Anal. Chem. 1980, 52, 1411-1415 (8) Rohrschneider, L. Fresenius' 2. Anal. Chem. 1959, 170, 256. (9) Kovats, E. sz. Helv. Chim. Acta 1958, 41, 1915. (10) Supina, W. R. I n "Modern Practice of Gas Chromatography", Grob, R. L.. Ed.; Wiley-Interscience: New Ywk. 1977; Chapter 3. (1 1) Okamura, J. P.; Sawyer, T. I n "Physical Methods in Modern Chemical Analysis", Vol. 1, Kuwana, T., Ed.; Academic Press: New York, 1978; Chapter 1. (12) Bertsch, W. J. High Resolut. Chromatogr., Chromatogr. Commun 1978, 1 , 187, 289. (13) Bertsch, W. J . High Resolut. Chromatogr., Chromatogr. Commun. 1979, 2, 85. (14) Laub, R . J.; Wellington, C. A. I n "Molecular Association", Vol. 2, Foster, R.. Ed.; Academic Press: London; Chapter 3. (15) Laub, R. J.; Pecsok, R. L. "Physicochemical Applications of Gas Chromatography"; Wiley-Interscience: New York. 1978; Chapter 6. (18) h u b , R. J. I n "Physical Methods of Modern Chemical Analysis", Vol. 3, Kuwana, T., Ed.; Academic Press: New York, in press. (17) Laub. R. J.; Purnell, J. H. J. Chromatogr. 1975, 112. 71. (18) Laub, R. J.; Purnell, J. H. Anal. Chem. 1976, 48, 799, 1720. (19) Laub. R. J.; Purnell, J. H.; Williams P. S. J. Chromatogr. 1977, 134, 249. (20) Laub. R. J.; Purnell, J. H.; Summers, D. M.; Williams, P. S.J. Chromatogr. 1978, 155, 1. (21) Laub, R . J.; Purnell, J. H. J . Chromatogr. 1976, 161, 49, 59. (22) Laub, R. J.; Pelter, A.; Purnell, J. H. Anal. Chem. 1979, 57, 1878. (23) AI-Thamir, W. K.; Laub, R. J.; Purnell, J. H. J. Chromatogr. 1977, 142, 3. (24) AI-Thamir. W. K.; Laub, R. J.; Purnell, J. H. J . Chromarogr. 1979, 176, 232. (25) AI-Thamir, W. K.; Laub, R. J.; Purnell, J. H. J. Chromatogr. 1980, 180, 79. (26) Laub, R. J.; Purnell, J. H.; Williams, P. S. Anal. Chim. Acta 1977, 95, 135. (27) Mann, J. R.; Preston, S. T., Jr. J. Chromatogr. Sci. 1973, 1 7 , 216. (28) Lynch, D. F.; Palocsay, F. A.; Leary, J. J. J . Chromatogr. Sci. 1975, 13, 533. (29) Parcher, J. F.; Hansbrough. J. R.; Koury, A. M. J. Chromatogr. Sci. 1978, 16, 183.
