810

FEATURE

Supercritical fluids attracting new interestIn the 1970s, it was the energy crisisthat brought supercnrtcal fluid tech-nology into the limelight: the 19905are bringing environmental and healthconcerns that have refocused theefforts of supercnncat fluids re-searchers.

Rapid energy costs during the1970s sparked interest in supercrtncatfluid technology as commercial pro-cessors sought 10 lower their energyconsumption and to improve extrac-tion methods. Supercrincat fluidextraction (SFE). which can be carriedout at lower temperatures than con-ventional extraction methods, is oftena lower energy consuming process.

There are examples of commercial-ization of SFE. In Europe. severalSFE plants for decaffeinating coffeeand tea. and processing hops andsome spices. have been in operationfor several years now. ln the UnitedStates. General Foods Corp. has a cof-fee decaffeinarion plant in Houston.Texas: Pfizer has a hops SFE facilityin Nebraska. and John I. Hass is build-ing one in Yakima. Washington(scheduled for completion in 1991).SKW Chemicals. Inc .• in Marietta,Georgia. uses supercritical fluids toextract hops. essential oils and spices.

But for each commercially success-ful application of SFE technology.there are many examples where itfailed. "There was unbridled enthusi-asm about the potential for supercriu-cal fluids," said Val Krukonis, presi-dent of Phase x Corporation. "butthere were many misapplications ofsupercritical fluid technology, espe-cially when directed to the separationof large volume chemicals. Energysavings alone do not assure economicviability of any process. I do feet.however. that supercritical tftuidextraction is a viable technology inthose cases where other separationsprocesses cannot solve the problem oropportunity."

The energy crisis has abated. andthe gfiuer of supercritical fluids as"magic solvents" has faded. New con-cerns about environmental. consumerand worker safety. as well as theemergence of new extraction prob-

lems , have refocused anernion onsupercritical fluid technology. Mostprocessors say that supercritical fluidextraction belongs in the high-value orhigh-profit margin sector, such as spe-cially oils. or in cholesterol removal. adifficult task using conventionalmeans.

A major impetus toward SFE use isenvironmental concern about organicsolvents. Supercritical carbon dioxide.

Two pIIot'lCalemoehines 10. sup«-crtllcalnuldestree-HOf'1. OM of /hemwtlhonlinesuparcrHI-coilluid ehromotog-raptlYequipmllfll,!Tom S/TEC-SleberEngineering In MOUl!Zurich.Swl1zer1and.

an especially good solvent for nonpo-lar substances such as lipids, is non-toxic, nonflammable and environmen-tally acceptable. SFE solvent cleanupis easy: depressurize the extractedsample. SFE has the mild critical tem-perature of 31·C. making it ideal forprocessing heal labile compounds.Thecost of disposing of a conventionalsolvent may now exceed the originalcost of the solvent itself; companies

INFORM, Vol. 1, no. 9 (September 1990)

812

Heat

FEATURE

The extraction process for the removal of cholesterol from buller.

and government laboratories areincreasingly aware of the health haz-ards to lab workers of chronic expo-sure to organic solvents; and con-sumers are demanding more and more"pure" products free from chemicalresidue. Rolf Sieber. of SITEC-SieberEngineering AG. a supercriucal fluidequipment manufacturer in Switzer-land, said. "We already have cus-tomers who must convert productionunits 10 supercriticaJ fluid extractionbecause of new laws on air pollution,worker safety and waste disposaldirected against organic solvents andhazardous residues in foods. ,-

So where does the fats and oilsindustry fit in? To begin. perhaps abrief refresher on supercnncet fluidtechnology is in order, When a gas isheated above its critical temperature.it cannot be liquified, regardless of thepressure applied. As one appliesincreasing pressure, up to severalthousand pounds per square inch, thedensity of the gas starts to increaseand approaches that of a liquid, A gaswhich has been heated above itscritical temperature and pressurizedabove its critical pressure is called asupercriticai fluid. It has solvatingproperties approaching those of theliquid state, and high diffusivity andlow viscosity resembling the gaseousstate. By varying such parameters astemperature and pressure, selectedcomponents can be differentiallyextracted from a mixture, somethinglike fractional distillation. Other sol-vents can be used rather than super-critical C02. of course. and may benecessary when extracting polar sub-stances.

involves some pre-extraction prepara-tion (such as cracking. dehulling andflaking the oilseeds). passing a streamof supercritical C02 (above SO'C)through the seed matrix. venting theC02-oil solution into another vesseland lowering the pressure. The C02may be vented. stored or recycled.leaving the oil free of solvent residue.A system has been constructed toinclude a parallel series of three ves-sels, which allows two vessels to be inthe extraction mode while the third isbeing emptied and refilled.

