERATURE CITED
(1) Amy, J. W., Brand, L., Baitinger, W.,
“Progress in Industrial Gas Chromatography,” Vol. 1, H. A. Szymanski, ed., p. 147, Plenum Press, New York, 1961. (2) Bosanquet, C. H., “Gas Chromatography 1958,” D. H. Desty, ed., p. 107, Butterworths, London, 1958. (3?(Bosanquet, C. H., Morgan, G,., O., Vapour Phase Chromatography, D. H. Desty, ed., p. 35, Butterworths, London, 1957. (4) Golay, M. J. E., Nature 202, 489
(1964). (51, Guild L. V., Bingham, S., Aul, F., Gas dhrornatography 1958,” D. H. Desty, ed., p. 226, Butterworths, London, 1958.
( 6 ) Haarhoff, P. C., van der Linde, H. J., ANAL.CHEM.,in press. ( 7 ) Hodgman, C. D., “Hmdbook of Chemistry and Physics, 44th ed.,
Chemical Rubber Publishing Co., Cleveland, Ohio, 1962. (8) Krige, G. J., D.Sc. thesis, University of Pretoria, Pretoria, South Africa, 1965. (9) LittlyTood, A., “Gas Chromatography, p. 40, Academic Press, New York, 1962. (10) Locke, D. C., Brandt, W. W., “Gas Chromatography, L. Fowler, ed., p. 55, Academic Press, New York, 1963. (11) Schay, G., “Theoretische Grundlagen
der Gaschromatographie,” Cha IV, VEB Verlag der Wissenschaften, gerlin, 1961.
(12) Scott, R. P. W., ANAL. CHEM.36, 1455 (1964). (13) Scott, R. P. W., ANAL. CHEM.37, 1764 (1965). (14) van de Craats, F., “Gas Chromatography 1958,” D. H. Desty, ed., p. 248, Butterworths, London, 1958. (15) Weinstein, A., ANAL. CHEM. 32, 288 (1960). (16) Ibid., 33, 18 (1961). (17) Wilke, C. R., J. Chem. Phys. 18, 517 (1950).
RECEIVED for review March 19, 1965. Accepted June 14, 1965. The Director General of the Atomic Energy Board is thanked for permission to publish this paper.
Gas Chromatographic Determination of 2,3-Diketones at Nanogram Concentrations Using Electron Affinity Detect0 r B. J. GUDZINOWICZ1 and
K. A. JOHNSON
Research Department, Jarrell-Ash Co., WaHham, Mass.
b By proper selection of operating parameters, aryl and alkyl 2,3-diketones can be quantitatively determined by gas chromatography using the electron affinity detector at concentrations ranging from 0.10 to 1.2 nanograms. Calibration data are presented for acetylpropionyl, acetylbutyryl, and acetylvaleryl, in addition to benzil, Alfuril, and p-diacetylbenzene. though p-diacetylbenzene does not possess vicinal ketone groups, it is a good electron acceptor because of its conjugated structure. This is in contrast to 2,4-pentanedione (acetylacetone) which exhibits no tendency to capture electrons. By injecting a constant volume of a known three-component diketone mixture into the chromatograph at various potentials applied to the detector, the resulting chromatographic data clearly show the effect of applied potential on both peak resolution and distortion, and give the well established applied potential/response relationship.
I
N CONTRAST to
the numerous methods available for the determination of carbonyl compounds based on either volumetric (5, 11, 18, Z2), gravimetric (8, I S ) , spectrophotometric (9, 14), or descending and centrifugal thin layer ( I @ , paper (Z), and liquid-liquid (3, 17) chromatographic techniques, few procedures have been reported in the literature specifically for the analysis of aryl and/or alkyl 2,3-diketones a t low concentrations.
