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tri(n-alky1)phosphines. We correlate this with the penultimate Acknowledgments peak in all thc chromatograms which exhibits the same behavior. In the NMR spectra, the ratio of the phosphine oxide and phosphinate ester peaks appears to change depending on whether the oxidation is in moist air, or in dry oxygen. This is not supported by the SFC evidence, and it is possible that processes other than oxidation are taking place.

4 Conclusion Tri(n-alky1)phosphines and their oxidation products have been successfully separated using solvent-free injection for SFC on a poly(cyanopropy1)siloxane column. This method of analysis also resolved the parent organophosphine into components, which may be isomers. There is no interaction between tri(n-alkyljphos- phine and carbon dioxide over the time scale of chromatographic analysis, at 165 "C and 10 MPa or 80 "C and 30 MPa. Capillary SFC has been shown as a good method of detecting impurities in tri(n-alky1)phosphine.

The authors wish to thank Robert Moulder for helpful discussions, and Simon Barrett for performing NMR analyses M H C thanks the Royal Society for a scholarship, and S E C the Science and Engineering Research Council for a studentship

References

Ill G. M Kosolapoff, "Organophosphorus Compounds", J. Wiley, New York (1950), p 32.

121 Reference 111, p. 24

131 H. Brown, J. Am. Chem. SOC. 71 (1949) 2751

141 B. J Walker, "Organophosphoius Chemistry", Penguin Books Ltd..

[5] G. M Kosoiapoff and L. Maier (Eds.), "Organic Phosphorous Com-

161 Reference 111, p. 16.

Harmondsworth (1972), Chapter 1.

pounds", Vol. 3, Wiley-Interscience. New York (197%), pp. 343.

Ms received: May 17, 1990

Quantitative Determination of Solerone and Sotolon in Flor Sherries by Two-Dimensional-Capillary GC Bruno Martin and Patrick Etievant* Laboratoire de Recherches s u r les ArBmes, 17, rue Sully, 21034 Dijon Cedex (France)

Key Words: Multidimensional capillary GC Quantitative determination Solerone and Sotolon Wine

I Introduction Numerous papers have been published concerning the qualitative aroma composition of flor sherries [ 1-61, wines aged by the flor yeast (Saccharomyces cerevisiae species) which grows as a film on the surface. Few of the numerous components detected [7] have been quantified [81 and therefore it is difficult to draw conclusions about their respective sensory impact. Nevertheless, because of the odors detected for these compounds, Sotolon (4,5-dimethy1-3-hydroxy-Z(5H)-furanone) or Solerone (4-acetyl- y-butyrolactone) were claimed to be responsible for some aroma characteristics of these wines 191 although no quantitative data were available to confirm these statements. Since Solerone [ 11 and Sotolon [lo] are only minute constituents of wines and, moreover, chemically unstable [ll-131, the aim of this study was to optimize their extraction and separation in order to acquire reliable auantitative data for wines.

2 Experimental

2.1 Reference Compounds

4-acetyl-y-butyrolactone and 4,5-dimethyl-3-hydroxy-Z(5H)- fiiranone were provided by the Laboratory of Organic Chemistry of

the "Institut National des Sciences Appliquees", Villeurbanne (France).

2.2 Two-Dimensional GC

Capillary GC was performed on a two column system made of two gas-chromatographs coupled with a four port switching valve (N4-WT-FSR, Valco Instruments) maintained at 110 "C. The columns, injector 2 and detector 1 were connected to the switching valve via deactivated fused silica tubing (0.32 mm i.d.) using press-fit glass connectors to make the system versatile. Oven 1 (Girdel 3000) was equipped with an on-column injector connected to a retention gap (15 m, 0.32 mm i.d.), and then to DB-5column(30m, 0.53rrAmi.d., 1 pm, J&WInc.). Thecarriergas was set at 10 ml/min at room temperature using a pressure regulator. Oven 2 (Girdel 30) was equipped with an on-column injector, and a DB-1701 column (30 m , 0.53 mm i.d., 1 pm, J & W Inc.). Hydrogen flow (4.5 ml/min) was controlled by a flow regulator.