King, along with vegetable oilresearchers Gary List andTimothy Mounts, is currently

investigating using supercritical C02at lower extraction pressures to refinecrude soybean oil to a finished edibleproduct. These lower pressure-basedrefinement processes should reducecapital costs and alleviate problemsassociated with the higher pressureextraction of soybean flakes, and yetyield an equivalent or better product,said King.

Although SFE results in high oilyields and "good quality. it may do itsjob too well: phospholipids are essen-tially insoluble in supercritical C02(thus eliminating the need for degum-ming of C02-extracted oils). butphospholipids help protect crude oilsfrom oxidative deterioration in stor-age. Gary List and other NRRCresearchers have improved the stabili-ty of C02-extracted oils by addingantioxidants.

Researchers elsewhere are examin-ing supercritical C02 processing of

OnseedsNo lab has done more research onSFE and oilseeds than the high pres-sure research lab at the U.S. Depart-ment of Agriculture's NorthernRegional Research Center (NRRC) inPeoria, Illinois. Much of its work dur-ing the early 198Ds, headed by John P.Friedrich, focused on extracting oilsfrom commodities such as soybeans,com. ccuonseed and peanuts: today,the focus under the the current leadscientist Jerry King includes highervalue oils such as jojoba and eveningprimrose oil. Basically. the technique

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other oilseeds. R. Eggers, at the Tech-nical University of Hamburg-Harburg,in collaboration with U. Sievers andW. Stein, at Krupp in Germany, hasexamined supercritical extraction ofrapeseed. They conclude that anycommercial plant to process oilseedmust be designed to operate continu-ously without loading, degassing oremptying periods. One possibility.they suggest, is to design the systemso that the solid material enters andexits the system through a screwpress. A group in Italy has examinedusing supercritical C02 to deacidifyolive oils; another Italian group hasconducted preliminary tests onextracting oil from fresh olive paste.

P.E. Turpin, at the Institute of FoodResearch in England, and colleagueshave used supcrcrnical C02 on a pilotplant scale to extract triglyceridesfrom crude Shea nul oil. The resulting"Shea butter" is a raw material in theproduction of fractions as substitutesfor cocoa butter in chocolate. Theresearchers found that polyisoprenoldgum, along with other contaminants,could be successfully removed fromthe crude oil using supercritical C02.thus eliminating the degumming step.They also noted that their proceduremight be used to extract oil fromground Shea nuts.

Another possible SFE oilseed pro-cessing application under study at theNRRC is the regeneration of bleach-ing clay. "We've found that supercriri-cal C02 can effectively remove the oilfrom spent bleaching clay. down to1-2%. Adding diatomaceous earth as

INFORM. Vol. 1. no. 9 (September 1990)

813FEATURE

a dispersing agent speeds the extrac-tion process. The regenerated clay(perhaps) could then be used as is, ormixed with virgin clay," To dale, Kingand his colleagues have nOI testedreusing the extracted clay for funherbleaching purposes.

Raben Hasten, a ccnsuftam to thefats and oils industry, questions theeconomic feasibility of using a rela-lively high-cost technology 10 recyclethe relatively inexpensive clay: "Dis-posal of spent bleaching clay Isn'treally a problem now, although aslandfills begin to reach capacity, asmany of them are, the cost of truckingthe clay to more and more distantspots may become prohibitive. Thereare other. less COSily. alternatives todisposing of the waste. however:'

List. however, has noted that a typ-ical soybean oil refinery incurs lossesof $1.100 each day in used clay plusthe disposal costs. Mounts. who isalso collaborating with King on the

bleaching clay project. agrees that dis-posal of bleaching clay has the poten-tial to become a problem, adding."Using supercritical fluids to recyclebleaching clay may become economi-cally viable in the future. though. ifthe EPA decides to impose environ-mental controls on its disposal."Mounts feels that the industry will beeventually directed by the EPA toaddress the disposal problem and theassociated fire and odor problemsinvolved with bleaching clay.

