CA2009062A1

CA2009062A1 - Method of determining wood species

Info

Publication number: CA2009062A1
Application number: CA 2009062
Authority: CA
Inventors: Lorne Elias; Andre H. Lawrence; James J. Barbour; Roger Sutcliffe
Original assignee: Individual
Current assignee: Individual
Priority date: 1990-01-31
Filing date: 1990-01-31
Publication date: 1991-07-31

Abstract

TITLE
A Method of Determining Wood Species INVENTORS
André H. Lawrence Lorne Elias R. James Barbour Roger Sutcliffe ABSTRACT OF THE DISCLOSURE
A wood species is determined by isolating, e.g. thermally extracting, extractives or exudates from a heartwood sample of the wood, and then identifying by, for example, ion mobility spectrometry, at least one ionic species of the volatile chemicals which characterize the species of the wood sample.

Description

2 ~ 2 1 Thi~ invention relates to a method of determinill~ wood species.
It has already been proposed in ~Analysis of l.xplosives and Explosive Residues with Ion Mobility Spectrometry (IMS)", G.E. Spangler, J.P. Carrico and S.H. Kim, Proceedings of the International Symposium on the AnalysiS
and Detection of Explosives", March 29-31, 1983, FBI
Academy, Quantico, Virginia, U.S.A., to detect and analyze explosives using ion mobility spectrometry (IMS). The sample can be introduced into the lMS using ambient air carrier gas, a sample wire probe/syringe, a solids probe, a desorption oven, a membrane inlet, an exponential dilution flask, a standards generator, a surface sampler, and gas chromatography.
The rapid on-site characterization of different wood species of logs, lumber, and other wood products is not an easy task since visual cues are often lacking or obscured when these materials arrive at the mill. This problem has preoccupied the forest products and pulp and paper i~dustries for some time. A number of simple approaches have been attempted, such as visual inspection, colour tests, to develop a reliable screening procedure with varying degrees of success. Other methods are also being investigated, e.g. reflectance Fourier Transform Infrared Spectroscopy (FTIR) and Fourier Transform Nuclear Magnetic Resonance (FTNMR), with limited success.
It has already been proposed in "Applicatlons of a ~9~

continuous-mode pyrolyzing inlet for GC", l~ Wright and P. I~awes, American Llbora~ory, November, 1986, to pyrolyze a wood sample and differentiating wood types by gas chromatography from the products of the pyrolysis.
While the proposal of Wright et al is useful, it has been found that only a limited number of wood types can be identified in this manner.
There is a need for a simple, reliable method for the on-site characterization of a wide variety of different wood species of logs, lumber, and other wood products.
According to the present invention there is provided a method of determining a wood specied, comprising:
a) removing extractives or exudates from a heartwood sample of the wood, and b) identifying by ion mobility spectrometric analysis, gas 15 ~ chromatographic analysis or mass spectrometric ~nalysis of the extractives or exudates, the species of the wood sample.
The analysis may identify the species of the wood sample by the presence of at least one chemical in the extractives or exudates.
The analysls may identify the species of the wood sample by the absence of at least one chemical in the extractives or exudates.
The extractives or exudates may be isolated from the sample by being thermally released therefrom.
When the analysis is by ion mobility spectrometry, at least one ionic species may be identified which has a negative polarity.
When the analysis is by ion mobility spectrometry at least one ionic species may be identified which has a positive polarity.
The present invention makes use of the fact that the heartwood portion of a tree is rich in compounds such as hyclrolyzable and condensed tannins and many other phenolics, alkaloids, resins, essential oils, and 20a~06~

specialized contpourtds which are capable of protecting ~hese metabolically inactive tissues against biological ~ttack, and so the hear~wood c,~n be used to identify a wide variety of wood species, in contrast to those identifiable by constituents of the sapwood.
The at least one chemical may be identified by ion mobility spectrometry.
In the accompanying drawings, which illustrate the results of tests to verify the present invention:
Figure 1 shows the negative-ion mobility spectra of to j ack pine heartwood, Figure 2 shows the positive-ion mobility spectra of balsam fir heartwood, -- -Figure 3 shows the positive-ion mobility spectra of white pine heartwood, and Figure 4 shows the positive-ion mobility spectra of red pine heartwood.
Apparatus Used to Verify the Present Invention The Ion Mobility Spectromet~r ( IMS), also known as the Plasma Chromatograph, is an ambient pressure ionization d~tector closely related to the dc electron capture detector. The basic components of the instrument include a heated inlet, an ionization/reaction chamber ( usually containing a 63Ni radioactive source), an ion drift chamber, a shutter grid interposed between the two chambers, 25 and an ion collector. A constant accelerating electrostatiC

