strates t h a t t h e p-glucosides predominate over the a-glucosides. As opposed to D-galactose no trace of aldehydes or septanosides occurs. The mixture obtained from direct methylation in D M F however contained 0.3y0 of the aldehyde with a relative retention of 2.32 (Table IV). I n addition, traces of the sugar anhydride, 2,3,5trimethyl - D - glucosane - a - [1,4] p - [1,6], and incompletely methylated compounds were present in these mixtures. I t has not been resolved whether this anhydride takes part in the glucose equilibrium in solution or is an artificial product formed by water elimination from incompletely methylated glucose. Arabinose. This case is analogous t o glucose in t h a t t h e methyl ethers formed from the methylglycoside contained only the furanosides and pyranosides. The mixture obtained by direct methylation was found to exhibit a peak with a relative retention of 2.50 indicating the presence of the aldo form (0.47,). CONCLUSION
I t is possible to determine the amounts of various ring forms and carbonyl forms of equilibrium mixtures of sugars in solution. The proportion of isomers changes under varying conditions. Investigations of this nature are very important in studies concerning the mechanism of mutarotation. S o t only should a-p-isomerization and transitions of furahoses and pyranoses be Considered, but, as in the case of D galactose, the presence of septanosides must be taken into account. CrPyranOse 4
r, bPVranoee
r r - F ~ m ~p i d o - f o r m 8-FUl’mO@ a-Septanoee p e-septanose
Table V.
Content of Different Ethers in Methylated D-Arabinose
2-m. column (0.4 mm.) with 2 0 7 , polyethylene glycol on kieselguhr (0.2-0.3 mm.). T = 150” C. Retention relative t o succinic acid ester
Relative retention Substance 2,3,5-Trimethyl-a-methyl-~-arabinoside 1 60 2,3,5-Trimethyl-p-methyl-~-arabinoside 2.04 2,3,4,5-Tetramethyl-al-n-arabinose 2 50 2,3,4-Trimethyl-/3-methyl-~-arabinoside 3 05 2,3,4-Tr~rnethyl-~-methyl-~-arabinoside 3 20
Gas chromatography is the first reliable method that demonstrates the existence of carbonyl forms of sugars in solution which, according to the above scheme, are important intermediates in transitions of the ring forms. By using the results of analytical investigations it is possible to devise simple syntheses of pure isomeric methyl ethers ( 3 ) . Tables I1 to V indicate the feasibility of obtaining very high yields of any desired component merely by varying the conditions under which the methylglycosides and permethyl ethers are formed. I n the past the synthesis of pure isomers was always a troublesome task which included many steps and, as in the case of carbonyl and septanose forms, was not always successful. Direct methylation and subsequent separation by preparative gas chromatography now produces the desired substances in a very short time. LITERATURE CITED
(1) Bayer, E., Survey on Application of
Gas Chromatography in Sugar Chemistr in E. Bayer, “Gas-Chromatograplie,” Springer-Verlag Berlin, 2. Auflage, 1962. (2)Bayer, E.,Hupe, K. P., Witsch, H. G., Angew. Chem. 73, 525 (1961).
Glyc. 0.013% HCI Ag*O/CHJ 61 1y0 26 5 7 , 6 3% 5 9%
Dir. perm. BaO/CH31 3 3% 34 1 % 0 47, 26 0% 36 6%
(3) Bayer, E.,Widder, R.,Liebigs Ann. Chem. In press., See also Ph.D. thesis, R . Widder, Cniversity of Tubingen, 1964. (4) Cox, E. G., Goodwin, T. H., Wagstaff, A. J., J . Chem. SOC. (London) 1935, 1495. ( 5 ) Henri, V., Schou, S., Hoppe Seylers, 2. Physiol. Cheni. 174, 295 (1928). (6) Kuhn, R., Trischmann, H. Low, I., Angew. Chem. 67, 32 (1926); 72, 805 (1960). ( 7 ) Kwiecinski, L., Marchlewski, L., Hoppe Seylers, 2. Physiol. Chem. 169, 300 (1939). (8) Levene, P. A , , Meyer, G. M., J . Biol. Chem. 69, 176 (1926); 74, 695 (1927). (9) Micheel, F., Suckfull, F., Chem. Ber. 66, 1957 (1933). (10) Overend, W. G., Peacocke, A. R., Smith, J. B., J . Chem. SOC.(London) 1961,3487. (11)Petuely, F., Meixner, IT., Chem. Ber. 86, 1255 (1935). (12)Sweeley, C.C., Bentley, R., Makita, M., Wells, W. W., J . A m . Chem. SOC. 85. 2497 (1963). (13)’Sweeley, C,’ C., Walker, B., ~ ~ N A L . CHEM.36, 8, 1461 (1964).
