Analysis of Terpene Hydrocarbons and Related Compounds by Gas Chromatography W. J. ZUBYK' and A. Z. CONNER Research Cenfer, Hercules Powder Co., Wilmingfon, Del.
b
The qualitative and quantitative analysis of natural and synthetic mixtures of terpenes i s difficult and time-consuming. Gas chromatography i s of great potential value in this field. Relative retention data for 44 terpene hydrocarbons and related compounds are given for didecyl phthalate and Carbowax 4000 columns. The use of these data in identifying the constituents of a monocyclic and a bicyclic terpene mixture is described and the limitations of the method are discussed. Some of the quantitative aspects of the gas chromatography of terpenes were investigated, and the results obtained in the analysis of known mixtures are presented. The information obtained in the above work was applied to the analysis of apinene hydration products and of a sample of crude wood turpentine.
T
HE CHARACTERIZATION and quantitative analysis of mixtures of terpene hydrocarbons and their derivatives are extremely difficult. Most natural and synthetic terpene mixtures contain many compounds, and large groups of these compounds include geometric, positional, and optical isomers that have similar physical and chemical properties. I n addition, many terpenes readily isomerize or oxidize. Gas chromatography possesses inherent advantages that make it particularly attractive for the characterization and quantitative analysis of terpene mixtures. These include high separation efficiencies, short residence times in the chromatographic column, the use of an inert atmosphere during analysis, freedom from azeotropes, and the applicability to very small samples. I n addition to providing a direct method of analysis for many terpene mixtures, gas chromatography has proved to be a powerful adjunct to ultraviolet, infrared, and mass spectroscopic techniques. Other early investigators have recognized the potential value of gas chromatography for the analysis of terpenes. Bernhard (1, 2) has used it and other techniques in an attempt to characterize lemon oils. Kaves (6, 7)
* Present address, Hercules Powder Co., Brunswick, Ga. 912
ANALYTICAL CHEMISTRY
and coworkers have analyzed and separated cis-anethole from essential oils for toxicity studies. Liberti and Cartoni (6) have suggested a scheme for the characterization of essential oils in which gas chromatography is applied to fractions separated by other physical and chemical methods. Stanley and Mirov (8)have reported the use of gas chromatography in the analysis of pine turpentines. Groth (3) has applied it and infrared techniques in an extensive investigation of the composition of Swedish turpentines. Because of the complexity of most synthetic and naturally occurring terpene mixtures, many problems related to their analysis remain unsolved. This paper presents preliminary data obtained as a part of a long-range investigation of the application of gas chromatography to the analysis of mixtures of terpenes. EXPERIMENTAL
G a s Chromatography Apparatus. The apparatus used in the majority of this work was a Perkin-Elmer Vapor Fractometer Model 154A modified as follons: The air bath thermostating was changed to include a 100-watt cartridge heater controlled by a thermocouple attached to a Brown potentiometer pyrometer. The voltage through the main heater was set by a variable transformer to maintain a temperature just below the control point. The auxiliary 100-watt heater then cycled to give temperature control in the air bath to 50.5' C. The outlet from the thermal conductivity cell was replaced by a straight 6-inch length of stainless steel tubing 1/4 inch in outside diameter to which a Luer-Lok fitting had been soldered. This exit tube extended through a 3/4inch hole drilled in the back of the air bath directly opposite the cell outlet fitting. Hypodermic needles and collection devices could be attached to Chis tube to trap separated fractions as soon as they left the thermal conductivity cell. Some data were obtained on an instrument constructed in this laboratory. The column and detector were mounted in a 14 X 14 X 16 inch thermostated air bath designed for operation in the range of 40' to 225' C. Temperature could be controlled t o i 0 . 5 " C. For ordinary analytical work, col-
