CONCLUSION
Data presented show that the two-diameter column gives enhanced resolution of normally difficult separations for typical preparative and trace analyses. The two-diameter technique can be used for large samples without significantly increasing the time of analysis for both gases and liquids. This method may be applied to a combination gas chromatograph connected in series to a mass spectrometer. Frequently a trace component is too small to be identified by the mass spectrometer. The two-diameter column allows a much
larger sample to be introduced into the gas chromatograph for a separation, without column overloading, and allows a satisfactory determination by the mass spectrometer, ACKNOWLEDGMENT
The author gratefully acknowledges the technical assistance of T. C. Harby in preparing the column used in these experiments. RECEIVED for review July 10, 1967. Accepted October 23, 1967.
Gas Chromatographic Determination of Diethylene Glycol in Poly(Ethy1ene Terephthalate) Leonard H. Ponder American Enka Corp., Enka, N . C . PRODUCERS OF POLY(ETHYLENE TEREPHTHALATE) yarns maintain that ether linkages resulting from incorporation of diethylene glycol in the polymer chain adversely affect light and oxidative stability, wash-and-wear properties, and dyeing properties ( I , 2). Ethylene glycol used in production of the polymer contains small quantities (approximately 0 . 0 4 x ) of diethylene glycol and more is formed during polymerization (2). A method suitable for routine use by technicians was required for quality control of polymerization, for evaluation of polymer quality, and for additional studies of the effects of ether linkages on fiber properties, Consequently, the method should have a minimum of separate steps and be capable of handling a large number of samples in minimum time. The methods of Janssen and coworkers, and Mifune and Ishida for determination of diethylene glycol in poly(ethy1ene terephthalate) have been reviewed by Kirby, et a/. ( 2 ) in a published modification of the latter procedure. While the former method requires a long reaction time (16 hours), the Kirby method is too cumbersome for handling a large number of samples. A method presented by Esposito and Swann (3) for characterization of polyhydric alcohols in synthetic resins has been extended to include poly(ethy1ene terephthalate). In each of these procedures, as in the procedure reported here, the polymer is first decomposed. Gaskill, et a / . ( 4 ) have proposed that it is not essential to liberate all the diethylene glycol from the sample because the diethylene glycol-ethylene glycol ratio is constant after a 0.5-hour saponification. The procedure is not suitable for handling a large number of samples because of the time and bench space required. Further, the required use of glass columns is a serious disadvantage in routine gas chromatographic analysis. More recently Kalal and Hornof (5) reported a complete (1) R. Sakurai and K. Kazarna (to Teikoku Jinzo Kenshi Kabushiki Kaisha), British Patent 960,460 (June 10, 1964). (2) J. R. Kirby. A. J. Baldwin. and R. H. Heidner. ANAL.CHEM.. 37, 1306 (1965). (3) G. G. Esoosito and M. H. Swann. Zbid.. 33. 1854 (1961). (4 D. R. Gaskill, A. G . Chasar, and C . A. Luchesi, ibid.,39, 107 (1967). (5) J. Kalal and V. Hornof, Man-Made Textiles, February, 1967, pp. 2 6 7 . .
