water. I t is evaporated to remove the excess of hydrogen peroxide and chlorine water and tested for nitrogen. The blue color on the resin beads which indicates the presence of nitrogen, becomes dark on standing for a few minutes. Sulfur also obscures the test for nitrogen because sulfide ions produce a black precipitate when copper solution is added for the test for nitrogen. The following compounds gave a positive test: Thiourea (0.228 pg), mandelonitrile (0.399 pg), cacotheline (12.82 pg), sulfanilic acid (8.65 pg), dimethylamine (2.25 pg), methyl cyanide (1.23 pg), aniline (0.25 wg), p-dimethylaminobenzaldehyde (7.79 pg), pyridine (4.864 pg), and 7-iodo8-hydroxyquinoline-5-sulfonic acid (10.53 pg). Several attempts were made to test bromine by the ionexchange method but a negative response was obtained every time.
After removing the sulfide ions, the sodium fusion is divided into two parts and the remaining three ions (CI-, I-, CN-) are tested. The detection of CI- ions may be interfered by I- and CN- when cation exchange resin beads in the Ag+ form are added to one part of the sodium fusion. T h e sparingly soluble salts of I-, CN-, and CI- with Ag+ ions are precipitated on the resin bead surface (K,,AgI < K,,AgCN < K,,AgCl). But the property of fast blackening of AgCI to the exposure of sun light over the other precipitated species helps its determination. The following compounds gave a positive test: Chlorobenzene (33.75 wg), odichlorobenzene (44.10 pg), p-dichlorobenzene (5.81 pg), acetyl chloride (3.925 pg), acridine hydrochloride (6.47 pup), carbon tetrachloride (6.16 kg) and chloroform (4.78 gg). The I- ions are detected by the formation of violet color on the resin surface. This is due to the fact that triiodide is formed by the partial oxidation of the I- ion when chlorine water and 30% hydrogen peroxide are added to the second part of the sodium fusion. The resin beads turn violet in color because of the adsorption of triiodide ions. I t is observed t h a t if one drop of 1%starch solution in 10% acetic acid having a linear structure ( 1 0 ) is added to the violet colored resin beads, the color immediately turns deep violet or purple and, hence, increases the sensitivity of the test. I t can be assumed that not all iodine gas is reacted with the I- ion, a little of it is adsorbed on the resin surface which interacts with the starch molecule and produces a deep violet color. The following compounds gave a positive test: Iodoacetamide (5.54 wg), iodoform (5.90 Fg), methyliodide (35.48 gg) and 7-iodo-8-hydroxyqunoline-5-sulfonic acid (8.96 wg). The nitrogen was detected by the cyanide ion test ( 1 1 ) .A number of substances including iodide ion, oxidizing, and reducing agents interfere with the test. I t is therefore necessary to remove iodide ion before the test of nitrogen. The resin beads in triiodide form are removed form the mixture contents and tested separately for iodine by adding a drop of starch solution. If iodine is present, the resin beads immediately turn deep violet in color. The filtrate is free from the iodide ion but contains hydrogen peroxide and chlorine
ACKNOWLEDGMENT We thank W. Rahman, Head of the Department of Chemistry for providing research facilities.
LITERATURE CITED (1)Nicholas D. Cheronis and John B. Entrekin, "Semimicro Qualitive Organic Analysis", Thomas Y. Crowell Company, New York, 1947,pp 89-91. (2) F. Feigl, "Spot Test In Organic Analysis", Elsevier Publishing Company, Amsterdam, 6th ed.. 1960,pp 83-93 and 96. (3) Masatoshi Fujimoto, Bull. Chem. SOC.Jpn, 29, 567 (1956). (4)M. Qureshi and S. 2. Qureshi, Anal. Chim. Acta, 34, 108 (1966). (5) P. W. West, M. Qureshi. and S. 2. Qureshi, Anal. Chim. Acta, 47, 97 (1969). (6)M. Qureshi, S. 2. Qureshi. and N. Zehra, Anal. Chim. Acta, 47, 169 (1969). (7)S.2 . Qureshi, M. S. Rathi, and Shahana Bano. Anal. Chem., 46, 1139 (1974). (8)M. Qureshi, S. 2. Qureshi, and S. C. Singhal. Anal. Chem., 40, 1081 (1968). (9)M. Fujimoto. Chem. Anal. (London). 49, 4 (1960). (lo)Herbert A. Laitinen. "Chemical Analysis", McGraw-Hill Book Company, New York, 1960,p 396. (11)S. K. Tobia, Y. A. Grawargious, and M. F. El-Shaht, Talanata, 20. 513 (1973).