2.3 Optimization of the Effluent Transfer

Calibration curves of five solutions were first determined from triplicate injections through injector 2 as described in Tables 1

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and 2. The same solutions were then injected in triplicate through injector 1. The lactones and undecane peaks were transferred onto the second column. The yield of the transfer was estimated from the ratio of the lactone amounts calculated for both New calibration curves in the optimum conditions of transfer (0 "C experiments with the previous calibrations at three condensation and transfer of PE) were calculated and used for quantification.

temperatures and using, or not, the total transfer of the partially coeluted 2-phenyiethanol (PE).

Table 1

Transfer recovery of Solerone (YO).

Oven 2: initial temp. Transfer of PE Soiution injecteda) 1 2 3 4 5

20 "C 10 "C 10 "C 0 "C 0 "C

No No Yes No Yes

f 58 8(14)b' f I 77 8(9) Nd 58 8(5) 68 9(6) 68 4(9) 80 3(5) Nd 64 7(3) 81(5) 78 2(4) 81 2(5) 43 2(10) 73 5(8) 86 2(3) 82 2(4) 90 6(5) 86 4(0) 91 2(0) 2032) 82 $2) 100 8(4)

a) 1 = 3 52 ppm; 2 = 8 8 ppm; 3 = 19 2 ppm, 4 = 19.2 ppm, 5 = 26.4 ppm; Solutions 1 to 5 contained 10 ppm undecane. h, Coefficient of variation.

2.4 Kinetics of Extraction of Sotolon and Solerone

Extraction was performed using a white wine containing 64 ppb Sotolon and 71 ppb Solerone. The wine (500 ml) was continuously extracted 5, 9, 15, and 18 h by 120 ml of a 1 : 9 dichloro-

organic phase was concentrated to 2-3 In1 and analyzed by GC.

Table 2

Transfer recovery of Sotolon (%).

.Oven 2: Transfer Solutions injecteda) methane/freon 11 mixture. After addition of undecane (IS), the Initial temp. of PE 1 2 3

NO 79(8) 85.7(7) 9@.5(4)

2.5 Repeatability of Quantification 0 Yes 63.3(4) 71.4(4) 88.1(2)

Repeatability of quantification was estimated from six similar experiments undecane.

ai 1 = 2 ppm, 2 = 4 ppm, 3 ~ 6 ppm; so~utlons 1 to 3 contained 50 ppm

3 Results and Discussion Direct Of Sotolon In wine extracts by GC appeared to be

partially decomposed at a high pH [ 141, a chemical enrichment 1151 was not possible For these reasons, 2D GC was chosen since

The kinetics of the extraction demonstrated that the two lactones

methane azeotrope

dlfflcult because Of peak maslung Sotolon was shown to be ere quan;itatlvely extracted after 18 11 by the freon Il-d;chloro.

it allows quantification of trace amounts in complex mixtures without requiring previous fractionation. On-column inlection was used because of thermal degradation of Sotolon in heated injectors 112, 141. Such thermal degradation was not observed in the heated valve, probably because of shorter residence time in the valve (a few milliseconds) and because of the absence of oxygen in the system during the transfer. Cryofocusiny was obtained by cooling the whole D3-1701 colun?~ because it needed no modification of the chromatograph.

As expected, recovery of Solerone and Sotolon is low when condensation of the transferred effluent occurs at 20 "C (Table 1). A decrease of the temperatuIe of the oven from 10 to 0 ° C increases the recovery significantly. Since the recovery was still low when low amounts were transferred, attempts were made to improve it with a simultaneous transfer of a major peak of the chromatogram, 2-phenylethanol (Retention Index on DB-5, RI = 1173) with Sotolon (21 = l l l O ! , Solerone (RI = 1136) and uridecane. The effect of the condensation of large amounts of PE reduces the variation between replicates and at 0 "C, it also increases recovery up to 83-100 % for Solerone and to 79-91 % for Sotolon with a repeatability better than 4 % (average 2.13 %).