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1 ~ield is establish~ a~ong t~le length of the IMS cell usually by ~eans o~ a series of equally hiased guard rings.
When a negative voltage is applied to create the electric field, negative ions formed in the ioni~ation/reaction chamber are periodically allowed to enter the drift chamber through the gated shutter grid. These ions are accelerated toward the collector (which is almost at ground potential) against the countercurrent of a drift gas and separate into ~ their individual chemical species as a result of their different mobility. Negative (or positive) mobility spectra are obtained by measuring the time of flight of the ions as they drift through positive (or negative) the electric field . ~ .....
gradlent at atmospheric pressure.
It is well established in IMS as well as in chemical ionization mass spectrometry (CIMS) that the dominant positive reactant ions formed when air is used as the carrier gas are hydrated protons (H20)nH ; similarly, the dominant negative reactant ions are hydrated oxygen (H20)nO2 . These ions transfer their charge through a ~eries of complex ion-molecule reactions to the gaseous species of interest, and positively or negatively charged ions characteristic of the injected sample are produced.
Although the IMS procedure (like mass spectrometry) is non-chromatographic, it functions similarly in separating the components of a mixture - this separation being perf~ormed after, rather than before, ionization, as is the case with gas chromatography!electron capture detection; at 2~9~2 .; ., 1 ~he same time, the IMS procedur~ o~viates the high-vacuum requirement of mass spectrometry.
The drift time, td~ of an ionic species (e.g. 2)' is a qualitative parameter that represents the time taken for a pulse of the ions to travel from the shutter grid to the collector. The relationship between the drift time of a particular ion and its mobility, reduced to standard temperate and pressure, is ~iven by: -Ko = (d/td.E)(273/T)(P/760) (1) where Ko is the reduced mobility in cm2 V-ls~l, d is the drift length in cm, td is the drift time in s, E is the electric~field strength in Vjcm, T is the absolute -temperature of the drift gas, and P is the atmospheric pressure in Torr. Since reduced mobi~ity constants are independent of the experimental conditions used, they are a useful parameter for ionic species identification and remain the most common form of IMS data presentation.
The mobility of most polyatomic ions depends not only on their mass but also on their collision cross-section with the drift gas, and thus on the size and, to a lesser extent, on the shape and charge distribution of the ion; as a result, attempts to relate mobilities to ionic masses are not always accurate. However, one reliable way to assign masses to ions observed in the IMS mobility spectrum is to couple the IMS to a quadrupole mass spectrometer (MS). This is accomplished by providin~ a small hole in the collector plate of the IMS to allow passa~e o~ ions from the IMS to 1 the MS. A potentia] is applied be~ween the collector of the IMS and the ~ 25 micron aperture into the high vacuum regior of the MS. Using electrostatic focussing techniques (already developed for atmospheric pressure ionization (API) techniques), the ions from the IMS can be collected and analyzed by the quadrupole mass spectrometer. Typical IMS
and IMS MS data obtained in tests to verify the present invention and given below were obtained using a Phemto-Chem 100~ ion mobility spectrometer and a Phemto-Chem MMS-160~ ion mobility spectrometer-mass spectrometer, respectively (PCP Inc., West Palm Beach, FL, U.S.A); the experimental parameters used to operate each instrument are given in Table I.
, 2 ~