RECEIVEDfor review September 16,1974. Accepted February 24, 1975.
Analysis of Microgram Quantities of Organic Vapors by Combined Capillary-Column Gas Chromatography and Vapor Phase Infrared Spectrometry Robert F. Brady, Jr. Technical Services Division, U.S. Customs Service, Washington, DC 20229
The identification of compounds in complex organic mixtures is a challenge to the analytical chemist. The use of gas chromatography and mass spectrometric techniques in tandem is routine ( I ) . However, data obtained from mass spectrometry is characteristic of molecular fragments and not of intact molecules; close structural isomers often cannot be distinguished by this method. Complementary data can be obtained through the combined use of gas chromatography and infrared spectrometry (2-5), as infrared spectra are characteristic for most compounds, and usually provide sufficient information for identification.
Many indirect methods for recording the infrared spectra of gas chromatographic effluents have been described (5-7). The smallest amount of sample that can be analyzed with these techniques is dependent upon the efficiency of the trapping; loss of material and time involved in the manipulations pose limitations. For direct recording of vaporphase infrared spectra of chromatographic effluents, infrared spectrometers have been developed (8-1 1 ) to scan rapidly from 4000 to 660 cm-l in less than 30 seconds, but with some loss in quality. Infrared spectra of chromatographic effluents can also be measured directly by inter'
ANALYTICALCHEMISTRY, VOL. 47, NO. 8 , JULY 1975
*
1425
Table I. Minimal Amounts of Selected Compounds Which Give Interpretable Vapor Phase Infrared Spectra Property
iYFRIRED
3?EC I ROPHOTOilETER
/PElCKUCij Figure 1. Schematic diagram of the Gas Chromatograph-Infrared Spectrometer analytical system
ferometric techniques (12-14), or by a corner-mirror dispersion system (15, 16), but the cost and sophistication of these limit their use. In this work, components isolated by capillary-column gas chromatography were separately trapped in a vapor cell, and their infrared spectra were recorded. Several compounds having boiling points over a wide range of temperature, and containing different functional groups were examined, and the minimal amount of each needed t o produce a n interpretable spectrum was determined. Condensation of certain high-boiling compounds to permit removal of the carrier gas, followed by revaporization for measurement of an infrared spectrum, permitted a two- t o fivefold increase in sensitivity. Amplification of the spectrometer signal with noise filtering gave a further four- t o tenfold increase in sensitivity. For certain compounds, the increase in sensitivity was 40-fold when both steps were used consecutively. An application t o the analysis of coal tar distillates is described, in which quantitative information was obtained from the chromatogram, and identification of each compound was made from its infrared spectrum. EXPERIMENTAL A schematic diagram of t h e gas chromatograph-infrared spectrometer analytical system is shown in Figure 1. Gas chromatography was performed on a Perkin-Elmer Model 900 gas chromatograph equipped with a stainless steel capillary column (200 feet by 0.5-mm i.d., coated a t a flow rate of 1 ml/min with a solution of 10% w/w diisodecyl phthalate and 0.5% w/w phosphoric acid in acetone), an effluent splitter, and a hydrogenflame detector ( 1 7 ) . An injector splitter was eliminated. One percent of the column effluent was directed into t h e flame detector, a n d 99% was passed into the infrared vapor cell. T h e column was held a t 135O, the injector and detector manifolds were kept a t 250°, and t h e helium carrier gas flow rate was 2 ml/min. Retention times and peak areas were calculated by a Perkin-Elmer Model PEP-2 Chromatographic Data System. Infrared spectra were recorded on a Perkin-Elmer Model 457 Grating Infrared Spectrometer fitted with a modified Wilks Model 41B GC-IR Interface in the sample beam. This interface contained an optical system designed t o collimate and focus t h e sample beam through a gold-plated cell measuring 60 m m X 10 m m X 1 mm. T h e small cell volume (600 fil) enabled rapid flushing and minimized memory effects. Transmittance through t h e empty cell was 34%. T h e spectrum could be expanded u p t o 40-fold with a PerkinElmer Model DM-100 Data Manipulator. Filtering of noise was accomplished using a Model 1020 Electronic Filter (Spectrum Scientific Corp., Newark, D E ) , and the expanded spectrum was recorded on a strip-chart recorder. Flow through the interface was controlled by a 4-port switching valve, which directed t h e effluent from t h e gas chromatograph ei1426
ANALYTICAL CHEMISTRY, VOL.
