Anal. Chem. 1985, 57,2867-2869
indebted to John Bjorkstam for a careful reading of this manuscript.
Registry No. Methanol, 67-56-1; tert-butyl alcohol, 75-65-0; neopentyl alcohol, 75-84-3; isobutyl alcohol, 78-83-1; 1-propanol, 71-23-8; ethanol, 64-17-5; 2-propanol, 67-63-0. LITERATURE CITED Anderson, E. V. Chem. Eng. News 1984, 62, 9-16, Thomas, K. The Avlation Consumer 1983, 13, 15-21. Pauls, R. E.; McCoy, R. W. J. J. Chrornatogr. Sci. 1981, 19,
---
--..
RRA-661
Alary. J.; Couer, M. A. Bull. Trav. SOC. Pharm. Lyon 1971, 15, 13-22. Chem. Abstr. 1872, 7 6 , 358658. Durand, J. P.; Petroff, N. R ~ VInst. . Fr. pet. 1982, 3 7 , 575-578. Chem. Abstr. 1982, 9 7 , 112187a.
2867
(6) Sevcik, J. HRC CC,J . High Resolut. Chromatogr, Chromatogr. Commun. 1880, 3 , 166-168. (7) Luke, L. A.; Ray, J. E. Analyst (London) 1984, 109, 989-992. (8) Lockwood, A. F; Caddock, B. D. Chromatographla 1983, 17, 65-68. ( 9 ) Zinbo, M. Anal. Chem. 1984, 5 6 , 244-247. (10) Wong, J. L.; Jaselskis, B. Analyst (London) 1982, 107, 1282-1285. ( 1 1 ) Battiste, D. R.; Fry, S. E.; White, F. T.; Scoggins, M. W.; McWiiiiams, T. B. Anal. Chem. 1981, 5 3 , 1096-1099. (12) Bessier, E. Cienc. Cult. (Sa0 Paulo) 1977, 2 9 , 928-930. Chem. Abstr. 1878, 8 8 , 9357w. (13) Aiexandrov, A. N.; Tysovskii, G. I. Neftepererab. Neftekhim. (Moscow) 1968, 37-39. Chem. Abstr. 1966, 6 5 , 160659. (14) Franke, G. Erdoel Kohle 1861, 14, 816-820. Chem. Abstr. 1963, 5 9 . 9701b.
for review February 20, 1985. Resubmitted July 26, 1985. Accepted July 26, 1985.
RECEIVED
Rapid Determination of Lignocellulose by Diffuse Reflectance Fourier Transform Infrared Spectrometry Tor P. Schultz,* M. Curry Templeton, and Gary D. McGinnis Mississippi Forest Products Laboratory, Mississippi State Uniuersity, Mississippi State, Mississippi 39762
Analysis of solid lignocellulose Is a lengthy, multlstep procedure. This study was inltlated to determine if an FTIR procedure Is feasible. Sweetgum and white oak were pretreated to obtain 26 samples with a wide range of compositions. FTIR spectra were collected by using a DRIFT cell. On the bask of the spectra of lignin, cellulose, and hardwood Samples, 18 peaks In the 1600-700 cm-' region were selected. The absorbances at the selected peaks were first base-line corrected and then normalized by uslng nine Internal peaks to give nine data sets of absorbance ratios. The lignin, glucose, and xylose contents, determined by conventional methods, were separately regressed against each data set using stepwlse elimination regression. This procedure gave an equation for lignin (five varlables, R 2 = 0.949), glucose (five variables, R 2 = 0.921), and xylose (three variables, R 2 = 0.973).
Cellulose, lignin, and hemicelluloses are major constituents of lignocellulose materials. Cellulose is similar in all plants units. and consists of repeating (1-*4)-~-D-glucopyranose Hemicelluloses are polysaccharides made up of several different carbohydrates; the type and quantity of the hemicellulose carbohydrates depend on the plant material. Lignin is a highly branched, alkylated phenolic polymer, the exact structure of which also depends on the plant material. The conventional procedure for analyzing solid lignocellulosic samples involves many steps, including determination of the moisture content ( I ) , a two-step acidic hydrolysis then gravimetric determination of the insoluble lignin ( 2 ) )measurement of the soluble lignin by UV spectrometry (3),and derivatization of the hydrolyzed carbohydrates and analysis by gas or liquid chromatography (4-6). A trained scientist can analyze only 15-30 samples per week. Because of the difficulty in analyzing polymeric carbohydrates, analyses among duplicate samples have an error in the 5-10% range (6). Several researchers have used IR spectrometry to examine lignocellulosic materials. Michell et al. ( 7 ) studied the delignification of pulp samples by the use of IR spectrometry.
