Detection and Identification of Alcohols, Alkoxy Groups, Lignin, and Wood by Gas Liquid Chromatography K. F. SPOREK and M. D. DANYI Owens-lllinois Technical Center, Toledo 7, Ohio
b A simple and rapid procedure is described for the conversion of alkoxy groups and alcohols to the corresponding iodides. No special apparatus is required and the reaction time is substantially shorter than that employed in the classical Zeisel method. Mixtures of iodides are separated and identified by a gas liquid chromatograph employing silicone gum rubber on Chromosorb P for column packing, and a strontium-90 ionization detector. The method was successfully applied to testing samples of wood, lignin, paper products, miscellaneous fibers, pure alkoxy compounds, and alcohols; it is considered as potentially suitable for the detection of wood on milligram quantities and of traces of alcohols in aqueous and other media.
T
HE DETERMINATION of alkoxy groups is of interest in many fields, particularly those involving work with wood, lignin, certain types of polymers, alcohols, and many pure organic chemicals. The classical method using the Zeisel procedure is rather complicated and tedious and requires a special apparatus. These considerations led to several attempts recently to adopt the Zeisel method with gas chromatographic analysis to simplify the procedure and also t o extend its usefulness. X a r t i n and Vertalier (3) distilled the iodides liberated by the Zeisel method into 0.2 ml. of chloroform which contained 5y0 of methylene dichloride as internal standard. They used this mixture for testing b y gas chromatography and supplemented the information by a n iodimetric determination of total alkoxy groups. Apparently in their method the iodides were not retained quantitatively and Ilaslam, Hamilton, and Jeffs ( I ) modified it so that complete recovery of the iodides was possible. I n this way they provided internal standardization only as far as the gas chromatographic determination was concerned. The standardization did not take into account any errors that could have been introduced during the formation of the iodides in the Zeisel procedure. The time required in the above method for the Zeisel step alone was over 90
minutes. The method mas modified b y Miller, Samsel, and Cobler (4) t o include propyl and butyl groups. The complete determination required about 5 hours. I n a method described b y Kratzl and Gruber ( 2 ) gas chromatographic separation of alkyl iodides was used only to allow their individual absorption in the brominating reagent. The determination was then completed b y titration. The chromatographic separation was effected on a column of tricresyl phosphate a t a temperature of 8 4 O c. The presently described method has been devised to simplify the operation and shorten the total time required for the determination. A simple reflux apparatus is used for the conversion of alkoxyls to iodides; there is no need to pass nitrogen or any other gas during the reaction; no phenol is used; there is no need for a n absorbing apparatus and therefore there is no need for special arrangements like cold traps; internal standardization is employed which also covers the Zeisel procedure; no specially purified HI is required. I n contrast to all previous methods the new internal standardization makes quantitative recovery or absorption of the iodides unnecessary, and the conversion t o iodides is effected in a substantially shorter time, the total determination usually requiring feJTer than 30 minutes. The gas chromatographic part of the procedure involves the use of a nelv column packing-silicone gum rubber-and the separation is possible a t room temperature or only slightly above, if preferred. High sensitivity is obtained by using a strontium-90 ionization detector and this, in part, makes it Table 1.
