1228
ANALYTICAL CHEMISTRY, VOL. 50, NO. 8 , JULY 1978
Poly( perfluoropropylene oxide) as a Reference Standard for Mass Measurement to Mass 2000 Woodfin
V. Ligon, Jr.
General Electric Company, Corporate Research and Development, Schenectady, Ney York 1230 1
A number of compounds and substances have been reported and used as mass references in analytical mass spectrometers. In order to be useful, such materials must possess several special characteristics. First, they should ideally provide a significant number of evenly spaced ions of adequate and preferably similar intensity in the mass range of interest. Second, for most applications, the ions produced should have large negative mass defects such that they are easily resolved at moderate resolutions from sample ions of the same nominal mass. Third, the materials are most conveniently utilized if they possess sufficient volatility that they can be admitted to the ion source using heated batch type inlet systems. Reference materials which require a solid probe are less useful because most spectrometers are equipped with only one such probe and this probe is required for sample introduction. Fourth, the reference should have minimal adverse effects on the ion source itself. Frequent problems of this kind include failure to pump away a t an adequate rate (memory effects) and accelerated ion source contamination by decomposition products. In the mass range below about 700 amu, perfluorokerosene and perfluoro-tert-butylamine are the most widely used mass standards. Recently perfluoroalkyltriazines (I) and perfluoroalkoxyphosphazines (2, 3) have been described for use in the mass range above 600 amu. In both of these cases, the number of ions produced in a given mass range is rather small and the ions observed vary widely in intensity. We report the low resolution mass spectrum of poly(perfluoropropylene oxide). The electron impact mass spectrum of a low boiling fraction (average m / e 1800) sold under the trade name of Fomblin-L (trademark of Montecatini-Edison, distributed in the United States by PCR Inc.) is shown in Table I. This perfluorinated polyether is reported to have the following general structure ( 4 ) : CF, I
CF,O-( -CF-CF,-O),-(
CF,-0), -CF,
A gas chromatographic analysis of this sample is shown in Figure 1. The repeat unit of this polymer, (CF(CF,)CF,-0) has a molecular weight of 166 amu. This periodic feature of the material results in long repeating series of ions separated from other members of the same series by 166 amu. Table I is arranged so that this periodicity is clearly evident. Each vertical column is separated from adjacent columns by 166 amu and each line in the table is a series of ions related by the addition or subtraction of monomer units. The intensities (which are not reported at this time) decrease roughly monotonically with mass 169 as 100%. Masses within a given series decrease from about 100% to about 0.02% over the range 169 to 1000 and then from 0.02% to about 0.0004% at mass 2000. It should be noted that when normalized at mass 1000 the decrease between 1000 and 2000 is only from 100% down to 2% so that ions in the 1000-2000 amu range are of very comparable intensity. Preliminary results indicate that improved relative intensities a t high mass can be obtained using high boiling distillation fractions of Fomblin-L. It should be further noted that PFK goes from 100% at mass 69 to -0.00007% a t mass 1005 under the same instrumental conditions. Above mass lo00 the spectrum consists of the pattern shown in Figure 2, repeated every 166 amu. This section of the 0003-2700~78/0350-1228$01 .OO/O
Table I. Nominal Mass Assignments to Mass 2000 in the Electron Impact Mass Spectrum of Poly(perfluoropropy1ene oxide) ELECTRON IMPACT MASS SPECTRUM POLY (PERFLUOROPROPYLENE OXIDE 1
861 1027 I I93 865 lo31 I197 867 1033 I199 545 711 877 1043 1209 880 IO46 1212 551 717 883 1049 1215 567 733 899 065 1231 579 745 911 IO77 1243 749 915 1081 1247 595 761 927 1093 1259 601 767 933 1099 1265 617 783 949 1115 1281 629 795 961 I I27 1293 633 799 965 1131 1297 645 811 977 II43 1309 II47 1313 651 817 983 I149 1315 993 1159 1325 996 I162 1328 667 833 999 1165 1331 683 849 1015 1181 1347
1691 1695 1697 1707 1710 1713 1729 1741 1745 1757 1763 1779
1857 1861 1863 1873 1876 1879 1895
rr95 1807 1811 1813 1823 1826 1829 1845
1961 1973 1977 1979
IONS PRESENT BUT NOT PART OF AN ION SERIES:75,78,81,85,93,100+, 150,231,257,281,291,316,3&,347,369,535 *IONS PRESENT ABOVE TRACE LEVELS UNDERLINED.