EconomicsWhat about the economics of the pro-cess? Although SFE often results inhigher yields and reduced refiningrequirements, and solvent costs arelower. commercialization of the pro-cess for commodity oilseeds is farfrom imminent. "The capital and oper-ating COSIS are extremely high." saidR.G. Krishnamurthy, senior groupleader at Kraft Research and Develop-

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ment. "For that reason, I doubt thatSFE of commodity oilseeds will becommercially viable in this century.People should begin to look at relatedalternatives to SFE: subcritical extrac-tion (using gasses), paired with co-sol-vent extraction. for example, wouldbring down capital and operatingCOSIS. There may be some areas inwhich SFE may be useful in the ex-traction of high-value or high-profitmargin oils, or those fatty acids thatare difficult to process using conven-tional methods."

Krishnamurthy cites eicosapen-taenoic acid (EPA), docosahexaenoicacid (DHA), and j-Hnolenlc acid asexamples of fatty acids that might beprofitably purified by SFE. Not onlyare they expensive, but they are alsohighly unsaturated and difficult topurify in their original forms usingconventional extraction methods.

King agrees, saying that high-valueoils such as jojoba and evening prim-

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INFORM, Vol. 1, no. 9 (September 1990)

814

FEATURE

Inorganic salts, ethanol and a cannonThe ability of a supercritical fluid to dissolve low vapor pressure solidmaterials was first reported by J.B. Hannay and J. Hoganh III a meetingof the Royal Society of London in 1879. Hannay and Hoganh describedtheir experiments. carried OUI in small-diameter glass tubes, in whichthey observed that changes in pressure caused several inorganic salts(e.g., cobalt chloride, potassium iodide. and potassium bromide) 10 dis-solve in or precipitate from ethanol at a temperature above the criticaltemperature of ethanol (Tc = 234°C). They found thai increasing the pres-sure on the system caused the solutes to dissolve and thai decreasing thepressure caused the dissolved materials 10 nucleate and precipitate "as asnow."

For creativity, none of Hannay and Hogarth's predecessors can topBaron Cagniard de la Tour. who demonstrated the critical poim of a sub-stance in 1822. In fact, for many years the critical point was referred to asthe "Cagniard de la Tour" point. In his earliest experiments. de la Tourused a piece of rifled cannon for his high-pressure investigations. Hesealed a liquid and a flint ban in the cannon barrel. heated the barrel. androcked it while listening for changes in the sound of the rolling ball or forchanges in the sound made when the barrel was tapped. Discontinuities inthe sound (noted. incidenlally. while the baron held his ear to the sealedend of the cannon) led him to describe the pcira we today know as thecritical point. He later carried out experiments in glass tubes so thai hecould visually observe critical phenomenon.

From Supercruicat Fluid Extraction. Principles and Practice. by MarkMcHugh and Val Krukonis, Butterworth Publishers. Stoneham. MA,1986. pp. 13-14.

rose may be some good bets for com-mercial SFE. Evening primrose oil isa major source of jclinolenic acid andmay have some medical value. espe-cially in the treatment of atopiceczema. Thousands of tons of seedsare produced each year, although theUnited States and Canada account foronly about 300 tons annually. and theoil sells for as much as $14 an ouncein some places. Fabio Favati, a visit-ing scientist from Italy. and King havefound that supercritical C02 extrac-tion of evening primrose oil is fasterand more efficient than hexane extrac-tion. and leaves no chemical residuein the oil. At 122' F and 10.000 psi,they reported more than 95% recoveryin 10 minutes.

Using petroleum solvents to extractwax esters from jojoba is unaccept-able 10 the cosmetic industry. a majoruser of jojoba oil. Cold pressing orexpelling has therefore been theextraction method of choice for jojo-ba. but such processes leave up to

15% of the wax esters in the press-cake. Friedrich and his colleagues ini-tiated work on jojoba oil extractionand found that, although the waxesters are less soluble in supercriticaJC02 than are soybean oil trig Iyc-erides, wax esters were very misciblewith supercriucal C~ at higher pres-sures.

For people who need highly purifiedfractions. however. supercritical C~may be a great solution."

William Nilsson. a scientist at theNational Marine Fisheries Service(NMFS) in Seattle, Washington. isusing SFE to fractionate fish oilesters. Purified sources of the 00-3Iany acids EPA and DHA are inincreasing demand. especially in clini-cal settings where they may be used instudies on the prevention or treatmentof cardiovascular disease or rheuma-roid arthritis. Pure fonns of EPA andDHA must be obtained by first con-vening the triglycerides 10 alkyl esters(Since the fatty acids are randomlypositioned on the glycerol backbone),followed by urea fractionation. Super-critical C02 can then separate theesters according to carbon number(C 18, C20, C22. erc.). Nilsson hasachieved a fraction that is 96% EPAusing these methods.

