reference compound or chromatographConsequently, ing to completion. saniplm such as naphthas in catalytic cycle oil and gasoline diluent in motor oil may be analyzed by this approach. Table 111 shows the results on successive days with encapsulated samples of a highly volat,ile mixture. Agreement b-tween the two analyses is within the experimental error to be expected in the measurement' of the peaks. 130th the individual determinations and the total recoveries show complete retention of all components. Wilkrns Instruments and Research,
Inc., has been licensed by Standard Oil Co. (Indiana) to manufacture commercial models of the indium tube introduction system. The commercial models are constructed of metal and can be operated a t 250' C. LITERATURE CITED
(1) Dimbat, M.,Porter, P. E., Stross, F. H., ANAL.CHEM.28, 290 (1956). (2) Ehrhardt, C. H., Grubb, H.. M., Moeller, W. H., L. S. Patent 3,103,277, Sept. 10, 1963. (3)rGrubb, H. M., Ehrhardt, C. H., 5ander Haar, R. W., Moeller, W. H., presented before ASTM Committee
E-14 on Mass Spectrometry, Los Angeles, California, May 1959. (4) KeulFmans, A., "Gas Chromatography, pp. 61-8, Reinhold, New York, 1957. (5) Meyerson, S.,Grubb, H. M.,I-ander Ham, R. W., J . Chem. Phys. 39, 1445 (1963). (6)h'erheim, A. G., ASAL. CHEM.35, 1640 (1963). ( 7 ) Sei-heim, A . G., U. S. Patent 3,063,286, Xov. 13, 1962. (8) Williams, A . F., Murray, R . T., Talanta 10,937 (1963). A. G. NERHEIM
Research and Development Department, American Oil Co. Whiting, Ind.
Infra red Determination of Hydroxyl Content of Epoxy Resins SIR: The reactive groups in epoxy resin are hydroxyl (-OH) and terminal 0 epoxide
/\
(-C-CH),
Inasniuch
as
H H hydrosyl is a functional group and inasmuch as the equivalents of hydroxyl per unit weight vary with molecular weight, a rapid, accurate, reproducible, standard method for determining hydroxyl should be available. Even though the resin was invented in the early 1940's no standard, mutuallyagreed-upon method is available. Classical methods of determining hydrosyl using acetic anhydride, acetyl chloride, or phthalic anhydride are well known (4)but these reagents are not applicable for determinat,ion of hydroxyl in epoxy resin because of the interference of the terminal epoxide group ( 5 ) . One approach that has been taken to eliniiriate epoxide interference is determination of reactive hydrogen and calculation of hytlroxyl since 1 mole of hJ-drogen ib equiralent to 1 hydroxyl. Steiirnark and Weiss ( 5 ) determined thc hydrosj~lcontent of epoxy resin by liberating the active hydrogen using lithium aluminum hydride as reagent. The amount of liberated hydrogen was determined by measuring its volume. 1Zartin and Jay (3) employed diborane as reagent to liberate the act'ive hydrogen and measured the amount liberated by pressure increase in the systeni. This laboratory used the diborane procedure of Martin and Jay. I t was concluded that the procedure was not applicable in o w laboratory for use by technicians because of the toxic, exploaire, and unstable properties of diborane and the meticulous attention to all details necessary to get a reliable answer. The lithium aluminum hydride procedure of Stenmark and Weiss offered no advantage. The near infrared procedure report'ed by Dannen1688
ANALYTICAL CHEMISTRY
berg ( 1 ) using the absorption band a t 1.456 microns was unsatisfactory because it was necessary to calibrate the instrument using either an internal standard or an epoxy resin of known hydroxyl content as determined by the lithium aluminum hydride procedure. This correspondent report's a procedure using conventional infrared equipment with NaCl optics. Hazards and terminal epoxide interference are eliminated and the determination can be performed by a technician. Nonpolar solvents with a window in the OH stretching region will not dis3olvt. cposy resin. Several of the solvent* used in the commercial application of eposy resin either absorb in the OH stretching region or contribute to intermolecular hydrogen bonding to some degree so these were not applicable. Pyridine was chosen as a solvent bccause it will dis;jolve all commercially available epoxy resins and because it possesses one other property of importance contributing to the success of the determination. The interaction between pyridine and alcohol molecules give an associated hydroxyl band exclusively according to the work of Valladas (6). Kabasakalian, Townley, and Yudis (2) employed pyridine as a solvent on 27 difficultly soluble hydroxyl containing compounds and found absorbance to be linear with concentration for the associated band which appears near 3.05 microns and is essentially independent of the type of hydroxyl group. Thus, pyridine as a solvent eliminates the complications of solubility i n d partial hydrogen bonding. This inforniat,ion also suggests a marked simplification of calibration compared to near infrared because it should be possible to use a high purity hydroxyl containing compound soluble in pyridine as a primary standard. From the data of Kabasakalian et al., it appeared glycerol was satisfactory for calibrating the instrument.