1 4 11
(30) Reinbold, 9. L.; Risby, T. H. J . Chromatogr. Sci. 1975, 73, 372. (31) Figgins, C. E.; Reinbold, B. L.; Risby, T. H J. Chromatogr. Sci. 1977, 15, 208. (32) Butler, L.; Hawkes, S . J. J . Chromatogr. Sci. 1972, 10, 518. (33) Kong, J. M.; Hawkes, S . J. J . Chromatogr. Sci. 1976, 1 4 , 279. (34) Rotzsche, H. Plaste Kautsch. 1968, 15. 477. (35) Trash, C. R. J. Chromatogr. Sci. 1973, 11, 196. (36) Coleman, A. E. J. Chromatogr. Sci. 1973, 1 1 , 198. (37) Smidrod, 0.; Guillet, J. E. Macromolecules 1971, 4 , 356. (38) Lavoie. A.; Guillet. J. E. Macromolecules 1969, 2, 443. (39) Patterson, D.; Tewari, V. B.; Schreiber, H. P.; Guillet, J. E. Macromolecules 1971, 4 , 356. (40) Guillet, J. E.; Stein, S.N. Macromolecules 1970, 3 , 102. (41) Meen. D. L.; Morris. F.; Purnell, J. H.; Srivastava, 0.P. J. Chem. Soc., Faraday Trans. 11973, 69, 2080. (42) Roberts, G. L.; Hawkes, S. J. J. Chromatogr. Sci. 1973, 1 1 , 16. (43) Huber, G. A.; Kovats, E. sz. Anal. Chem. 197:,, 45, 1155. (44) Fritz, D. F.; Kovats, E. sz. Anal. Chem. 1973, 45, 1175. (45) Martire, D. E. Anal. Chem. 1974, 46, 626. (46) Laub, R. J.; Purnell, J. H.; Williams, P. S.; Harbison, M. W. P.: Martire, D. E. J . Chromatogr. 1978, 155. 233. (47) Laub. R. J.; Purnell. J. H. J. High Resolut. Chromatogr., Chromatogr. Commun. 1980, 3 , 195. (48) Primavesi. G. R. Nature (London) 1959, 184, 210. (49) Hildebrand, G. P.; Reilley, C. N. Anal. Chem. 1964, 3 6 , 47. (50) Keller, R. A.; Stewart, G. H. Anal. Chem. 1964, 36, 1184. (51) Klein, J.; Widdecke, H. J. Chromatogr. 1978, 147, 384. (52) Chien, C.-F.; Kopecni, M. M.; Laub, R. J. Anal. Chem., preceding paper in this issue. (53) Purnell, J. H. J . Chem. SOC. 1960, 1268.
RECEIVED for review March 31, 1980. Accepted May 21, 1980. We gratefully acknowledge support from the National Science Foundation, grant no. CHE-7820477, ;and from the Graduate School of The Ohio State University.
Determination of BHT, Irganox 1076, and Irganox 1010 Antioxidant Additives in Polyethylene by High Performance Liquid Chromatography J. F. Schabron" and L. E. Fenska Phillips Petroleum Company Research Center, Bartlesville, Oklahoma
A method was developed for the rapid extraction of the three most common antioxidant additives, BHT, Irganox 1076, and Irganox 1010, from polyethylene pellets. The pellets were dissolved In decalin at 110 OC followed by codlng to precipitate the polymer. The concentrations of the additives present were determined by normal-phase high performance liquid chromatography (HPLC) of a portion of flttered extract. The HPLC stationary phase was pPorasli and the mobile phase was a heptane to methylene chloride gradient. The relative standard deviatlons were 1.2% for BHT, 1.3% for Irganox 1076, and 2.0% for Irganox 1010. The limits of detection were 0.0006% for BHT, 0.002% for Irganox 1076, and 0.004% for Irganox 1010 in polyethylene,
T o ensure that additives or combinations of additives have been added properly to polyolefin batches following synthesis, reliable and rapid analytical methods are needed. The methods would be used for both quality control and lot certification analyses. In some limited cases, rapid additive analysis can be carried out without extensive pretreatment steps such as extraction. Direct spectroscopic methods such as ultraviolet absorption, infrared, fluorescence or phosphorescence ( I ) , and X-ray fluorescence (2) have been re0003-2700/80/0352-1411$01.00/0
74004
ported. In some cases these methods we useful, but generally they suffer disadvantages from interferences due to nonspecificity ( I ) . A more desirable approach for most additive packages is the separation and determination of each additive in the polymer. This requires extraction of the additives followed by chromatographic separation. Wheeler ( I ) reviewed several polyolefin extraction procedures. Most involved lengthy treatment of ground polyolefin with a volatile organic solvent under heat. Crompton (3) extracted polyolefins in various volatile organic solvents from 6-24 h prior to chromatographic analyses of the extracts. Wims and Swarin ( 4 ) extracted 8-mesh polypropylene pellets for 24 h using tetrahydrofuran. The extracts were separated by size exclusion chromatography (SEC) or normal-phase high performance liquid chromatography (HPLC). Lichtenthaler and Ranfelt (5) extracted ground polyethylene with chloroform in Soxhlet apparatus for 6 h. The extracts were concentrated by evaporation prior to separation by HPLC. The separations were on a 5-pm silica column using mobile phase gradients with heptane and methylene chloride. Another procedure involved a 2-h extraction of thin polyolefin slabs with refluxing dichloromethane (6). This was followed by concentration of the extract and separation by reversed-phase HPLC on p-Bondapak CIS The British Standard Method involves dissolving ground 1980 American Chemical Society
1412
ANALYTICAL CHEMISTRY, VOL. 52, NO. 9, AUGUST 1980
ER
Figure 1.
