(2) H. J Hancock, Jr.. L. A. Dahm. and J F. Mukloon, J. C h m m t o y . Scf, 8, 57 (1970). (3) H. M. Giadney. B. F. Dowden, and J. D. Swaien. Anal Chem.. 41, 883 (1969). (4) A. H. Anderson, T. C. Gibb, and A. B. Linlewood. ''Advances in Chromatonranhv 1970". A. Zlatkis. Ed., Chromatography Symposium. Deoarti e n t of Chem~islw.University of Houston. Texas, 1970. (5) D. W. KirmSe and A. W. Westerberg, Anal Chem., 43, 1035 (1971). 161 B. Mldbera. J. Chromatoor. Scl.. 9. 287 (1971). i7i S.M. Rob&s, D. H. Wilk&on, &b L. R: Walker. Anal Chem., 42, 886 (1970). (81 S.M. Roberts, Anal. Chem., 44,502 (1972). (9) A. W. Westerberg. Anal. Chem., 41, 1770 (1969). (IO) C. Bosshard, 0. Piringer. and T. Gauman. Hslv. C h h . Acta, 54, 1059 =
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tative Chemical Analysis". 4th &., The Macmillan Ca.. New Yolk. 1969. p 976. (15) H. K. Hughes. Anal Chem., 24, 1351 (1952). (16) R. C. Hirt. F. T. King. and R. C. Schmidt, Anal. Chem., 26. 1270 (1954).
Y. Mori, J. Chromatogr.,9, 66(1972). N. Ostoiic. Anal Chem., 46, 1653 11974).
H. Veening. J. Chem. Educ.. 47, 676A (19701. I. M. Kolthoff. E. B. Sandell, E. J. Meehan. and S.Bruckenstein. "Quanti-
J. M. Clemons H. M. NcNair Chemistry Department Virginia Polytechnic Institute and State University Blacksburg, Va. 24061 RECEIVEDfor review March 11,1975. Accepted August 25, 1975. One of the authors, RGB, is indebted to the Conselho Nacional de Pesquisas, Brazil for financial assistance.
AIDS FOR ANALYTICAL
I
Novel Approach to Micro Infrared Sample Preparation D. H. Anderson and T. E. Wilson Industrial Laboratory, Eastman Kodak Company, Rochester, N.Y. 14650
In the quality assurance work done to control the physical defects on photographic products, we often are sample limited. As a consequence, we have endeavored to develop micro techniques to handle progressively smaller samples. In 1953, Anderson and Miller ( I ) described a silver chloride lens beam condensing system which enabled infrared records to be obtained on 20- to 50-pg samples. However, infrared spectrometers at that time could not resolve radiation levels transmitted by samples less than 20 wg from electronic noise. During the 60's and early 70'9, various improvements were made in both sample preparation techniques and instrumentation. These improvements still resulted in poor resolution of spectra from submicrogram samples. Presently we are utilizing watch jewels as sample apertures to accommodate and generate IR data from materials as small as 50 ng. Handling of these submicrogram quantities and preparation of the pellets require tecbniques provided only by microscopy. A high sensitivity infrared unit is also needed to detect the low energy levels transmitted from the sample. This paper will discuss the microscopic techniques employed in preparing samples for micro infrared analysis using Fourier Transform Infrared Spectrometry. Griffiths (2) has described various factors determining the sensitivity of infrared sampling for FTIR spectrometry. The IR unit we use is a Digilab Model FTS-14 Fourier Transform Infrared Spectrophotometer. With this instrument, it is possible to do multiscan averaging and improve the separation of the real signal from noise. Normally 100 scans each of approximately 1-sec duration are made. These are stored in a mini-computer and recalled at will as a composite, infrared, noise-reduced curve. Routine micro samples are prepared by making 1%dispersions of the material in potassium bromide (KBr) and compressing in a 0.5- or 1.0-millimeter (mm) stainless steel aperture. Approximately 2 to 10 pg of sample are used for the 1.0-mm size and 0.5 to 2 pg for the smaller aperture. T o ensure a good dispersion, the sample and KBr are ground together using a mortar and pestle. For samples less than 0.5 pg, aluminum oxide watch jewels (0.15- to 0.35-mm di2482
ameter) were giuea mstae tne 1.u-mm aperture t o runner reduce the sample compartment. These jewels can he ordered easily from a jeweler's catalog and are very inexpensive items; a quantity of 50 can be purchased for a few dollars. Figure l compares the aperture of a 0.25-mm jewel and a common sewing needle eye. The fiber passing through the needle eye and jewel is a strand of human hair approximately 0.1 mm in diameter. For these apertures, various sample preparation techniques can be adapted for the size and type of sample. For example, microtomy can be used to expose a thin, transparent, uncontaminated, representative portion of a particle covered with another material. This sample can be placed over an appropriate size aperture and held in place with transparent adhesive tape. A low-powered microscope is required when mounting the section, to ensure the sample is centered across the aperture and that the tape is not covering the aperture. Microtomy can also be used to prepare thin films of opaque materials. Transparent films, less than 1 pm thick can be obtained from black materials such as carbon or dye-impregnated polymers. These thin films eliminate many of the spectral effects which may result
ANALYTICAL CHEMISTRY, VOL. 47, NO. 14, DECEMBER 1975
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infrared spectrum of approximately 75 ng of a polyethyl-
Figure 2. Infrared spectrum of a carbon-filled co-polymer generated through a 3 0 0 - ~ maperture
Figure 3.