SKW Chemicals has also workedout a process to produce 80% 00-3concentrated Iauy acids through ester-ification of purified salmon oil by acombination of fractionation withsupercriucal C02 and crystallization.On the basis of lab data obtained atNMFS. Krukonis estimated thai thecost of producing 90% EPA in a smallpilot plant operating at 10 pounds/daywould be about $IOO/pound, exclusiveof the feed material costs.

INFORM, Vol. 1, no. 9 (September 1990)

Fish oilsAs with the oilseed industry. thefuture of supercrirical C02 extractionand fractionation of fish oils is likelyto lie in the high value sector. Accord-ing to Anthony P. Bimbo. director ofapplied development at Zapata-Haynie, "It is difficult to determinewhere the supercritical fluid processwould fit into the refining of fats andoils: Could it replace all of the refin-ing steps. or is it an add-on or finisherstep? Capital start-up costs wouldseem to make supercritical C02 pro-cessing of edible fish oil. a cheapcommodity. prohibitively expensive.

Other processesFrom a medical standpoint, the bene-fits of reducing dietary cholesterol aredebatable; from a marketing stand-point. foods containing reducedcholesterol mean money. According toa 1988 survey (cited in the November1989 Food Processing magazine).America's most dramatic health/safe-ty-related behavioral change wasreflected in efforts to limit dietarycholesterol. According to the survey.48% of U.S. adults "try a lot" to limitcholesterol intake,

There has been some research anda considerable amount of hype regard-ing supercritical C02 extraction 10remove cholesterol from buller, eggs.milk. even whole steaks. Much ofwhat has been claimed, according toKrukonis. "appears to be impossible.The researchers who claimed that

816

FEATURE

'we'll be eating supercrltlcal fluiddecholestcrolized steak' certainlymust have found in their very firstexperiment that they could extmct nei-ther fat nor cholesterol because. forstarters. the mass transfer resistanceprevents extraction. On the more fun-damentally limiting side. the fat andcholesterol are, literally, inextricablyentwined in cell. membrane andlipoprotein structures," he said."Many such claims of. for example.cholesterol extraction from milk andliquid eggs serve 10 confuse the read-ers and consumers. When the cluirns<IreInter shown to be false, SFE losesits credibility. Thus, it is of lenregarded with skepticism when it isproposed for some other (legitimate)opportunity,"

Aho,estero,-reduced butter. onthe other hand, is feasible andsomething for which con-

sumers might be willing to pay a rea-sonable premium, "1 estimate that atproduction of 20 to 30 million poundsof cholesterol-reduced butler a year,the operating costs would be about20~ a pound," Krukonis said.

Other research efforts have beenaimed at removing cholesterol frombeef tallow and dried egg yolk. SKWChemicals Inc .. who for years hasbeen in full-scale production of super-critical C02 plants. has exploredsupercritical C02 cholesterol removalfrom beef tallow and "just didn't findit economically attractive," accordingto product manager Gene Carbonell.He added that SKW is exploringanother, more economical avenue ofremoving cholesterol from beef tallowand possibly lard.

Still another possible application ofsupercritical fluid technology to thetreatment of beef tallow is the separa-tion of greaves from animal fat. "Theseparation of greaves from animal fatis only partly an extraction process,"said Sieber. "Under supercritical CO".a large pan of the fat melts at 40 io50'C, leaving the greaves as fullyactive proteins. Combining this withan extraction with supercriricel C02results in a clean. white fat andgreaves which can be used for the pro-duction of hamburgers or sausage."

More in keeping with the use ofsupercritlcal fluid technology in the

high value sector. SK W ChemicalsInc. is exploring with a potential clientthe use of SFE in the purification oflecithins, a process which they havepatented. SKW is also one of severalenterprises involved in the SFE ofessential oils and spices.

Several new supercritical fluidapplications for the processor lieahead, according to Sieber. One isspray-drying in supercrhlcat fluidextractors. "The upstreaming super-critical fluid absorbs the liquid solventfrom the droplets which fall from thetop of a column and reach the bottomas solid balls:' he said. "By changingthe gas pressure, the contact time forthe absorption of the solute can bevaried. The density difference can beadapted very easily." Others includecell cracking and controlled catalyticchemical reactions and enzyme cat-alyzed reactions in supercritical fluids.Nippon Oil and Fats, for example. hasbeen granted a Japanese patent for themanufacture of EPA- or DHA-enriched fats and oils using lipase insupercritical C02.