RECEIVEDfor review March 26, 1964. Accepted April 27, 1964. 2nd International Symposium on Advances in Gas Chromatography, University of Houston, Houston, Texas, March 23-26, 1964. We are indebted to the Deutsche Forschungsgemeinschaft for supporting this work.
Pressure Changes during Passage of a Solute through a Theoretical Plate in Gas Liquid Chromatography R. P. W. SCOTT Unilever Research laboratory, Sharanbrook, Bedford, England
b Peak distortion owing to solute partial pressure is considered theoretically and the elution curve equation, derived from the plate theory, is modified to account for the effect. A pressure curve, coincident with the elution curve, is confirmed experimentally using a novel pressure transducer. The effect of solute partial pressure is negligible on analytical packed columns for charges of less than 1 mg., but significantly distorts early peaks on preparative scale columns. The increase in exit flow from a column during the elution of a
peak is also considered and a simple method given for molecular weight determinations using an anemometer detector.
D
of a solute through a theoretical plate the column pressure will increase owing to the partial pressure of the solute. This change in column pressure will cause transfusion of the solute band away from the normal peak maximum due to the difference in volume flow of carrier gas on either side of the peak. To assess the significance of this pressure URING THE PASSAGE
effect on peak shape, column efficiency, and retention volume, the plate theory has to be modified and another elution curve equation derived. Such an equation would indicate conditions where this effect would cause errors in results or reduce column performance. To confirm the existence of a pressure pulse coincident with the elution curve, i t was necessary to employ a suitable pressure transducer that would continuously monitor the pressure a t a point in the column as a solute band passes ( I ) and it will be seen that this transducer acts as a detector n i t h a sensitivVOL. 36, NO. 8, JULY 1964
e
1455
ity commensurate with that of the kathai oineter. The po"sibi1ity of determining moleculai weights by volume measurements taken duiing the elution of a peak ha': ako been considercd theoretically and verified exl)eriinentally
the pressure difference between the plates and plate impedance. Thus, volume of gas pasLsing from plate p - 1 to plate p in time 6t =
[w
+
(AP,-1
r.
273
V
u =
6t
- AP,)] ;
V"
+ Kl'L
The justification for making the necessary assumptions to transform Equation 4 to Equation 5 is given in the .Ippendix.
THEORY
The mass of gas passing any point in a column is assumed to be constant for a given flow. This assumption is, a t present, conti,oversial but as the theory derived from this premise is in accord with esl)erinierital data the assumlition is taken as correct. I t foll o w that a i solute vapor enters a theoretical plate the number of molecules in the gas phase will rise and the pressure incmase. The increase ill pressur(' is equal to the partial pressure of the solute vapor and in the p'th plate is given by the expression :
where the flon of gas is nieabured in plate volumes and the variable T' iq changed to v where
Let 10,
=
+
1-Q
.fP(z')
where fP(2J)
uwof the solutc distorts the normal ( ~ r o fuiictioii r curve and the ainount of distortion varies directly with the charge sizt. and inverscly with t h r molecular \rt.ight of the solute and the column imli(dancc. Froni Equation 7 the elution curves for different charges and for the same ~ h a i y y but . taken at different points in thc colurnri. are s h o w in Figures 1 and 2 , reqiectively. I lie curvc~s w r e calculated for the followiiig column solute . tems : roluniii length, 120 cm.; coluniii dianic t r r , 6 nini.; liquid phase, squalane: liquid j)hascx on support, 15o/G ; efficiency, 2500 thcolctical plat[,>; volume of gas iilate, 0.010 id.; volume of liquid 1)h asc 11la t cs , 0.00 109 rn1, ; t em11era t ur e 'it?' ('.: solute, n-heptane; molecular \wight of solute, 100: partition coefficitTiit of uolute at 75' 150; sample di-trihutcd initially ovcr 10 tlicorctical 1)latcw. 0.5 ctii.; pwssure droll acaross c~olrimi~.7 l3.s.i.; roluiii~i flo~v-: 60 nil. p c r miiiutc; l'I,rssure drop 'plate at 60 1111. iirr minute, 0.15 mm.of mcrcwi'y. Finally! y: 20 = 7 . 2 x 106. It i. cmi)ha&d that the curves in 1'igut.r.s 1 and 2 do not account for the initill1 11aiid width of 10 th(wretica1 i)latcs> due. to the distribution of the c h a i , g \ ovcr 0.5 m i . of coluniii length. 'l'hi, initial band width of the charge \rill bloaclcxn thc elution curve in the rnaniicr drscribed b ~ .1l;lirikeribcrg (4) and may l i v e>titiiattd by summing the variaticw of the initial and filial band.. I t ihould be iiotcsd that the curveq obtaiiicd fmni the 10-111g. charge should be con-itlcwtl very appi,oximatr~as Equation 7 i+ not apl)licable t o large c h a r p s (,wlAil)l)e~idix).For this reason Equatioti 7 \vas not alii)lied to charges greater tliaii 10 mg.; fui,thermorc, they could riot bix accommodatcd initial]!. by 10 tlicwrctical 1)latrh. I k e s x i v e chargcs Iii,tiducc~high 1)ai~ialpressuiw of d u t e rcs\ilting in the rapid transfusion of the F
Volume
Figure 1.