1 TABLE I - INSTRUMEN'I'S PARAM~TERS
Parameter Yalue Ion Mobility Spectrometer (Phemto-Chem 100) cell length 14 cm drift length 8 cm carrier gas (purified air) 200 mL/min drift gas (purified air) 600 mL/min inlet and drift temperature ~ ~ 200C
drift voltage t2700 V
dwell time .20 ~s/channel gate width 0.2 ms delay timea 6 ms number-of scans - - 128,256:-scan time 3-6 s lon Mobilit~ Spectro~eter - Mas~ Spectrometer (Phe~to-Chem MMS-160) cell length 15 cm drift length (bet~een shutter grid and IMS collector) 5 cm carrier gas (purified air) 200 mL/min drift gas (purified air) - 600 mL/min drift voltage '2700 V
inlet and drift temperature 200C
dwell time 20 ~s/channel gate width 0.2 ms mass spectrometer pressure 6xlO 6 I'orr scanning speed 1000 amu/s :
aTime between gate opening and start of data collection ~, Wood al-d Chemical Samples Usecl in the Tests Two hundred and fifty wood samples in ~he form of sawdust particles were obtained from I-orintek Canada Corporation, Ottawa, Canada and were stored at -10C. They consisted of heartwood, sapwood, 5 decayed and weathered samples, from the following species: black spruce, jack pine and balsam fir ~representative of eastern SPF), white spruce, lodgepole pine a~d alpine fir (representatiYe of western SPF), white pine, ca~bg t~a~
red pine,l~Douglas-fir, interior Dou~las-fir; amabilis fir, Sitka spruce, ~_~spruce, red spruce, western hemlock and western larch. All 10 sample identities were verified microscopically by Forintek Canada Corporation prior to IMS analysis. Taudomatuic acid was obtained from the Forest Products Laboratory, USDA, Madison, WI, U.S A. through the courtesy of Dr. D Zinkle, and the methyl ester was prepared by reaction with diazomethane. Pinocembrin, chrysin, pinobanksin and 15 dihydroquercetin were obtained from the reference collection of Forintek Canada Corporation and were used without further purification.

Test Method I
One or two sawdust particles (~ 5mg) were inserted into a narrow 20 probe (6 cm long x 0 3 cm O D. glass tube) which had a restriction and silanized glass wool plug in its middle A carrier gas stream (200 mL/min) of purified air was made to flow through the probe before the latter was inserted in the heated inlet of the IMS Upon sample .

2 ~

1 injectio~, the volati~e chemic~ls evaporated immediately and were flushed by the carrier gas to the ion reaction chamber of the ins~rument, wi~h the glass wool plug serving to prevent any solid particles from entering the IMS.
Authentic samples of juvabione, pinocembrin, pinobanksin, chrysin and dihydroquercetin were injected in the IMS by depositing with a syringe l/uL of a standard solution (~l x 10.8 g/~uL in methanol) on the glass wool plug of the probe; after evaporation of the solvent by the carrier gas stream, the probe was inserted in the heated inlet of the IMS. A similar approach was used to obtain IMS-MS data.

Test Method II
A sample desorption apparatus des'cribed and claimed in United States Patent No. 4,732,046, dated March 22, 1988, was used in which the inner walls of a syringe needle is used as a trapping/injection interface between a sample tube and a chromatographic column. Sawdust particles were placed in the sample tube upstream of a filter plug. During a desorption cycle, the sample tube is enclosed between two perforated polytetrafluoethylene (PTFE) caps. A nitrogen carrier gas stream was allowed to ~low through the sample tube. The needle of a gas-tight syringe was inserted about 1 cm in the PTFE cap (vapour tight conditions are insured) after the plunger was removed. An aluminum heating block was then rested on the sample tube at 250C for 2-3 min.
.