The futureUltimately. if stricter governmentalregulations may dictate economic con-siderations by toughening environ-mental regulations on the oilseedindustry. SFE of oilseeds may become

a commercial reality. A hint at whatlies ahead may be found in the CleanAir Act now moving through the U.S.Congress. The way the bill is shapingup now, many oilseed crushing plantsare likely to be required to install newemission control equipment some timein the late I990s. Hexane is one ofapproximately 200 pollutants listedfor scrutiny by the EPA. which meansthai EPA would be mandated to createstandards for any industry with indi-vidual plants emitting more than iOtons of hexane per year.

Ron Moeller. the Narionnl OilseedProcessors Association's technicalcommittee chairperson. cautions thatnobody really knows the full impactof the bill on the crushing industry. "Afew plants may be forced to shutdown 10-20 years down the road,especially those which. due to meteo-rological conditions or propeny con-figuration, can't meet the require-ments of the Clean Air Act. We maybe forced someday to revert tomechanical extraction methods used50 years ago. Whatever happens. theClean Air Act will probably heightenwhat has been, to date, an academicinterest in SFE."

(This report 011 supercritical fluidtechnology was prepared by INFORMnewswmer Sara Ulfta.)

Analysts find new ways to use SFC, SFEPerhaps the most rapidly growingapplication of supercritical Iluld tech-nology today is in analytical chem-istry. Analytical chemists, with differ-ent economic constraints than thosefaced by the commercial processingindustry. 'find supercritical fluidtechnology an attractive alternativeextraction and analytical method.

Supercritical fluid extraction (SFE)may be used to prepare samples foranalysis; supercritical fluids can alsobe used as the mobile phase in super-critical Fluid chromatography (SFC).Although SFE can be coupled withSFC. it also can be used independentlywith gas chromatography (GCl orhigh performance liquid chromatogra-phy (HPLC). SFE coupled with SFC

or GC offers an analyst the possibilityof placing an unprepared sample in II

container, then extracting and analyz-ing its components in one continuousstep with any number of components.There are interesting applications forsupercritical Fluid analytical tech-niques in the food, cosmetics and agri-cultural/environmental industries.

SFE as a technique for preparinganalytical samples is really a much-improved alternative to a traditionalextraction method-the Soxhletextraction. Steven B. Hawthorne, ascientist at the University of NorthDakota. commented, "It is ironic thatsome modern chromatographic tech-niques have become so highly devel-oped that they can separate, identify

INFORM. Vol. I. no. 9 (September 1990)

FEATURE

and quantitate hundreds of samplecomponents per hour. yet analystsoften rely on sample extraction proce-dures-such as liquid solvent extrac-tion in a Soxhlct apparatus-that werein use when Tsweu first reported chro-matography in 1906."

W.J. Hurst. of the analyticalresearch and laboratory service groupat Hershey Foods. is particularlyenthusiastic about using SFE as atechnique to prepare samples forHPLC or GC. Hurst. whose group isusing SFE for lipid fractionation. says."It's a very exciting tool with greatpotential. SFE makes it possible tomake sample preparation trivial. Con-ventional extraction techniques. suchas Soxhjet extraction, require severalhandling steps, each of which intro-duces additional errors. SFE is a muchmore reproducible technique becauseit can be automated and thereforeeliminates a lot of the steps."

Automated SFE can be pro-grammed, by varying temperature lindpressure. to be selective in the extrac-tion of particular classes of com-pounds-reducing the time needed forsample preparation. What used torequire a 24-hour Soxhlet extraction,for example. could be completed inless than one hour using SFE.

Marvin Hopper, II scientist lit theFood and Drug Administration's TotalDiet Research Center (TDRC) inKansas City. Missouri. is using SFE toprepare samples for gas chromato-graphic analysis. TDRC analyzes foodproducts from grocery stores for heavymetals and pesticides residues. andthen uses computer technology to esti-mate the dietary intake of these com-pounds by consumers-from toddlersto the elderly. "We can detect parts perbillion levels of pesticides in peanutbuner or hamburger, for example,using these methods." Hopper said."We can achieve the same sensitivityusing conventional extraction meth-ods, but we're making a real effort toget rid of organic solvents in the lab.This (SFE) not only cuts down on theinitial cost (of buying the solvents).but also on the cost of disposing ofthem. The disposal costs can now bemore than the solvent's original cost."