47, NO. 8,
JULY 1975
Compound
Roiliiiq point, 'C
Diethyl ether Acetone Butanal Ethyl acetate Propionic acid 3,4-Dimethylphenol Anisole Methyl benzoate 1-Propanol Nitroethane 1- Butanol Acetophenone p-Cresol Nitrobenzene 2-Bromobutane Propionitrile 1-Chloropentane Chlorobenzene Ethylbenzene +Pinene )[-Decane o-Dichlorobenzene Benzonitrile
35 56 76 77 141 227 154 199 97 115 118 202 202 211 91 97 108 132 136 164 174 180 191
hloieiular weight
74 58 72 88 74 122 108 136 60 75 74 120 108 123 137 55 106 112 106 136 142 147 103
Sample Volume, n l On-
the-fly
Coidensedrevaporized
10
10
20
10
50
5
50
10
100
50
ther away from t h e interface t o exhaust or through a 50 m m X 0.5 m m support-coated open tubular (SCOT) column into t h e vapor cell. When required, t h e SCOT column was cooled t o -78" by carbon dioxide t o condense t h e effluent while permitting the carrier gas t o flow on; the column was then heated rapidly, a n d the revaporized fraction moved into the vapor cell for analysis. T h e SCOT column, t h e connecting line, and the vapor cell were held a t 220' t o facilitate passage of the effluent. Prior t o use, the flow rates through the interface in the bypass and in t h e trapping mode were equalized, t o preclude a change in t h e 99-to-1 split ratio (with concomitant recorder pen excursion and loss of quantitation) when the interface valve was moved. To trap an unknown compound in the vapor cell on-the-fly, a test compound was chosen and t h e spectrometer was set to a wavelength where i t absorbed strongly. T h e time interval between the appearance of the peak top on t h e chromatographic trace and t h e absorption maximum on t h e spectrometer was measured and, in subsequent work, t h e valve was closed after this interval had elapsed. T o trap a test compound on the S C O T column, t h e latter was cooled to -78' by carbon dioxide, and t h e valve was held in t h e bypass position until t h e compound eluted; only this vapor was then passed into the interface and condensed on t h e SCOT column. T h e valve was then closed, and the SCOT column heated rapidly t o 220'. T h e revaporized compound was bled into t h e vapor cell, and t h e time interval between opening t h e valve and a t taining maximal absorbance on t h e spectrometer was measured. For subsequent work, this interval was carefully observed. T h e infrared spectra were measured a t 1000 cm-'/min from 4000 t o 2000 cm-'; and a t 500 cm-'/min from 2000 t o 600 cm-'.
RESULTS A N D DISCUSSION Sensitivity Limits. It was first necessary to determine the minimal amount of a compound needed t o obtain an interpretable infrared spectrum by using two different techniques: a) trapping of a chromatographic fraction on-thefly; and b) condensation of a chromatographic fraction on the SCOT column followed by revaporization into the vapor cell. Results obtained with various compounds are recorded in Table I. The data show that the minimal amount of sample needed is determined by the intensity of
Figure 2. Infrared spectrum of 5 nl of anisole (see text for details)
the infrared spectrum of each compound. Hydrocarbons, aryl and alkyl halides, and nitriles have relatively weak absorption in the carbon-hydrogen bending modes (15001300 cm-’), and 50 nl of each is typically required in the condensation-revaporization mode, or 100 nl is required for trapping on-the-fly. However, such polar molecules as ketones, esters, alcohols, ethers, and nitro compounds show intense infrared absorption, and the greatest degree of sensitivity is reached with these. Typically, 10 nl is required t o produce an interpretable spectrum in the condensationrevaporization mode, or 50 nl is required for trapping onthe-fly. An enhancement in sensitivity has been realized by expansion of the transmission scale. T o record an interpretable spectrum without this amplification, sample requirements are usually 500 nl of liquid for direct trapping and 200 nl for condensation-revaporization, and the signal-tonoise ratio determines the limit of sensitivity. When scale expansion and noise filtering are used, the intensity of infrared absorption by the compound determines the ultimate limit of sensitivity. The minimal amount of sample needed is reduced by four- to tenfold, and liquid samples as small as 5 nl give interpretable spectra. An increase in senstivity was accomplished when certain compounds were condensed and revaporized for measurement of an infrared spectrum. Compounds having low vapor pressures can be efficiently condensed, and data are shown in Table I where the limits of detection of two high boiling compounds, methyl benzoate and anisole, are decreased tenfold by condensation and revaporization. In Figure 2 is shown a spectrum obtained from 5 nl of anisole after such concentration. The spectrum was recorded in 4.8 minutes with a 25-fold ordinate (% transmission) expansion and noise filter cut-off of 0.1 Hz. This high degree of filtering causes the pen to respond sluggishly, however, and introduces some distortion in the shape of the bands. T h e increase in sensitivity resulting from condensation and revaporization of compounds having moderate vapor pressures is normally two- to fivefold. However, vapor pressure is not a factor in the analysis of such highly volatile compounds as acetone and diethyl ether, as they elute in narrow peaks, and are completely trapped in the vapor cell onthe-fly. Thus, no effective concentration is accomplished by this technique, and no increase in sensitivity is observed. These methods can be applied to the analysis of compounds or mixtures that can be chromatographed and that give infrared spectra. The intensity of infrared absorption by a compound and its vapor pressure determine the minimal amount that can be identified. No relationship between the minimal identifiable amount and the molecular weight of a compound is evident (cf., Table I). The enhancement in sensitivity realized by applying both scale expansion-noise filtering and condensation-revaporization can be as great as 40-fold for certain compounds.
