942
Anal. Chem. 1981, 5 3 , 942-943
Voltage stabilized at 3.995 voltsN
Open valve 1 for 9.3 seconds
Lopenvalve 2 for 2.31 seconds 1
I I 1 TIME, IN MINUTES
I 2
Figure 5. Actual data showing ability of the system software (see Figure 4) and hardware to adjust the pressure to a final value between 3.992and 4.000 V. Adjustment from an initial value of approximately 0.6 V to a final value of 3.995 V Is completed In about 2 min.
open and likewise for “CLOSE”. The control system is virtually immune to electrical noise picked up on the lines leading to the three-position switches, which are located several meters from the control circuitry. The automatic power-up reset circuitry ensures that the 7474 edge-triggered flip-flop (Figure 3) powers up with the Q output low and the solenoid valve deenergized. Therefore, when the “AUTO” mode is selected, the valves will remain closed after a power outage rather than powering up in an unknown state. Only two connections to the calculator or computer are required for operation. A high or low on the DATA input (Figure 3) will open or close a valve after a CLOCK pulse is
received. The 7474 is updated during a low to high transition of the CLOCK input; therefore, DATA must remain stable before and during this transition. Linear Dynamics solenoid valves have provided Satisfactory service and were selected because they use only 2 W. They are small, enabling them to be mounted conveniently near the pneumatically operated valves. In actual use, the major ion beam current can easily be adjusted to within 0.2% of a preset value in about 2 min by a Tektronix 31 calculator. The fiie-adjust valve can be opened for a little as a few milliseconds to as long as necessary. The primary factor causing a slow response time between pressure adjustment and signal change is gas flow through the capillary tube inlet. Figure 4 is a flow diagram of the software that employs feedback to adjust the mercury piston volume such that the final ion beam intensity lies between 0.99813 and U, where U is the desired electrometer output voltage of the major ion beam. Figure 5 is a plot of the major ion beam electrometer output voltage vs. time for actual data, and it shows that once the ion beam intensity is stabilized with the piston lowered, adjustment to specified limits was completed in 2 min. Adjustment of smaller and larger samples is also compreted in about 2 min. ACKNOWLEDGMENT I appreciate the reviews and discussion of this manuscript by J. Wildman and C. Kendall. LITERATURE CITED (1) Nier, A. 0. Rev. Sci. Instrum. 1947, 78, 398-411. (2) Coplen, T. B. “Isotropic Fractionation of Water by Ultra-filtratlon”; Ph.D. Thes , University of Chicago, 1970. (3) DesMarais,l%. J. Geochim. Cosmochlm. Acta, Suppl. 1978, No. IO, 2451-2467. (4) O’Neil, J. R. U. S. Geological Survey, Menlo Park, CA, oral communication, 1972.
RECEIVEDfor review October 24, 1980. Accepted February 20,1981. Use of trade names and trademarks in this publication is for descriptive purposes only and does not constitute endorsement by the U.S. Geological Survey.
Pyrolysis Mass Spectrometric Method for Polymer Characterization John Chlh-An Hu Qua1;ty Assurance Laboratories, Boeing Aerospace Company, MS 23-22, P.O. Box 3999, Seattle, Washlngton 98 124
Mass spectrometry (MS) has been extensively used in the studies of high polymers since the 1940s (1-3). Most of the early studies involved sophisticated apparatus and complicated operations for sample pyrolysis and introduction of pyrolyzates to the mass spectrometers (1-11). Since GC-MS data instruments equipped with a direct probe became commercially available, many recent works have involved sample introduction either a t the ion source by a direct probe or a t the gas chromatograph (GC) injection port by a pyrolysis probe. For practical applications such as routine inspection of incoming industrial goods and materials in quality control laboratories, either of these two modes of sample introduction can be considered ideal with respect to specificity, speed, and cost. Pyrolysis-GC-MS requires a relatively long time for sample elution through the GC column and for evaluation of the bulky data obtained. Sample introduction through direct probe usually produces a large number of varying mass spectra from a single sample; evaluation of the varying data can be laborious. In addition, loss of the sample holder inside the
instrument can occur, resulting in possible contamination of the ion source. In industry the daily inspection of incoming nonmetallic goods and polymeric materials in large numbers requires practical analytical methods which are simple, fast, and specific. This paper describes a previously unreported method for rapid characterization of polymeric materials with potential industrial quality control applications (12). A Model CEC 21-llOB double focusing mass spectrometer with a heated all-glass inlet was used. The ionizing energy of an electron impact ion source was 70 eV. The accelerating voltage was 4 kV. The all-glass inlet, the conduit from inlet to ion source, and the ion source block were maintained a t a temperature of 200 “C. Figure 1 illustrates a simplified pyrolysis unit which is connected with a mechanical vacuum pump through a stopcock and the glass inlet of a mass spectrometer through another stopcock. A long slim glass test tube (approximately 120 mm length X 5 mm 0.d.) was used as a sample holder. A piece of polymer sample in convenient size (approximately
0003-2700/81/0353-0942$01.25/00 1981 Arnerlcan Chemical Society
ANALYTICAL CHEMISTRY, VOL. 53,NO. 6,MAY 1981
TO MASS SPECTROMETER INLET SYSTEM
MECHANICAL VACUUM PUMP
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RUBBER SAMPLE
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Mass spectrum of a silicone rubber.
