shows no absorbance above 250 n m but has a modest absorption coefficient at 224 n m . Figure 6 depicts the analysis of Virazole at this wavelength.
who provided the special low volume flow-through cells. I also would like to especially thank Ron Majors for help and advice in preparing the manuscript.
ACKNOWLEDGMENT
Received for review August 27, 1973. Accepted December 13,1973.
I would like t o acknowledge the help of Miner Munk
New Spray Reagent for the Identification of Accelerators in Unvulcanized Rubber Compounds by Thin Layer Chromatography Marjorie B. Millingen Olympic Tyre & Rubber Company, Cross Street, West Footscray, Victoria, Australia
Existing thin layer chromatographic methods for the analysis of accelerators in rubber compounds are concerned, in the main, with the identification of residues in vulcanized stocks. Methods which can be applied to the analysis of unvulcanized stocks rely on several visualizing reagents to classify different chemical types. No reference is made in either case to interference from other compounding ingredients present in the extracts, particularly to that from processing oils and antioxidants (1-5). This procedure highlights interference from other compounding ingredients and describes, in detail, means for overcoming this. Recommendations are also made to aid the analyst in the interpretation of the chromatogram. EXPERIMENTAL Equipment. Machery Nagel Polygram Si1 G UV254 pre-coated plastic sheets, an IKA Janke Kunkel Laboratory mill with freeze drying attachment, and a Chromatovue Model CC20 UV viewing cabinet were used. Reagents. Liquid nitrogen was used as reagent. The developing solvents were (1) Petroleum ether (30"40"C):diethyl ether 110:20 (predeveloping solvent); (2) benzene: ethyl acetate:acetone, 100:7:2 (primary solvent mixture); (3) cyclohexane; (4) to1uene:ethyl acetate:ammonium hydroxide, 100:5:0.1; (5) cyclohexane:diethylamine, 75:25; (6) chloroform: benzene, 100:90; (3), (4), (5), (6) (improving separations when required); and ( 7 ) acetone:ammonium hydroxide, 100:l (confirmation guanidines). Visualizing reagents used were (1) Iodoplatinate solution, 3 cm3 of 10% platinum chloride solution is mixed with 97 cm3 of water to which are added 100 cm3 of a 6% aqueous solution of potassium iodide; (2) dibromo benzoquinone chlorimide, 1% solution in methanol; (3) sodium hypochlorite, 4% solution in water; and (4) sodium bicarbonate, 1% solution in water. Procedure. Immerse 3.0 grams of unvulcanized sample, cut into small pieces, in liquid nitrogen until hard and grind to a fine state using the IKA Janke Kunkel laboratory mill with freeze drying attachment. Transfer the finely ground sample to a glassstoppered 30 cm3 test tube, add 5 cm3 of AR isopropanol and extract by infusion for 1 hour at room temperature. Decant off extract and leave overnight in freezer, filter into small crucible, and evaporate off solvent at room temperature. Redissolve extract in 1 cm3 of chloroform and apply amounts of 1-10 ~1 to a thin layer chromatography sheet using a 10-pl syringe, evaporating off solvent with cold air between applications. (1) J . G. Kreinerand W. C. Warner, J. Chromatogr., 44, 315 (1969). (2) W . Hofmann and H. Ostromow, "Technicai Notes for t h e Rubber Industry," No. 41, 57 (1968). (3) T. Yuasa and K . Kamuya, Bunseki Kagaku, 13,966 (1964). (4) J. R. Davies and T. W . Kam, J. Inst. Rubber Ind., 2, 86, 89 (1968). (5) R. Amos, J . Chromatogr., 31, 263 (1967)
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After development, examine plate under short and long UV, and record observations. Spray the sheet with the iodoplatinate solution until saturated. Dry in an air oven at 100 "C, taking care not to overheat the sheet. When using the combination of sprays, spray with the chlorimide and dry at 65 "C. Examine and then spray with iodoplatinate, and dry at 100 "C. DISCUSSION Great care must be taken to avoid the deleterious effects of heat a t any stage of the analysis. This is especially important where delayed action accelerators are present. On these grounds, milling of the samples was avoided and fine grinding of the freeze dried rubber was adopted as standard procedure. Concentration of the extracts in small crucibles a t room temperature, and cold-air drying of the spots after application to the thin layer chromatography sheet, were strictly adhered to. Isopropanol was used as the eluting solvent, in the main, and acetone only when it was known that this solvent would not cause decomposition of the accelerator. Although extraction with isopropanol is incomplete, the reasons for its selectign over acetone are threefold. Acetone causes decomposition of certain types of accelerators -e.g., thiurams are decomposed to dithiocarbamates. Isopropanol obviates any such risk (6). The method is for the analysis of unvulcanized stocks. Substantial quantities of accelerator can be recovered using isopropanol as extractant. The method is qualitative. A complete extraction is not of paramount importance. Circumstances where acetone is the preferred extractant are: (a) Guanidines. These are frequently used as activators for thiazoles and sulfenamides and may be present a t very low levels. Alternatively, a larger sample may be eluted with isopropanol. (b) Zinc diethyldithiocarbamate (ZDC), copper dimethyl dithiocarbamate (Cumate), and zinc salt of mercapto banzothiazole (ZMBT) elute very slowly from isopropanol. Acetone may be used to confirm their presence. Isopropanol would not appear to be a n effective solvent for eluting accelerator fragments from vulcanized stocks and its use should be restricted to the analysis of unvulcanized material. (6) William C. Wake, 'Analysis of Rubber and Rubber-like Polymers." Maclaren and Sons, London, 1969.