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1 Volatile chemicals present in ~hc wood were vapourized by the action of heat an(i ~lushed with the carrier gas stream (30 mL/min) to the inner cold wa]ls of the syringe needle, where they were trapped, while the carrier stream was vented through the barrel bore. No special cooling was applied to the exposed portion of the needle; due to the little mass flow of the carrier stream, the stainless-steel walls of the needle stayed relatively cool.
For injection into the gas chromatograph (GC), the needle was withdrawn from the PTFE cap. The plunger was inserted in the syringe down to the midpoint and a conventional septum injection into the GC was performed.
Thè heated injector port vapourized the chemicals trapped in the needle of the syringe upon insertion through the septum;
simultaneously, the plunger was fully depressed drivlng~the vapours into the carrier stream of the GC (capacity 1-10 mL/minj.
A Finnigan 1020R GC-MS was used and the chromatographic conditions were as follows: column, DB-l, ~0 m~x 0.2 mm l.D.; carrier gas, helium at 6 mL/min; oven temperature, 150-250C at 5C/min; injector temperature, 250C.
Test~Method III
In this method, the surface of the heartwood is heated as a suction device is drawn across it to collect thermally released chemicals therefrom.
If desired, the carrier gas used in Tests I and III to 1 transfer tlle vapol-s to ~lt IMS In~y, (~s fauyllt in "I)etectior of Ethylene Glycol Dinitrate Vapors by lon l~obility Spectrometry Using Chloride Reagent lons", ~ H. Lawrence and P. Neudorfl, Analytical Chemistry, Vol. 60, No. 2, Januar~
5, 1988, pages 104-109, contain trace amounts of chemicals such as chlorinated or nitrated substances. These trace chemicals provide alternative reactant ions, e.g. chloride ions or nitrate ions, which react with chemicals of the wood sample to form the characteristic ions by which that wood species may be identified.
Test Results IMS Signatures of Heartwood SamPles As previously stated heartwood and outer bark portions of a tree are rich in compounds such as hydrolyzable and 15~ condensed tannins and many other phenolics, alkaloids, resins, essential oils, and specialized compounds which are capable of protecting these metabolically inactive tissues against biological attack. These chemicals, generally known as extractives, can be removed with inert solvents such as ~ther, benzene-alcohol, acetone and cold water; they can be used as chemotaxonomic markers and, in some cases, can be correlated wlth some specific property of the wood such as decay resistance or colour.
Table II gives the results of tests devoted largely to examining a large number of heartwood samples. The investigation was carried out under controlled laboratory conditions and the major emphasis was on establishing the .

opt;im~lm experiment,~ conditions ~or the fast thermal release and ~S analysis o~ the heart~lood extractives.

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; , ' IMS Signature of 131ack Spruce,lack Pine and T3alsarll Fir (Eastern SI~F) e ~ ~ t ~-'~
~ lack spruce, jack pine and balsam fir are marketed as SPF. The field implementation of a fast and reliable species segregation technology would allow the wood products industry's strategy to produce 5 higher value lumber grades and specialty products.
A large number of analyses were made of the black spruce, jack pine and balsam fir (eastern SPF) heartwood samples. The samples were obtained from various mills in different Canadian geographical locations in Québec, Ontario and the Maritimes. As shown in Figures 1 and 2, the pine and fir samples gave unique IMS peaks at Ko = 1.29 and Ko = l.38 cm2V-Is-l, respectively, the pine signature being obtained in the negative mode and the fir signature in the positive mode. The spruce samples displayed no suchpeaks in either rnode yielding broad unresolved peaks in the region of Ko = 1.10-1.00 cm2V-~s~l; thus, given a sample that is either 15 spruce, pine or fir, the sample identity can be deduced by monitoring the peaks at 1.29 and 1.38. The reproducibility among similar samples was - excellent, and different sawdust particles from the same sample producedidentical spectra. Furthermore, the storage time did not affect the results.
In some experiments, the samples were stored for up to three months 20 prior to analysis; neither spurious peaks nor change in IMS signatures were observed. Experiments conducted on .

2 ~ 2 -l5~
l benzene-ethanol extracts from jack p:ine and balsam fir confirmed the above results.

IMS Siqnatures of White Spruce, Lodq~pole_Pine and Alpine ~ir Drift patterns were obtained from white spruce, lodgepole pine and alpine fir (western SPF) samples. Like their corresponding eastern species, lodgepole pine exhibited an intense peak at Ko = l.29 cm2V~ls~l in negati~e IMS, and alpine fir can be easily idéntified by the peak at Ko = l.38 cm2V~ls~l in positive IMS. White spruce was characterized by the lack of any such signatures, and thus its presence in the western SPF mix can also be arrived at ;by inference. ~
The identity of the ionic species associated with the IMS peaks was determined in two sets of separate experiments as outlined below.
(a) GC-MS Experiments B - ~oth juvabione and dehydrojuvabione (ratio - lO:l) were detected from 20 ~ balsam ir. The mass spectra showed splitting patterns completely in agreement with the expected structures.
These two chemicals with juvenile hormone activity have been previously isolated from balsam fir (see Bowers, W.S., Fales, H.M., Thompson, M.J. and Vebel, E.C., Science, 154, 1020, l966~. The base peak of dehydrojuvabione at m/z 83 has been attributed to - , - ~-cleavage of the ketonic side chain (see Cerny, V., Dolejs, L., ~:abler, L., Sorm, P. and Slama, K, "l~cJhydrojuv~biorle - A
New Compound with Juvenile ~-Iormone Activity from l~alsam Fir", Coll Cæech Chem. Commun 32, 3926 ,1967) Dehydroabietic acid (m/z 300) and other abietic acid derivatives were detected from jack pine. Wnoleic aad and trans-neoabienol were also found to be present in black spruce but these are of no chemical taxonomical value.

