Control Larvae
Aba to! Killed Larvae
Control Larvor
Abatee- Killed Larvae
Inject
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.
5np Abatr' 5nq Abote'(5Larvac)
4 ;;;;;, MINUTES
; ; : ; A MINUTES
Figure 7. Detection of Abate in extract of whole larvae pesticide. Five Abate-killed larvae and five control larvae were extracted with a minimum quantity of chloroform, which was then reduced to 10 microliters and injected into the liquid chromatograph. The chromatograms in Figure 7 indicate about 5 nanograms of Abate in the extract of the pesticide-killed larvae. Assuming an average larva weight of 1 rng, the concentration of Abate on each of the five larva was approximately 1 pprn. This was about 100 times the concentration of Abate in the water which was used to kill the larvae. Similar results were obtained by placing freshly killed and control larva directly in the inlet of the chromatographic column, and pressurizing the system to effect an instantaneous extraction by the heptane mobile phase. Figure 8 shows the chromatograms obtained by this in situ extraction method. The quality of the chromatograms is not as good as in Figure 7 because the base line requires several minutes to stabilize after starting the flow at maximum sensitivity (0.005 absorbance unit full
b i b ; ;
I , ; : ; ;
MINUTES
MINUTES
Figure 8. Detection of Abate on larvae by an in situ extraction in the inlet of a chromatographiccolumn scale). Also contributing to base-line disturbance were air bubbles, which were introduced while positioning larvae in the injection port. Results obtained by the in situ method were in qualitative agreement with those found by the extraction method. From these data, it appears that the larva are concentrating Abate about 100 times the bulk pond concentration. Further work would have to be done to determine whether the pesticide is concentrated on the surface of, or inside, the larva. ACKNOWLEDGMENT
The authors thank Robert W. Lake and Kenneth M. Lornax of the Department of Entomology, University of Delaware, for their assistance. RECEIVED for review February 12, 1971. Accepted April 22, 1971.
Laser Pyrolysis Gas Chromatography-Application to Polymers 0. F. Folmer, Jr. Continental Oil Company, Ponca City, Okla. 74601
I n a continuation of previous work, the effects of different operating conditions and methods of sample preparation on fragmentation patterns have been studied. Clear or translucent samples give reproducible results if mixed with carbon. The concentration of carbon is critical: it has a reat effect on the fragmentation pattern. Some poyymers were run whose pyrolysis chromatograms show great difference in pattern. Others had patterns which were quite similar. To better compare these similar patterns and the patterns arising from different operating conditions, a statistical method was devised. An attempt was made to correlate these comparisons of patterns with some of the known characteristics of the polymers.
PREVIOUS PUBLISHED WORK (1-4) on laser pyrolysis has pointed out some of the advantages of laser pyrolysis (rapid heating (1) 0. F. Folmer, Jr., and Leo V. Azarraga, J. Chrornatogr. Sci., 7. 665 11969).
(2)'Bohdan T:-Guran, Robert J. O'Brien, and Don H. Anderson, ANAL. CHEM., 42, 115 (1970). (3) Tsugio Kojima and Fujio Morishita, J. Chromatogr. Sci., 8, 4710 (1970). --(4) William T. Ristau and Nicholas E. Vanderborgh, ANAL. CHEM., 42, 1848 (1970). -I.
and cooling of the sample, and relatively simple fragmentation patterns) and some of the disadvantages (dependence on sample color). That work was largely qualitative in nature depending upon correlation of data by inspection of pyrolysis chromatograms. The work reported here is a continuation of that of Folmer and Azarraga (I). It is an attempt to describe results in numerical terms ; to quantitatively correlate the fragmentation patterns with operating conditions and with sample structure. The effects of various operating parameters and methods of sample preparation on fragmentation patterns were investigated. The knowledge gained was used in applying laser pyrolysis to some polymer samples. EXPERIMENTAL
A Gen-a-lite Model 3R laser (General Laser Corp., Natick, Mass. 01760) and a Focuscope (General Laser Corp.) focusing device were used. The laser uses a 31/&1, ruby rod with a maximum energy outut of 2 joules with a pulse length of 600 microseconds. The instruments were anounied on an optical rail so that the focused beam entered a box containing a ANALYTICAL CHEMISTRY, VOL. 43, NO. 8, JULY 1971
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from the electrometer was connected to an Infotronics Digital Readout Systems Model CRS-104 (Infotronics, Inc., Houston, Texas 77042), and the output from this system went into a IO-mV Honeywell (Honevwell. Inc.. Philadelnhia. Pa. 191441 strip chart recorder. In the earlier Dart of this work. a 223-cm (7-ft). 