Precolumn Inlet System for the Gas Chromatographic Analysis of Trace Quantities of Short-Chain Aliphatic Amines C. E. Andre and A. R . Mosier U S . Department of Agriculture, Agricultural Research Service, P. 0. Box E, f t . Collins, Colo. 80527
Recent emphasis on environmental quality has focused attention on cattle feedlots as a possible source of nitrogen pollution ( 1 ) . Nitrogenous bases (reported as ammonia) volatilized from large feedlots can enrich nearby lakes ( 2 ) . Likewise, certain plants can take up atmospheric ammonia through foliar absorption (3, 4 ) . In addition to ammonia, significant quantities of nonsteam-distillable, N-containing compounds may also be volatilized from feedlots ( 5 ) .Because amines have long been implicated in animal waste odors, preliminary experimentation was undertaken to confirm the presence of these nitrogen bases in feedlot volatiles. Losses inherent in the collection and direct gas chromatographic (GC) analysis of field air samples containing volatile amines necessitated an indirect analytical scheme. Most of the handling problems can be eliminated by conversion of the amines to their respective hydrogen sulfate salts. This paper describes a GC system capable of analyzing aqueous solutions of salts of short-chain aliphatic amines.
EXPERIMENTAL Apparatus. Gas Chromatograph and Instrumental Parameters. All analyses were performed on a Tracor MT-220 gas chromatograph equipped with a dual flame ionization detector (FID). The helium carrier gas flow was maintained a t 120 ml/min, while detector hydrogen and air flows were maintained a t 75 and 350 ml/ min, respectively. The column oven was operated isothermally a t 130 "C, the inlet a t 200 "C, and the detector a t 315 "C. Electrometer attenuation settings ranged from 4 X 10-I' to 128 X lo-" A full scale (AFS) using a 1-mV recorder. Samples were injected with a 10-rl Hamilton syringe (701-RN) inserted through a Microsep F-174 Teflon-faced septum (Canton Biomedical Products). Column. A 2-m X 6.35-mm 0.d. X 4-mm i.d. (6 f t X Y4 in.) glass U-tube packed with 50/60 mesh Chromosorb 103 (JohnsManville) was used for separation of amine mixtures. A U-tube designed for on-column injection was shortened so that only 1 cm of the glass protruded into the inlet chamber. The internal glass surface was silanized using dimethyldichlorosilane in toluene (6). The column was pressure packed a t 10 psi above maximum operating head pressure, plugged with silanized glass wool, and conditioned for 72 hr a t 250 "C. Precolumn Inlet Tube. The precolumn inlet consisted of an 8-cm x 7.9 mm 0.d. X 6.35 mm i.d. (3Ys-in. X S,,3-in. 0.d. X l/4-in. i.d.) FEP Teflon tube (Penntube Plastics Co., Clifton Heights, Pa.) filled with 20 to 30 mesh Ascarite (Arthur H. Thomas Co.) and plugged with 5 mm of silanized glass wood in both ends. The tube is positioned in the GC inlet so that one end slides over that portion of the column which extends into the inlet chamber (Figure 1). Reagents. The monomethyl (MMA), dimethyl (DMA), trimethyl (TMA), and monoethyl (MEA) amines and ammonia used for initial evaluations were purchased from Matheson Gas Products in lecture bottles. Diethyl- (DEA), isopropyl- (IPA), npropyl- (NPA), N-butyl- (NBA), isobutyl- (IBA), sec-butyl(SBA), tert-butyl (TBA), and n-amylamines (NAA) used were F. G. Viets, Jr.,Agr. Sci. Rev., 9 ( l ) ,1 (1971). G. L. Hutchinson and F. G. Viets, J r . . Science, 166,514 (1969). L. K. Porter, F. G. Viets, Jr., and G . L. Hutchinson, Science, 175,
759 (1972). G . L. Hutchinson, R. J. Millington, and D. B. Peters, Science, 175, 771 (1972). L. F. Elliott, G . E. Schuman, and F. G . Viets, Jr., Soil Sci. SOC. Amer. Proc.. 35,752 (1971). Applied Science Laboratories, "Gas-Chrom Newsletter," May/June 1970, State College, Pa.