Diagram of extract solution filter apparatus, not drawn to
scale polyethylene in refluxing toluene for at least 1 h followed by precipitation of the polymer on addition of ethanol or methanol (7). This method requires constant operator attention, and some additive decomposition has been observed ( 4 ) . Several HPLC systems have been used for polyolefin additives separations. These include SEC ( 4 ) ,normal phase ( 4 , 5 , €3, and reversed-phase (6) HPLC systems. SEC systems are limited severely in the number of components which can be resolved since many additives may be of similar molecular size ( 4 ) . Reversed-phase HPLC systems require evaporation of the extract solutions, since injection of compounds such as phenols in a typical polyolefin extraction solvent such as chloroform can result in distorted or split peaks (9). Normal-phase HPLC systems based on silica supports do not suffer from the above two disadvantages ( 4 , 5 , 9). In the present work, a rapid extraction procedure for polyethylene pellets followed by a rapid HPLC procedure was developed for the specific determination of the three hindered phenol type polyethylene antioxidants most commonly used in the industry today. These were 2,6-di-tert-butyl-4methylphenol (BHT), octadecyl3,5-di-tert-butyl-4-hydroxyhydrocinnamate (Irganox 1076), and tetrakis[methylene (3,5-di-tert-butyl-4-hydroxyhydrocinnamate)] methane (Irganox 1010). The structures of these three additives are shown in Ref. 5 . Preliminary studies suggest that the method could possibly be extended to a t least five other less commonly used specialty additives in both polyethylene and polypropylene matrices.
EXPERIMENTAL Instrumentation. The liquid chromatograph used in this study was a Waters Model 204 liquid chromatograph equipped with two Model 6000-A pumps, a Model 660 solvent programmer, and a U6K injector. Elution was monitored with a Waters Model 450 variable wavelength detector set at 280 nm and a 10-mV strip chart recorder. The column used was a 3.9 mm i.d. X 30 cm p-Porasil column packed with 10-pm porous silica obtained from Waters Associates, Milford, Mass. Two thermolyne Type 1000 stir plates were obtained from Sargent Welch. Stir bars were 3 / 8 inch 0.d. X l'/z inch Teflon coated magnetic stir bars. The sample filtering apparatus used is shown in Figure 1. A Waters 20-30 pm stainless steel solvent reservoir filter was connected to about a 5-inch length of 3-mm i.d. Teflon tubing. The other end of the Teflon tubing was connected to a l'/*-inch long blunt 16-gauge Luer lock needle with a 1/16-inchstainless steel nut and ferrule at the end of the needle. The needle was connected to a Hamilton No. 1010 W gastight 10-mL syringe with Teflon plunger. Reagents. Heptane was distilled in a glass obtained from Burdick and Jackson, Muskegon, Mich., or spectro grade obtained from Phillips Chemicals, Borger, Tex. Chloroform was Mallinckrodt AR grade from Scientific Products. Methylene chloride was Burdick and Jackson distilled in glass. The above mobile phase solvents were all fdtered through Millipore Type F-H 0.5ym filters prior to use. Eastman decalin was obtained from Sargent Welch and was used as received. Naugard BHT was obtained from Uniroyal Chemical, Naugatuck, Conn. Irganox 1010 and Irganox 1076 were obtained from Ciba-Geigy, Ardsley, N.Y. Santonox R was obtained from Monsanto, St. Louis, Mo. UV 531 was obtained from American Cyanamid, Bound Brook, N.J. Ethyl 330 was obtained from Ethyl