(b) IMS-MS Experiments - The IMS-MS experiments consisted of a three-fold approach. First, total ion mobility spectra were obtained by gating the shutter grid of the IMS cell and allowlng the IMS electrometer to collect the data;~under these conditions, the quadrupole mass filter was not used. Second, mass spectral data were obtained by holding the grid of the IMS open, thus allowing all ions formed in the IMS to drift through the tube and into the mass spectrometer. Finally, mass-identified ion mobility spectra were recorded by gating the shutter grid of the IMS ceil as in the first procedure, but with the mass spectrometer tuned to a ~ specific m/z value; in~this case, the detector responded to only one ionic species and, consequently, the mobility spectrum conta~ined one peak which corresponded to that ion.

IMS-MS experiments of balsam fir and alpine fir samples showed that the peak of Ko = 1.38 units is composed of two ions, m/z 207 and m/z 205. These ions were formed by loss of a methoxycarbonyl radical from the molecular ion of 1 juvabione and dehvdroj~vabione, I-espe~ctively. It should be noted that the drift time of the m/z 2C)7 ion in the mass-identified ion mobility spectrum was slightly longer than that observed in the corresponding total ion mobility spectrum. This is attributed to the fact that in mass-identified mobility spectra measurements the ion lens and orifice interface of the mass spectrometer increase the length of the drift region. These results were further confirmPd by analyzing an authentic sample of taudomatuic acid methyl ester (juvabione). Mass spectral measurements of alpine fir showed the presence of a small peak at m/z 265 which could be attributed to the loss of a proton from the molecular ion of juvabione.
The characteristic peak of jack pine and lodgepole pine of Ko = 1.29 cm2V~ls~l was shown to be m/z 255, which could be formed by loss of a proton from the molecular ion of pinocembrin (see von Rudloff, E. and Sato, A., ~The Heartwood Extractives of Pinus Bankslana Lamb", Can.J.Chem.41, 2165, 1963.). This was confirmed by a?nalyzing authentic samples of pinocembrin, chrysin and pinobanksin. It should be noted that, in the case of lodgepole pine, a broad unresolved peak was also observed in the negative ion mobility spectrum; mass spectral data clearly showed that this broad asymetric peak was composed of two ions, m/z 279 and m/z 301. These ions were probably formed by loss of a proton from the molecular ion of trans-abienol and abietic acid, respectively. Similarly, 2~)~f~

1 the broad unresolv,d peaks from black al~ W]lite sr,ruce were shown to be due to two ions: m/z 27g and m/z 2gg w~lic~l can be due to the loss of a proton from the molecular iorl of trans-abienol and dehydroabietic acid, respectively.
IMS Si~natures of White and Red Pine Positive ion mobility spectra for a number of samples of white pine and red pine were obtained. As shown in Figure 3, white pine gave two characteristic ion peaks at 17.24 and 17.94 ms with Ko ~alue of 1.29 and 1.26 cm2V~ls~l, respectively. It was shown by IMS-MS
experiments that the two peaks in the white pine spectrum were produced by ions with masses 269 and 283 (probably-protonated flavones). In contrast to white pine, the positive IMS spectrum of red pine shown in Figure 4 changes as a function of time, and a characteristic triplet signature was only obtained 30 seconds after injection of the sample. This relatively long response time can lead to contamination of the instrument and, in turn, to a cleardown time of approximately one minute.
~MS Siqnature of ouqlas-fir For some time the pulp and paper industry has been interested in rapid and reliable test procedures to monitor the raw material supply to pulp mills, particularly the species makeup of the wood chip supplies.
The detection of Douglas-fir in the material furnished to the chemical thermal mechanical pulping (CTMP) process is of vital importance, as this species is responsible for :

