Application of conductive polymer analysis for wood and woody plant identifications

An electronic aroma detection (EAD) technology known as conductive polymer analysis (CPA) was evaluated as a means of identifying and discriminating woody samples of angiosperms and gy~itnosperins using an analytical instrument (electronic nose) that characterizes the aroma profiles of volatiles released from excised wood into sanipled lieadspace. The instrument nieasures electrical-resistance changes generated by adsorption of volatiles to the surface of elecuoactive. polymer-coated sensors. Unique digital electronic fingerprints of wood aromas. derived from ~nultise~tsor-responses to distinct mixtures of wood volatiles. were obtained from woods of i~itlividual tree species. A reference library containing aroma 5ignature patterns for 23 tree species was constructed for identifications of unknown saniples using pattern-recognition algorithnts. The 32-sensor array usecl with an Aromascan A32S instrument was sensitive to a wide diversity of organic compounds and produced outputs of distinct electronic aroma signature patterns in response to wood volatiles that efiectively identilied unknown samples fi.om individual tree species included in the reference library. Sonie potential applications of CPA ~iiethods for research in ecology, forestry, pl:uit taxononiy. and related disciplines were identified with some significant advantages anci limitations. Other applications of this technology were discovered for the niittiagement of forested stands and ecosystems based on the iclentilication of roles that woocf-inhabiting organistns play in stand dynamics and long-term ecosystem functions. Re\ults pertaini~ip to tree systematics and phylogeny are discussed in the context of prevailing opinions of oak taxonomy. ( ' 2005 Else~~ier B.V. All rights reserved. R~~yit.~rcI.\: Artificial ollhctio11: I'.lecrsol1ic nose detection: I-'orc\i ecology: Forest manrigen~ent: Plant chemot;txonomy: Q~~('R.II.\: Worjtly a m p l e idcntiiication Analyttcal method\ arc lieedcd in foi-e\t ecology re\carch to provide reliable mean\ of ~deiit ifytng C o l r e y x x ~ l ~ n g 'tuthoi Tcl +I 662 08h 3 180 f,ix + I 662 680 ?I95 woody \ample\ from a variety ot \ourcc\ and location\ E IIIOII c i t ~ r / r r ~ ~ ~ r \ i i ~ \ ~ ~ \ o n ~ ? @ I \ led ( I \ ( A 11 WIIWII) that are not readily ~dentifiable by co~ iven t~ona l ~ o h e ~ l cl I \ teti u \ tC 5 O b c ~ le) lneaiii Traditional chemical and ~nicroscopic method\ 0378-1 1271'; bee l'ront matter I 2005 Else\ier N.V. All ~riglits re\c~-\ecI. doi: 10. 1 0i6/~.iorcco.2005.O1 ,030 u\ed for wood rdcntrhcatron h~therto ale cumber\ornc becdu\e they often requrrc cxtcnuve s~irmplc pr epdrdtton 'ind 'rnaly\i\ New method\ yleldlng raprd woody \,imple ident~hcat~on\ could facil~tdte dctcrmrnation\ of brologic~l dcti~ltle\, rntcractron\, 'ind ecologrc,il roles of mrcroorpanr\rns. rn\ect\, and other rnvertebrate5 tli'it rnter,ict wrth wood In I~vrng dnd dead tree4 or c o a \e woody debrts on the toicst float Organr\m\ d\\ocr,ited wrtli wood in toie\t eco\y\tcm\ ,Ire ln\olved 111 wch rieti\~tte\ a\ wood deconipo\rt~on. nut1 rent cyclrng. and other tunct~onal nrchc\ that dftcct t o ~ c \ t \t,ind \tructurc. dyriamrc\. and eco\ystcrn pr oces\e\ (Andrew\ 'tnd H'II I 14. 