I
hydrolysis requiring 48 hours with the final determination by titration. In the following procedure up to 22 samples are hydrolyzed simultaneously in 4 hours with quantitation of diethylene glycol by gas chromatography directly on the hydrolyzate. EXPERIMENTAL Apparatus. Hydrolysis of samples was accomplished using a Paar Item 4501 pressure-reaction vessel equipped with a stainless-steel wire basket to prevent direct contact between the sample containers and the walls of the vessel's chamber. For construction of sample containers j/*-inch o.d., thick-walled borosilicate glass tubing was used. The analysis was performed on two commercially available gas chromatographs: a Micro-Tek Model DSS-172 and a Varian Aerograph Model 1520. Both thermal conductivity and hydrogen flame detectors on the Micro-Tek unit and a hydrogen flame detector on the Varian Aerograph instrument were used. A Sargent Model SR recorder equipped with a 1-mV range plug was used for recording detector responses. Chromatograph inlets were maintained at 260" C and detectors at 270" C. Helium was used as the carrier gas at a flow rate of 50 ml per minute through a column maintained at 180" C. Small changes in column temperature and/or flow rate have been made on occasions in changing from one column t o another or as a column aged. Columns. Packings have been made from various silanetreated diatomaceous earths using a 10 (by weight) coating of Carbowax 20M ; a perfluorocarbon coated diatomite (Gas Pack F) similarly prepared with Carbowax 20M was obtained (Chemical Research Services, Addison, Ill.). The silane treated products used were Chromosorb W-HMDS, 60-80 mesh, Gas Chrom Z , 60-80 mesh (Applied Science Laboratories, State College, Pa.) and Aeropak Number 30, 100-120 mesh (Varian Aerograph, Walnut Creek, Calif.). Ten-foot columns of l/s-inch X 0.055-inch id., Type 316 stainless steel (Stainless Piping Supply, Charleston, W. Va.) were made in each case. Columns were conditioned for 24 hours at 200" C before connecting to the detector. Matched columns were usually used with the Micro-Tek instrument only, but columns were sufficiently stable so that differentia! analysis was not necessary. Reagents. Standards employed were polymer grade ethylene glycol (Dow Chemical Co.), polymer grade diethylene glycol (Jefferson Chemical Co.), and Fisher certified grade VOL 40, NO. 1, JANUARY 1968
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Table I. Recovery of Diethylene Glycol Added (mg)
Recovered (mg)
Recovery (per cent)
10.8 10.8 10.8 20.8 20.8 20.8
10.5 11.6 10.8 21.3 21.7 20.7
97 107 100 102 104 100
lated from the original weight of the polymer, the quantity of internal standard added, and the areas of the internal standard and diethylene glycol peaks by reference t o the standard curves. RESULTS AND DISCUSSION
Above 0.5% diethylene glycol in polymer, the response of the thermal conductivity detector was adequate using a 15-pl aliquot. The sensitivity of the hydrogen flame detector is preferred at lower concentrations and the desired range can be covered using 5-pl aliquots. As little as 0.05% diethylene glycol gives a measurable peak. The columns packed from Table 11. Typical Results. Per cent diethylene glycol the supports listed were of equal quality in this analysis. Sample 1 Sample 2 Sample 3 Sample 4 Retention times for benzyl alcohol and diethylene glycol were 1.42 2.45 2.49 0.97 typically 6.5 minutes and 8.5 minutes from injection. 1.56 2.47 2.30 0.92 With a standard sample a gradual change in response was 1.42 2.43 2.33 0.94 observed throughout the day with the Micro-Tek instrument. 1.62 2.35 2.50 1.00 1.52 2.26 2.48 0.89 Samples of water showed the familiar "ghosting" or memory 1.51 2.21 2.53 0.93 effect which could be corrected by flushing the injector with 2.28 2.41 0.91 water (6). The results of this treatment were not satisfactory Av. 1 . 5 1 i 0 . 0 8 2 . 3 5 i 0 . 1 0 2 . 4 2 i 0 . 0 9 0 . 9 4 3 ~ 0 ~ 0 3 because only a few samples could be analyzed before the treatment had to be repeated. Use of a glass injector liner (supplied with the instrument) did not improve the condition, possibly because of the distance between the end of the glass Table 111. Comparison of Methods a t the One Per Cent Level liner and the beginning of the column. The carrier flow must Method Standard deviation averages make a 90" angle turn before entering the column. The same columns used with the Varian Aerograph instruKirby 0.17% ment gave constant responses without on-column injection Janssen 0.10% Author 0.06% and a glass liner. Although reasons for the failure of one instrument and the success of another are not known, it is concluded that the source of the trouble is not with