2 0 ~ 6' ~
.. Iq brightness reversion in the pulp and, as a consequence, lowers the quality of the final product. The commonly used approach for species identification is time consuming and involves the use of morphological/anatomical methods of analysis.
Thirty coastal Douglas-fir samples and ten interior Douglas-fir samples were examined using the procedure previously described. In some cases, the positive ion mobility spectrum exhibited a characteristic triplet in the drift region 16-20 ms, and it was shown that none of these ions corresponded to the chemical responsible for brightness reversion, dihydroquercetin. However, sample-to-sample variation was observed and, more importantly, variations within samples were also detected. It should be noted that variability of ~ouglas-fir wood extractives with geographical location has been previously reported (Manville, J.F. and Rogers, I.H., "Insect Juvenile Hormone Analogs in Conifers. m.
Variability of Douglas-fir Wood Extractives with' Geographical Location", Can.J.For.Res.7, 42~, 1977). In addition, the negative ion mobili~y spectra obtained from all the samples did not give a characteristic signature pattern. These results indicate that IMS does not respond selectively to the vapours~ thermally released from Douglas-fir, and thus restricts the usefulness of this approach for identification purposes.
i .

. . .

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. qo--IMS Signatule of Si~ka Spruce, ~mabilis ~ir, Interior Spruce, ~ed Spruce, Western Hemlo~k and Western ~arch The remaining species investigated namely, Sitka sprùce, amabilis fir, red spruce, interior spruce, western hemlock and western larch 5 displayed no characteristic IMS peaks in either mode and, therefore, could not be identified by this method.

IMS Siqnatures of Sapwood Samples Inner bark and sapwood are general~y rich in nutrients : such as fats, starch, simple sugars and simple glycosides;
however, they tend to be deficient in the types of extractives present in the heartwood and outer bark portions of a tree.
Ion drift patterns were obtained from sapwood samples of ~ack pine, lodgepole pine and balsam fir. As expected, pinocembrin was not detected from sapwood samples of jack or lodgepole plne, nor was juvabione detected in balsam fir or alpine fir sapwood. In general, no characteristic IMS
peaks were obtained from any sapwood samples.
IMS Siqnatures of Aqed and Weathered Heartwood Sam~les ~ ~ Tests were also undertaken to determine whether the presence of decay and/or weathering would affect the IMS
signature obtained from the heartwood portion of a tree.
These tests showed that the juvabione peak at Ko = 1.38 cm2V~ls~l was not detected from either aged or decayed ~5 balsam fir samples. In contrast, aged or weathered jack pine samples exhibited a relatively small but distinct - pinocembrin peak a- KO - 1.29 cm2V ls~1.

:. ~

Scope of the Inventio_ While the chemicals have been described as being identified by ion mobility spectrometry (IMS), or by gas chromatography, it is within the scope of the present invention for the chemicals to be identified by, for 5 example, mass spectrometry.
Preferably the chemicals are identified by ion mobility spectrometry which is much faster than gas chromatography and also does not require the vacuum equipment that is essential with mass spectrometry.

Claims

1. A method of determining a wood species, comprising;
a) removing extractives or exudates from a natural, heartwood sample of the wood, and b) identifying by ion mobility spectrometric analysis, gas chromatographic analysis or mass spectrometric analysis of the extractives or exudates, the species of the wood sample.

2. A method according to claim 1, wherein the analysis identifies the species of the wood sample by the presence of at least one chemical in the extractives or exudates.

3. A method according to claim 1, wherein the analysis identifies the species of the wood sample by the absence of at least one chemical in the extractives or exudates.

4. A method according to claim 1, wherein the extractives or exudates are isolated from the sample by being thermally released therefrom.

5. A method according to claim 1, wherein the analysis is by ion mobility spectrometry and at least one ionic species is identified which has a negative polarity.

6. A method according to claim 1, wherein the analysis is by ion mobility spectrometry and at least one ionic species is identified which has a positive polarity.