olatiI e Additives
.
Eappin and J. S . Zannucci Research Laboratories, Tennessee Eastman Company, Division of Eastman Kodak Company, Kingsport, Xenn. 37662 UANTITATIVE DETERMINATION of additives in a polymer is a difficult task ; however, gas-liquid chromatography (GLC) has been used successfully for some analyses. For example, GLC has been used (I, 2 ) to determine a number of additives and unreacted monomers in polystyrene. More recently, GLC has been used for the determination of certain antistatic additives (3) and 2,6-di-tt.rt-butyl-p-cresol (4) in polyethylene. This report concerns a method of determination by GLC of those additives in polypropylene that are thermally stable and have an appreciable vapor pressure at 350 "6. Many ultraviolet stabilizers and hindered phenolic antioxidants are in this category.
EXPERIMENTAL Apparatus and ~ ~ An F~ & M gas ~ chromatograph 0 ~ ,Model 5750 equipped with a flame ionization detector was used for this work. Copper columns, in. X 5 ft, packed with 10% SE-30 on 40- to 60-mesh Chromosorb W were
used. (The column may require silylation.) The injection port and detector oven were held at a constant temperature of 330 "C. Helium was used as the carrier gas. Samples (1) P. Shapras and C ,C . Claver, ANAL.CHEW,36, 2282 (1964). (2) C. B. Roberts and J. D. Swank, ibid., p 271. (3)J. Davis and B. Denham, Analyst, 93, 336 (1968). 39, 1493 (4) R.E. Long and G. C. Guvernator 111, ANAL.CHEM.,
(1967).
Table I. Analyses of o ~ y p r ~ ~ y for ~en BHT e and Additive found, Sample composition Run 1 Run 2 Run 3 0.05% BHT 0.02 0.02 0.03 0.3QxDBBF 0.25 0.32 0.20
DOBP
Run 4 0.02 0.35
Table 11. Elution Data for Additives Eluted within 1 Hour 2,6-Di-lert-butyl-p-cresol 4,4 '-Methylenebis[2,6-di-ter~-butylphenol] 2,2 '-Methylenebis[G-(1-methylcyclohexyl)-p-cresol] 4 4 '-Thiobis[6-ter~-butyl-m-cresol] 4,4'-Butylidenebis[6-ter~-~u~yl-m-cresol] 1,3,5-lrimethyl-2,4,6-tris(3,5-di-teut-butyl-4-hydroxybenzyl)benzene Qctadecyl 3,5-di-tert-butyl-4-hydroxyhydrocinnamate Tris(2,6-di-tert-butyl-4-hydroxyphenyl) phosphate
2-Hydroxy-Cmethoxybenzophenone 2-Hydroxy-4-(octyloxy)benzophenone 4-(Dodecyloxy)-2-hydroxy benzophenone 2-(2W-Benzotriazol-2-yl)-p-cresol 2,4-Di-rer~-butyl-6-(5-chloro-2a-benzotriazol-2-y~)p~enol Eluted with Decomposition 2,2 '-Thiobis(6-lerr-butyl-p-cresol) Dilauryl 3,3 '-thiodipropionate DioctadecyP 3,5-di-tert-butyl-4-hydroxybenzylphosphonate
Distearyl pentaerythritol diphosphate Not Eluted within 1 Hour Pentaerythritol tetrakis(3,5-di-rert-but~.l-4-hydroxyliydrocinnamate) Zinc dibutyl dithiocarbamate
0
~
.