Repeatability of the quantification was estimated from six extrac- tions and further quantifications of both lactones were quantified in the wine used for the kinetics study. The average amounts determined from the calibration curves are close to the actual amounts, which demonstrates the efficiency of the extraction. Moreover, the repeatability of the measurements is considered as good (6.15 and 6.03 %) if one takes into accoiint the low concent.ration of the compounds determined (Table 3).

Table 3

Results of repeatibility of lactone determination.

na) Meari Stbl CVC)

Sotolon 6 61 3.75 6.15 Solerone 6 68 4.41 6.03

dl Number of replicates h, Standard deviation cJ Coefficient of varjation = St/mean

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Table 4

Quantification of Solerone and Sotolon in different wines.

Type of wine

Amounts ( m b ) Red White Rancio Sherry ~

Sotolon O(11)") O(4) O(5) 36-143(16) Solerone 0-30(11) 0-12(4) 18-115(5) 44-492(16)

a) Number of wine samples analyzed

Results of the quantification of the two lactones are summarized in Table 4 and a typical chromatogram is given in Figure 1

These results show that the method of quantification we devel- oped led to a simultaneous quantification of Sotolon and Solerone for the first time in wines at concentrations as low as a few ppb by 2D-GC. Sotolon concentration varies from 40 to 150 ppb in flor sherry wines only. Solerone seems to be less specific, but its higher concentrations in flor sherry wines (455500 ppb) explains why it was first identified in this type of wine.

Acknowledgments

This study vms supported financially by the "Corlseil general" and the "Conseil Regional de Franche-ComtB" Dijon, France. Great thanks are expressed to Mrs Agnet and Arbault from the "Laboratoire DBpartemental d'analyses de Poligny" for valuable discussions and help in obtaining samples and funds. to Mr Henry for lactone synthesis and to Mr Langiois for the drawings

References

111 M. Brock. R. Kepner, and A. Webb, Am. J. Enol. Vitic. 35 (1984) 151.

[Zj G. Pagan, I?. Kepner. and A. Webb, Am. J. E:nol. Vitic 33 1982) 47.

131 W. Cnddle, R Goswell, and M. Williams. A T J. Enol Vitic. 34 (1983) 61.

I41 A. Webb and R. Kepner, Am. J . Enol. Vit,ic. 13 (1962) 1.

[51 A. Webb, R. Kepner, and W. Baletto, Am J. Enol Vitic. 15 (1964) 1.

161 A. Webb, R . Kepner, andL Mayylora, Am J. Enol. Vitic. 18 (1967) 190.

171 H. Maarse and C. Visscher (Eds), "Volatile Compounds in Food, Volume 11", TNO-CIVO. Zeist (1989) p. 584

181 X. Tressl, R. Renner, and M. Apetz, Z. Lebensm. Uters. Forsch. 162 (1976) 115.

191 A. A. VIL!iams. "Le sostanze aramatiche dell'uva e del vino", Istituto Agrario Provinciale. Trento (1989) p 201

1101 P. Dubois, J Riyaud, and J Dekimpe, Lebensm. Wiss u. Technol. 9 (1976) 366.

I I -1 Y

2 PHENYL -ETHANOL

Figure 1

Chromatograms of the wine extract on the DB-5 column (top) and of the transferred fraction on the DB-I701 column (bottom).

[lll 0. Augustyn, C. Van Wyk, C MulIer, R. Kepner, and A. Webb, J. Agr. Food Chem. 19 (1971) 1128

1121 P. Girardon, Y . Sauvaire, J. Baccou, and J . Bessiere, Lebensm. Wiss. u . Technol. 19 (1986) 44.

1131 A. Kobayashi, "Flavor chemistry, trends and development", ACS Symposium, series 388 (1989) 49.

1141 B . Martin, P . X. Etievant, and N. Henry, in Flavor Science and Technology. Y . Beinere and A F. Thomas (Eds), Wiley, Chichester (1990) pp 53-56

[151 P Etievant, Agric. Food Chem. 29 (1981) 29

Ms received September 12, 1990

Journal of High Resolution Chromatography VOL. 14, FEBRUARY 1991 135