I n all diketone methods reported 4, 6, 12, 20, 22), these were either qualitative, concentration-limited, or time-consuming and incapable of identifying individual species in multicomponent mixtures without prior separation. To circumvent some of the disadvantages previously encountered for carbonyl analysis, gas chromatography has been successfully applied for the separation of multicomponent samples. Recently, Soukup, Scarpellino, and Danielczik (19) described a direct method for the analysis of carbonyls as their 2,4dinitrophenylhydrazone derivatives in contrast to those using an exchange procedure with alpha-keto acids (15,II). With the flame ionization detector, Soukup et al. (19) reported that the detectability of these hydrazones was between and 10-5 mg. On the other hand, with the electron affinity detector, Gudzinowicz ( 7 ) showed that 2,4-dinitrophenylhydrazones can be quantitatively determined a t I- to 8nanogram concentration levels, the hydrazone’s favorable electron-capturing ability resulting primarily from its 2,4-dinitrophenyl radical. Although no quantitative data have appeared in the literature relative to the gas chromatographic analysis of 2,3diketones, Lovelock (10) reported that the -CO-COelectrophoric group in diacetyl showed a high affinity for electrons relative to that of chlorobenzene which was taken to be unity. Based on this observation, the present work was undertaken. The purpose of (1,
this paper is to show that both aryl and alkyl 2,3-diketones can be determined without difficulty a t 0.1- to 1.0-nanogram concentration levels. EXPERIMENTAL
The Jarrell-Ash Model 28-710 chromatograph equipped with flame ionization and electron affinity detectors and a Bristol Dynamaster hlodel lP12H560, 1-mv., 11-inch strip-chart recorder was used for these 2,3-diketone studies. The chromatographic column was made of borosilicate glass (6 feet by 3/ls-ineh i.d.) packed with 5y0 by weight of General Electric’s SE-30 methyl silicone gum rubber on 80- to 90-mesh Anakrom AS (Analabs, Inc., Hamden, Conn.). Prior to use, the packed column was conditioned a t 250” C. for 72 hours. To determine the chromatographic behavior and elution characteristics of the alkyl 2,3-diketones, the flame ionization detector (FID) was initially employed with argon as the carrier gas. For this preliminary investigation, the other F I D gas chromatographic operating parameters used were column temperature, 27” and 50” C.; injector temperature, 120” C.; detector temperature, 140” C.; air flow rate, 1.00 cu. feet/hour; hydrogen gas pressure, 5.0 p s i ; argon carrier gas flow rate, 58.2 cc./minute; sensitivity setting, 1 x 10-9 and 1 x 10+ ampere; and recorder chart speed, 2.0 minutes/inch. With the electron affinity detector (EAD), the chromatograph was maintained as noted below: column tem1 Present address, American Cyanamid Co., Stamford, Conn.
VOL. 37, NO, 13, DECEMBER 1965
1745
silanized solid support through a rubber septum. At the 1 X 10-lO ampere sensitivity setting, chloroform was preferred to acetone because it yields a much smaller, narrower peak with the flame detector per unit amount of solvent injected. Furthermore, because flame sensitivity is related directly to carbon content, the chloroform signal is further inhibited by the presence of chlorine atoms; this decreased response permitted better resolution between component and solvent peaks. For the EAD investigation] the solvents used were acetone for acetylpropionyl, acetylbutyryl, and acetylvaleryl and benzene for furil, benzil, and p-diacetylbenzene. Whereas the alkyl 2,3-diketones were evaluated a t 25 volts, the detector was operated at 30 volts for the furan/beneene derivatives.
I
16
RESULTS AND DISCUSSION
I
1 2 1 0 8 6 4 RETENTION TIME, MINS.