0
4
8
12
16
20
24
28
TIME, MINUTES Figure I. Chromatogram of a polypropylene extract Peaks are ( A ) biphenyl; ( B ) BHT; ( C ) DOBP; and (D)unknown impurity
of the solution injected ranged in size from 0.05 to 0.20 ml. The chromatograph was programmed from 100 to 340 "C at a rate of 15 "/min and was held at the upper limit for 1 hr. Preparation of Samples for Analysis. A 3.0-g sample of the polymer was added to 150 ml of p-xylene in a roundbottom flask equipped with a reflux condenser and a magnetic stirrer. The mixture was heated at reflux and stirred until solution was complete, and then 1.0 ml of a 0.3% solution of biphenyl (or benzophenone) in p-xylene (internal standard for GLC) was added. The solution was diluted with 150 ml of p-dioxane, cooled in an ice bath, and filtered. The filtrate was concentrated to about 1.0 ml of a rotary evaporator at 45-50 "C. p-Dioxane was added to bring the volume to approximately 6.0 ml. The solution was filtered once more and chromatographed. RESULTS AND DISCUSSION A number of ultraviolet light absorbers as well as antioxidants can be quantitatively determined on an SE-30 column. SE-30 has a maximum operating temperature of about 350 "C, which is 50 "C above that of other organic liquid phases commercially available. This high temperature permits elution of some high molecular weight additives. Two methods of separating the additives from the polymer were tried. GLC of a hexane extract of the polymer produced numerous extraneous peaks, probably owing to a decomposition of dissolved amorphous polymer in the injection port, rendering the chromatogram useless. When the polymer was dissolved in p-xylene and reprecipitated with an equal volume of p-dioxane, a relatively clean Chromatogram was obtained from the filtrate. The position of decomposition peaks from unstable compounds, such as dilauryl 3,3 '-thiodipropionate and distearyl pentaerythritol diphosphite, are predictable and do not interfere with the determination of those additives
ANALYTICAL CHEMISTRY, VOL. 41, NO. 14, DECEMBER 1969
included in this study. The optimum size of polymer sample was 3.0 g; however, some runs were made with as little as 200 mg. Biphenyl (in some instances, benzophenone) was used as an internal standard for quantitative analysis. Figure 1 is a typical chromatogram. Two common polypropylene stabilizers, 4-(dodecyloxy)-2hydroxybenzophenone (DOBP) and 2,6-di-tert-butyl-p-cresol (BHT), were quantitatively determined by this technique. The results, calculated from peak areas, from four separate runs are summarized in Table I. The precision for the BHT determination was good, but the quantity found (0.02 %) was less than the amount added (0.05%). BHT is very volatile, and some loss probably occurred during compounding. DOBP determinations ranged from 0.20 to 0.3.5z for a sample that originally contained 0.30%. These data reflect the poor resolution between DOBP and some other components that appear as shoulders on the DOBP peak (Figure 1). To demonstrate the scope of the method, a number of common polypropylene additives were determined by GLC (Table 11). Most of these additives were eluted without
Spectrophoto
decomposition in less than 1 hr; this group included 1,3,5trimethyl-2,4,6-tris(3,5-di-~ert-butyl-4-hydroxybenzyl)benzene, mol wt 774. However, pentaerythritol tetrakis(3,5-di-tertbutyl-4-hydroxyhydrocinnamate) mol wt 1058, although stable, was not eluted from the column within 1hr. A few compounds decomposed, as evidenced by peaks of low molecular weight fragments. For some compounds, such as dilauryl 3,3'-thiodipropionate, thermal instability could be predicted from the structure of the additive; however, such a prediction is not always possible. The marked difference between the unstable 2,2 '-thiobis[6-tert-butyl-p-cresol] and its stable isomer, 4,4'thiobis[6-tert-butyl-m-cresol], was unexpected. For additives other than those listed, the thermal stability must be determined by experiment. For a number of commonly used polypropylene stabilizers, this GLC method provides a rapid, quantitative determination and requires only a small sample of polymer. RECEIVED for review July 17, 1969. Accepted October 2,1969.
ination of Glyoxal iazolinone Hydraz
Fred W. Neumann Analytical Laboratory o j The Midland Dizision, The Dow Chemical Company, Midland, Mich.