Flow
Theoretical elution curves for different charges of n-heptane
\
~
e.,
solute t o neighboring plates. This transfusion continues until the partial pressure of the solute is reduced to a level \There t,lie normal elution process takes place. Resulting from the pressure pulse that accompanies the solute band down the column, ai1 inciaease in carrier gas flow must occur as the solutr is eluted from the end of the column into the detector. This effect has been noted by van der Craats ( 2 ) . The increment of gas volume 3Q occupied by .11 grami of the solute vapor is given by t h r following equation assuming the fugacity of the vapor to be unity.
For two solutes .I and B
and if K is large
Thus if a sensitive anemomet,er is employed a>a detector in such a manner that no properties of the solute ran affect thc drtecting system, then Equation 9 affoi& a siniple method of measuring molecular w i g h t .
If @A
mA, T T Z B ,arid .llA are kn0n.n. and and AQB measured, then
DISCUSSION OF THEORY
During elution, thc 1)artial 1ii'e>bui'e of the solute sharpens the leading edgc of a peak arid slopes the trailing edge. This phenomena has been discusxd by Littlewood ( 5 ) and has been tiemonstrated exl)erimentally by l'ollaid and Hardy (6). Thew ~ v o r k c r ~rrsultq, ' however, include the tffwt of thcrinal changes in a column ( 7 ) v,-Iiicali cannot be differentiated from the peak distortions owing t o solute Iiartisl preswre alone. The exiilanation given by Littlewood is not mact as hr 'a.~: \~llIll?. that the high concentrations i n the elutions curve move mow i,apidly through the coluniii than thc lo\ver concentrations. In fact, bec,auw of a pre.;sure gradient along the column, it i- the peak front that moves mot'r quickly through the column than thr. 1)c~Atail. On a packed column t h t effwt i.: miall for charges of less than 1 mg. The Iicak . causcd by thr i)w-sure similar to that I)rotluwd hy thermal effect< in a rolunin ( 7 ) . 'l'hc relative proportion. of the Iwak aqynimetry dur to the thermal anti i)res~'urc effects are difficult to asses.., a i thc VOL. 36, NO. 8, JULY 1964
1457
3
I
c
I
O
i 8 c
.-E 6
.-P E 0
t t
51 > 0 c
P
t -0
1458
ANALYTICAL CHEMISTRY
2mm
Metal foil
Rubber diaphragm
Figure
3.