reagent grade chemicals from Eastman Kodak. The hydrochloride salts of MMA, DMA, TMA, and MEA (Eastman Kodak) were purchased to provide suitable standards for quantitation of the gases. Reagent grade sulfuric acid and demineralized water were used in making all working dilutions. Procedure. Working solutions were prepared by adding the appropriate quantity of gaseous or liquid amine or amine salt to 0.01N sulfuric acid in volumetric flasks and diluting to volume. Gas-tight syringes were used to measure and transfer the gases, and capillary pipets were used to transfer the liquid amines. The GC procedure is similar to that used for the analysis of any liquid sample. Extra precolumn tubes are made up before use and stored in a jar containing a layer of desiccant. The tubes were conditioned by heating them in empty GC inlets overnight. To ensure reproducibility, the tubes were changed after 75 to 100 five-microliter injections. Spent tubes were reused by removing the old Ascarite and refilling with fresh materials. Quantitative information was obtained using peak height.
RESULTS AND DISCUSSION A representative chromatogram is shown in Figure 2 . Reproducibility of the system is presented in Table I, using the standard deviations and coefficients of variation for 5 and 50 ppm MMA and 20 ppm IPA. Linearity in the 5 to 50 ppm working range was confirmed by a linear regression coefficient significant at the 0.1% level. Umbreit et al. (7)and Keay and Hardy (8) have described GC systems that use base-loaded columns to analyze acidified aqueous solutions of amines from fish. This in situ release of the free amines from their salts produces a chromatographic column that changes considerably with every injection, has a very short usable lifetime, and is subject to loss of reproducibility after extended use. A standard GC inlet modified with the Ascarite precolumn described above provides the reproducibility, sensitivity, and convenience necessary for routine analyses. Because the Teflon reactor tube is easy to inspect and because it is not part of the column, routine replacement involves no more work than changing a septum. We have used one Chromosorb 103 column in conjunction with a precolumn for over a year with little or no loss of its original chromatographic properties. The availability and convenience of Ascarite coupled with its high capacity and temperature limit provide more flexibility than a base-coated packing. Should a specific analytical application require an inlet temperature higher than 205 "C (maximum service temperature for FEP Teflon), glass can be used. The glass to glass seal on the end of the column does increase dead volume slightly. Although not essential, the overnight conditioning of the precolumns is helpful in quickly establishing a steady base line after replacement. Care should be taken to minimize the exposure of the Ascarite to air or moisture. Each time a precolumn is replaced, equilibration with a standard is required to eliminate active sites on the Ascarite. Reproducible conditions are reached by injecting a fast eluting working standard such as MMA five to ten times. (7) G . R . Umbreit, R. E. Nygren, and A. J. Testa, J. Chrornatogr.. 43, 25 (1969). (8) J. N. Keay and R . Hardy,J. Sci. Food Agr.. 23,9 (1972).
ANALYTICAL CHEMISTRY, VOL. 45, NO. 11, SEPTEMBER 1973
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4
a
FLON TUBE CARRIER GAS
I
I5
: 8 p:
.ASS WOOL
:T
MINUTES
Figure 2. GC chromatogram of a mixture of 8 amines (5 pg/ml each) using an Ascarite precolumn
1, #-,
Peaks are: (1) injection, (2) methyl-, (3)dimethyl-, (4)ethyl-, (5) isopropyl-, (6) n-propyl-, (7) diethyl-, (8) sec-butyl-. and (9)n-butylamines, Chromosorb 103 column run isothermally at 130 " C
COLUMN
Figure 1. Cross-sectional view of G C inlet showing precolumn
inlet tube
Minimum additional treatment of the Tracor GC was required to prevent tailing and memory and to provide reproducible amine analyses. Injecting 5 t o 10 five-microliter aliquots of a 500-ppm standard amine directly onto the packed column proved superior to silane treatment for deactivating the column tubing and stainless steel transfer lines. Teflon (FEP) transfer lines did not offer any real advantage over deactivated stainless steel. Transient memory effects were finally eliminated by using a Teflonfaced septum and by maintaining a continuous He flow ( 5 ml/min) when the instrument was not in use. Dilute sulfuric acid was used to make up the standards instead of the hydrochloric acid previously reported (7, 8). The main advantage is that no HC1 gas is released onto the column. Tailing and memory effects encountered by other works (7, 8) probably arise from the on-column formation of the ionic salt KC1, the reaction of the HC1 with the column liquid phase and support, and, in the case of Chromosorb 103, the irreversible absorption of HC1 on the polymer surface (9). These problems can be eliminated by using the Ascarite precolumn and sulfuric acid as the acid medium.