Corporation, Baton Rouge, La. Goodrite 3114 was obtained from B. F. Goodrich, Cleveland, Ohio. Topanol Ca was obtained from ICI, Wilmington, Del. All additives were used without further purification. Procedure. Heated Standard Solution. A 50-mL portion of a standard solution containing about 0.02 mg/mL each of BHT, Irganox 1076,and Irganox 1010was pipetted into a 100-mL beaker. A stirring bar was added and the solution was heated to 110 "C with gentle stirring for 30 min. The solution was transferred to a cool stirrer and cooled to room temperature. This heated and cooled standard solution was used to obtain quantitative data on the sample extract solutions. About 2 g of polyethylene pellets was weighed into a 100-mL beaker. A stirring bar was added and 50 mL of decalin was pipetted into the beaker. The mixture was heated to 110 "C on a hot plate with gentle stirring for about 30 min or until dissolution was complete. The beaker was then transferred to a cool stirrer and cooled to room temperature with stirring to precipitate the polyethyelene. The precipated polyethylene from the above extraction was pushed aside with a microspatula. The porous metal filter portion of the filter apparatus (Figure 1) was inserted into the solution and about 5-10 mL of solution was drawn into the syringe. The Teflon tube was removed from the ferrule on the needle and the filtered solution was dispensed into a small vial. The filter apparatus was rinsed with acetone and dried between samples. After extensive use, the metal filter became partially clogged and was regenerated by placing it in hot decalin and stirring. The Model 660 solvent programmer was set at Program 6 (linear) going from 100% heptane to 100% methylene chloride in 5 min. The total flow rate was 2 mL/min. The Model 450 UV detector was set at 0.2- or 0.4-absorbance unit sensitivity and the recorder chart speed was 1 cm/min. Duplicate injections of 100 pL of each of the standard and sample solutions were made. The mobile phase gradient was started at the point of injection. The retention volumes (Vd for BHT, Irganox 1076, and Irganox 1010 were 10.3, 14.8, and 22.2 mL, respectively. The amount of each additive was determined from each sample injection by comparing peak heights for samples and standards. A blank decalin injection was made to determine from what points on the base line, peak heights should be measured. Gradient reset was instantaneous, from 100% methylene chloride to 100% heptane. Sample injection could be made anytime after the appearance of a refractive index peak from the UV detector, signifying the emergence of heptane from the column.
RESULTS AND DISCUSSION Preliminary Studies. Initially the separation of BHT, Irganox 1076, and Irganox 1010 was studied on SEC, normal phase, and reversed-phase HPLC systems. Irganox 1076 and Irganox 1010 were not separated from each other, but were separated from BHT on 1-500 Angstrom followed by 3-100 Angstrom p-Styragel SEC columns with a methylene chloride mobile phase. The VR values for BHT, Irganox 1076, and Irganox 1010 were 31.8, 25.5, and 23.0 mL, respectively. Nonaqueous reversed-phase HPLC on p-Bondapak C18with an acetonitri1e:tetrahydrofuran (7525) mobile phase (6) was studied also. B H T was not retained in this HPLC system. The VR values for BHT, Irganox 1076, and Irganox 1010 were 3.4,6.4, and 4.2 mL, respectively. BHT showed some retention on p-Bondapak CISwith a methano1:water (955) mobile phase. With this HPLC system, the VR values for BHT, Irganox 1076, and Irganox 1010 from injections of 1-5 pL of about 10 pg/pL solutions in chloroform were 4.1, 23.3, and 10.9 mL, respectively. I t was found, however, that injection of about 0.6 pg each of BHT and Irganox 1010 in 25-pL decalin solution resulted in a distorted B H T peak and a broadened Irganox 1010 peak. Thus, this reversed-phase HPLC system could not be used. Normal-phase HPLC systems on p-Porasil using mixed heptane and chloroform mobile phases were studied also. BHT showed some weak retention on p-Porasil, while Irganox 1076 and Irganox 1010 showed stronger retention. Therefore,
ANALYTICAL CHEMISTRY, VOL. 52, NO. 9, AUGUST 1980