from the fillers. Figure 2 shows the spectrum of a 2+m, thin section of a carbon-filled polystyrene-butadiene copolymer blend. The record was generated using a 0.3-mm jewel aperture. Figure 3 shows the spectrum of a polyethylene film approximately 75 ng generated through a 0.25-mm aperture. Both spectra were recorded between 0 to 100% transmittance. This microtomy technique has been of great value when studying the homogenity of mixed polymeric systems. Small areas showing abnormal physical features by microscopy can be isolated and analyzed by FTIR to obtain chemical information. Sample preparation also includes pressing materials into jewel apertures. This is accomplished by manually compressing the sample into the aperture using two thingauged, flattened needle tips while viewing under the microscope. It is important to note this sample may or may not require KBr as a matrix. Owing to the micro amounts of sample used, contamination is always a problem to consider. Preventive measures
included the following steps: 1) Use a low-powered microscope to check all equipment and apparatus coming in contact with the sample. 2) Clean all needles, stainless steel apertures, and other major metal parts by rinsing in various solvents, e.g., methylene chloride and acetone, and heating over a low-flame micro burner. Check under a microscope and use a tungsten needle to remove any remaining material before storing in a clean glass container. The watch jewel apertures can be cleaned by rinsing in hot water and air drying. 3) View the sample with a microscope while using a small mortar and pestle to grind the KBr matrix. Also make sure both the pestle and mortar surface are smooth to prevent loss of material in digs and crevices. 4) Most important, do not touch prepared samples; use clean tongs or tweezers.
ene film
LITERATURE CITED (1)D. H. Anderson and 0. E. Miller, J. Opt. Soc. Am., 43,777-779 (1953). (2) P. R. Griffiths and F. Block, Appl. Spectrosc., 27, 431-434 (1973).
RECEIVEDfor review April 24,1975. Accepted July 9,1975.
Evacuated Gas Sampling Valve for Quantitative Head Space Analysis of Volatile Organic Compounds in Water by Gas Chromatography William F. Cowen, W. J. Cooper, and Jerry W. Highfill
U.S. Army Medical Bioengineering Research and Development Laboratory, Fort Detrick, Md. 2 170 1
The quantitative analysis of volatile, soluble organic compounds in water has been reported by Weurman ( I ) , Ozeris and Bassette (2); and Kepner et al. ( 3 ) . These authors sealed the water sample in a bottle, removed a sample of the head space gas with a syringe, then injected the sample through the septum of a gas chromatograph for separation and quantitation of the volatile compounds. Our preliminary tests with this method of head space sampling have resulted in septum failures, with consequent loss of sample and unsatisfactory analytical reliability. In the work reported here, the construction of a device for septumless injection of head space gas is presented and its performance compared with that for syringe injection.
EXPERIMENTAL Apparatus. Gas Chromatography. A 6-ft long, 2-mm i d . glass column was packed with GP 0.4% Carbowax 1500 on Carbopack A (Supelco, Inc., Bellefonte, Pa.). All studies were performed with a Hewlett-Packard 5750B gas chromatograph equipped with flame ionization detectors and interfaced with an Autolab System IV integrator (Spectra-Physics, Santa Clara, Calif.) for acquisition of
retention time and peak area data. After injection of sample, the column temperature was held at 80 "C for 2 min, then increased a t 2 OC/min to 100 OC. Gas flows were: helium carrier, 10 ml/min; hydrogen, 30 ml/min; and air, 250 ml/min. The injector and detector blocks were maintained a t 170 and 150 "C, respectively. Gas Sampling Deuice. Figure 1 shows a diagram of the gas sampling device for septumless injection of head space gases. A Valco 8-port gas sampling valve with %-in. zero dead volume fittings (purchased from Aadco, Rockville, Md.) was fitted with two l-cm3 stainless steel IA-in. 0.d. sample loops and was connected into the helium carrier gas line of the gas chromatograph between the instrument's flow controller and the Yl6-i~0.d. capillary coil in the injector block. The connection of the valve to the capillary coil was made with Ih-in. 0.d. stainless steel tubing, using the %-%6-in. Swagelok connector supplied with the instrument. The valve and sample loops were mounted outside the chromatographic column oven and were warmed to 70 OC with heating tape, as measured a t the body of the valve. A stainless steel Luer-Lok syringe needle (Yale 24 gauge, l-in. length, SGA Scientific Inc., Bloomfield, N.J.) was soldered to the ferrule end of a Swagelok %-in. port connector for connection to a Whitey toggle valve (VI) (both available from Crawford Fitting Co., Cleveland, Ohio). This valve was connected to the Valco valve by a short length of l/~-in.0.d. stainless steel tubing to provide a leak-tight sample input line. The remaining port
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