umns '/4 inch in outside diameter and up to 20 feet in length could be accommodated. The detector was a GowMac, 4-filament, Yodel 9285, thermal conductivity cell. The carrier gas flow rate through both gas chromatography units was maintained constant within 0.2 to 0.3 ml. per minute. Preparation of Columns. The solid supports used in this work were all diatomaceous earth products manufactured by Johns-Manville Co.: Celite 545, 50- to 100-mesh; Sil-0-Cel C-22 firebrick, 35- to 60-mesh; Chromosorb C-44857, 35- to 80-mesh; and Chroniosoi b C-48560, 60- t o 100-mesh. The Celite 545 and the C-22 firebrick 11-ere washed and size-graded before use. The two types of Chromosorb are manufactured specifically for gas chromatography and were used without treatment except for removal of fines by water washing. The t\To stationary liquid phases were didecyl phthalate (Deecy Products Co., 120 Potter St., Cambridge 42, Mass., trade-mark Staflex) and a poly (ethylene glycol) (Carbowax 4000, Union Carbide Chemicals Co.). Preparation of Column Packings. Column packings were prepared by dissolving a weighed amount of liquid phase in a low boiling solvent and slurrying the resulting solution with a weighed amount of solid support in a 2-liter, creased, round-bottomed flask. The flask n.as then attached to a rotating evaporator and the solvent removed under vacuum during continuous rotation and mixing. This method is preferred over conventional handstirring because it is rapid, requires less attention, minimizes liquid phase migration, and results in very uniformly coated packings. Microscopic examination of Chromosorb particles after coating by hand stirring has occasionally revealed the presence of particles that appear to contain less coating than others. I n addition, all other factors being equal, some hand-stirred column packings have caused isomerization of sensitive terpenes, while those prepared with the rotating vacuum evaporator have not. Diethyl ether was used as the solvent for didecyl phthalate; methylene chloride was used for Carbowax 4000. Selected lengths of stainless steel tubing I/4 inch in outside diameter and inch in inside diameter were filled with the dry, free-flowing packings prepared as described above. The packings were poured into the columns a t a
slow uniform rate while vigorously vibrating the columns with an air-driven vibrator. After the insertion of glass wool plugs in each end of the tubing, the columns were bent or coiled to fit the respective instruments. Conditioning was carried out by passing a stream of helium through the column while heating for several hours at the maximum proposed operating temperature. Compounds for Testing. T h e 44 terpene hydrocarbons a n d related compounds used in this work were obtained in t h e course of a long-range program designed t o build u p a stock of purified materials for t h e study of terpene reactions and for use as analytical standards. After chemical treatment and/or preliminary isolation, t h e compounds were purified b y fractional distillation through columns of approximately 100 theoretical plates a t reflux ratios of about 100 to 1, and pressures in the range of 50 to 100 mm. of mercury. Sample Collection. K h e n the constituent of a mixture l\-as t o be collected for e.;amination b y infrared spectroscopy, t h e effluent gas from t h e column was passed through a 20-gage hypodermic needle into a small test tube (103 mm. long X 9 mm. in outside diameter, with t h e bottom 30 mm. constricted t o 4 mm. in outside diameter) containing carbon disulfide. A clean needle was used for each collection to avoid contamination and the volume of carbon disulfide was maintained a t 0.5 to 1.0 ml. For collection periods of over 2 to 3 minutes, the collection tube was cooled in an ice bath to minimize loss of carbon disulfide. A Beckman IR-4 spectrophotometer m s used to obtain the infrared spectra. RESULTS AND DISCUSSION
Qualitative Analysis. Relative Retention Ratios. It is common practice t o relate retention times or volumes t o those of a reference compound. These relative retention data provide a convenient method for t h e identification of constituents of mixtures. a-Pinene was selected as t h e referencc compound because i t is frequently prrsent in many natural and synthetic terpene mixtures. Measurement of the chart distance between a n air peak and the maximum of a compound peak gives a value proportional to the retention volume corrected for the dead volume of the apparatus. The ratio of this value to the corresponding value for e-pincne is called the relative retention ratio. The ratios obtaincd for a number of terpene hydrocarbons and related compounds are listed in Table I. Corrected retention volumes, ( V i ) ' (4), for cypinene are listed a t the end of this table. The operating conditions are shown in Table 11. Didecyl phthalate was nonselective as a liquid phase for the separation of
Table I.