2000, H'insen and Gol~ecri, 7000, Whrpp\, 2001) Many rnrcrobc\ h'ive cttcct5 on tore\t health 'tnd eco\y\tern function\ becaii\c they lncludc c d ~ ~ \ a l 'igerit\ ot tlee ~nottallty. t o ra t dr\ea\e\. wood dec'iy, 'ind lumber defect5 ot ttnpol tance in eco\y\tern drld trmber m~nagcment, and In the lnanufacture of fora t product\ Al\o. certain type\ ot ecolog~cal \ tud~e\ In fore5t \clcnce and related rc\edrch di \c~pl~nel have need of \pec1alr7ed 'inalyt~cal equiprncnt capable ot qutchly 1ecognt7rng 'ind d~scrinirnat~tig between vdrrou\ types of woody \,imple\ wrth rnr~iir~ial dcstructrvene\\ du~rng \ampl~ng Such In\trunicnt\ 'ind method\ are needed wltli the capabtltty of p~ovldlng thew deter mrnatrons bawd o n d raptd chernlc,il rneam of dctcctron Eldborate analytrcal method\ \uch a\ pa\ cliromatogr,iphy-m:i\\ \pectro\copy are only capable of rdcntrtylng the chcmrc,il compounds prc\ent rn wood. but thrs rnfi)lm,ltron doe5 not nece\\a~ily provrdc the ~nforrnation needed tor wood ~dentrhc,itron\ There 'ire numcrou\ tn\t,ince\ where moody \,imple\ collected tor re\edrch purpose5 ' I I ~ not re'idily tdcnt~fr~lble because ot the ditflculty In deterrntrirnp ~ndrvrdu,il source trees from whrch woody \,ilnplc\ wele cier~vcd, or bcc,iu\e \dnip1e\ were t'then trom woody pl,int\ du~rng trn~e\ ot the j w r \vIien ~dciltrtyt~lp ~ h ~ ~ r ' i c t e ~ \ (flower\. trurt\. 'tnd Ic,tvc\. etc ) 'itc ,ib\cnt Analytrc,il tools 'ind ]nethod\ c,ip,ible ot ~deritlfytng woody \,imple\ wlthrn thew Ilrnrt~ttron~ 'ire e \ \ e ~ ~ t i ~ i l tor cli~ir~ict~rr71ng 'ind deterrnrnrnp the role\. d,im,lgrng etlcct\. 'lnd rntc~relatron\hip\ arnonp wood-teedlng 'ind wood-rnli,ihrtrng oig.inr\rn\ th'it rntel'ict wrth tree\ In tore\t \t'ind\ and ultrm,itcly 'titcct tore\t hccilth, \rand stlucttile, compo\rtton. \tabrlrty. eco\y\tem plocc\\cs. ,ind tore\t d y n ~ n ~ w o\cr trriie Such c,tp,ibilrttc~ mere made po\\ible wrth the rnventlon of Instrument\ called "elcctrontc no\e\" that welt de\igned to produce drg~tdl elcctronrc \rgnature\ ot vol,itrle\ r e l e a d from any orpanrc souice (Dodd and Per\aud. 1982, Pelosl and Per \,lud, 1988. Shrr ley 'ind Perwud. 1990, Pel\aucl, 1992, Pei\aud et ' 11 . 1993) Unlike other ,in,ilytrc,~l rn\trumcnts. thew dc \~ce \ ,illow the ~deiitrfic~itron ot oigdnic \ample\ wrtliout havrng to ldentlty ~nd~vrdudl chemical component\ wtthrn the volatrle rnrxturc (G'irdrier. 199 1 , Davrdc et ' 11 , 1995, L.onctgan et a1 , 1996). 'ind avord opel'rtor tatiguc (Shu~ m a , 1990. Gdrdncr ,uid Shurmer, 1992) Agrrcultural and tood rndust~tes have utlllzed conductive polyriler '~naly\r\ (CPA), a type ot clectronrc diotna detectron (EAD) technology, to rnea\urc product dnd food qu'ilrty (Ar\hrti~'i, 1991. Hanakr et dl . 1996, Bartlctt ct 'il , 1997). \torage lrtc ~ D I Natalc et a1 . 