Astudyoftfrtgasliquid cbmnatogmphic bcbaviour of unsaturated fatty ahmhols aml a&a&s on a numtic liqpid uysta& 4+nethoxy@mimyloxy~- mctho%yaza~ as swimary phase has &own that excellent+xpamtions of isorcaersare~~withinthtnematicand~~~temperaturelimitpofthis ~scpatrrtiansofisomersofsomcmono-anddisnsaturatcdinsectpbero- moncs arc~givm’to Uustsaw tbc skctivity of &is liquid aystal towards oMnic isom

iMTRODUcIIoN

The dcvclopmcnt of bigh-polari~, cyanopropylsiloxam stationary phas+ has madc~~~theanalysisofisomaic,unsatunrtcdfirttyaciddaivativeson~ gasliquid chromatographic (GLC) coItmnn# J. However, &se isotropic phases have svmal disadvantages: high co1um.a tcmm irnd long analysis times are often requimP, rcsoXution ‘of the isomers of conjugated dimes is my not

. parhBh@ gcm& an& with some of tiaese pheses, e& O-V-275, dii anal+ of fatty alcohols is not possibk’.

We rccmtly repoti the use of a sm&ic Ii&d cry&al, diethyl4,4’-azoxy- . .

~asastationaryphescfor~scparatianofisomersofmono-mrsatunrted and co@- -ted long-chain acetam, aldehydes and metby estess on packed GLCcolumus. However, thisliquidcrystalphasiswasmsuitablefordirect dysis of tbc cormponding alcohols. It$ad also aep withdrawn from sale by the sppplias, &stman w. .Qmpany, @ho* follqwiag-the appwane of our *se compmmdisnowonthcmaskct-~*.

ContiMngimrcstigatiomintbislalmsatosyontbmseofliquidcsymlsas -_. . . _- _-_: . . . Y. . _... __ . ‘I . -_- , ._.

. .__ _ii;csnt.mi&&&OiOsnibmA‘ $&

- 1 . N-

8 . .s . ._

OLC OF UNSATURATED FATTY ALCOHOLS

RESULTS AND DISCUSSION

37

The chromatographic behaviour of the Z and E isomers of 9, l I-dodecadienylacetate was used as an indicator of the resolving power of the nematic liquid crystalstationary phase. These isomers constitute part of the sex pheromone of the femalered bollworm moth, Diparopsis castanea'", and our previous papers on the smecticliquid crystal stationary phase, diethyl 4,4'-azoxydicinnamate, was the first record ofdirect separation of these isomers on any OLC column.

In Fig. 2, the number of theoretical plates (N) with respect to the diene isomersis plotted against the column temperature CC), and this illustrates the way in whichthe state of the liquid crystal influences the efficiency of the OLC column. Startingfrom a point at which the liquid crystal is in the crystalline state, the column efficiencystarts to increase as the temperature is raised and the stationary phase approaches themesomorphic state. The efficiency passes through a maximum and then declines asfurther increases in temperature tend to dissipate the mesomorphic character of theliquid crystalline state. However, starting from a temperature within the mesomorphicregion, decreasing the column temperature then leads to a steady increase in columnefficiency as the mesomorphic state supercoolsv-P before it reverts sharply to thecrystalline form below 90 0

•

3'1'-,: "0... ,. ,, ,

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; b.._~

f ..~.., ,, 'I '

: 'l?· ,I ,· ,· ,: \· ,: \,.}

-'

70 90 110 130 150 170 190temperature rOC)

Fig. 2. Relationship between column efficiency as expressed by the number of theoretical plates(N) and column temperature CC) for (Z)- and (E)-9,1l-dodecadienyl acetate. e e, Heating;0- - - - -0, cooling.

The chromatograms used to obtain the results shown in Fig. 2 were also usedto produce Fig. 3 which shows the variation in the resolution (R) of the two isomersof 9,1l-dodecadienyl acetate with changing column temperature. With increasingcolumn temperature, no resolution of the isomers is observed below 1200

• Above thistemperature the resolution passes through a maximum corresponding to the change

F~Sshowsachromatogmm ofsomeofthesc tetmkmyl amtatcs. Although itisnotfcesibletoscparateall23isomcrsonasinglechromafagram itisposibkto di&r@shbctwccnanyZ/Epairinasinglenm .

dkQholsamnotbechmula~pbed~ollthesmccticliq~crystal stati- phase, dktbyl4#-azoxyd’ - e, or on the highly polar, iwcopic p~,OV~27~.F~6~theapsrat’ions~the~ofsomecoa~ ClkeSCkok~phd~~ oIf&mamylo%yA’-mcth~~Th~ idtMletik isomers of 8,lo-dodecad~l-ol w&h cbromatograph as well as the di- msatmdd aWaW. (EJ$S,10-~1431 is the sex pheromone of&c female

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-2JE 22 .