Diagram
of pressure transducer
External connec tionr for rta b i l iring initial pneumatic balance
thermal changes that occur will depend on the heat of solution of the solutetern concerned. Generally, the thermal effect will be the major factor contributing to peak asymmetry. The magnitude of the peak asyninietry due to the solute partial pressure depends on three factors, y, W , and X , . For a given charge, S ovaries inversely as the plate capacity and thus is also inverwly proportional to the partition coefficient of the solute and the percentage liquid phase on the support: y varies inversely as the molecular weight and w directly with packing density. The greatest peak asymmetry will thewfore occur on columns with loa- ljacking densities, carrying a ;mall percentage of liquid phase on the sup1)ort and for substances of low inolec~ularweight that are eluted early in chromatogram. Although the resulting asymmetry i; small for charges of l c ~ sthan 1 mg.>on 1)rel)arativr columns the pressure effect will make a significant contribution to the aqynimetry of the early peaks. For charges in excess of 1 mg. on packed columna the simple plate theory may not be applicable and efficiencies measured in the usual way ( 1 ) will be in excess of their true value (Figures 1 and 2). It should be stressed, however, that these apparent high efficiency lralues will only result from the pressure alone. If the pressure effect is accompanied by thermal effects and column 'over-load,' these latter will predominate and the measured efficiency will be lower than the true value. The effect of solute partial pressure on wtention volume measurements is alho ihonm in Figure 1 and 2. I t is seen that values for retention volumes can be significantly smaller than those measured in an ideal system. lleasurement of the increase in column flow during the elution of the solute from the colunin affords a simple method of molecular weight determination. Equat,ion 8 shows that the volume occupied by the solute vapor is invewely proportional to the molecular
Spiral cut to permit movcmen t of metal foil
weight. Thus by using an anemometer detector, the peak areas produced by given masses of solute can be used to calculate their molecular weights. I t may be that the GowlXac Gas Density Bridge, which is known to be flax sensitive, is in fact partly acting as an anemometer detector. Floiv changes during peak elution must effect the response of all flow sensitive detectors, particularly the flame thermocouple detector and katharometer. If a very accurate anemometer were used, it might be possible to determine the fugacity of the vapor for a substance of known molecular weight. EXPERIMENTAL
I t was required to establish that a pressure pulse did, indeed, accompany the solute band through the column and t,o verify the method of molecular weight deterniinat'ion using an anemometer detect'or. Measurement of Pressure Change. The column pressure was measured by means of the transducer shown in Figure 3. I t consists essentially of a plastic diaphragm with a metalized surface which acts as one plate of a parallel plate condenser. The diaphragm was made of thin latex rubber sheet to lvhich a thin sheet of aluminum foil was att,ached b y contact adhesive. The disk of foil carried a spiral cut to permit deformation without crinkling. The transducer ivah situated in one arm of a capacity bridge (lIarconi Cniversal Bridge Type T.F. 2700) the output of which was fed to a 1-mv. potentiometric recorder. The transducer was connect,ed to the column by a tube sealed into a small hole in the column wall by an epoxy resin. By opening the tap, (Figure 3) both sides of t8hediaphragm ivere maintained at, the same pressure while t,he column operating conditions were being established. Prior to charging the columns the metalized side of the diaphragm was isolat,ed by closing the taIj: 1he transducer was calibrated against static wat,er pressure and the calibration curves obtained were linear. The maximum sensitivity realized was 8 mm. of
11-ater a t a signal-to-noise ratio of 2. This corresponded t o a capacity change of 0.014 x IO-" farad> and a plate deformation of approximately 10-5 em. I t would appear that the sensitivity of the transducer could be further increased by the use of more sophisticated bridge unit operating a t a higher frequency. -1s a detecting system the transducer had sensitivities conimensurate with that of the katharometer detector. Charges of 0.5 to 10 p l . of diethyl ether !?-ere placed on the column and the resulting pressure pulses recorded. The curve relating charge size with peak height in mm. of water is shown in Figure 4,together with the trace of a pressure pulse derived from a 5-mg. charge. Determination of Molecular Weight. The anemometer detector used was the flame thermocouple detector (9) chosen because of its high sensitivity to changes in flow rate. This detector, hoivever, responds to both changes in column flow and to changes in calorific value of the carrier gas owing to the presence of the eluted solute. It was necessary, therefore, to operate the detector in such a way that it responded explicitly to changes in column flow and to ensure that the eluted solute never entered the detrctor. This was achieved by the following column systems. The eolunin, 30 cm. long, 4 mm. in diameter, packed with 100-120 B.S.mesh firehiirk carrying 15% squalane as a liquid phase, \vas connected to a 20-foot l e n q h of 5-nim. i d . copper tubing, which in turn, was connected to a second column, 20 cam. long, 4 mm. in diameter packed with 30-60 B.S. mesh active charcoal. X single substance injected onto the liartition column resulted in two peaks appearing on the chromatogram. The first, a positive peak, occurred as the solute it-as desorhed from the partition column; the second, a negative peak. occurred as the solute was irreversibly absorbed on the absorption column. The copper tube introduced a time lag ten1 and .served to separate on and adsorption peaks. Eight-microliter charges of a number of volatile solutes w r e injected sellarately onto the column and a measure of the area of each adsorption curve was obtained by cutting the peak out and weighing it. The adsorption (surve was used to circumvent the assumption that K >> 1 in Equations 9 and 10. Each peak mass was corrected by dividing by the specific gravity of the reolute to account for the varyties of the subbtances used. The corrected weight of each peak. which is proportional to the hame mas.? of solute is hhown plotted against t h e reciprocal of the reyective molecular weight in Figure 5, together with the desorption and adsorption curves for diethyl ether. DISCUSSION
OF
RESULTS
The calibration cur\ e. obtained indicate the lineal rcblionie of thr transducer to prcswre chanqe. The VOL. 36, NO. 8, JULY 1964
1459
.