1995, 1996). trcshne\\ (Egash~ra, 1997). agr~cultural waste detectron (Hobb5 et a1 . 1995, Persaud et a1 . 1996). rccognrtlon of organlc chcm~cals iKowar\ki and Bender, 1972), dragno\r\ of plant dr\ca\e\ (Wrlson et a1 . 2004), and many othel dppl~c~itrons (Ouellettc, 1999, Yea et dl , 1994) Wlthrn the field of forest pe\t rnandgemcnt, CPA ha\ proven usetul rn the dctectron ot bactcr~al wetwood rnfect~on\ In cottonwood, the detection dnd identrhcatron ot tungal forest patl~ogcn\ (e g Crr t r t o c \ t r r c f t r g c l c ftrr ~rrll), and the dr\crtnirnatron of wood decay tunpr III woody \ample\ (Wrl\on and I,e\tcl. 1999, Wil\on et al , 2004) A varrety of drtfcrcrit \en\or type\ h'ive been developed tor thew v,ilrou\ cipplicationr rncludrnp opttc'il sen\or\ (Whltc ct ' 11 . 1996). met'il oxrdei (Shur me1 et '11 , 1989. Eg~i\1iitct 'tnd Shimi7u. 1993. N'tnto et '11. 1993). \emi~onductivc polymer\ i Meyc~ hoft. 1993. Yrrii et '11 . 1993. Pr\,inclh ct ' 11 . 1994). 'ind cond~~ctrve polynlel\ (M,lthcld ct al , 1994. Frcund 'ind 1,ewrr. 1995. Lonerpan ct ' 11 . 1996) An electronic now typrc'tlly consr\t\ ot ,I multt\en\or ari~iy, in rntoim'itron-procc\\riig \p\tcni \uch ,I\ 'in art~hci~il neural networ h (ANN). \oftw,irc wrth cl1git.11 pattern-recognitron 'ilgorrthm\. 'ind ieterenceIrbr'lry d,itab'ise\ (Abe et ' 11 . 1988. Freund 'inct Lcwr\. 1995. Gar dner . 199 1 . G'~rcinet 'iild Shui met, 1992. KowCu\kr 'ind Bendct. 1972) The 5en\o1 arr'ty con\r\t\ ol rncrenicnt,illy dltlerent \enrol\ that re\pond to ,i wrdc r~inge ot c1iemrcLil cl,i\\e\ 'ind dr\crrnirnate dl\ er \e ~nrxture\ ot po\\rblc ,un'tlyte\ The output trom individual sensors are assembled and integrated to produce a distinct digital pattern of responses (aroma fingerprint) called an electronic aroma signature pattern (EASP), allowing classification and identification of the analyte. Using EASPs. representing unique aroma signtiturc patterns for complex mixtures of distinctive arotnas in the sample mixture. allows recognition of the sample as a whole without requiring the mixture to be separated into its individual cornponcnts prior to or during analysis. A reference library of EASPs for known samples is constructed prior to analysis of unknowns by assigning descriptor names (identifiers) to patterns of known origin. The ANN is configured through a learning process (neural net training) using patterli-recognition algorithn~s that look for differences between the patterns of 1111 the descriptor types included in the reference library. This process continues until a previously selected level of discrimination is met. Thc results are validated and assembled into the reference library to which unknown samples can be compared. Identification of unknowns is based on the distribution of aroma attributes or elements that the analyte pattern has in common with patterns present in databases of the reference library. This investigation focuses on the potential application of conductive polymers for the idctltification of woody sarnplcs for forest ecology and related research. The objectives of this study were to: ii) evaluate