Retention Times of Alkyl Iodides
Substance Methyl iodide Ethyl iodide 2-Propyl iodide 1-Propyl iodide 2-Butyl iodide I-Butyl iodide 2-Pentyl iodide 1-Pentyl iodide Carbon tetrachloride
Retention time, min. 0 7 11 2 3 3.3 5 5 7.6 11 3
17.1 2 1
possible to simplify the procedure and also to work with materials which n-ould otherwise be rather difficult. The new method has been iised for testing a large variety of materials containing alkoxy1 groups, particularly those related to wood and paper, loner alcohols, and pure substances. The method is thought t o be potentially suitable for the identification of wood and certain types of paper on milligram quantities, and for the detection and identification of lower alcohols in aqueous and other media. The operation of the gas chromatograph a t room temperature suggests its suitability for use under field or mobile conditions. EXPERIMENTAL
Apparatus. T h e reflu.: apparatus consisted of a 50-ml. round-bottomed flask, 14/20, with two stacked condensers, each about 10 em. long. It was found that in the case of methoxy the methyl iodide mas so volatile that in addition to the condenser it was also advisable to use a cold finger at the top to prevent loss. The gas chromatograph employed a strontium-90 ionization detector with argon carrier gas, The argon was purified through a column, 3 inches in diameter b y 2 ft. long, containing pellets of Linde Molecular Sieve 5-\. Sensitivity of the detector was thus increased by a factor of about 3 and &-as such that a 100-unit peak height was obtained at attenuation 1 with 0.02 pg. of methyl iodide. The column was a 4-ft. length of 1/4-inch stainless steel tubing packed with 207, silicone gum rubber on Chromosorb P 60-100. It was operated a t room temperature or slightly above mith argon pressure of about 20 p s i . The ionization detector mas operated at a voltage of 1400 volts and a n attenuation of 200. Usually 1 h of a carbon tetrachloride solution of the sample v a s injected for analysis. Reagents. Hydriodic acid, specific gravity 1.7, containing 577, HI (no special purification necessary). Carbon tetrachloride, spectro - grade. Sodium sulfate, anhydrous. Procedure. Weigh accurately into a 50-ml. round bottomed flask, 14/50, an appropriate quantity of the sample, add 5 ml. hydriodic acid, attach two stacked condensers and a cold finger, and boil for 15 minutes. Cool to room temperature, dilute with 10 ml. of water, VOL. 34,
NO. 12, NOVEMBER 1962
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Table
Standard substance Methosyphenol
II.
Calibration of Procedure
Weight alkoxyl group taken, mg.
Peak height in chart units
Calibration factor (peak height per g. alkoxyl group at attenuation 1)
6.11 6.39 6.48 6.44 6.47 6.49 10.09 10.29 10.11 9.99 9.72 9.28
9 3 . 2 13) 9 3 . 2 (5j 94.2 (3) 9 4 . 8 (3) 95.7 (4) 94.4 ( 5 ) 8 4 . 0 (3) 83.7 (3) 8 4 . 5 (4) 80.8 (6) 78.8 (5) 77.0 (3)
3 . 0 5 X 1O1O 2.91 2.91 2.94 2.97 2.91 1.67 X lOlo 1.63 1.68 1,62 1.62 1.66
Ethosyphenol
I n each case 10.0 ml. of CCl, was used for extraction and 1 X for injection at attenuation 200. Values in brackets indicate the number of injections from which the average peak
height values were calculated.
and pipet accurately 10 ml. of carbon tetrachloride down the condenser. Insert the cold finger and shake the whole apparatus to absorb all iodide fumes. Withdraw a volume of the carbon tetrachloride solution with a syringe, transfer it into a small vial containing anhydrous sodium sulfate, stopper, and shake well. Traces of free iodine usually present in the extract are without effect on the procedure. Inject 1x of the dried carbon tetrachloride solution into the gas chromatograph and observe formation of peaks for the individual alkyl iodides. For guidance use the values given in Tables I and 11.
Table 111. Effect of Reaction Conditions on Conversion of Alkoxyls to Iodides
Alkoxy1 reacted from Meth- Eth- Butoxyoxyoxyphenol phenol phenol
0 ' 9
Reaction conditions, min. Room temperature, 5 Boilinn.
15 20
0
0
...
2 62 97 100
0 21 91 89 100
0 34 95 95
...
...
.. .
...
100
Table IV.