128,
31
I97
363
47
213
379
69 81
219 235 247
385 401 413
263 269 285 297 30 I 313
429 435 451 463 467 479
319
485
335 351
501 517
97 119 131 135 147
169 185
529
695
1359 1363 I365 1375 1378 1381 1397 1409 1413 1425 1431 1447 1459 1463 1475 1479 1481 1491 1494 1497 1513
1525 1529 1531 1541 1544 1547 1563 1575 1579 1591 1597 1613 1625 1629 1641 1645 1647 1657 1660 1663 1679
191I 1923 1929 1945
1992 1995 2011
spectrum corresponds to the column headed 1691 in Table I. With very minor variations, this pattern of intensities repeats starting anew with each of the masses of the line (ion series) beginning with mass 31, in Table I. Because of the periodicity of the ion series, the elemental compositions of the various ions are easily deduced. For example, in the series beginning with mass 31, the elemental compositions are given by CF + n(C3F60). Composition assignments made in this way should be verified by actual measurements and these will be reported later. Two series of even mass ions appear in the spectra. These are (C3F60),starting at mass 880 and CF2 + (C,F,O), starting at mass 996. If it is assumed that the 880 series represents intact molecular species, then it must be concluded that the material is largely cyclic in nature. Note that unsaturation would result in irregularities in the ion series. Other ion series such as CF3(C3F60)nstarting at mass 69 suggest the presence of CF3 end groups as previously reported ( 4 ) . This apparent inconsistency can be resolved if it is assumed that only the cyclic species give significant molecular ions. The even mass series starting at mass 996 appears to be derived from a rearrangement process. Fomblin-L is a clear liquid with a boiling range of 80-210 "C (0.3-0.4 Torr.). It is therefore possible to admit samples to the mass spectrometer with a batch inlet. The material is reported to have long term (24 h) stability toward stainless steel at temperatures below about 290 "C under oxidizing conditions (5)and should therefore be quite stable in the mass spectrometer. The large negative mass defect of oxygen which exceeds that of fluorine results in the ions produced from Fomblin-L having mass defects greater than those observed with perfluorokerosene. The ions are therefore more easily 0 1978 American Chemical Society
ANALYTICAL CHEMISTRY, VOL. 50, NO. 8 , JULY 1978
L
i
80
loo
I
I
140 I80 TEMPERATURE
I
I
210
250
Flgure 1. Gas chromatographic analysis of poly(perfluoropropy1ene oxide), average molecular weight, 1800 amu. Gas chromatographic parameters: column, 10-ft OV-17 Pyrex; oven, programmed 80-300 "C @ 20°/min; detector, flame ionization 1729
Figure 2. Oscillographic recording of the electron impact mass spectrum of poly(perfluoropropy1eneoxide) between mass 1690 and 1850
resolved from sample ions of the same nominal mass at high resolution. Experiments to date have not revealed any problems of premature ion source contamination. Further, the material is cleanly removed from the ion source in a short time after admission is terminated. Poly(perfluoropropy1ene oxide) provides therefore a very useful mass standard for the mass range 31-2000. The ions are of useful intensity even at high mass and are spaced closely enough t o potentially allow high resolution data system acquisition in the 1000-2000 amu range. Low boiling fractions (115-140 OC) of Fomblin-L separated by fractional distillation give essentially the same ions below mass 1000 as the intact material. The significantly improved ion intensities relative to perfluorokerosene in the 800-1000 amu region suggest that such fractions should be considered as a replacement for perfluorokerosene in this mass range.