EXPERIMENTAL
Materials. The pyridine used was Eastman Kodak 1214 dried over KOH pellets before use. Shell Chemical Co. synthet'ic glycerol 99.9% was used as primary standard for calibration. The samples of epoxy resin tested had a weight per epoxide of 180-220 and a viscosity of 10,00016,000 centipoises a t 25' C. The resin was manufactured by the JonesDabney Co., Division of Devoe & Raynolde Co., Inc., and is marketed under the t'rade name of Epi Rez 510. Apparatus. All measurements were performed using a Llodel 21 PerkinElmer infrared spectrophotometer with NaCl opt'ics. The sodium chloride fixed cell had a sample path length of 0.07'o mm. Scans were made from 2.5 to 3.5 micronz in 1 minute with the instrument set at a resolution of 927, response 1, gain 5.8> suppiwsion 3, and a sodium chloride wafer in the reference beam. Procedure for Calibration. Two calibration curves are needed. For hydroxyl prepare five solutions of known concentration of glycerine in pyridine ranging from approximately 2.8 grams to 14 grams per liter. Fill cell with each solution and scan 2.5 to 3.5 microns. Read absorbance a t 3.08 microns. Fill cell with pyridine, scan, and read a t 3.08 microns to determine hackground. Plot net absorbance c s . grams OH for 10 ml. of solution. I n a similar fashion, prepare a calibration for water using five known solutions of water in pyridine
Table I. Hydroxyl Content in Equivalents Hydroxyl per 100 Grams Resin
Sample B-1339 B-1370 B-1434 B-1435 B-1529 B-1542
Infrared method Trial 1 Trial 2 0 048 0 047 0 052 0 052 0 041 0 043 0 041 0 044 0 045 0 043 0 050 0 048
Diborane method Trial 1 Trial 2 0 053 0 054 0 043 0 045 0 039 0 039 0 039 0 045 0 039 0 041 0 050 0 052
ranging in concentration from about 0.08 to 0.4 gram per liter. Procedure for Resin. T a r e a 10ml. volumetric flask on analyt’ical balance. Transfer into it 3.5 to 4.0 grams of resin sample. Reweigh and calculate sample weight. Fill t’o mark with pyridine, stopper, and agitate vigorously. Fill cell with pyridine and scan. Refill and repeat scan. Read absorbance a t 3.08 microns and record average. This is background. Fill cell with’sample solution and scan. Repeat scan. Read absorbance at 3.08 microns and record average. Corrcct this absorbance reading for background and water (as determined by Karl Fisher method) giving net absorbance at 3.08 microns. Refer the net absorbance t,o calibration curve to ascertain grams hydroxyl in the sample and calculate equivalents of hydrosyl per 100 grams. RESULTS AND DISCUSSION
Table I records the results in duplicate for hydrosyl determination on qiu samples of Epi Rez 510 by both the infrared procedure and the diborane procedure. Precision. An indication of t h e reproducibilitv of the method and how i t compares with t h e diborane procedure may be obtained from an evamination of the above d a t a . T h e mean of the differences between ‘Trial 1 and 2 for t h e six samples by t h e infrared method is 0.0017 or 3.8Oj, of t h e mean of the series of 12 recorded
values. T h e range is 0.000 to 0.003. The mean of differences between Trial 1 and 2 for the same six samples by the diborane method is 0.0022 or 4.8% of the mean of the series of 12 recorded values. Based on Table I, the infrared method has the higher precision. Accuracy. T h e accuracy of t h e infrared method can not be established with certainty because epoxy resin of known hydroxyl content is unavailable either by synthesis or by certification from a recognized bureau or agency. However, a n indication of accuracy can be obtained by comparing results of the infrared method to results of the diborane method. T h e mean of the 12 recorded values by infrared is 0.0462 and by the diborane method the mean is 0.0449. Assuming the latter value to be the true value, the mean error of the infrared method is 0.0013 equivalents hydroxyl per 100 grams resin and the relative error is 2.9%. With haste it is pointed out that it is only assumed the diborane method value is a true value and that more correctly the figures of 0.0013 and 2.9% should be thought of as differences. Taking into account the wide divergence in concept, theory, equipment, and technique of the two methods, the agreement is considered escellent. A11 subsequent determinations in this laboratory have been made by the infrared procedure using technical personnel. At the time the determinations reported herein were conducted, the only