Table I. Reactions of Accelerators (Included Arc a Few Peptizers)
Table 11. Reactions” of A n t i o x i d a n t s Trade name or abbreviation
Chemical
Acetone diphenylamine condensation product Butraldehyde aniline condensation product 4,4’-Butylidene-bis(6-tert-butyl3-methy lphenol)
Nonox BL
4-Phenyl-N’-cyclohexyl-p-
Antioxidant 4010
phenylene diamine 2,2 ’-Methylene-his i4-ethyl-6tert-butylphenol) Diphenylamine acetone reaction product N-Phenyl-N’-1,3-dimethyl butyl p-phenylenediamine 6-Dodecyl-1,2-dihydro-2,2,4trimethylquinoline Diphenyl-p-phenylenediamine Mixture of diary1 p-phenylenediamines 6-Ethoxy-1,2-dihydro-2,2,4trimethylquinoline N,N’-Bis(l-ethyl-3-methylpentyl)-p-phenylenediamine N,N’-Bis 1-methylhepty1)-pphenylenediamine N,N’-Bis 1,4 dimethyl pentyl)p-phenylenediamine 2,2’-Methylene-bis‘6 01-
Spray 1, iodoplatinate
...
Antox Santowhite powder Grey blue
Antioxidant 425 Ble Santoflex 13
Green blue (weak) Blue brown
Santoflex D D
Spray 2, chlorimide
Spray 2 plus spray 1
Primary solvent system Rg
Pale green
Green blue
0.53
Brown yellow edge Purple
Grey purple
0.40
Grey
0.37
Purple
Purple
Green white ctre Yellow
Rust yellow ctre Rust
Brown yellow Purple edge Yellow Rust yellow ctre Purple Purple
0.58 0.48 0.48
0.38
DPPD
Green
Wingstay 100 Santoflex AW
Brown green Brown yellow Purple edge Cyclamen Purple
UOP88
Cyclamen
Cyclamen
Cyclamen
Santoflex 217
Purple
Purple
0.25
Santoflex 77
Purple
Pink, grey edge Brown
Purple
0.23
Yellow
Yellow orange edge
Nonox WSP
methylcyclohexyl-4-methyl-
0.47 0.50 0.40
phenol) 4-Isopropylaminodiphenylamine
Nonox ZA
A substituted phenol
Nonox WSL
p-Naphthylamine Tri(nony1ated phenyl)-phosphite
Pol ygard
, . .
Substituted styrenated phenol Wingstay S 2,6-di-tert-Butyl-4-methylphenol Ionol 2,2 ’-Methylene-bis(4-methyl 6-tert-butylphenol) Modified phenyl 3naphthylamine A phenol condensation product
Antox 2246
A blend of arylamines Sym. di-p-naphthyl-pphenylenediamine Phenyl-$-naphthylamine
Nonox H F N Nonox C I
+
White , . .
...
Nonox D N Nonox EX
Nonox H P
diphenyl-p-phenylenediamine
A phenol condensation product Octylated diphenylamines 2,2,4-Trimethyl-1,2dihydroquinoline A phenol condensation product N,N’-Bis(1-methyl hepty1)-pphenylenediamine
Grey green
Nonox WSP 0c tamine Flectol Flakes A.F.D. UOP288
...
Brown yellow Purple edge Yellow purple Rust edge Brown Purple Purple, orange White purple edge Purple, blue Purple Rust Yellow brown edge Yellow Orange brown edge Pink Purple
0.33 0.55 0.22 0.57, 0 . 3 3 0.60, 0 . 3 7 0.90
0.57 0.53
Yellow
Weak pale green (Weak response) Cyclamen
Yellow purple 0.38 streak Pink Purple 0.53 Brown streak Lavender 0.00 streak 0.47, 0 . 5 3 Yellow, purple Purple Yellow Pale pink Turquoise
Rust Brown green Green
Grey Pink, blue
Purple
...