Table I. Comparison of Peak Heights for 100-kL Injections of Heated and Unheated Standard Solutions
solutiona
injection
unheated unheated heated-AC heated-A heated-B heated-B
1
2 1
2 1
2
Table 11. Peak Heights for Eight Replicate 100-pL Injections of a Standard Mixture
Peak Height in m m b Irganox Irganox BHT 1076 1010 169.0 170.0 174.0 175.0 174.5 175.0
42.5 42.0 44.5 44.5 44.5 44.0
heptane to chloroform mobile phase gradients were tested. However, small amounts of ethanol preservative in the chloroform appeared to cause variations in the activity of the silica surface. Ethanol-free chloroform was not tested since the problem was resolved when methylene chloride was substituted for chloroform. Following a heptane to methylene chloride gradient run, injection of a sample could be made as soon as heptane began eluting from the column following a gradient reset to 100% heptane from 100% methylene chloride. Injection of additive solutions in amounts of decalin up to 100 pL did not cause peak distortion on p-Porasil with a heptane to methylene chloride mobile phase gradient. Thus, the HPLC system on p-Porasil described in the Experimental section was chosen for analysis of polymer extraction solutions in decalin. Several experiments were performed to determine the optimum conditions for dissolving polyethylene pellets in decalin followed by precipitation of the polymer and recovery of a portion of an extract solution. Initially, 2-g portions of polyethylene in about 25 mL of hot decalin were precipitated by the addition of the nonsolvents butyl cellusolve or ethanol. The polymer contained about 0.05% each of BHT and Irganox 1010. While the nonsolvents effectively precipitated the polymer, analysis of the extract solutions showed poor to no recovery of the additives. This indicated that the nonsolvents probably were driving the additives back into the polymer matrix. By allowing a solution of about 2 g of polyethylene in 50 mL of decalin to cool with stirring following dissolution at 110 “C, the problems associated with the nonsolvents were avoided. Furthermore, on cooling a hot decalin solution, the precipitated polymer was usually in the form of a spongy gel which could be pushed aside easily with a microspatula prior to filtering. HPLC peak heights for two heated standard solutions, each containing BHT, Irganox 1076, and Irganox 1010, were compared with peak heights for an unheated solution. The results are listed in Table I and show that the peak heights generally tend to be higher for the heated solutions. This was due probably to some evaporative loss of decalin during heating. T o avoid some significantly high errors in results, it appeared necessary that heated standard solutions be used. Detection. UV detection at 280 nm was used since BHT, Irganox 1076, and Irganox 1010 all have hindered phenol type chromophores (5). The absorption maxima of most phenols is near 280 nm (10). Although a variable wavelength UV detector was used in this study, one of several commercially available fixed wavelength detectors having a mercury lamp and a phosphor light source (maximum intensity at 280 nm) could be used as well.
Peak Height in mma Irganox Irganox BHT 1076 1010
injection
26.0 26.5 27.0 26.5 26.0 26.0
a Original unheated solution contained 2.04 p g BHT, 2.01 p g Irganox 1076, and 2.02 pg Irganox 1010 per 100 pL decalin. Chromatographic conditions: p-Porasil with a 100% n-heptane to 100% methylene chloride mobile phase gradient in 5 min at 2 mL/min. U V detecAbout 50 mL solution heated tor at 280 nm, 0.2 Abs. for 30 min at 110 “C with gentle stirring.
1413
1
2 3 4 5 6 7 8
175.0
S =
175.3 1.60 i1.3
x= 95% confidence a
174.5 175.0 173.0 174.5 176.0 176.0 178.5
44.5 44.0 43.0 44.0 44.0 44.0 44.5
43.5
43.9 0.50 k0.41
26.0 26.0 26.5 27.0 26.0 26.0 26.5
26.5 26.3 0.37 +0.31
Chromatographic conditions same as in Table I.