1
b
1
C H l l C I llll
'PI)
-
I
I
d
0
A
Figure 4. Theoretical and experimental curves relating pressure at peak maxima to charge size Figure
curve relating peak height in cm. of water to charge size supports Equation 1 and substantiates the existence of a pressure pulse coincident with the solute band as it passes down the column. The pressure transducer affords yet another detecting system for use in gas chromatography although it does not offer any obvious advantage over those already in use. It should be noted, however, that for a linear transducer, predictable response will be inversely proportional to the molecular weight of the vapor detected.
IO"
-
I m q chorqe
5.
Graph of peak mass vs. molecular weight
The results in Figure 5 show how a gas chromatograph employing an anemometer detector may be used indirectly for the determination of molecular weights. A more precise control of the operating conditions and the use of an integrator could give measurements with a high degree of accuracy. The increase in column flow as a solute is eluted will affect all flow sensitive detectors and may account for some of the conflicting reports on the performance of such detectors. The increase in gas volume during the elution of a solute will contribute to the measured retention volume if liquid samples are employed but not if a gas sampling procedure is used. The effect of vapor volume on retention volume measurements using liquid samples will be small for charges of less than l-&, but if precise measurements are required a correction can be applied using Equation 8.
but the solution given by Equation 6 still gives a fairly good representation of the shape of the elution curve. The approximation used to transform Equation 4 to Equation 5 tends to smooth out the function. The elution curve maxima are shown in Figure 6 as a sudden change in the sign of d2 Xg
dv
which thus locates the position of the maxima. It is seen that the displacement of the peak maximum is even greater where no approximation is made and thus the distortion of the 5-mg. and 10-mg. peaks shown in Figure 1 is less than the true value. The deviations of the values of d4 yg' for the two dT. equations is very significant for a 10mg. charge and the curve for this charge size shown in Figure 1 can only be considered as a rough impression of the shape to be obtained. LIST OF SYMBOLS
APPENDIX
i 1 0 - e - t "e ".I".,
two respective values of
Y > 2500
n
Figure 6.
10.9
-
Computed values of
dXg, were dV
calculated by means of a digital computor. The conditions used were those given for the determination of the curves in Figures 1 and 2 and as
da dv
0 2150
YXg, -
YV
was a difference function, the results were calculated to 16 significant figures to eliminate 'rounding off' errors.
dap for charges of 1 and 5 dV
from true and approximate forms of differential equation
Values of
--
mg. are shown plotted against plate number in Figure 6. I t is seen that, for 1-mg. charges, close agreement between the curves is obtained. For a 5-mg. charge the deviation is greater
a Xg, ~
_ - _ -
from Eq. 4
aV
a X g , from Eq. 5 d V
1460
ANALYTICAL CHEMISTRY
Column pressure in the p'th plate, mm. of Hg = Small change in column pressure on the p'th plate = Temperature of p'th plate = column temperature = Molecular weight of solute = Partition coefficient of solute with respect to the liquid phase = Concent'ration of solut'e in the gas phase in the p'th plate, grams per ml. = Concentration of solute in the liquid phase in the p'th plate, grams per ml. = Initial concentrations of solute in gas phase on bhe first plate, grams per ml. = Volume of gaslplate, ml. = Volume of liquid phase/plate, ml. = Pressure droplplate, mm. of Hg = Plat,e impedance, mm. of Hg = Column efficiency, total number of theoretical plates = Volume of gas, ml. =
In the development of the equat'ions of the elut'ion curve, certain simplifying assumptions were made to transform Equation 4 to Equation 5 , and furthermore, the solution of Equation 5 was assumed to take a specific form. To test the validit,y of these assumptions the solution of Equation 5 was substituted in Equations 4 and 5 and the
ACKNOWLEDGMENT
The author thanks 1. E. Hawkins and G . W. Cates for help in the constructmion of the pressure transducer, I. A. Fowlis for assihtance n i t h the experimental work, and John Taylor for checking the mathematics and programming the digital eoinputer. LITERATURE CITED
(1) Beynon, J., Cairns, R., J . Sci. Znstr. 41, 111 (1964).