Chromosorb 103 (cross-linked polystyrene) exhibits several properties which should be considered for trace amine analyses. A primary advantage of Chromosorb 103 over conventional coated packings is its ability to handle water with no detrimental effects to the column. We found that pressure packing the column to 10 psi above maximum operating head pressure eliminated the gaps and separations inherent in vacuum and/or vibration packing of porous polymers. The plastic property of Chromosorb 103 prevents programming a t high sensitivities (10-11 AFS). Conditioning times considerably longer (48 to 72 hr) than those recommended by Johns-Manville (9) were necessary for use a t high sensitivities. After rigorous conditioning, concentrations as low as 0.25 ppm can be analyzed reproducibly with no inordinate deviation from the linear working curve. We found that amines having more than six carbons did not elute from the column. Pennwalt 223 Amine Packing (Applied Science Laboratories) was investigated as a possible replacement for Chromosorb 103 (10). Although the column did provide adequate separation of a complex amine mixture and did serve as an excellent confirmatory column for qualitative work, it could not be used a t 1 O - l 1 AFS because of excessive bleed. Our initial work with amines indicated that column tubing more inert than glass might be useful. Teflon (TFE and FEP) tubing was tried without success. While FEP Teflon is considerably less porous, both permitted low molecular weight compounds and carrier gas to diffuse through the walls a t elevated temperatures. Adaptation of this system to analyses using a thermal conductivity (TC) or helium ionization (HID) detector would be limited because of the large water envelope underneath the amine peaks. The precolumn inlet can be used with a TC or HID for ammonia analysis because the ammonia elutes quickly and well ahead of the water. On other gas chromatographs having smaller volume inlets,
(9)Johns-Manville Corporation, "FF-181 Chromosorb 103,"New York, N. Y., 1967.
(10) Applied Science Laboratories, "Use of Pennwalt 223 Amine Packing," State College, Pa.
Table I. Reproducibility of Amine Analysis Using an Ascarite Precolumn Inlet and a Chromosorb 103 Column Amine standard
MMA I PA MMA a
Concn. a/ml
5 20
50
mm
Stand dev, mm
Re1 stand dev, %
75.7 116.5 109.5
2.57 1.82 2.16
3.39 1.56 1.97
Mean peak height,a
Represents the mean of ten consecutive injections of each standard.
1972
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the bottom of a y4-in. Teflon precolumn can be shaved thin and flared to allow it to slip over a 3’4-h. column. Received for review November 3, 1972. Accepted January 22, 1973. Trade names and company names are included as a matter of convenience to the reader, and such inclusion does not constitute any preferential endorsement by
the U. S. Department of Agriculture of products named over similar products available on the market. Contribution of the Agricultural Research Service, USDA, in cooperation with Colorado State University Experiment Station, Scientific Journal Series No. 1787. This research was supported in part by the Environmental Protection Agency.