Table 111. Results of Six Replicate Determinations for a Polyethylene Sample sample amount, g
2.01 2.00 2.00 2.00 2.00 2.00 x= S=
95% confidence
Amount Found, wt 7’0 Irganox Irganox 1076 1010 BHT 0.050 0.050 0.050 0.05 1 0.051 0.050 0.050 0.00059 li. 0.00062
0.040 0.041
0.056 0.055 0.056 0.055 0.055
0.041
0.054 0.055 0.00073 +0.00077
0.042 0.041 0.042 0.041 0.00082 ?r 0.00086
Table IV. Recoveries of BHT, Irganox 1076, and Irganox 1010 from 2.0-g Portions of‘ Additive-Free Polyethylene Amount Added, Amount Found, Percent mg mg _ - Recovered BHT 1076 1010 BHT 1076 1010 BHT 1076 1010 0.51 1.51 1.02 1.02 2.04 2.04
0.50 0.51 0.53 0.50 0.51 0.53 1.00 1.01 1.09 1.00 1.01 1.08 2.01 2.02 2.06 2.01 2.02 2.14
0.51 0.52 1.10 1.07 2.09 2.16
0.44 0.46 1.05 1.02 2.01 2.08
104 101 88 104 105 92 107 109 104 106 107 101 101 104 99 105 108 103
Precision. The peak heights from eight replicate injections of a standard solution containing BHT, Irganox 1076, and Irganox 1010 are shown in Table 11. ‘These results show good precision for peak heights from HPLC:. The relative standard deviations were 0.9% for BHT, 1.1% for Irganox 1076, and 1.4% for Irganox 1010. A polyethylene sample containing all three additives was analyzed in six replicate runs. The results are listed in Table I11 and show good precision for the method. The relative standard deviations were 1.2% for RHT, 1.3% for Irganox 1076, and 2.0% for Irganox 1010. A chromatogram of one of the sample extracts is shown in Figure 2. The peaks correspond to about 2.0 pg BHT, 2.2 pg Irganox 1076, and 1.7 pg Irganox 1010. The chromatogram in Figure 2 was similar in appearance to one from injection of comparable amounts of the standards in 100 pL of decalin. Most of the small peaks and base-line ripples in Figure 2 appeared also in a 100-pL decalin “blank” injection. These were due to impurities in the decalin and the rapid mixing of heptane and methylene chloride during the 5-min mobile phase gradient.
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ANALYTICAL CHEMISTRY, VOL. 52, NO. 9, AUGUST 1980
Table V. Results of Duplicate Analyses of Three Polyethylene Samples Amount Found, wt 96 Irganox Irganox BHT 1076 1010 ~
amount, samplea
g
A
1.99 1.95 1.95 2.01 1.97 2.05
A
B B C C
___ ___
0.021 0.021 0.012 0.011
---
___ ___ ___ ___
___
~~
BHT
0.039 0.038 0.11 0.11
-__ -__
a Sample A, low mol. wt. polyethylene. Sample B, unspecified mol. wt. polyethylene. Sample C, high mol.
wt.
P O ‘ ABS
polyethylene.
Accuracy. Spiking experiments were performed by dissolving polyethylene samples in decalin containing known amounts of BHT, Irganox 1076, and Irganox 1010. The results from spiking 2.0-g portions of a polyethylene sample initially containing no additives are listed in Table IV. The results show good recovery of all three additives a t three different levels of spiking corresponding to about 0.02%, 0.05%, and 0.1 % of each additive, respectively. Spiking experiments were performed also for three polyethylene samples containing initially one or two of the three additives. The results of initial analyses of the samples are presented in Table V. The results of duplicate spiking experiments on these samples are listed in Table VI. The amounts found (Table VI) were corrected for additives present in the polyethylene (Table V). The results show good recoveries for all three additives. Recoveries for the additives for most spiking experiments in general tended to be near or slightly above 100% (Tables IV and VI). This was probably due to some evaporative loss of decalin, as discussed a t the end of the Preliminary Studies section above. The good recoveries observed in the spiking studies indicated that the additives were probably evenly distributed in the decalin both inside and outside the precipitated polyethylene “sponges” mentioned under Preliminary Studies above, prior to filtering. This even distribution is a prerequisite for the successful use of the rapid extraction procedure. S a m p l e Size. A polyethylene sample containing all three additives (Table 111) was analyzed in duplicate a t sample amounts of about 1, 2, and 4 g, respectively. The results are listed in Table VI1 and show the absence of significant constant error. T h e amounts of additives found for sample amounts of about 1 g vary slightly from sample amounts of 2 g and 4 g (Table VII). This is probably due to measurement of smaller HPLC peaks at the low sample amount. L i m i t s of Detection. The limits of detection for the additives were calculated for the method based on 2-mm peak heights at 0.2 Abs. This corresponds to a S I N ratio of about 2. T h e limits of detection for 100 pL of extract from a 2-g polyethylene sample are about 0.023 mg or 0.0006% BHT,
IRGANOX
IRGANOX
I
I
I
I
I
I
5
10 15 20 25 VOLUME FROM INJECTION, mL Figure 2. Chromatogram of 100-yL extract from 2.07 g of polyethylene.