Relative Retention Ratios for Terpene Hydrocarbons and Related Compounds
Relative Retention Ratio Compound Monocyclics a-Pyronene 8-Pyronene 3-p-Menthene trans-p-Menthane cis-p-Menthane a-Phellandrene @-Phellandrene a-Terpinene 1-p-Menthene 4(g)-p-Menthene Dipentene 7-Terpinene 3,8-p-PI.lenthadien~ 2,4(8)-p-RIenthadiene Terpinolene hromatics Cumene m-Cymene p-Cymene o-Cymene Bicyclics Bornylene a-Pinene a-Frenchene Camphene @-Pinene Isocamphane trans-Pinene cis-Pinane 3-Carene Alcohols a-Frenchyl alcohol @-Fenchylalcohol trans-Dihydro-a-terpineol @-Terpineol cis-Dihpdro-a-terpineol Borneol Isoborneol a-Terpineol Ketones and ethers 1,4-Cineole 1,8-Cineole Fenchone Estragole trans-Anethole IIiscellaneous Cyclofenchene Tricyclene Myrcene
Carboiyax
Ditiecpl Phthalate
Boi1i:g Point, C.
110°
c.
130" c.
15FE 0.08
4000 130" C. 1.02 1.35 1.18 0.97
157 169 169 170 17 1-172 168-1 70 174-176 175 176 176 176.5 182 183.5 185-186 18G
0.99 1.25 1.42 1.43 1.50 1.81 2.28 2.08 1.90 2.04 2.16 2.72 3.06 3.66 3.18
1.00 1.21 1.35 1.35 1.45 1.78 2.24 1.89 1.83 1.90 2.04 2.47 3 . 2ti 2.83
1.34 1.35 1.45 1.75 2.12 1.80 1.i7 1.85 1 ,no 2.46 2.56 2 92 2.75
152.5 175 2 177 178.3
1.27 2.45 2.46 2.94
1.26 2.25 2.35 2.38
1.I7 2.12 2.13 2.40
2.02 3.14 3.15
1-16 156 157 158 165 166
0.80 1.OO
0.83
1.13 1.16 1.52 1.45
1.14 1.20 1.44 1.40 1.34 1.41 1.74
0.86 1.00 1 16 1.21 1. 4 l 1.40 1.37 1.40 1.66
0.86 1.00 1.22 1.28 1.58 1.26 1.19 1.25 1.82
3.79
1.00
...
1.10
1.96 2.46 2.09 L72
1.71
2.29 2 88 3.12
3 .$l
...
...
1.31
168 170
1.39 1.77
201 201
...
...
6.10 6.49
5.13 5.60
. . ...
209 209
8.21
6.90 7.47
5.60 6.24
...
...
... ...
7.56
6.14 7.10 7.89 7.98
...
1.82 2.08 3.77 7.82 14.4
...
0.68 0.94
0.65 0.96 1.70
210 212 214 (subl.) 219 172 174
...
...
2.12
1.94 2.24 4.08 ...
... 2.33
193
...
4.92
216 237
... ...
143 152 167
0.64 0.90 1,46
...
...
0.67 0.91 1.44
1.33
... ... ... ... ...
...
...
...
Retention volumes, (VE)',for a-pinene corrected for pressure drop and dead volume, in ml. of helium a t column temperature and outlet pressure, are: Didecpl Phthalate Carbowas 4000 100" c. 130' C. 15007. 130" C. (T.;)', ml. 625 356 205 261
Table II.
Operating Conditions
Didecyl Phthalate Instrument
.. ". Helium f l rate, ~ ml./min. ~ Column length, ft. Temperature, O C. Inlet pressure, p. s. i. g. Outlet pressure Recorder range, mv. Chart speed, inches/hour
Carbowax 4000
Vapor Fracto]
,L.