Marton and Sparks (8)determined the lignin content of pulp and paper samples by multiple internal reflectance infrared spectrometry. Marton and Sparks developed a simple linear regression of lignin content vs. the absorbance ratio of 1510/1310 cm-l. A similar ratio method was used by Karklin and co-workers (9, 10) to determine the lignin content of various pulps and wood samples. Saad et al. (11)also reported on the use of a single absorbance ratio to determine the lignin content of soda bagasse pulp. Gould et al. (12) suggested that the relative lignin content could be determined by the frequency shift of a peak maximum in the 2900-cm-l region. Recently, near-infrared spectrometry has been used to determine the protein and moisture content of various forage materials (13). The objective of this study was to determine whether a technique could be developed which would utilize a FT-IR spectrometer with a programmable microcomputer to rapidly and with reasonable accuracy determine the three major components of lignocellulose. A DRIFT cell was used for several reasons, including avoidance of base-line errors caused by light scattering, ease of sample preparation, and the increase in sample size which would result in a more representative sample.
EXPERIMENTAL SECTION Sweetgum and white oak chips were pretreated by using a 1-min RASH process (14,15). The pretreatment temperatures ranged from 140 to 280 "C so that samples with a wide range of compositons could be obtained. A few samples were also extracted with hot 2% alkali (15, 16). The procedure for analysis of the lignocellulosic solids for Klason lignin, soluble lignin, and glucose and xylose contents was reported earlier (14,16). All values were determined in duplicate and then averaged. Since the lignocellulosic materials are hardwoods, the glucose content is directly proportional to the cellulose content, and the xylose content is representative of the hemicellulose content. The base-extracted samples were analyzed only for Klason and soluble lignin and glucose content (15). The pretreated samples were first air-dried and then ground with KC1 in a 1:12 ratio (sample/KCl). FTIR spectra were obtained with a Nicolet 20DX equipped with a liquid nitrogen MCT detector. A Harrack 2D, center-focus diffuse reflectance (DRIFT) cell was used (Harrick Corp., Ossining, NY) with 500 scans/sample collected. The background spectra were collected by using straight
0003-2700/85/0357-2867$01.50/00 1985 American Chemical Soclety
ANALYTICAL CHEMISTRY, VOL. 57, NO. 14, DECEMBER 1985
2868
.
60 -
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Flgure 1. DRIFT spectra of two lignocellulosic samples. Sample A is white oak treated by the RASH process (73, 14) at 280 O C and sample 6 is sweetgum treated by RASH at 180 'C.
KCl. The spectral resolution was 2 cm-', and a Happ-Granzel apodization function was used. The mirror scan velocity was 0.4 cm/s. The sample spectra were base-line corrected by using the average absorbance at 4140,3788,2250, and 2200 cm-'. Eighteen peaks between 1600 and 700 cm-l were selected based on the IR spectra of cellulose, lignin, and mixed hardwood. The 1600700-cm-' region was chosen to avoid any possible errors caused by peaks overlapping the broad water peak. The absorbances at the 18 selected wavenumbers were determined and subtracted from the averaged base line. Nine internal peaks were chosen from the 18 peaks and were used to obtain nine different standardized data sets, each containing 17 ratioed absorbance values per sample. Then the nine standardized data sets were each separately regressed against the glucose, xylose, and lignin contents using MINTAB stepwise regression. The minimum F value for the individual variables was set at 4 or greater. This value was chosen since it represents a minimum significance level of 0.10 and would thus ensure that each independent variable was significant.