the column. A glass column was not required. Erratic results were obtained with samples unless the wire benzyl alcohol (Fisher Scientific Co.). Two grams of benzyl basket was used to prevent direct contact between the walls of alcohol were accurately weighed into a 100-ml volumetric the chamber and the sample tubes. Consequently, for uniflask, 20 ml of ethylene glycol was added, and the volume form heating of the samples, the basket was used for each was brought to the mark with distilled water. For the hydrolysis. internal standard, a 10-ml aliquot was diluted to 100 ml with At 200" C for 4 hours, the hydrolysis was not complete distilled water. For calibration standards, a 10-ml aliquot according to visual inspection of the sample. At 240" C was added to a 100-ml volumetric flask containing 2.000 decomposition was evidenced by a strong odor and a yellow grams of diethylene glycol, the volume was made up with discoloration. Determination of terephthalic acid liberated distilled water, and appropriate dilutions were made to cover the desired concentration range. Additional ethylene glycol from hydrolysis at 230" C for 4 hours showed complete was incorporated in the dilution to approximate the concenhydrolysis, but hydrolysis was not complete in 2 hours. tration in a typical sample on the basis of 1 gram of polymer Mixtures of terephthalic acid, ethylene glycol, and diethyielding 0.2 gram of ethylene glycol. ylene glycol were made to approximate polymer hydrolyzates. Procedure. For each sample, 1 gram of fiber or polymer Typical recovery data for diethylene glycol after hydrolysis was accurately weighed in a tared glass tube sealed a t one of these mixtures is given in Table I. end, 3 ml of distilled water was added, and the other end of The standard deviation for four samples is shown in Table 11. the tube was sealed. The chamber of the pressure reaction A comparison was made with the method of Esposito and vessel containing the samples was filled with sufficient water Swann because data are occasionally compared with that of to cover the liquid level in the sample tubes and placed in the another laboratory where the latter method is standard. The heating mantle which had been preheated to bring the samples rapidly to 230" C. After 4 hours a t this temperature, 1 2 " C, reflux time was prolonged to 90 minutes. On duplicate runs the chamber was removed from the mantle and allowed t o for two samples, results were identical within the experimental cool. A 0.5-ml portion of the internal standard solution error. was mixed with each hydrolyzate and the sample centrifuged When the method of Kirby became available comparisons prior t o injection of an aliquot into the chromatograph. were also made with that procedure and with the method of A specific sample was designated as a "standard" and reJanssen. Analyses were made of several samples containing peated with each hydrolysis. If the hydrolysis conditions approximately 1% diethylene glycol and the average standard were inadvertently wrong, the standard would have revealed deviations compared (Table 111). The method of Kirby gave this. Calculation. The areas of the benzyl alcohol and diethylene glycol peaks were calculated by multiplying the peak height times the width at half its height. Curves were plotted of peak areas us. concentration for the DEG and internal (6) F. Woutman and F. M. de Ruyter, J. Gas Chromatog., 4, 394 standard. The weight per cent diethylene glycol was calcu(1 966) 230
ANALYTICAL CHEMISTRY
values 0.1% less than those obtained by the method reported here, and the method of Janssen gave 0.2% less. Two dozen samples are accommodated by the wire basket and the pressure-reaction vessel requires only a 21-inch by 19-inch area of bench space making the method well adopted for handling a large number of samples on a routine basis. Conceivably smaller sample tubes could be used, thereby increasing the sample handling capacity. Although a polymer sample of known diethylene glycol content is not available for an evaluation of the accuracy of the method, the results obtained show good precision and are useful for comparative purposes for quality control and experimental samples.
ACKNOWLEDGMENT
The data from the Esposito and Swann Method were obtained by John Dosier of American Enka Research Laboratories, and the data from the methods of Kirby and Janssen were obtained by R. Hildering of Algemene Kunstzijde Unie, N. V. The counsel of Miss Julia Morgan, Analytical Section, American Enka Research Laboratories, is acknowledged and appreciated.
RECEIVED for review April 6, 1967. Accepted October 27, 1967. Division of Analytical Chemistry, 153rd Meeting, ACS, Miami Beach, Fla., April 1967.