45 6.5
110, 130, 150 13.2, 13.9, 15.0
-4tmospheric 0-2.5
24
45 6
130 5.9
Atmospheric 0-10 16
VOL. 32, NO. 8, JULY 1960
913
r, S - P I N A H K I
A,R
-
TIMi
-
PlMPtt 1"
I r
*
(8)
* DlPEYTElE
11s
~~
- - , u p
Figure 1. Chromatograms of synthetic terpene mixtures on didecyl phthalate 6.5-foot column; 1 10' C. 45 ml. o f helium p e r minute
A.
-
Bicyclic Mixture Cyclofenchene Tricyclene a-Pinene a-Fenchene Camphene @-Pinene Isocamphane czs-Pinane 3-Carene
The results obtained in chromatographing the test mixtures on the didecyl phthalate column are shown in Table I11 and in Figure 1, -4 and B.
914
ANALYTICAL CHEMISTRY
U
6-foot column; 130' C. 45 ml. o f helium p e r minute
Bicyclic
A. B.
Monocyclic Mixture Cumene 3-p-Menthene trans-p-Menthane czs-p-Menthane a-Terpinene 4(8)-p-Methene Dipentene p-Cymene y-Terpinene 3,8-~-1Ienthadiene Terpinolene a-Pinene
-
Figure 2. Chromatograms of synthetic terpene mixtures on Carbowax 4000
B. Monocyclic
terpene hydrocarbons with the compounds generally eluted in the order of their boiling points. Carbowax 4000 shows some selective retention for unsaturated compounds. The two columns complement each other in that each will perform ceitain separations inore efficiently. Other liquid phases tested included mineral oil, tritolyl phosphate, Apiezon J and N, ethyl tetrahydroabietate, dihydroabietyl alcohol, and an alkyl phenol-ethylene ovide adduct. Kone of these materials posqessed significant advantages over those reported. To demonstrate the use of relative retention ratios in the characterization of terpene mixtures, t n o synthetic blends weie prepared. One mixture contained approximately equal parts by weight of 11 monocyclic terpenes plus a-pinene. The other contained approximately equal parts by weight of nine bicyclic and tricyclic terpenes. The compounds employed in these mixtures were:
mmt
2-TERP
Tiut
Similar data for the Carbowax 4000 column appear in Table IV and Figure 2, A and B. I n each figure the peaks are numbered consecutively in order of their appearance. Each table lists the experimentally determined relative retention ratio of each peak and the standard ratios for the constituents of the mixtures. I n most cases, agieement between the experimental and standard ratios was satisfactory and identifications could be made. However, some significant deviations viere noted, particularly where a peak contained tn-o or more unresolved constituents. On the basis of these and other results obtained from the analysis of synthetic mixtures and samples of known composition. the relative retention ratios in mixtures mere reproducible within 1 3 to 5%. This margin or error could be significantly reduced n i t h more precise temperature control, preferably to within j ~ 0 . 1 ' C. The use of reference materials with retention times greater than a-pinene would also improve the reproducibility of the relative retention ratios of the higher boiling compounds. The utility of any method employing relative retention ratios for qualitative analysis is dependent on the number of pure compounds available, the complexity and composition of the sample, and the completeness of resolution of the sample constituents. I n the case of a large group of compounds such as the terpene hydrocarbons and related compounds, the task of acquiring a n adequate file of retention timc data is substantial. Purified samples of terpenes
Bicyclic Monocyclic
are not readily available, and considerable work is involved to isolate them. Also, when new liquid phases are tested or higher efficiency columns are constructed, the entire series of standard compounds must be rerun. The analysis of complex mixtures by gas chromatography is not necessarily difficult unless many of the components possess similar rrtention times. However, the composition of the sample often limits the completeness of identification of the constituents. For example. t\To compounds that are marginally separated can readily be identified when they are present in approximately cqual amounts, but small amounts of one cannot be detected in large amounts of the other. Almost all of the above difficulties can be eliminated if complete resolution of all compounds is achieved. Isomerization. During t h e testing of various columns for