RESULTS AND DISCUSSION DRIFT spectra of two lignocellulosic samples are shown in Figure 1. The regression equations determined by using
80
GLUCOSE
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MEASURED GLUCOSE CONTENT, X Flgure 3. Measured glucose content vs. the DRIFT-predicted value.
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PREDICTED
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CONTENT
stepwise regression are
% glucose = -145.0 70.6(
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MEASURED XLYOSE CONTENT, X Flgure 4. Xylose content, measured by the conventlonal procedure, vs. the predicted xylose content.
A1461
R2 = 0.921 % xylose = -64.0
(2 ) 2 ) '(
+ 78.7 -cm-l +
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- 46.5
A1614 cm-' A1117
)
(2)
R2 = 0.973 % lignin = 70.7
+ 65.8
A1048
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A1087 cm-') A1048
(3)
The overall F tests for the glucose, xylose, and lignin regressions were all significant a t the 0.01 level. F values for the individual variables in all three equations are 4 or greater (0.1 level). Plots of the values determined by conventional analyses vs. the value predicted by DRIFT showed no trend in species nor the suggestion of a nonlinear slope. Figure 2 shows the plot of the lignin content measured by the conventional procedure vs. the lignin content predicted by DRIFT spectrometry. Similar plots are shown for xylose and glucose in Figures 3 and 4, respectively. The scan time necessary t o collect each spectrum was approximately 15 min, with a maximum time of 15 min needed to prepare each sample. By comparison, only about 15-30 samples can be analyzed per scientist per week using the conventional procedure. Other samples were also examined by use of this DRIFT procedure. It appears that by recalibrating the independent coefficients this procedure could be used to analyze RASHtreated mixed hardwoods and steam-exploded, water-extracted
Anal. Chem. 1985, 57,2869-2873
hardwoods. However, steam-exploded, base-extracted hardwoods gave widely variable results. The explosion-base extraction process has been shown to cause extensive degradation/modification of the carbohydrates (15,16). Thus, the carbohydrates may have been sufficiently degraded so that the DRIFT procedure would need to be extensively modified. Work in this area will continue to determine its application to other plant samples.
ACKNOWLEDGMENT The helpful discussions with K. Kalasinsky at Mississippi State Chemical Laboratory and with personnel at Nicolet Analytical Instruments are greatly appreciated. Registry No. Lignin, 9005-53-2; glucose, 50-99-7; xylose, 5886-6.
LITERATURE CITED (1) Browning, B. L. “Methods of Wood Chemlstry”; Intersclence: York, 1967; Vol. I,Chapter 4. (2) Browning, B. L. “Methods of Wood Chemistry”; Interscience: York, 1967; Vol. 11, Chapter 34. (3) Musha, Y.; Goring, D. A. I. WoodSci. 1974, 7 , 133-134.
New
2869
(4) Sweeley, C. C.; Bentley, R.; Makita, M.; Wells, W. W. J. Am. Chem. SOC. 1963, 85,2497-2507. ( 5 ) Chen, C. C.; McGlnnls, G. D. Carbohydr. Res. 1981, 90, 127-130. (6) Li, B. W.; Schuhmann, P. J.; Wolf, W. R. J. Agric. FoodChem. 1985, 33. - - , 531-536 -- . --Michell, A. J.; Watson, A. J.; Hlgglns, H. G. Tappi 1985, 48, 520-532. Marton, J.; Sparks, H. E. Tappi 1987, 50, 363-368. Karklin, V. B.; Trelmanis, A.; Gromov, V. S. Khim. Drev. 1975, 2 , 45-52. Chem. Abstr. 1975, 83, 44945e. (IO) Karklin, V. B.; Belkova, L. P.; Gromov, V. S.; Eidus, J. Khim. Drev. 1977, 4 , 91-96. Chem. Abstr. 1977, 87, 1 6 9 4 2 0 ~ . (11) Saad, S. M.; Issa, R. M.; Fahmy, M. S. Holzforschung 1980, 3 4 , 218-222. (12) Gould, J. M.; Greene, R. V.; Gordon, S. H. “Book of Abstracts”; 188th National Meeting of the Amerlcan Chemical Soclety, Phlladelphla, PA, Aug 1984; American Chemical Society: Washlngton, DC, 1984. (13) Wllliams, P. C.; Norris, K. H.; Sobering, D. C. J . Agric. Food Chem. 1985, 33, 239-244. (14) Biermann, C. J.; Schultz, T. P.; McGinnis, G. D. J. Wood Chem. Technol. 1984, 4 , 111-128. (15) Schultz, T. P.; McGlnnls. G. D. “Evaluatlon of a Steam-Explosion Pretreatment for Alcohol Production from Biomass”; Flnal report to USDA-SEA. Contract 59-2281-1-2-098-0, 1984. (16) Schultz, T. P.; Blermann, C. J.; McGinnis, G. D. Ind. Eng. Chem. Prod. Res. Dev. 1983, 22, 344-348.