Electron Spectroscopy (ESCA): Use for Trace Analysis David M. Hercules, Lawrence E. Cox, Stephen Onisick, Gary D. Nichols, and James C. Carver Department of Chemistry, University of Georgia, Athens, Ga. 30602
Electron spectroscopy (ESCA) has been adapted for use in trace metal analysis by using glass fiber mats with chelating groups on their surfaces. This represents a unique application of ESCA because to date, the technique has been used primarily for studying for atomic and molecular structure of gases and solids ( I , 2). ESCA has been particularly valuable in studying charge distributions in chemical bonds ( I , 3), and has considerable potential for the interpretive spectroscopy of organic and inorganic compounds (4).The use of ESCA for quantitative measurements has met with limited success except for determining relative numbers of the same atom in a molecule. Siegbahn et al. ( I ) , were able to establish elemental ratios in a variety of samples to *5-10%. Wagner has established elemental sensitivities for a number of elements using Na, F, or K as internal intensity standards (5). Workers in our laboratory (6) have developed a method for the analysis of molybdenum oxide mixtures that showed reasonable accuracy. Brinen and McC1ure (7) have used for trace analysis by electrodepositing metals on mercury coated platinum electrodes; however, they presented no estimate of detection limits. ESCA is primarily a surface technique, the photo-ejected electrons originating within the first ca. 20 A of the surface (8). ESCA has high intrinsic sensitivity because fractional monolayers on a surface have been measured; this indicates an inherent ability to measure 10-8-10-9 gram of a material or less. When applied to bulk analysis, ESCA is sensitive to concentrations of only ca. 0.1% even in the most favorable cases ( I ) . Although the use of high intensity X-ray sources and multichannel detector systerns could improve this figure by a t least two orders of magnitude, the limitation on ESCA would be for the use in the 10-100 pafis-per-million range or higher. Such senK. Siegbahn, C. Nordling, A. Fahlman, R. Nordberg, K. Hamrin. J. Hedman, G. Johansson, T. Bergmark, S. Karlsson. i. Lindgren, and B. Lindberg, “ESCA Atomic Molecular and Solid State Structure Studies by Means of Electron ~ p e c t r o s c o p y ,Aimquist ~~ and Wiksells. Uppsala, Sweden, 1967. K. Siegbahn, C. Nordiing, G. Johansson, J. Hedman, P. Hedan, K. Hamrin, U. Gelius. T. Bergmark, L. Werme, R. Manne, and Y. Baer, to Free North Elsevier, Amsterdam, New York. 1969. D. A. Shirley, Ed., “Electron Spectroscopy,” North-Holland Publishing Co., Amsterdam, 1972. . progr,, 32, 183 S. H. Hercules and D. M. ~ e r c u i e ~~ ,e c Chem, (1971). C. D.Wagner, Anal. Chem., 44, 1050 (1972). W. E. Swartz and D. M. Hercules, Anal. Chem., 43, 1774 (1971). J. S.Brinen and J. E. McClure, Anal. Lett., 5, 737 (1972). R. G. Steinhardt, J. Hudis, and M. L. Perlman, Phys. Rev. B., 5, 1016 (1972).
Figure 1. Diagram of holder for treating glass fiber disks with solutions for trace analysis. See text for details
sitivity is not sufficient to make ESCA attractive for use in geochemical, biomedical, or environmental applications where sensitivities in the parts-per-billion (ppb) range are required. In order to utilize the inherent sensitivity of ESCA for trace analysis, it is necessary to devise a way for the atoms Or ~ o l e c u l e sof interest to line UP on the Surface (in a monolayer Or less) SO they can be measured readily. Ion exchange Preconcentration has been used with X-ray fluorescence for measuring trace metals in solutions (9).Similarly thin layer chromatography (TLC) is widely used for the separation and preconcentration of organic materials for measurement by a wide variety of spectroscopic techniques. Unfortunately, diffusion within ion exchange resins and TLC piates limits the amount of (gadsorbed” material. directly on the surface. We have experienced difficulty in observing ESCA signals from TLC spots even in very favorable cases, What one needs is a “two-dimensional” ion exchanger or TLC plate in which diffusion into the bulk is limited, so that all “adsorbed” species can contribute to the ESCA signal. Use of silylizing agents for coating glass surfaces with organic functional groups is well known (IO). Silylizing (9) C. W. Blount, W. R. Morgan, and D. E. Leyden, Anal. Chim. Acta, 53,463 (1971). (10) M. L. Hair, ”Infrared Spectroscopy in Surface Chemistry,” Dekker, New York. 1967, Chap. 4.
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