(2) Craats, F. van der, “Gas Chrornatography 1958,’’ D. H. Ilesty, ed., pp. 245-61, Butterworths, London, 19%. ( 3 ) Keulenians, A , , “Gas Chroniatography,” p. 120, Reinhold, S e w York, 1937, (4) KlinkenbeSg, A,, “Gas Chrornatography 1960, R. P. W. Scott, ed., p. 182, Butterworths, London, 1960. ( 5 ) Littlewood, A , , “Gas Chroniatography, p. 40, Academic Press, S e w York, 1962. ( 6 ) Pollard, F. H., Hardy, ,C;. H., “\.apour Phase Chromatography, L). H. Desty,
ed., p. 115, Butterworths, Liltidon, 1957. ( 7 ) Scott, It., ASAI..CHEM.35, 481 (1963 i : ( 8 ) Scott, It., “(his Chromatography, 1). H. Ilesty, ed., p. 189, Buttei,norths, London, 195s. (9) Scott, It.,,, “\.apour Phase Chromatography, I). H. llesty, ed., p. 131, Butterworths, London, 1957. RECEIVED for review 11arch 3 , 1!)34. Accepted h p r i l 30, 11184. Presented a t 2nd International Synipclsiuni i j i i Advances in Gas Chromatography, University of Houston, Houston, Texas, 1Iiirclt 2 - 2 6 , 1064.
Determination of Carbohydrates in Glycolipides and Gangliosides by Gas Chromatography CHARLES C. SWEELEY and BARBARA WALKER Department o f Biochemistry and Nutrition, Graduate School o f Public Health, University o f Pittsburgh, Pittsburgh, Pa.
b Simultaneous gas chromatographic determinations were made of glucose, galactose, galactosamine, and sialic acid in neutral glycolipides and gangliosides. Methanolysis in dry, dilute methanolic HCI was used to convert the oligosaccharide portion of the glycolipides to monomeric carbohydrates. Hexoses were converted to methyl glycosides, N-acetylhexosamine was partially converted to hexosamine hydrochloride, and sialic acid gave the 2-0-methyl ketal of methyl neuraminate. Separate procedures were used to convert these products of methanolysis to trirnethylsilyl derivatives for gas chromatography. Samples of sialolactose and cerarnidetrihexoside were used to validate the procedures for determination of hexose and neuraminic acid. Reproducible determinations of these components were made with a relative error of f5%. Problems were encountered in the quantitative determination of hexosamine b y gas chromatography. Several alternative methods are given, and possible explanations for the difficulties are discussed.
Since 1958, when 11cTnnes et a2. (11) reported a classic study on the separation of tri-0-methyl derivatives of methyl pentopyranosides and trtra0-methyl derivatives of hexopyranosides by gas chromatography, a number of reports have been madeof thedetermination of various sugars in the form of polymethyl ethers. Generally adequate separations have been achieved on both polar and nonpolar columns: h i t anomerir pair. arc hoinetirnes difficult to resolve. 1’rol)alily the nioht scrious problem in wing the methyl ethers as general t1erivativc.s for routine analyses results from thP long timc rcquired for thtlir preparation and the pohsibility of variable yields. For some purl)ose~, ho\vevcr, esl)ecG~ilyin .structural >tu&+ on thc location of glyco>idic bond> in oligosaccharides, the u>e of thwe dcrivatives has proved to be of consideralilc value The .;elisration of polyac~tyl derivativch of carlwhydratch by gas chroniatogi,aphy \vas first inve>tigated by I h h o p arid Coopw (3) in 1960; d e t w minations of a variety of sugars, a:: acetateh, have since been recorded. The \datilit>. of 0-acetyl wters of carbohydrate> is generally sufficient for q i a r a t i o n s on tioth polar and nonpolar colunins. \Yith sul~htanc*es having relatively high nlolrcular \wight. such as disiccharides. .Jones and I’crry (9)reiport that glash I)cads are thc liest inert ;.upport for liquid phase. Ilecmtly. I3ibhop, Cooper, anti M u r r ~ y(.$) have investigated srveral t y l w of thcrnially catalyzed changes of acetyl derivative:: during gab t-hroiiiatography. ‘fhc>y noted that dcaniidat ion, changes in ring size, and rr’arl‘angciiir.tits of acetal, kctal, and .Y-acctyl gi~oulisai’c Ii!-xl>- to oc(*ur with thew tlcrivatives. Foi.’ t h i h reason, the polyacet\.l chrivati\-wh hould VOL. 36, NO. 8, JULY 1964
1461