1229
It is of interest that a material with the same structure but with an average molecular weight of 3700 is available under the trade name Fomblin-M. The application of this material to the 2000-3700 amu mass range is being investigated. Spectra were recorded on a Varian-Mat 731 mass spectrometer (Serial #0214) equipped with an EI-FD ion source operated in E1 mode. The source temperature was 250 "C. Nominal masses were determined from oscillographic recordings with reference to the digital mass marker integral with the instrument. For these measurements, the mass marker was calibrated with perfluorokerosene immediately prior to use. In addition the mass assignments for the major ions in the range 1185-1297 have been verified by peak matching against the 1185 ion of perfluorotrihepthyltriazine (I). Further verification of mass assignment was obtained by a process of stepwise repetitive peak matching. In this procedure, a particular ion was arbitrarily chosen as a known and other ions were shown to occur a t correct peak match ratios relative to this ion. Whenever the 10% switching limit of the peak match unit was exceeded, a second ion was chosen as the known from among those already compared in a previous step. In this way all major ions between mass 1031 and 2011 were shown to occur a t voltage ratios to other ions consistent with the assigned masses and consistent with the masses assigned with reference to perfluorotriheptyltriazine. These measurements can reasonably be expected to ensure accurate assignment of nominal masses to better than f0.4 amu. ACKNOWLEDGMENT The author gratefully acknowledges the assistance of J. Carter Cook, School of Chemical Sciences, University of 11linois, Urbana, Ill., in the early stages of this work. LITERATURE CITED (1) Thomas Aczel, Anal. Chem., 38, 1058 (1966). (2) H. M. Fales, Anal. Chem., 40, 1917 (1968). (3) K. L. Olson, K. L. Rinehart, Jr., and J. C. Cook, Jr., Biomed. Mass Spectrom., 4, 284 (1977). (4) . . D. Slanesl. V. Zamboni. R. Fontanelll, and M. Blnaghi, WEAR, 18, 85 (1971). ( 5 ) PCR Technical Bullefin #500-173. 139.
RECEIVED for review December 9, 1977. Accepted April 25, 1978.
Portable Device with XAD-4 Resin Trap for Sampling Airborne Residues of Some Organophosphorus Pesticides James E. Woodrow and James N. Seiber" Department of Environmental Toxicology, University of California, Davis, California 956 16
A significant proportion of applied pesticides may enter the air from drift during application and by evaporation from treated surfaces (1,2). To determine residue levels in the air, sampling techniques have been developed which, in principle, partition residues into trapping media compatible with established analytical techniques. For example, glycol-filled glass impingers ( 3 , 4 )and solid trapping agents, such as porous polystyrene macroreticular resins ( 5 , 6 ) ,have been successfully employed for sampling airborne pesticidal residues. However, these techniques have generally employed relatively large blowers or vacuum pumps (6-8) and require fuel-powered generators when used in the field. The associated bulk and expense limit the opportunity for flexibility and replication in designing air sampling experiments. We describe here a readily assembled, portable battery-powered sampler which
circumvents these disadvantages, and further offers ease in post-sampling workup prior to analytical determination by utilizing a simple resin-filled vapor trap. The sampling efficiency of the device was determined using the resin trap or an ethylene glycol impinger under laboratory conditions for three relatively common organophosphorus insecticidesmalathion, mevinphos, and parathion- and one organophosphorus defoliant-DEF. EXPERIMENTAL Chemicals. Analytical standards of DEF, malathion, mevinphos (Phosdrin), and ethyl parathion were obtained from the U.S. Environmental Protection Agency, Beltsville, Md. Commercial grade solvents were distilled twice in glass, except for ethylene glycol (EG) which was purified from reagent grade solvent (Mallinckrodt Chemical Works, St. Louis, Mo.) by the procedure
0003-2700/78/0350-1229$01.00/00 1978 American Chemical Society