New
RECEIVE^ for review May 30,1985.
Accepted August 5,1985.
Comparison of Calcium Fluoride and Lanthanum Fluoride as Host Lattices for the Determination of Lanthanides by Selective Excitation of Probe Ion Luminescence Stephen K. Doom and John C. Wright* Department of Chemistry, University of Wisconsin, Madison, Wisconsin 53706
LaF, has been compared to CaF, as a host lattice for the determination of rare earths by selective excitation of probe ion lumlnescence. Comparlsons were done between obtainable fluorescent Intensity, behavlor In the presence of Interfering cations, reproduciblilty, and background llmltations to sensitivity. The two host preclpltates are comparable In the Intensity levels, Interference effects, and reproduclblllty. The purlty of lanthanum salts, however, prevents use of LaF, at ultratrace levels.
Extensive work has been done on the development of CaFz as a host lattice for the ultratrace determination of the lanthanides and actinides by selective excitation of probe ion luminescence (SEPIL) (1-3). Ensor et al. (4) have recently found that LaF, was potentially a more suitable host precipitate for such determinations. In their work, they showed that the fluorescence intensities of rare earths in LaF3 were comparable to those in CaFz, and the reproducibility was also good. By comparing the effects of Na(I), Ca(II), and Fe(II1) on the fluorescence from LaF, and CaF2, they showed that LaF3may be less susceptible to cation interference than CaF, and suggested that it may be a better host for use in this method. The fact that charge compensation was not required for lanthanides in LaF3 was suggested as the reason for greater resistance to interference. This work presents a more extensive comparison of the two systems. Fluorescent strengths of several transitions in Er(II1)and Eu(II1)-doped calcium and lanthanum fluorides are
presented as a comparison of the potential sensitivity for the two hosts. Er(II1) and Eu(II1) were employed as the fluorescent probes because their different sizes lead to different site distributions that are representative of the range of lanthanides. The onset levels of five cationic interferences are determined and compared. The five interfering ions chosen for this study (Na(I),AI(III), Mg(II), Fe(II), and Cr(II1)) are representative of the major interference mechanisms. In addition, the real limits to sensitivity posed by background contamination are presented for the two systems. We find the transition intensities, the susceptibility to interference, and the ease of sample preparation are equivalent for the two systems. LaF,, however, cannot be obtained in purities sufficient to allow lanthanide measurement at low concentrations.
EXPERIMENTAL SECTION Reagents. All reagents used in this study were analytical reagent grade and used as supplied. All solutions were prepared by using distilled, deionized water. Stock solutions of 1.2 M Ca(N03)2and 0.3 M NH4F were prepared by weighing and dissolving the undried salts. Stock solutions of 0.1 M La(II1) were prepared by dissolving the hydrated chloride (99.9%, Research M HC1 to Organic/Inorganic Chemicals, Belleville, NJ) in prevent hydrolysis of the lanthanum. A 0.01 M stock solution of erbium was prepared by dissolving the oxide (99.9%)in 30 mL of 3 M “OB, evaporating to dryness on a hot plate, and redisM ”OB. This solution was standardized by the solving in copper-EDTA titration method described by Haskin et al. (5) using a sodium acetate/acetic acid buffer to keep the titration solution at a pH of approximately 5. Dilutions of this solution M HN03. A previously prepared solution of were made in europium(II1)was used as the source for this ion. This solution
0003-2700/85/0357-2869$01.50/0 0 1985 Amerlcan Chemical Society