Testing of Materials ,lgt?t and
uation
Wool cloth Silk cloth Rayon Nylon Cotton cloth Cotton wool Filter paper (Whatman 41) Filter paper (Whatman 541) Filter paper (Whatman 42) Writing paper (white) Writing paper (yellow) Cardboard Cypress wood Black gum wood Elm wood Pine wood Holocellulose (cypress) Holocellulose (black gum) Kraft lignin Blank
80 82 81 80 82 85 81 82 86 83 80 83 83 86 80 82 78 83 37
Nil
41, att. 2 4, att. 2 14, att. 2 41, att. 2 8, att. 2 12, att. 2
Nil
11, att. 2 8, att. 2 77, att. 2 64, att. 200 27, att. 200 66, att. 200 94, att. 200 78, att. 200 70, att. 200 88, att. 200 96, att. 200 83, att. 200 Nil, att. 2
Et1 68, att. 2 100, att. 2 42, att. 2 2; att. 2 Nil Xi1 Nil 4, att. 2 Nil Nil Nil Nil Nil 7, att. 50 Xi1 Nil Xi1 Nil Xi1 ?Til
Found, Methoxy Ethoxy 0.02.i .. . _ _0.130
0,003 0.012 0.035 0,007 0,007
Xi1 0,009 0.006 0.063 5.46 2.1 5.2 7.1 6.4 5.8 7.4 7.6 14.4
Xi1
0.112 0.064 0,007
ANALYTICAL CHEMISTRY
RESULTS A N D DISCUSSION
The retention times of the chromatographic procedure for some of the common alkyl iodides are shown in Table I ; the separation is satisfactory between the different compounds and between their isomers and is substantially faster than that obtained by Miller and coworkers ( d ) , even though it is carried out at room temperature. The reproducibility of results is reflected in values (Table 11) obtained in periodical calibration of the authors' procedure. The precision of these values is similar to those obtained in this laboratory b y the classical Zeisel method. To shorten the time required for a determination, the reaction conditions were tested for the conversion of alkoxyl groups to the corresponding iodides. Results obtained for methoxyphenol, ethoxyphenol, and butoxyphenol (Table 111) indicated that refluxing for 5 minutes would provide sufficient conversion for qualitative work; for quantitative determinations 15 minutes boiling was chosen for the final procedure. Practically no difference was noted in the rates of conversion for the three tested compounds. Because the iodides were separated from the reaction mixture by extraction, the time required in the classical Zeisel method for prolonged sweeping with a stream of gas is
Nil Nil Nil
0.006
Nil Xi1 Nil Nil Nil
1.0
Nil Nil Nil Nil Nil Nil
All reactions were run for 15 minutes, extracted with 10 ml. CClI, 1 X injected, ionization detector used at 1400 volts.
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The above simple procedure is satisfactory for qualitative estimation of different alkoxy groups. For quantitative work it should be standardized by means of a pure alkoxy compound. Internal standardization can be achieved b y weighing a n appropriate pure alkoxy compound with the sample and carrying the mixture through the entire procedure. I n this work the procedure was calibrated b y means of methoxy- and ethoxy-phenol and a calibration factor was calculated which was then used for the calculation of the alkoxy group content of the tested samples.
Table V. Effect of Reaction Conditions on Conversion of Alcohols to Iodides
Conc. of
HI in 5 ml.
reaction mixture: (conc. HI = 5 7 5 )
11% 11% 11% 11%
+ 2 g. K I + 3 ml. H2S04 + 2 g. KHSO, llyc + 3 ml. HaPO:
Yc Conversion t o iodide of,illeth- Ethanol anol 100 83 91 36 3 46
65 7
100 95 26 3 1 14 35
13
In each test 0.05 ml. of the respective alcohol was used.
saved. The total time required for a determination is therefore usually less than 30 minutes. The results obtained on a wide variety of materials are shown in Table IV. As most of the above materials did not dissolve in the reaction mixture, the results cannot be considered as quantitative. However, they give a reasonably good indication of levels of alkoxy group contents and in many cases could provide rapid and reliable means of identification of certain of the above materials, especially woods. I n the case of wood, the methoxy groups are derived almost entirely from lignin; the procedure could therefore provide useful information as t o
the purification degree of paper pulp and lignin content of cooking liquors and by-products in the productions of paper and pulp. As a further check on the method and a possible application to the determination of free alcohols, the effect of diluting the hydriodic acid with water in the reaction mixture on the results was tested. The values obtained with methanol and ethanol (Table V) indicated t h a t methanol could be converted to the iodide a t a reasonable rate even with a solution containing 34% HI (3 ml. 57% HI 2 ml. water); ethanol required higher concentration of HI (46% or 4 ml. 57% HI 1 ml. water), but the addi-
+
+
tion of concentrated sulfuric acid increased considerably the efficiency of conversion. The procedure is therefore potentially suitable for the detection and determination of alcohols in dilute solutions. LITERATURE CITED
(1) Haslam, J., A. R., Analyst ( 2 ) Kratzl. K., Chem. 89, 618
Hamilton, J. I3., Jeffs,
83, 66 (1958).