0
Chromatographic conditions as in Table
I
0.092 mg or 0.002% Irganox 1076, and 0.15 mg or 0.004% Irganox 1010. These limits are quite sufficient for the analysis at additive levels of about 0.05% which are typical for polyethylene. Conclusions and F u t u r e Work. The method described in this report can be used for rapid analysis of BHT, Irganox 1076, and Irganox 1010 in polyethylene pellets. This should be useful for both quality assurance and lot certification analysis. This method has been investigated extensively for the analysis of polyethylene. Polypropylene also dissolves readily and precipitates on cooling under the conditions of the decalin extraction. Spiking studies also showed quantitative recoveries of BHT, Irganox 1076, and Irganox 1010. The average recoveries from duplicate spiking studies a t levels corresponding to 0.26-0.28 wt 70in polypropylene were 101%, loo%, and 9770, respectively, for the three additives. Some low molecular weight polymeric material was present in some polypropylene extracts studied which caused significant pressure increase problems on p-Porasil. Studies indicated that this problem could be avoided by using a 4 mm i.d. X 3 cm guard column packed with 37-pm CI8 Corasil. The use
Table VI. Recoveries of BHT, Irganox 1076,and Irganox 1010 from Three Polyethylene Samples Amount Added, mg Amount Found, mg Percent Recovered amount, Irganox Irganox Irganox Irganox Irganox Irganox 1076 1010 BHT 1076 BHT 1076 1010 1010 g BHT sample“ 108 102 A 1.96 103 1.02 1.00 1.01 1.04 1.08 1.03 110 112 104 A 2.01 1.13 1.02 1.00 1.06 1.10 1.01 107 98 B 2.02 1.02 1.00 100 1.01 1.02 1.07 0.99 109 93 B 1.97 98 1.02 0.94 1.00 1.01 0.99 1.09 C 1.97 1.02 105 97 1.00 1.01 1.04 1.05 0.98 102 106 104 C 2.04 1.02 1.00 105 1.01 1.07 1.06 1.05 “ Samples same as in Table V.
Anal. Chem. 1980, 52, 1415-1420
Table VII. Sample Size Variation Results with Polyethylene sample amount, g
BHT
1.03 0.99 3.96 4.05 2.07 1.91
0.046 0.046 0.048 0.049 0.047 0.049
Amount Found. wt % Irganox 1076 Irganox 1010 0.045 0.047 0.053 0.056 0.053 0.053
0.034 0.034 0.040 0.041 0.040 0.040
Table VIII. VR Values and Typical Detector Responses for Some Additives typical response,
additive
V R , mLa
BHT Irganox 1076 Irganox 1010 Santonox R U V 531 Ethyl 330 Goodrite 3114 Topanol CA
10.2 15.1 26.0 16.4 21.0b 12.0 18.8 23.2
d m m 0.01 0.05 0.13 0.08
capacity of the guard column was exceeded, the system could be restored by replenishing the guard column and replacing the outlet filter on the p-Porasil column. The only additives investigated extensively with the described extraction and HPLC separation were BHT, Irganox 1076, and Irganox 1010. Other additives with UV chromophores which preliminary studies indicate may be amenable to this method are Santonox R, UV 531, Ethyl 330, Goodrite 3114, and Topanol CA. The VRvalues of the above additives on the p-Porasil HPLC system used in this work are shown in Table VIII. The VR values of BHT, Irganox 1076, and Irganox 1010 in Table VI11 do not match exactly the VR values from Figure 2 since different batches of mobile phase solvents were used. Some typical response factors a t 280 nm for the additives are shown in Table VI11 also. The response was linear for each additive up to 4 pg except for UV 531, which tailed badly. This problem may be avoided by using a bonded normal-phase column, such as p-Bondapak CN. The extension of the described method to include all the above additives and possibly others in polyethylene and/or polypropylene is currently under investigation.