t h e analysis of terpene mixtures, it became erident t h a t reaction n-as occurring on some of the packings. K h e n samples of pure a-pinene were chromatographed on these columns, sereral nen peaks appeared. The compounds corresponding to these peaks Il-ere collected and identified by infrared analysis as camphene and dipentene. Similar experiments with 6-pinene showed that a-pinene, camphene, dipentene, and a-terpinene were being formed. The nature of these compounds indicated that an acid-type isomerization )vas taking place. T o trace the source of the acidic activity, glass columns \%-ere packed with uncoated Celite 545, C-22 firebrick, and Chromosorb C-
44857. Chromatographing of samples of CY- and p-pinene on these columns, collection, and infrared analysis of the eluted compounds showed that isomerization had occurred in all cases. The degree of isomerization on Celite 545 was considerably less than the other two materials \There the reaction was essentially quantitative. Evaluation of other solid supports showed that a flux calcined aggregate known as Chromosorb C-48560 showed no activity ton-ard CY- and p-pinene and has since been selected as the standard support for terpene analysis. Testing of various liquid phases also showed the presence of free acidity in some of the compounds. One conimercial batch of didecyl phthalate possessed sufficient acidity to isomerize CY- and P-pinene. The didecyl phthalate recommended in the Experimental Section has thus far been satisfactory. I n testing the two columns used in this work, i t was also established that, if the reactive supports were completely coated with sufficient unreactive liquid phase, no significant isomerization OCcurred. The three types of tubing commonly employed for gas chromatography columns-glass, stainless steel, and copper-!\ ere filled with a noiiisomerizing packing and tested with samples of CY- and P-pinene. The copper column caused isomerization but the glass and steel columns showed no effect. Quantitative Analysis. Khen a thermal conductivity cell detector is employed with helium as t h e carrier gas, t h e area under each peak on t h e chromatogram is approximately proportional t o t h e amount of t h e constituent represented by t h a t peak. Although for very accurate work i t is invariably necessary t o calibrate t h e apparatus, satisfactory results can sometimes be obtained by measuring the areas of all of the peaks and normalizing. This is most often the case \Then a relatively close range of similar compounds is involved. K h e n only the relative increase or decrease of the amounts of various components during the course of a reaction is follon-ed, calihration is often not necessary. Some of the quantitatire aspects of the gas chromatography of terpenes were investigated. Table I11 lists the known weight per centage compositions of the monocyclic and bicyclic mixtures used in the qualitative n-ork. These tables also include the area percentages obtained by measuring the peak areas by two different methods and normalizing the results. Areas IT-ere measured by planimeter and were also calculated by multiplying the peak height by the peak width a t half height. When the planimeter was used, the incompletely resolved peaks mere defined (height) by dropping perpendicular lines from
the point of overlap to the base line (Figure 1, B ) . When the procedure of multiplying the peak height by the width at half height TT-as used, the areas of the clearly defined halves of the incompletely resolved peaks were measured and the resulting areas doubled. The area of peak 4 in Figure 1, B, was estimated by subtracting the contributions of peaks 3 and 5 from the
Table 111.
Chromatography of Terpene Mixtures on Didecyl Phthalate at 1 10' C.
Exptl. Relative Retention Peak Ratio YO.
...
1
2 3
1.00 1.2s
4
1.39
5 6
1.51 2.01
7
2.22 2.55
i9
2.73
10 11
2.98 3.20
1 2
...
0.64
4
5
1.00 1.19
G
1 49
7
1.76
0.92
3
Table IV.
Standard Relative Retention Area, % Compound Ratio T t . r0 Triangulation Planimeter Monocyclic Terpene Mixture Air ... ... ... ... a-Pinene 1.00 7.9 7.2 7.4 Cumene 3-p-Slenthene trans-p-Xenthane cis-p-?\fenthane 4(S)-p-Menthene a-Terpinene Di entene p-Ey mene 7-Terpinene 3,8-p-lIenthadiene Terpinolene
1 2
1.00
...