25
1
Xlh?iiS
Figure 3. Gas chromatogram of a typical coal tar distillate
L-L---3500 ‘TO
400
2500
--
?Or5
1W
rl~VtlUP6Ei
.n33
I
L
1~ 3
1
CM
Figure 4. Infrared spectra of compounds separated from a typical coal tar distillate; A , phenol; B, o-cresol; C, p-cresol, D, m-cresol
Analysis of a Coal Tar Distillate. The techniques described were applied to the identification of the constituents of a coal tar distillate. These distillates contain principally rn- and p-cresol, and they may also contain one or more of the six isomeric dimethylphenols, o- cresol, and/or phenol. A typical distillate contains both m- and p-cresol in a total amount of about 90%, and the remainder consists of smaller amounts of one or more phenols. In Figure 3 is shown a separation made on a representative coal tar distillate where four compounds, designated as A, B, C, and D, in concentrations of 2, 9, 72, and 17%, respectively, are clearly separated. It is not possible to distinguish between isomers of cresol or of dimethylphenol solely on the basis of mass spectral data ( 1 8 ) ;however, identification was made using available vapor state reference spectra (5). Separate 1.O-pl injections were made for the identification of peaks B, C, and D of Figure 3. Peak R was condensed on the SCOT column, revaporized, and moved into the vapor cell, where it was identified as o-cresol (Figure 4, spectrum B ) . Peak C was trapped in the vapor cell on-thefly before contamination by partially overlapping peak D was anticipated, and identified as p-cresol (Figure 4,spectrum C). Peak D was condensed on the SCOT column only after the interval when contamination by partially overlapping peak C was anticipated. I t was revaporized, moved into the vapor cell, and identified as rn-cresol (Figure 4, peak D). ANALYTICALCHEMISTRY, VOL. 47, NO. 8, JULY 1975
1427
Peak A did not give a satisfactory spectrum when it was condensed from a 1.0-pl injection of sample. An elution analysis experiment (19),involving no loss of resolution or overlapping of the peak of interest, was performed in which severe overloading of the capillary column was necessary to purify enough material to obtain an interpretable infrared spectrum. This was achieved when 5.0 p1 of the sample mixture was injected onto the column, and'the first peak to emerge was trapped on-the-fly. The infrared spectrum of this fraction showed it to be phenol (Figure 4, spectrum A ) . I t is to be noted that vapor-phase spectra differ from condensed-phase spectra in three principal ways: a) the relative intensities of some bands are changed; b) some bands show rotational branching; and c) stretching bands involving protons subject to hydrogen-bonding in the condensedphase shift to higher frequencies and are sharper. Nevertheless, infrared correlation charts are as useful with vaporphase spectra as with condensed-phase spectra for characterization of organic compounds. The spectra shown in Figure 4 were measured without using scale expansion or noise filtering, and are representative of the quality that can be obtained with 100-300 nl of sample. The results reported here demonstrate clearly that the combined use of capillary column gas chromatography in tandem with vapor-phase infrared spectrophotometry is a simple and effective procedure for the analysis of volatile complex organic mixtures. The capillary column effected the high degree of chromatographic resolution that was essential for the separation and quantitation of m- and p cresols, as these are not separated on conventional packed columns (17). Amounts of material as small as 20-100 nl can readily be identified by use of common chromatographic and infrared equipment. The limits of detection can be. lowered to 5-50 nl when scale expansion and noise filtering are included. As the chromatographic fraction is analyzed in the same physical state as it elutes from the column, no losses occur from condensation and transfer of the sample.