14
2
0
Figure 1. Gas chromatographic separation of ( I ) acetylpropionyl, (2) acetylbutyryl, and (3) acetylvaleryl at 27' and 50' C. (flame ionization detector)
perature, 25", 40", and 180" C.; injector temperature] 140' and 240' C.; detector temperature, 210' C.; nitrogen carrier gas flow rate, 72.8 cc./minute; detector potential, 25 and 30 volts; sensitivity setting, 1 X ampere; and recorder chart speed, 2.0 minutes/ inch. Conditions used for the analysis of furil, benzil, and p-diacetylbenzene were : column temperature, 180' C. ; injector temperature, 240' C.; and detector potential, 30 volts. For F I D calibration purposes, 1-p1. Hamilton microsyringe injections of microgram amounts of 2,3-diketones in either acetone or chloroform as solvent were made directly onto the coated
00
1 0.0
0.1
'
0.2
1
1
I
0.1
0.2
Figure 2. tion
03
'I
I 0.3
YICROOOAMS 0.4 0.5 0.6
;I
I
1
I
0.4 0.5 0.6 NANOQRAMS
0.1
0.8
0.9
i
i
I
0.1
0.8
0.9
0
l!O
Peak height vs. concentra-
FID, microgram scale) EAD, nanogram scole
1746
1.0
ANALYTICAL CHEMISTRY
Preliminary gas chromatographic feasibility studies were performed with the flame ionization detector. At 27" C. and a 1 x 10-9 ampere gain setting, the three alkyl diketones in acetone as solvent can be chromatographed easily and determined with the flame detector in 14 minutes (Figure 1). Furthermore, nearly linear relationships between peak heights and 0.5- to 6.0-pg. amounts of each component injected are obtained. With chloroform as solvent and a t a sensitivity of 1 x 10-'0 ampere, lower concentrations of acetylvaleryl can be detected. For example, the valeryl derivative shows good linearity as noted in Figure 2 in the range of 0.1 to 1.0 pg. (upper scale). However, a t this higher column operating temperature (50' C.), acetylpropionyl and acetylbutyryl cannot be resolved because both are eluted as a single peak. However, the limits of detection can be lowered nearly a thousandfold with the electron affinity detector ("1 X 10-lo gram) provided that proper operating parameters such as column temperature and detector voltage are experimentally established to yield maximum sensitivity. For example, superimposed chromatograms obtained a t column temperatures of 25' and 40' C. with a detector voltage of 25 volts for acetylpropiony!, acetylbutyryl, and acetylvaleryl are shown in Figure 3. The data show that better separations result a t 25" C., whereas more favorable peak symmetries occur a t the higher column temperature. However, by injecting varying amounts of each alkyl diketone separately a t 40' C., nearly linear relationships between peak heights and nanograms are obtained (lower scale, Figure 2). For 0.32, 0.59, and 0.50 nanogram of acetylbutyryl, acetylpropionyl, and acetylvaleryl, respectively, injected separately and five times consecutively into the chromatograph, the mean of the five peak measurements for each
14
I2
I I I IO 8 6 4 RETENTION TIME, MINS.
2
0
Figure 3. Gas chromatographic separations of ( I ) acetylpropionyl, (2) acetylbutyryl, and (3) acetylvaleryl (electron affinity detector)
component was as follows: acetylbutryryl, 430; acetylpropionyl, 265; acetylvaleryl, 255. The relative standard deviations for the butyryl, propionyl, and valeryl compounds were 3.3, 3.1, and 3.4%, respectively. The importance of selecting the proper cell voltage cannot be overemphasized. Whereas the form of the theoretical current/voltage curve should be gaussian in a d. c. polarized cell, in actual practice a t a single flow rate, the experimental current/voltage curve is distorted by space charge effects as shown by curve A in Figure 4. This was established a t a 1 x 10-8 ampere sensitivity range by applying voltage to the detector in &volt increments; and the total current flowing was recorded when the system stabilized after each increase in voltage. At approximately 80 to 90% of the maximum value of the standing current (1.18 X 10-8 ampere) the optimum operating voltage (25 volts) for the detector is 350 I
I
i1.4
Figure 4. Relationships between current (A) and peak response (6, C, and D) and applied potential
benzil, furil, and p-diacetylbenzene can be separated in less than 5 minutes (Figure 7). Like the alkyl derivatives, these compounds exhibit good quantitative characteristics as indicated by their nearly linear plots for nanograms injected us. either peak heights or peak areas. From the peak area data, the sensitivity per unit weight of material decreased as expected in the following manner: benzil > furil > p-diacetylbenzene. The greater electron affinity exhibited by benzil is attributed to its more favorable conjugated structure. Although p-diacetylbenzene does not possess vicinal ketone groups, it is a good electron-acceptor, having a -CO-C=C-C=C-COstructure which shows good electron-capturing 16
14
12
IO 8 8 4 RETENTION TIME, MINS.