0
1.11 1.18 1.72
6
2.03
8 9
2.30 2.82 3.12
10
3.39
1 2 3
...
0.61 1.oo
4
1.31
5
1.60 1.86
G
12.2 8.4
3,06 3.18
7.7 7.6
2.72
S.3 9.0
j17.0 10.9 10.2 8.8 7.6 6.5
...
12.6 10.2 9.1
7.3 6.4
...
11.6 12.4 10.6
11.7 10.6 11.2
8.8
9.3
Chromatography of Terpene Mixtures on Carbowax 4000 at 130" C.
Peak 1-0.
4
8.0
2.04 3.08 2.16 2.49
Bicyclic Terpene SIixture -4ir ... *.. Cj-clofenchene 0 . 6 4 11.0 Tricyclene 0.90 10.8 a-Pinene 1 . 0 0 11.1 a-Fenchene Camphene cis-Pinane Isocamphane 6-Pinene 1 . 7 7 11.6 3-Carene
Exptl. Relative Retention Ratio
3
total area, assuming that all peaks r e r e symmetrical. The results obtained were in moderately good agreement with the actual composition, with the planimeter results being significantly better. I n the monocyclic mixture, the greatest deviations from the known composition were in the values for p-cymene and terpinolene. The former is an aromatic
Compound 1Ionocyclic Terpene Mixture Air trans-p-Menthane a-Pinene cis-p-Menthane 3-p-Menthene 4(8)-p-hlenthene Cumene a-Terpinene Dipentene -pTerpinene 3,s-p-RIenthadiene p-Cymene Terpinolene Bicyclic Terpene Mixtiire Air Cyclofenchene Tricyclene a-Pinene a-Fenchene Isocamphane cis-Pinane Camphene &Pinene 3-Carene
Standard Relative Retention Ratio
... 0.97 1.00 1.10 1.18 1.71 2.02 2.09
2.29
2.88
3.12 3.15
3.51
0.65 0.96 1.00 1.22 1.26 1.25 1.28 1.58 1.82
VOL. 32, NO. 8, JULY 1960
0
915
I iirr
-
Figure 4. phthalate
Figure 3. Chromatogram of sample of partially hydrated a-pinene on didecyl phthalate
Analysis
2
1
.i
Area,
Compound
Wt. 70
70
Diff.
Wt,%
Diff.
\Tt. ' L
a-Pinene Dipentene Terpinolene or-Terpineol
79.2 5.3 5.6 9.9
77.3 6.4 6.5 9.7
-1.9 +0.9 -0.2
59.6 10.0 10.5 19.8
58.2 10.6 11.5 19.8
-1.4 $0.6 $1.0 0.0
40.1 15.2 15.2 29.5
a-Pinene Dipentene Terpinolene a-Terpineol
20.5 20.3 19.8 39.3
4 19.0 21.0 21.6 38.4
-1.5 +0.7 +1.8 -0.9
11.0 20.0 19.8 49.2
5 10.0 20.4 21.8 47.9
-1.0 +0.4 +2.0 -1.3
...
Table VI.
Peak No. 1
2 3 4 5 6 7 8 9 10 11 12
Composition, Area, 5%
NO. 1 2 3
4 5
6 7
916
fl.1
4.5
0.3 9.6 0.8 12.6 2.6 1.3 0.9 33.4
( (
37.0 16.1 16.6 30.3
DIE. -2.9 $0.9 +1.4 +0.8
6 25.2 25.1 49.7
2i.k 25.7 47.6
+1:4
f0.6 -2.1
Identification Gas chromatography
Air Solvent a-Pinene Camphene a-Terpinene Dipentene 7-Terpinene Terpinolene a-Fenchyl alcohol No reference compound No reference compound a-Terpineol
... 34.0
Area,
Analysis of Hydration Products of a-Pinene
Table VII.