This is the first report in which a capillary column is coupled to a micro vapor cell for measurement of the infrared spectrum of an effluant. The close correspondence between the volume of the cell and that of the carrier gas containing the sample eliminates the need for complex sample-handling techniques and makes possible the identification of samples one-tenth as large as previously reported.
ACKNOWLEDGMENT I thank Melvin Lerner for his support during the course of the work, and Guy T. Barry for helpful criticism of the manuscript.
LITERATURE CITED (1) R. Ryhage and S.Wikstrom in "Mass Spectrometry: TECHNIQUES AND Applications", G. W. A. Milne, Ed., Wiley-lnterscience, New York, NY, 1971, p 91. (2) J. E. Crooks, D. L. Gerrard, and W. F. Maddams. Anal. Chem., 45, 1823 (1973). (3) J. 0. Lephardt and B. J. Bulkin, Anal. Chem.. 45, 706 (1973). (4) F. D. Mercaldo, Amer. Lab., 5 (3), 63 (1973). (5) D. Welti. "Infrared Vapour Spectra", Heyden & Sons, Ltd., London, 1970. ( 6 ) S. K. Freeman in "Ancillary Techniques of Gas Chromatography". L. S. Ettre and W. H. McFadden. Ed., Wiley-lnterscience, New York, NY, 1969, p 227. (7) J. G. Grasselli and M. K. Snavely in "Progress in Infrared Spectroscopy", Vol. 3, H. A. Symanski, Ed.. Plenum Press, New York, NY. 1969, p 55. (8) A. M. Bartz and H. D. Ruhl, Anal. Chem., 36, 1892 (1964). (9) P. A. Wilks and R. A. Brown, Anal. Chem., 36, 1896 (1964). (10) B. Krakow. Anal. Chem.. 41, 815 (1969). (1 1) H. Bober and K. Burner, Fresnius'Z. Anal. Chem., 236, 1 (1968). (12) M. J. D. Low and I. Coleman, Spectrochim. Acta, 22, 369 (1966). (13) M. H. D. Low and S. K. Freeman, Anal. Chem., 39, 194 (1967). (14) K. L. Kizer, Amer. Lab., 5 (6), 40 (1973). (15) S. A. D o h , H. A. Kruegle, and G. J. Penzias, Appl. Optics, 6, 267 (1967). (16) G. J. Penzias and M. H. Boyle. Amer. Lab., 5 (10). 53 (1973). (17) R. F. Brady, Jr., and B. C. Pettitt, J. Chromatogr., 93,375 (1974). (18) "Eight-Peak Index of Mass Spectra," First ed.,Mass Spectrometry Data Centre, Aldermaston. U.K., 1970. (19) S. Dal Nogare and R. S.Juvet. Jr.. "Gas-Liquid Chromatography", Interscience Publishers, New York, 1962, pp 14-19.
RECEIVEDfor review October 22, 1974. Accepted February 28, 1975.
Determination of Epoxy Side Groups in Polymers: Infrared Analysis of Methyl Methacrylate-Glycidyl Methacrylate Copolymers Swaraj Paul and Bengt RBnby The Royal Institute of Technology,Department of Polymer Technology, S- 10044, Stockholm-70, Sweden
Infrared spectrometry has frequently been used for the analysis of copolymer composition, e.g., Ref. (1-5). An infrared method has been developed here to estimate the composition of copolymers containing epoxy side groups, based on measurements of absorbances due to the epoxy and carbonyl groups. Two different methods to characterize methyl methacrylate (MMA)-glycidyl methacrylate (GMA) copolymers have been reported by Iwakura et al. (6) and Boerio e t al. (7), respectively. The main advantages of this method in comparison to the earlier ones (6, 7) are that the analysis can be performed on very small amounts of sample and in a very short time. The method requires only commonly avail1428
ANALYTICAL CHEMISTRY, VOL. 47, NO. 8, JULY 1975
able equipment and has been successfully applied to MMA-GMA copolymers containing more than 0.05 mol fraction of GMA. Copolymers containing epoxy side groups are of technical interest, e.g., they provide means to introduce hydrophilic or ionic groups into the polymer chains by suitable modification of the epoxy groups. The authors have investigated this class of copolymers as hemectants and antistatic agents for acrylic plastics as poly(methy1 methacrylate).
EXPERIMENTAL Materials. Copolymers of MMA a n d GMA of low molecular weights have been synthesized for this investigation b y radical po-