Hopper also cited concerns aboutlab technician safety as a reason 10 use

SFE. "Many of these technicians haveworked with organic solvents for 20 to25 years," he said. "They're in it forthe long haul. and the fewer solventsthey are forced to handle, the better,"

Hopper. who has been conductinghis SFE work in collaboration with theNRRC's King, is building a multi-ves-sel extractor much like the one in Peo-ria. With that, he said. he will easilybe able to analyze off-the-shelf prod-ucts.

An advantage to supercritical fluidextraction of fats from meats for pesti-cide analysis. according to King, isthat very small amounts of fat in asample can be analyzed successfully."Our tests showed," King said. "thatthis process can handle low-fat hams.for example. where the other methodsusing chemical solvents have beenineffective," King's research on theextraction of pesticides from meats ison behalf of USDA's Food Safety andInspection Service; he is also begin-ning to pursue the extraction of pesti-cides from grain samples for theUSDA's Federal Grain Inspection Ser-vice.

Analytical chemists also are find-ing uses for SFC as an alternative toGC and HPLC. SFC has advantages inanalyzing some polymeric materials,drugs, surfactanrs, isocyanates, carbo-hydrates, agricultural components,steroids and antibiotics, according toMary Ellen McNally, an analyticalchemist in the Agricultural ProductsDepartment at Dupont. McNally hasused SFE to study herbicides inoilseeds: "We're looking at a class ofherbicides. the sulfonylureas, whichare moderately polar compounds.Many people think of using SFE onlyfor nonpolar compounds. but we'vehad good success with the technique,"

According to Thomas L. Chester,an analytical chemist at Procter &Gamble, "When the solute isn'tvolatile or is thermally unstable, andthe solute isn't easy to detect or themixture to be analyzed is very com-plex, neither GC nor HPLC will work.About one-fourth of all separationproblems faced by analytical chemistsremains beyond the limits of theseconventional techniques, and this iswhere SFC comes in," For Chester,SFC is useful in analyzing molecules

817

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Raymond Houck, vice president atSuprex Corp., an analytical scalesupercrirical Fluid extraction equip-ment supplier. estimates that theimmediate market for SFE is thereplacement of 25-30% of the exist-ing 5,000 Soxhlet apparatuses in lab-oratories. and that number shouldcontinue to grow. The search for newand safer extraction methods may nOIbe a matter of choice in the future. It'sfeasible that, in the next five to tenyears, the Environmental ProtectionAgency (EPA) may mandate SFE forenvironmental testing. In 1989. theEPA began a four-year program todevelop SFE' methods with the ulti-mate goal of reducing the amount ofmethylene chloride used for extrac-tions in EPA methods by 95% frompresent levels.

in surfactants and emulsifiers.An interesting application of SFE-

SFC is the characterization of singleseeds with respect to their triglycerideand fatty acid compositions. Suchinformation, according to King, is ofvalue to scientists involved in seedhybridization and genetic engineeringof plants. Ideally, a very small sampleoff a seed could be taken for analysis,leaving the rest of the seed still viablefor planting.

Capillary SFC is also an excellenttechnique for defonnulating commer-cial products that contain nonpolar tomoderately polar components, espe-cially those with lipophilic com-pounds such as lotions, lip balms andlipsticks. "We've used capillary SFCto separate the components containedin natural lanolin. lanolin derivatives,supercritical fluid extracts of wool

grease,jojoba oil and chemical deriva-tives of jojoba oil." King said. SFC issufficiently sensitive to separate suchclosely related mixtures as natural andsynthetic lipids.

A unexplored option in couplingSFE with chromatography,according to King, is the pos-

sibility of conducting reactions undersupercritical fluid conditions. Oneexample of a supercritical C02-cat-alyzed reaction was shown by Kingand his colleagues John France andScott Taylor at the NRRC. They cou-pled the analytical SFE of triglyc-endes with capillary gas cascmcrogra-phy, and observed the formal ion offauy acid methyl esters over a solidalumina catalyst in the presence ofsupercritical C02' This, King and hiscolleagues concluded, permits directanalysis of fany acid methyl esters.

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INFORM, Vol. 1, no. 9 (September 1990)