Peak
Chromatogram of wood turpentine on didecyl
of Known Terpene Mixtures on Didecyl Phthalate at 150" C.
Area,
Infrared
...
...
a-Pinene Camphene a-Terpinene, trace 1,4- and 1,s-cineole Dipentene, trace p-cymene 7-Terpinene Terpinolene a-Fenchyl alcohol No absor tion Unidentiled a-Terpineol
Analysis of Crude Wood Turpentine
Esptl. Relative Reten tion Ratio
Area, %
1.00 1.08 1.13 1.21 1.32
77.5 2.9 8.4 6.2 4.0
1.80
0.7 0.3
2.06
ANALYTICAL CHEMISTRY
Identification a-Pinene Unidentified a-Fenchene Camphene Any trans-Pinane or all 3-p-ment.hane trans-p-Menthane 3-Carene Dipentene
i
p
All identifications based on relative retention ratios 13-foot column; 1 3 0 ' C.; 45 ml. o f helium p e r minute
6.5-foot column; 150' C.; 45 ml. o f helium p e r minute
Table V.
lint
compound and would be expected to differ significantly in its thermal conductivityresponse from the other terpene hydrocarbons. I n both the monocyclic and bicyclic mixtures the accuracy of the results seemed somewhat poorer at the higher boiling end-vie., terpinolene and 3-carene. I n all cases the results r e r e within 1 to 2% absolute of the true value. It seems preferable t o treat groups of unresolved peaks as one peak in quantitative estimations. Prior to the analysis of some apinene hydration products (see following section), six known mixtures of the four main constituents of these samples were analyzed quantitatively. Because all four peaks were completely separated from each other, the triangulation method of area estimation was used. The known sample compositions and experimentally determined area percentages are shown in Table V. Again moderately good agreement was observed with maximum deviations from the true values of 1 to 2% absolute. Because of the random nature of the deviations, and because high accuracies were not required for these analyses, calibration factors were not employed. Analysis of a-Pinene Hydration Products. T h e d a t a and techniques discussed above were applied t o t h e analysis of a-pinene hydration products. Gas chromatography on t h e didecyl phthalate column was used t o follow t h e course of t h e reaction during hydration, and t o identify some of t h e minor constituents of t h e reaction mixtures. Figure 3 shows a chromatogram obtained for a typical reaction mixture. The quantitative analysis of this sample is shown in Table VI. I n addition to four major constituents, the presence of at least five minor constituents is indicated. Three of the five minor constituents were tentatively identified on the basis of their relative retention ratios. To confirm these identifications, a large sample of the hydration mixture was
fractionated and the various cuts from the distillation were analyzed by gas chromatography. Large samples (100 pl.) of the cuts rich in the minor constituents were rechromatographed, the desired peaks collected in carbon disulfide traps, and their infrared spectra obtained. The gas chromatography and infrared identification are compared in Table VI. The peak numbers correspond to those shown in Figure 3. Agreement between the two methods was good for all of the constituents, with the infrared spectra revealing the presence of several additional trace components. Camphene (peak 4) was present in the starting material and was not a product of the reaction. Analysis of Wood Turpentine. Figuie 4 was obtained by chromatographing a sample of crude wood turpentine on didecyl phthalate. The area percentages and the identifications made on the basis of relative retention ratios are given in Table VII.
Infrared analysis of this sample showed the presence of 79% a-pinene, 14% of a compound containing an exocyclic terminal methylene group (calculated as camphene), and 4% tricyclene. The absence of the tricyclene peak in the chromatogram is probably due to the fact that it is obscured by the large a-pinene peak. The (Ypinene values by both methods show good agreement, and the 14y0 of a compound or compounds containing an exocyclic terminal methylene group is accounted for by the presence of 8.4% a-fenchene and 6.2% camphene. Three of the four additional minor constituents were also tentatively identified by gas chromatography.