Spectrophotometric Determination of Hydrogen Peroxide in Aqueous Media with 1,2-Di-(4-pyridyl)ethylene T.R. Hauser and M. A. Kolar National Center for Air Pollution Control, Cincinnati, Ohio
HYDROGEN PEROXIDE gives positive interference in the 1,2di-(4-pyridyl)ethylene (DPE) method for the analysis of ozone in air (1-3). The interference was judged to be large enough to warrant investigating the possibilities of modifying the DPE method for the analysis of hydrogen peroxide in aqueous solutions. Essentially, it was found that hydrogen peroxide cleaves the ethylenic double bond of DPE in somewhat the same manner as does ozone ( I ) , resulting in the formation of pyridine-4-aldehyde, among other products. Once the pyridine-4-aldehyde is formed, it is easily analyzed via reaction with 3-methyl-2-benzothiazolinone hydrozone (MBTH) ( I ) . With this modified procedure, the molar absorptivity for hydrogen peroxide is 36,500, which is somewhat higher than the molar absorptivities obtained with other methods available for the analysis of hydrogen peroxide .(3,4). EXPERIMENTAL
The various reagents used were prepared on a weight-volume basis (grams per 100 ml of solution). A 5 solution of 1,2-di-(4-pyridyl)ethylene (DPE) in glacial acetic acid was used in the procedure. This reagent, as well as the pyridine-4-aldehyde (redistilled before use) was purchased from K and K Laboratories Inc., Plainview, N. Y. The color-developing reagent was a 0 . 2 5 z aqueous solution of 3-methyl-2-benzothiazolinone hydrazone hydrochloride (3-MBTH). The 3-MBTH was purchased from the Aldrich Chemical Co., Milwaukee, Wis. The hydrogen peroxide test solutions were prepared by diluting an ACS grade, 30% aqueous hydrogen peroxide solution that was standardized iodometrically. Apparatus. A Cary Model 1 5 ratio recording spectrophotometer with 1.0-cm cells was used for all quantitative analyses. Reagents.
(1) T. R. Hauser and D. W. Bradley, ANAL. CHEM.,38, 1529 ( 1966). (2) T. R. Hauser and D. W. Bradley, Zbid., 39,1184 (1967). (3) I. R. Cohen, T. C . Purcell, and A. P. Altshuller, Enciron. Sci. Technol., 1,247 (1967). (4) I. R. Cohen and T. C. Purcell, ANAL.CHEM., 39, 131 (1966).
Analytical Procedure. Five milliliters of DPE solution and 1 ml of the aqueous hydrogen peroxide test solution were successively pipetted into a test tube and thoroughly mixed. The mixture was then heated on a boiling water bath for 15 minutes and cooled to room temperature under a water tap. One milliliter of the color-developing reagent was then added, and the mixture was again heated on the boiling water bath for 1 to 1.5 minutes and cooled under the water tap. The absorbance was then measured at 442 mp against an appropriate blank prepared by substituting distilled water for the test solution in the analytical procedure described above. The concentration of hydrogen peroxide in the test solution (in micrograms of hydrogen peroxide per milliliter of test solution) can be calculated readily from the absorbanceconcentration curve described below. Calibration. The Beer's law curve was linear from 0.30 to 15.0 Mg of hydrogen peroxide per ml of test solution over an absorbance range of 0.07 to 2.30. The curve was not exactly linear, however, for test solutions containing less than 0.30 pg per ml of hydrogen peroxide, resulting in slight curvature in the plot from 0.00 to 0.07 absorbance unit. DISCUSSION
The reaction mechanism for the procedure is probably very similar to that published for ozone (1). Hydrogen peroxide reacts with DPE to form pyridine-4-aldehyde, which is reacted with 3-MBTH to form the yellow pyridine-4-aldehyde3-methyl-2-benzothiazolyl azine ; the latter is then analyzed by spectrophotometry. The evidence for the mechanism was based on the spectral characteristics of the synthesized azine (for which the carbon, hydrogen, and nitrogen analyses agreed closely with theoretical values), and on observations noted when redistilled pyridine-4-aldehyde was carried through the analytical procedure. When measured in the same solvent system, the wavelength maximum of the azine (442 mp, E = 28,000) coincided with that of the dye produced in the analytical procedure. The visible absorption spectra of the synthesized azine, the yellow compound obtained during analysis, and the blank solution L'S. acetic acid are shown in Figure 1. When 33 pg of pyridine-4-aldehyde in glacial acetic acid was carried through the analytical procedure, an absorbance VOL 40, NO. 1 , JANUARY 1968
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