the feasibility of using CPA technology as a means of identifying anci discriminating woods of angiospertns and gymnosperms based on electronic signarures of volotilcs released from excised wood cores, iii) develop CPA neth hods and applications L ~ S C ~ L I ~ for forest ecology through woody plant identifications, and iiii) examine he potential applicability of these rnethods to plant taxonomy and fix determining chernical relatedness bctulecn plant species. Some preliminary results of this work were reported previously (Wilson and Lester. 1999). 2. Materials and methods 2 1 C'ollt~c trorr ~1r1tl \foi(rgt> of 1t ood\ \(rr~tplt~\ Incrcrnertt core\ of \t:indard d~mcn\lon\ ( 5 mm dtamcter x 5 ctn length) wcre collected in wlnter and early \prlng trom sapwood t ~ \ \ u e \ of pl'ints, reprcsent~ n g 23 \ ~ C C I C \ o t t teej '~nd \hrub\ trotn 14 plant t,ln1111c\ typlc'll ot bottoml,~nd and upland fore\t types In the southern Unlted State\ (Table 1) Two tree cote\ wcre extracted tlo1-11 the bole\ of at leait I 0 tndlvldual Ilkrng tlce\ o t each \pccle\ tlotn varlou\ iociit~on\ (5tands) u\trig a Hdglot tree ~ncrcment borct iFo1e5t Supplleli. Inc . Jacltwn. MS) 'tnd pl'lccd Into 14 8 lnrn gla\\ vial\ Incretnent core\ uwd in the analyst\ were collected primarily from he'tlthy tree5, Llithough some core5 weic collected t r o ~ n d ~ \ e a \ e d ti\\uc\ of ttees for colnpan\on wlth healthy core\ ot the \ame tree \pec~e \ to tn\e\tlgatc I~m~t '~ t ton \ on ,ippltcatlons of the ~netl-rod\ Woody core5 In ' 111 c a w \ were tro7en at -20 C in long-term itolage and thawed ~tnrnediately plrot to sample analy\ts Core\ that became desiccated due to \ u b l ~ m a t ~ o n durlng stor'tgc wcre rehydrated by \oakin& 111 \terllc dl\ttlled water tor 15 mrn followed by blottlng on Chemwlpc ttrsue paper to rctnove exce\\ free lnotcture ~ m m c d ~ a t e l y prior to analys~\ Woody cote \ample\ In 14 8 ml &la\\ vial\ were uncapped and placed Into ' I 500 n ~ l gla\\ \ampling bottle fitted wlth ~ctercnce arr, 4ampllng. and exhaust port\ on a polyptopylene bottle cap Rctercnce air entered the wnplrng bottle through ' I 3 mm polypropyle~ie tube cxtet~dtng to ju\t '~bovc the bottom o t the \ampllng bottle The \ampling bottle ~ ' 1 4 held In the \ampling chambe] within the Instlument at a constant alr tc~npcxdture ot 25 C The \'~rnplmg bottle wr\\ pu~gcd wrtl~ filtelcd, t~~ot\ t~~re-condlt tnncd reference a11 tor 2 tnln prlot to bulldlng head\p'tce The \ampling bottle wa\ sealed and vol:~ttle\ from the \'imple werc allowed to build hcdd\pacc and equ~l~bra te ot 30 nlln prior to e'lch run Plentn te5t\ wctc pertor~ned 'I\ needed to cictct lnlne \'implc ,Itr 1~1'1tl.ve l~umidity (RH) compared wlth that of retcrcnce C I I ~ Reference ' I ~ I w,~s {et at 4% RH tot mo\t rum 'ind xIlu\teci to wtthtn 2% below \ample 'ill at 25 C The \arnphng bottle cap 'tnd cxhdu\t port werc opened between run\ to purge the pteviou5 \ample with cond~tloncd retc~cnce a11 All analy\e\ wcte conducted w ~ t h 'in Arorna\can A33S (O\n~etech, Inc . Wohurn. MA) ~ n \ t r ~ u n e n t fitted