LITERATURE CITED
(1) Bernhard, R. A., Food Research 23,
ACKNOWLEDGMENT
213 (1958). (2) Bernhard, R. A., J . Assoc. 0 8 c . Agr. Chemists 40, 915 (1957). (3) Groth, A. B., Svensk Papperstidn. 61, 311 (1958). (4) Johnson, H. W., Stross, F. H., ANAL. CHEM.30, 1586 (1958). (5) Liberti, A., Cartoni, G. P., “Gas Chromatography 1958,” D. H. Desty, ed., p. 321, Academic Press, New York, 1958. (6) Naves, Y. R., CGmpt. rend. 246, 1734 (1958). ( 7 ) Eaves, Y . R., -4drizi0, P., Favre, C., Bull. SOC. chim. France 1958, 566. (8) Stanley, R. G., hIirov, N. T., Division of Agricultural and Food Chemistry, Abstract 16, 133rd Meeting, .4CS, San Francisco, Calif., April 1958.
The authors acknowledge the technical assistance of W. A. Smith in obtaining some of the data, and of W. C. Kenyon for helpful discussion throughout this work.
RECEIVEDfor review April 27, 1959. Accepted April 21, 1960. Symposium on Terpene Chemistry, ACS Southeastern Meeting, Gainesville, Fla., December 12, 1958.
Cation Exchange Separation and Spectrophotometric Determination of Microgram Amounts of Rhodium in Uranium-Base Fissium Alloys J. 0.KARTTUNEN and H. B. EVANS Argonne National laboratory, lemont, 111. )Uranium is extracted with 30% tributyl phosphate in carbon tetrachloride from a nitric acid solution of the fissium alloy which contains uranium, molybdenum, ruthenium, palladium, and zirconium, and the raffinate i s strongly fumed with perchloric acid. The solution is then passed through a Dowex 50W-X8 cation exchange resin. Palladium is eluted with 0.3M hydrochloric acid, and the rhodium is then eluted with 6M hydrochloric acid. Rhodium is determined spectrophotometrically with tin(ll) chloride.
I
Experimental Breeding Reactor 11, the fuel plates contain zirconium, molybdenum, ruthenium, rhodium, niobium, and palladium in addition to uranium. This reactor is initially fueled with enriched uranium fissium, but later will operate on plutonium fissium. I n the pyrometallurgical processing of irradiated or spent fuel plates, studies have indicated that a certain group of the fission products cannot be removed and that these elements would bend to build up N THE
to an equilibrium value after several successive recycles of the fuel. The elements that tend to build up upon repeated pyrometallurgical processing and their equilibrium percentages are present>ed in the simulated 5 weight % fissium alloy (Table I). Fortunately, these elements are harmless and even beneficial because of the markedly increased radiation stability and improved metallurgical properties of the fuel plates. I n this may they also aid in achieving higher burn-up. They all have small capture cross sections for fast neutrons and hence do not interfere with the breeding properties of the reactor. To avoid dealing with a fuel of changing composition in the reactor, this fuel alloy (called fissium) is made t o contain originally the equilibrium concentration of these fissium elements (except technetium). The rhodium, once separated, could be determined spectrophotometrically in hydrochloric acid solution with tin(I1) chloride (1, 4). Uranium, molybdenum, palladium, and ruthenium interfered with the spectrophotometric procedure. Ruthenium could be easily
and completely evolved as the volatile tetraoxide, so this interference was easily resolved. Uranium is known to extract with 30% tributyl phosphate in carbon tetrachloride, so this source of error n-as also easily eliminated. Stevenson et al. (6) reported the separation of certain platinum group metals with cation exchange resins. This basic approach by Stevenson’s group was elaborated upon to develop a quantitative method for the separation of rhodium from palladium.
Table I. Calculated Equilibrium Fission Product Concentration (5) (5 weight % of new fissium metal is added
per cycle)
Element Zr Nb 110 Tc Ru Rh Pd U
Weight yo 0.10 0.01
3.42 0.99 2.63 0.47 0.30 92.08
VOL. 32, NO. 8, JULY 1960
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