IT IS OFTEN important to determine glyoxal when it occurs in biological systems, as a hydrolysis product, or as an oxidation intermediate in systems containing only two adjacent carbon atoms such as triethanolamine. Glyoxal can conveniently be determined at the parts-per-million level in aqueous and organic media by formation of the diazine of 3-methyl-2benzothiazolinone hydrazone (MBTH). Glycolaldehyde interferes in the semiquantitative method of Blumenfeld, Paz, Gallop, and Seifter (1). To avoid this interference the method was modified, and a quantitative procedure is described for the determination of glyoxal in the presence of glycolaldehyde and triethanolamine. The molar absorptivity of the pure diazine is determined for the first time. Formation of the diazine in situ is shown to be quantitative. Differences in previously recorded, qualitative spectral characteristics are shown to be the result of varying amounts of water in the solvents. When triethanolamine is present, it must be converted to the amine sulfate to attain the desired spectral Characteristics of the diazine. EXPERIMENTAL
Apparatus. Cary Model 14 spectrophotometer and 1-cm cells were used. Reagents. MBTH, 0.4%. Dissolve 0.40 f 0.01 g of 3-methyl-2-benzo-thiazolinone hydrazone hydrochloride monohydrate (Aldrich Chemical Company) in 100 ml of 80% acetic acid, and filter. The reagent should be prepared fresh daily, or else stored in a refrigerator to keep it from discoloring. GLYOXAL, 50 ppm standard solution. Dilute 20 ml of 40% glyoxal (Matheson, Coleman and Bell 7204) to 250 ml using distilled water and determine the exact concentration (1) 0. 0. Blumenfeld, M. A. Paz, P. M. Gallop, and S . Seifter, J. Biol. Chem., 238, 3835 (1963).
using the caustic-titration method of Salomaa (2). The calculated amount of this solution is then diluted to l liter using 80% acetic acid. GLYCOLALDEHYDE (HOCH2CHO) was obtained from Aldrich Chemical Company. A purified sample of diazine was prepared using 40% glyoxal and 3-methyl-2-benzothiazolinone hydrazone hydrochloride in water at room temperature. The crude product was recrystallized using dimethyl sulfoxide, washed with methanol, and dried at 105 "C under 5 mm Hg pressure. Yellow needles were obtained, mp 296-299 OC; the reported value is 296-297 "C (3). Anal. Calculated for ClsHlaN$32: C, 56.8; H, 4.24; N, 22.1; S, 16.9. Found: C, 56.0; H, 4.17; N, 22.2; S, 17.0. Differential scanning calorimetric analysis ( 4 ) indicated 99.5 mole per cent purity. The molar heat of fusion was calculated to be 13,094 calories. Calibration. Appropriate dilutions in 80% acetic acid were made using water, acetic acid, and a stock solution of the pure diazine (6.09 mg/100 ml acetic acid). The net absorbances at 407 mp were measured using 80% acetic acid as reference. The net absorbance was linear in the range of 0-1200 pg diazine per 100 ml; the molar absorptivity is 46.4 x 103. Procedure (For Triethanolamine). Weigh 1.OOO-1.030 & 0.001 g sample into a 50-ml volumetric flask and add the calculated amount of 1N sulfuric acid to neutralize the base present; 6.70 ml is required per gram of triethanolamine. Then pipet 2.50 ml of the 0.4% MBTH reagent into the flask and dilute the mixture to volume using 80% acetic acid. Shake well and allow to stand at room temperature for at least 2.5 hours. Concurrently a reference solution is pre(2) P. Salomaa, Acta Chem. Scarad., 10, 306 (1956). (3) G. Henseke, G. Hanisch, and H. Fischer, Ann. Chem., 643.3, 161 (1961). (4) C. Plato and A. R. Glasgow, Jr., ANAL.CHEM., $1, 330 (1969).
ANALYTICAL CHEMISTRY, VOL. 41, NO. 14, DECEMBER 1969
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