100 mg) was loaded into the sample holder with the sample placed at the center of the test tube bottoml. The loaded test tube was placed inside the pyrolysis unit with the test tube bottom touching the bottom of the pyrolysis chamber. After the pyrolysis unit was evacuated first by the mechanical pump and then by the high vacuum system, it was isolated from both vacuum sources. The bottom of the evacuated pyrolysis chamber was directly heated for 30 s with the flame of a small burner (microflame gas torch, Applied Science Laboratories, Inc., State College, PA, or the equivalent). The polymer sample was pyrolyzed a t approximately 1000 “C. The upper wall of the long slim test tube functioned as a condenser of the less volatile pyrolyzates. Only the highly volatile components of the pyrolyzates were used for the quick analysis. The sample size can be reduced to the range of sub-milligram to microgram without affecting the detectability of the instrument. A fraction of the gaseous components of the pyrolyzates was withdrawn through the stopcock to an expansion reservoir (2 L capacity) where a homogeneous composition at constant pressure was maintained during the entire period
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Mass spectrum of a fluorosillcone rubber.
of analysis. A trace amount of gaseous pyrolyzates was admitted into the ion source through a gold molecular leak a t a constant rate. From this a uniform and unique mass spectrum was produced. This mass spectrum can be used as a fingerprint or can be interpreted to confirm the polymer structure. Figure 2 shows the mass spectrum of the gaseous pyrolyzates of a hot air duct material conforming to Boeing Material Specification BMS 8-17H, Type 3. The presence of the trimeric siloxane ion peak at mass 207 and tetrameric siloxane ion peak at mass 281 confirmed that the hot air duct was made of a silicone rubber which was known to be heat resistant. Figure 3 is a mass spectrum of a high-temperature fuelresistant rubber material conforming to military specification MIL-R-25988. Peaks at mass 281 and mass 207 of siloxane ions indicated a silicone rubber. Additionally, peaks at mass 96 and mass 77 of fluoropropylene ions confirmed that the material was a fluorosilicone rubber which was known to be fuel resistant at elevated temperatures. Although this simple and fast method is not a complete analysis of the whole sample, it is useful and suitable for industrial quality control applications.
LITERATURE CITED Madorsky, S. L.; Straus, S. Ind. Eng. Chem. 1048, 40, 878. Madorsky, S. L.; Straus, S. J. Res. Natl. Bur. Stand. ( U . S . ) 1048, 40, 417. Wall, L. A. J. Res. Natl. Bur. Stand. (U.S.)1048, 41, 315. Zemany, P. D. Anal. Chem. 1952, 24, 1709. Zemany, P. D. Nafure(London) 1953, 777, 391. Bradt, P.;Dibeler, V. H.; Mohier, F. L. J. Res. Natl. Bur. Stand. (U.S.) 1953, 50, 201. Bua, E.; Manaresi, P. Anal. Chem. 1950, 37,2022. Phillips, J. K. Appl. Spectrosc. 1063, 17, 9. Gohlke, R. S. Chem. Ind. (London)1963, 948. Meuzelaar, H. L. C.; Kistemaker, P. G. Anal. Chem. 1973, 45, 587. Lurn, R. M. Am. Lab. (Falrfeld, Conn.) April 1978, 70(4), 47. Hu, J. C. A. “Abstracts of Papers”, 179th Natlonal Meetlng of the Arnerican Chemical Society, Houston, TX, Mar 23-28, 1980; Amerlcan Chemlcal Society: Washlngton, DC, 1980; Dlv. Anal. Chem., Syrnposlum on Industrial Problem Solving, paper No. 47.
RECEIVED for review November 10,1980. Accepted February 3, 1981.