Gruber, K., Monatsh. (1958). (3) hlartin, F., Vertalier, S., XVth International Congress on Pure and Applied Chemistry (Analytical Chemistry), Lisbon, September 8 to 16, 1956. (4)Miller, D. L., Samsel, E. P., Cobler, J. G., ANAL.CHEW33,677 (1961). RECEIVEDfor review June 29, 1962. Accepted August 29, 1962.
Acylated Cyclodextrins as Stationary Phases for Comparative Gas Liquid Chromatography HERMANN SCHLENK, J. L. GELLERMAN, and D. M. SAND The Hormel Instifute, Universify o f Minnesota, Austin, Minn. b 0-Cyclodextrin acetate, propionate, butyrate, and valerate have been used as stationary phases for gas liquid chromatography (GLC) of cyolefins, alcohols, aldehydes, esters, aldehyde-esters, and diesters. The retention times of homologs follow the rule of logarithmic linearity. The shifts of retention times of a compound from phase to phase facilitate its classification and tentative identification. Esters of fatty acids having one, two, or three side methyl groups have been chromatographed and the phases compared for separation of such isomers. The heat stability of (3-cyclodextrin esters makes them very suitable for comparative GLC.
T
HE advantage of gas liquid chromatography (GLC) with phases of different polarity has been pointed out in numerous cases where mixtures of different chemical types or closely related compounds were to be separated and tentatively identified. Retention time is regulated, in part, by the relat i r e polarities of sample and stationary phase. Therefore, shifts of retention times of a compound on different polarity phases are characteristic for that compound and its class. Conclusions dran n from these data are particularly important for those components of mixtures which are not more fully characterized. The more subtle differentiation of closely related compounds, like isomers, is not as obviously connected with polarity but still is aided b y com-
parative chromatography where superpositions on one phase may be resolved by another. It is of advantage in comparative GLC to use phases t h a t are heat stable, so that column performances are reproducible and constant. Further advantages of heat-stable phases are in better exploitation of the sensitivity of detectors and in preparative GLC. The stationary phases which are commonly used in high temperature GLC are polymers-Le., neither their melting points nor molecular weights can be defined precisely, and their preparation and quality are difficult to control. Accordingly, the heat stability of these phases may vary from batch t o batch and their performance may change considerably with time a t temperatures higher than 180" to 200" C. The use of cyclodextrin (CDX) esters for GLC of fatty esters has been reported and the stability of p-CDX acetate at 236" C. has been emphasized ( I O ) . This investigation has been extended t o cover the homologous series, p-CDX acetate to valerate. The stability of these carbohydrate esters was very satisfactory a t 220" C. in the analytical experiments reported here and a t 236" C. in preparative GLC. Because of their different polarities, these esters are promising phases for comparative chromatography. a-Olefins, alcohols, aldehydes, methyl esters, dimethyl esters, and aldehyde methyl esters have been chromatographed and their retention on the different phases has been
compared. Furthermore, the efficiency of the phases for separating isomeric fatty esters has been evaluated. Some results with p-CDX ester phases in preparative GLC have been outlined ( 5 ) , and the procedure will be detailed elsewhere (11). EXPERIMENTAL
Materials. T h e compounds to be chromatographed were obtained from commercial sources or from T h e Hormel Foundation, or were prepared in this laboratory. Aldehydes and aldehyde esters were obtained b y ozonization reduction of authentic unsaturated f a t t y esters. Some branched C17 acid methyl esters are listed in Table I with references to the method of their preparation.
Table I.
Branched C l i Acid Methyl Esters
2-Methylhexadecanoate 3-Methylhexadecanoate 7-Methylhexadecanoate 14-Methylhexadecanoate 15-Methylhexadecanoate
3,6-Dimethylpentadecanoate 2,14-Dimethylpentadecanoate 3,6,13-Trimethyltetradecanoate 9,lO-Methylenehexadecanoate
p-CDX and its esters were prepared essentially as described by French for the carbohydrate and its acetate ( 3 ) . b-CDX propionate and butyrate were purified by repeated crystallization from ethanol. The valerate was used VOL. 34, NO. 12, NOVEMBER 1962
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