0.25-cm i.d. (a/,6-in. o.d.jstainless steel coiumn of 70-io mesh Anakrom ABS coated with 10% UCW-98 was used to separate the products of pyrolysis. This column was operated at room temperature for one minute, then heated to 70 OC at the end ofthesecond minute; its temperature wasincreased 2O0/minuntil a maximum temperature of 210 "C was reached. This temperature was maintained until all of the components had apparently eluted. Helium was used as a carrier gas at a flow rate of 40-50 ml/min. Hydrogen and air flows were optimized and maintained at those values. Most of this work was done with a 476-cm (15-ft), 0.20-cm i.d. ('/sin. 0.d.) stainless steel column of 70-80 mesh Anakrom ABS coated with 10% UCW-98. It was operated at room temperature for two minutes, at 70 "C for another minute, then programmed at lO"/min to the end of the analysis or to a temperature of 260 "C, whichever came first. Column flow rate was 22 ml/min. Detector flows were the same as with the other column. Energy output of the laser rod was measured with a Quantronix Model 504 energy meter equipped with a Model 500 energy receiver, each calibrated at the factory and used as received. Sample Description. DYLT and D Y " are low density, straight chain polyethylenes made by Union Carbide Corp. DYNH is of higher molecular weight. Epolene E and Epolene N are made by Tennessee Eastman Co. Epolene E is an oxidized low molecular weight polyethylene and is emulsifiable in water. Marlex 50 is a polyethylene (probably of high molecular weight) made by Phillips Petroleum Co. EMD 416 is a high ethylene content, ethylene-propylene copolymer made by Enjay Chemical Co. The Elvax compounds are made by E. I. DuPont de Nemours and Co., Inc., and are copolymers of ethylene and vinyl acetate: Elvax 150, 32-34% vinyl acetate; Elvax 260, 27-29% vinyl acetate; Elvax 420, 17-19% vinyl acetate. Several samples of plastic tubing made by Imperial Eastman were used; black polyethylene, green polyethylene, and Nylon. A sample of Saran tubing and samples of Teflon polymer and polystyrene were also used. Sample Preparation. Three different types of sample preparation were used. AU samples were run as solids. ~I
Figure 1. Lsser pyrolysis apparatus sample holder and a beam-diverting prism. The prism is mounted so that the beam can be moved in two directions and can thus be aimed at any desired portion of the sample. The sample holder is a borosilicate glass tube 6 mm 0.d. by 25 mm in length. It is clamped between two Teflon (Du Pont) gaskets so that carrier gas can sweep through the tube into the chromatograph. The carrier gas enters the chromatograph through a 0.d. tube which pierces the injection port septum and extends into the injection port. Figure 1 is a photograph of the assembled apparatus, and Figure 2 is a schematic drawing which shows the light paths. The chromatograph used was an F & M Model 810 (F & M Scientific Corp., now Hewlett-Packard Corp., Avondale, Pa.) modified by the substitution of a pair of flame ionization detectors for the original thermal conductivity detectors. The flame ionization detectors and the associated dual electrometer were from a Varian Aerograph (Varian Aerograph, Walnut Creek, Calif. 94598) instrument. The output signal
1. None. Small pieces of the sample were run as-is. Coated. Sample pieces were coated with graphite by rubbing them with a 6B drawing pencil. Gold coating was accomplished in a vacuum evaporator.
2.
E Y E P I E C E (FOR L I M I N G AND FOCUSSlNO)
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TOTALLY REFLECTINQ PRISM,
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Figure 2. Schemstk drawing of laser pyrolysis apparatus 1058
ANALYTICAL CHEMISTRY, VOL. 43. NO. 8. JULY 1971
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L A S E R ROD FLASH TUBE
.-
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Figure 3. Pyrolysis chromatogram of green Eastman Imperial polyethylene tubing 3. Added carbon. Weighed amounts of sample and finely ground premium coke are melted and intimately mixed in a porcelain dish. In some cases the sample was ground and mixed with coke before melting and further mixing.
With non-opaque samples, run as-is or coated; only one shot was made on each piece. Multiple shots (at different spots) were made on opaque sample pieces, including those with added carbon. Fragmentation pattern results indicate homogeneity within sample pieces and among different pieces of the same sample.
RESULTS AND DISCUSSION One of the primary concerns in pyrolysis gas chromatography is the reproducibility of the fragmentation pattern. Tables I and I1 show typical results of replicate runs. Naturally, these estimates of standard deviation represent the whole system-pyrolyzer, chromatograph, and integrator. The pyrolysis chromatograms arising from some polymers give patterns so different from each other that it was readily apparent on inspection. Examples of such chromatograms are those shown in Figures 3, 4, 5 , 6 , and 7 which arise from pyrolysis of green Eastman Imperial polyethylene tubing, black Eastman Imperial polyethylene tubing, Saran tubing, Teflon polymer, and polystyrene, respectively. Other polymers give patterns which are quite similar and differences are not readily apparent to the eye. Two examples are pyrolysis chromatograms of Epolene E polyethylene mixed with 4.64% coke (Figure 8) and type DYNII polyethylene mixed with 5 . 5 % coke (Figure 9). To enable distinctions to be made between such similar chromatograms, a statistical method of comparison was devised. To better determine the effect of operating parameters and to better compare similar samples, replicate runs were made under each set of conditions. The fraction of the total area contributed by each peak, expressed as area per
I _ _ _
Table 1.. Reproducibility of Fragmentation Pattern of a Black Polyethylene Relative Estimate cf estimate Retention Peak area, %; of std dev, time: min. mean of 4 runs std dev 0.089 7.2 1.0 1.23 0.959 2.0 1.1 48.4 0.326 3.9 1.5 8.33 0.032 5.9 1.7 0.540 8.1 2.94 0.392 13.3 10.1 0.514 0. 100 19.4 0.130 18.5 21.1 0.704 0.200 30.2 22.6 0.663 Only a representatie sampling of a Not all peaks are listed. the total of forty plus peaks is listed. Retention times of replicate runs agree to =to.1 min. Table 11. Reproducibility of Fragmentation Pattern from Epolene E Mixed with 4.64% Carbon Relat.ive Estimate estimate Retention Peak area, %; mean of 3 runs of std dev of std de.