0.37 0.99
0.45, 0.35, 0.20, 0.13, 0 . 0 5 0.60 0.50, 0 . 0 8
a Color reactions given in the tables refer to pure compounds. At the dilution level in a rubber stock, many of the positive responses given by antioxidants to the idodoplatinate reagent are weak and, in many instances, could be regarded as negative. Those antioxidants which remain clearly evident a t such dilution are Santoflex 13, Santoflex 7 7 , Santoflex 217, and Nonox ZA.
the accelerator spot, and the analyst should be aware of this. We have adopted the procedure of running two plates simultaneously, per analysis. Plate 1 is sprayed with the iodoplatinate reagent, visualizing accelerators as white, yellow, orange, and brown spots on a brick red background (Figure 1). Plate 2 is sprayed with chlorimide reagent (Figure 2 ) . Both accelerators and antioxidants produce colored spots with this reagent. On overspraying 748
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with the iodoplatinate (Figure 3), the antioxidant spots retain their color, while the accelerator spots fade or become a darkened center with an intense white halo. The bonding effect of the antioxidant present in the extract is immediately evident. Accelerators studied were representative of a wide range of chemical types including guanidines, thiazoles, thiurams, sulfenamides. dithiocarbamates, and morpholine disulfides. All the accelerators tested gave a positive response to the iodoplatinate reagent
Figure 3. Plate sprayed with chiorirnide reagent. Oversprayed with iodopiatinate
and a list of color reactions is included (Table I). Also described are the color reactions of a wide range of antioxidants tested involving both phenolic and amine types (Table JI). Only those antioxidants based on phenylene diamine gave a color reaction with the iodoplatinate reagent. Colors produced are distinctively different-cyclamens, purples, and greens. An overspray of sodium bicarbonate, immediately following the chlorimide spiay, and then overspraying with
nothio)benzothiazole (Santocure MOR); and mercaptohenzothiazole (MBT). Chromatograms should be observed a t intervals through a period of 48 hours. Colors tend to become more definite or fade, leaving a pale spot with a discolored center. This would appear to he characteristic of accelerators treated with the iodoplatinate reagent, and could serve as a distinguishing feature when analyzing accelerators in the presence of antioxidants. The presence of guanidines should he confirmed hy developing a third plate in acetone/ammonium hydroxide and spraying with sodium hypochlorite. This is necessary because some peptizers give a similar color reaction to guanidines with the iodoplatinate reagent, and also remain a t the point of application on the chromatogram. Finally, extracts from compounded stocks, and not pure material, must be used as reference, as the heating effects during compounding can result in chemical changes in some accelerators. All extracts and reagents are stored under refrigeration.
ACKNOWLEDGMENT The technical assistance of G. Di Giantomasso is acReceived for review September 18, 1973. Accepted De cember 26,1973.
Gas Liquid Chromatographic A,nialysis of Alkyl Alcohols, Alkyl Cyanoacetates and Alkyl 2-Cyanoacrylates Ramchandra K. Kulkarni, Eric C. Johnson,' and Clarenc e w. n. waoe U.S. Army Medical Bioengineering Research &DevelopmentLaboirat The wide spread interest in alkyl 2-cyanoacrylates as promising tissue adhesives in surgical practice made it necessaly to set down a quick and easy method of identification and analysis of these chemical compounds and their mixtures. The gas-liquid chromatograph with hydrogen flame-ionization detector has been used for the quantitative estimation of these compounds in this report. It is known that the molar response measured in recorded chromatographic peak areas for members of homologous series of hydrocarbons, carboxylic acids, alcohols, esters, ethers, etc. is linearly related to the number of carbon atoms in the molecules, when the individual samples do not differ in number and kind of functional groups (2-5), structural or stereo isomerism or variation in molecular structure, other than the increase or decrease in the numPresent address, Continental Oil Co., Ponea City, Okla. (1) H. Brudereck, W. Schneider, and I. H a i k z , Anal. Chem., 36, 46173 (1964). (2) G. Perkins, Jr., G . M. Rauayheb, L. D. Liverly. and W. C. Hamilton. Gas Chromatog. 3rd International Symposium, pp 269-285. (3) R. F. Addison and R. G. Ackman. J. Gas Chromatogr., 6 , 135-7
(1968). ( 4 ) A. Janik, J. Chromarogr., 54, (3) 21-25 (1971). ( 5 ) L. S. Ettre,J. Chromarogr., 6,525-30 (1962)
teria, the logarithms of the retention volumes in the flame ionization detector are also linearly related t o the carbon number. Applying the same principle, the normal straight chain alcohols and their esters with cyanoacetic acid and 2-cyanoacrylic acid were studied for retention volumes and molar responses, and the instrument, calibrated with respect to these parameters, was used to evaluate t h e composition of the known synthetic mixtures, with sufficient accuracy, a s reported in the present article. The chemical analysis of alcohols and alkyl cyanoacetates is easy but time consuming, but alkyl-2-cyanoacrylates do not lend themselves t o chemical analysis without the use of thiophenol, which has a strong stinking odor making analysis difficult. The gentle techniques, like liquid chromatography, have not been successful in the quantitative evaluation of these compounds within the admissible error limits. Therefore the gas-liquid chromatography, when previously investigated and worked out as regards columns, liquid phase, solid support, physical condition of the phases, temperatures, eluting gas, and other incidental details in the technique of gas chromatography, becomes the method of choice for quick evaluaANALYTiCAL CHEMISTRY, VOL. 46, NO. 6 . MAY 1974
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