2
0
Figure 5. Effect of applied potential on sensitivity, resolution, and peak symmetry (5 to 30 volts)
determined. Because response to sample entering the detector is a function of the free electron density or concentration, sensitivity is increased as the potential is increased in proportion to the standing current, reaching a maximum when the saturation level is attained. In Figure 4, curves B , C, and D obtained for 8.5, 9.5, and 10.0 nanograms of acetylbutyryl, acetylpropionyl, and acetylvaleryl, respectively, exhibit maximum responses a t approximately 25 volts, a voltage slightly lower than that theoretically required for saturation. Apparently, the effect of the positive ion space charge through molecular ion recombination is reduced by the presence of sample molecules. At potentials exceeding that required for maximum responses, the probability of ion recombination and electron absorption is reduced by further acceleration of the charge carriers in the cell, the sensitivity being nearly inversely proportional to the square of the applied potential. Another interesting observation can be made from the sensitivity/voltage chromatographic data. By superimposing the chromatograms obtained for constant amounts of these diketones injected into the chromatograph a t various potentials as shown in Figures 5 and 6, the data suggest that both resolution and peak distortion are also functions of the applied potential. This might be important in some instances where, with some sacrifice in sensitivity, resolution of components is desired. At a column temperature of 180' C. and a 30-volt cell potential, higher molecular weight diketones such as
Figure 7. Superimposed chromatograms of benzil, furil, and p-diacetylbenzene at 180" C. (electron affinity detector)
(4) Feigl, F., Neto, C. C., Ibid., 28, 397 (1956). (5) Fritz, J. S., Yamamura, S. S., Bradford, E. C., Ibid., 31, 260 (1959). (6) Fulmer, E. I., Kolfenbach, J. J., Underkofler, L. A,, IND.ENG.CHEM., ANAL.ED. 16,469 (1944). (7) Gudzinowica, B. J., Jarrell-Ash Co.,
Waltham, Mass., unpublished work.
.SO!
.-...,.
R
1
4
I
2
.___.. __...I
/ , I !
'
,j
.
l O e 6 4 RETENTION TIME, MINS.
-_-_._ ."4 ~
2
0
Figure 6. Effect of applied potential on sensitivity, resolution, and peak symmetry (35 to 60 volts)
qualities. This is somewhat analogous to the quinone structure, -CO-C= C-CO-, for which Lovelock (IO)determined an electron affinity value of -5000. However, a p-diketone such as 2,4-pentanedione (CH3-CO-CH2CO-CH3) shows no tendency to capture electrons. ACKNOWLEDGMENT
The authors thank Fritzsche Brothers, Inc., New York, for samples of acetylpropionyl, acetylbutyryl, and acetylvaleryl used for this study. LITERATURE CITED
(1) Adkins, H., Cox, F. W., J . Am. Chem. SOC.60, 1151 (1938). (2) Buyske, D. A., Owen, L. H. Wilder, P., Jr., Hobbs, M. E., ANAL. HEM. 28, 910 (1956). (3) Corbin, E. A,, Ibid., 34, 1244 (1962).
(8) Iddles, H. A,, Jackson, C. E., IND. ENG.CHEM.,ANAL.ED. 6, 454 (1934). (9) Lappin, G. R., Clark, L. C., ANAL. CHEM.23, 541 (1951). (10) Lovelock, J. E., Nature 189, 729 (1961). (11) Mitchell, J., Jr., Smith, D. M., Bryant, W. M. D., J . Am. Chem. SOC. 63. 573 (1941). (12) 'Pasternak,' R., Helv. Chim. Acta 31, 753 (1948). (13) Plein, E. M., Poe, C. F., IND.ENG. CHEM.,ANAL.ED. 10,78 (1938). (14). Pool, M. F., Klose, A. A,, J . Am. 011Chemists' SOC.28, 215 (1951). (15) Ralls, J. W., ANAL. CHEM.32, 332 (1960'). \__._
(16) Rds-mus, J., Deyl, Z., J . Chromatog. 6,187 (1961). (17) Schwartz, D. P., Ibid., 9, 187 (1962). (18) Siggia, S., Maxey, W., IND.ENG. CHEM.,ANAL.ED. 19, 1023 (1947). (19) Soukup, R. J., Scarpellino, R. J., Danielczik, E., ANAL. CHEM.36, 2255 (1964). (20) Speck, J. C., Jr., Ibid., 20, 647 (1948). (21) Stephens, R. L., Teszler, A. P., Ibid., 32, 1047 (1960). (22) Trozzolo, A. M., Lieber, E., Ibid., 22, 764 (1950).
RECEIVED for review September 2, 1965. Accepted October 6, 1965. Analytical Division, 150th Meeting, ACS, Atlantic City, N. J., September 1965.
VOL. 37, NO. 13, DECEMBER 1965
1747