---
0.08 0.26 0.44
Chromatographic conditions same as in Table I. Tailed badlv.
a
of a reversed-phase guard column takes advantage of the strong interaction between the stationary phase and the polymeric material, which has a large aliphatic carbon number ( 1 1 ) . The polymeric material is thus effectively removed by the guard column. BHT, Irganox 1076, and Irganox 1010 are not retained by the guard column with a heptane mobile phase. T h e normal-phase separation of these additives on p-Porasil with a reversed-phase Bondapak C18 guard column was nearly identical to the noraml-phase separation without a guard column (Figure 2). In several instances when a pressure increase problem occurred on p-Porasil because the
1415
LITERATURE CITED (1) (2) (3) (4) (5)
(6) (7)
(8)
(9) (10) (1 I)
Wheeler, D. A. Tabnta 1968, 15, 1315. CM, G. R . SOC. Plast. Eng. Tech. Pap. 1977, 23. 496. Crompton, T. R. Eur. Polym. J . 1968, 4 , 473. Wims, A. M.; Swarin. S. J. J. Appl. Polym. Sci. 1975, 79, 1243. Lichtenthaler, R . G.; Ranfelt, F. J. Chromatogr. 1978, 749, 533. Liquid Chromatography Procedure for Polyolefin Additives, WAPP-100, Waters Assoc., Milford, Mass., 1978. British Standards 2782, Part 4, Method 405 D; British Standard Institute: London, 1965. Telepchak, M. J. Appl. Study No. 37, Perkin-Elmer Corp.: Norwalk, Conn., 1974. Schabron, J. F.; Hurtubise, R . J.; Silver, H. F. Anal. Chem. 1978, 5 0 , 1911. Schabron, J. F.; Hurtubise, R . J.; Silver, H. F. Anal. Chem. 1979, 5 1 , 1426. Schabron, J. F.; Hurtubise, R . J.; Silver, H. F. Anal. Chem. 1977, 49, 2253.
RECEIVED for review March 26,1980. Accepted May 21,1980. Presented in part at the 22nd Rocky Mountain Conference, Denver, Colo., August 1980.
Linear Parameter Estimation in Rapid-Scan Spectrophotometry Kenneth L. Ratzlaff Department of Chemistry, The Michael Faraday Laboratories, Northern Illinois University, DeKalb, Illinois 60 1 15
When two absorbance spectra are to be quantitatively compared, the ratio of the spectra should be detennlned using the weighted least-squares method with a two-parameter model. The precision of the measurement is Improved, and errors due to flicker and stray light are rejected. A computer program is demonstrated for use with spectra produced by a spectrophotometer using an optoelectronic imaging device.
Rapid-scan spectrophotometers, based on optoelectronic imaging device (OID) detectors, are capable in seconds or less of producing molecular absorption spectra of good precision and accuracy in the visible and often in the ultraviolet regions of the spectrum. Consequently, entire spectra can be made available to a user as easily as single absorbance measurements. However, little has been done to develop efficient and 0003-2700/80/0352- 14 15$0 1.OO/O
useful ways of using this information for quantitative analysis. In this paper, the application of linear parameter estimation to single component analysis is developed for the unique characteristics of certain OID-based spectrophotometers. A comparison of the various OIDs is necessary to determine the appropriate signal-processing methods. Silicon vidicons have been used in the laboratories of Pardue ( 1 ) and Enke (2) with outstanding success for obtaining equilibrium (3) or kinetic ( 4 ) measurements operating in rapid-scanning ( 4 ) , derivative ( I , 5) or dual wavelength (6) modes. Photodiode arrays have also been used for molecular spectrophotometry, chiefly in the laboratories of Dessy Milano (8) and OKeefe (9). Finally, a charge-coupled device (CCD) photoarray (10) has been used for the same purpose in our laboratory (11). T h e commonly used OIDs integrate light energy over the exposure time, which generally is the period between readout sequences. This gives rise to a multiplex advantage since
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0 1980
American Chemical Society