resin under test was resin with a weight per epoxide of 180-220. Resins of higher weight per epoxide values containing more equivalents of hydroxyl per 100 grams resin would require use of smaller sample size. For example a sample size of 0.65 f 0.02 gram would be in order for a resin with a weight per epoxide of 2000. ACKNOWLEDGMENT
The author acknowledges the work of V. L. Watson in development of this procedure. LITERATURE CITED
(1) Dannenberg, H., Division of Organic Coatings and Plastics Chemistry, 142nd Meeting, ACS, Atlantic City, N. J., September 1962. (2) Kabasakalian, P., Townley, E. R., Yudis, M. D., ANAL. CHEM.31, 375 (1959’r. \ - - - - ,
(3) Martin, F. E., Jay, R. R., Zbid., 34, 1007 (1962). ( 4 ) Illehlenbacher, 5’. C., “Organic Analysis,” T’ol. 1, pp. 2-65, J . Mitchell, Jr., ed.. Interscience. Sew York. 1953. ( 5 ) Sknmark, G . A , , Weiss, F. ‘I?, ANAL. CHEM.28, 1784 (1956). (6) Yalladas-Dubois, H., 13ulI. SOC.Chem., France 16, 604 (1949).
11,It.
AnAMs
Jones-Dabney Company Division of Devoe & Raynolds Co., Inc. Louisville 8, Ky. PERMISSION of the Jones-Dahney Co., Division of Devoe & Raynolds Co., Inc. to publish this paper, is acknowledged.
Determination of Peroxide by Automatic Colorimetry SIR: I n the study of the radiolysis of aqueous solut,ions it is necessary to determine the amount of hydrogen peroside formed a t very low radiation doses. Low doses are required to minimize the effect of secondary reactions. The large number of samples and low concentrations of peroside require a sensitive, rapid analytical method. We developed an automatic colorimetric method that is very suitable for this purpose. The method is applicable to nearly neutral solutions, gives good precision over a range of 5 p.p.b. to 8 p.p.m., and is sufficiently sensitive to determine the amount of peroside formed by < l o 4 rad in many systems. Automatic colorimetry has been applied to various determinations ( I , 4, 6, 7 ) and the analysis of very low concentrations of chloride, nitrate, nitrite, ammonia, and ferrous and ferric iron was the subject of a previous report from this laboratory ( 2 ) . The reaction adapted for the peroside analysis consists of the osidat>ion of the leuco
base of phenolphthalein by peroside in the presence of C U + ~ . The resultant phenolphthalein color is measured a t 534 mb. This reaction has been used as the basis for a qualitative test for peroyide ( 5 ) , but the instability of the color formed in the reaction makes quantitative determination difficult by ordinary manual methods. The automatic colorimeter system makes quantitative determination possible by precise proportioning and proper mixing of sample and reagents and by precise timing in the color development step.
Apparatus. All operations, from reagent additions t o absorbance measurements are performed automatically with a Technicon AutoAnalyeer manufactured by Technicon Instruments Corp., Chauncey, S . Y. Complete descriptions of this instrument are available in the literature ( I , S, 7 ) . Components of the .l utoXnalyzer used in the peroxide determinat,ion are tbe sampler, proportioning pump> mixing coils, colorimeter, range expander, and strip chart recorder. The flow diagram including the manifold €or the proportioning pump is shown in Figure 1 . RESULTS AND DISCUSSION
EXPERIMENTAL
REDUCED PHENOLPHTHALEIN. Dissolve 100 grams of sodium hydroxide in 200 ml. of distilled water and add 50 grams of zinc dust. Add 10 grams of phenolphthalein (C20Hlr04) and boil under reflux for 2 hour.: or until the solution is colorless. COPPERSULFATE.Dissolve 0.4 gram cf coppcr sulfate (CuSO4.5H&) in 1 liter of distilled water. Reagents.
This method has been applied in numerous determinations of pcroside in nearly neutral nitrate solutions. Concentrations as low as 5 p.p.b. were determined with good preciiion (relative standard deviation, 2.3oj,). Working curves were not linear but were quite reproducible over the range of concentrations of interest. Preckion data obtained are summarized in Tahle I . VOL. 36, NO. 8, JULY 1964
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