Perfluorotriheptyltriazine: Reference Standard for Precise Mass Measurement up to m / e 1600 Thomas Aczel ESSOResearch and Engineering Co., Baytown, Texas HIGH RESOLUTION MASS SPECTROMETRY is acquiring an increasingly important role in analytical chemistry. The usefulness of this technique derives mainly from the capability of measuring precisely the mass to charge ratio of the ions in the mass spectrum of a compound or mixture, allowing one to calculate the elemental formulas of the ions in question. These precise mass measurements are made with the aid of a reference standard that yields a large number of ions of known mass. This note describes a new reference standard, 2,4,6-tris(perffuoro-heptyl)-l,3,5-triazine (perfluorotriheptyltriazine), which is particularly useful for precise mass measurement in the mass region 600 to 1600. The two most widely used standards, peril uorokerosene and perff uorotertiarybutylamine are of little or no use in this mass range because they do not possess peaks of sufficient intensity above mJe650. Perfluorotriheptyltriazine, on the other hand, gives 36 usable ions in the mass region 650 to 1185, including an intense parent peak at m/e 1185 and abundant fragments at m/e 1166, 1066, 966, 866, 771, etc. The precise theoretical masses
and relative intensities of the significant ions in the spectrum of this compound are reported in Table I. The mass values reported in Table I are theoretical. However, the formulas of all the major ions have been confirmed experimentally. Examples of pertinent mass measurements are in Table 11. The formulas of the minor ions, whose masses were not measured experimentally, were deduced from similarity with the mass spectra of other fluorinated compounds. For example, the formula of the ion at mle 1078 could be easily deduced from the formulas obtained with precise mass measurement of the adjacent ions at m/e 1066 and 1090. It might be noted here that the fragmentation of perfluoroheptyltriazine is rather interesting. The main fragments are those due to loss of F and CF entities, the most abundant fragment deriving from a p cleavage of the sidechain (m/e 866, P-CeF13). The highest mass ion containing only two N atoms is formed from the ion at m/e 866. It involves the loss of a CzF3N entity and thus the cleavage of the triazine ring. This proposed mechanism is confirmed by the meta-
Table I. Mass Spectrum of Perfluorotriheptyltriazine Relative Formula Precise mass" sensitivity Formula Precise maw CirHz,Nz 670.966202 C24F4 5N3 1184.937319 2.24 Cz4F44N3 1165.938917 35.55 Ci4Fz4N3 665,970874 1146.940515 Cz4F43N3 Ci4FzzNa 627,974069 0.11 Ci3FzaNz 620.969398 Cz4F4zN3 1127.942113 1.83 Cz3FazN3 1115.942113 CiaFzzN3 615.974069 0.71 Ci 3FzoN3 577.977265 Cz3F4iN3 1096.943711 0.03 Cz4F4oN3 1089.945308 0.22 CizFziNz 570,972593 Cz3F4oN3 1077.945308 0.04 CizFzoN3 565,977265 CzzF4oN3 1065.945308 1.12 Ci3FigNz 544.975789 1027.948504 CzzF3sN3 CiiKsNz 520.975789 0.09 CziF3sN3 1015,948504 0.81 CiiFisN3 515.980461 CziF36N3 977.951700 0.32 CioFi7Nz 470.978985 CzoF36N3 965.951700 2.41 CsFijNz 420,982180 CZOF~SN~ 946.953298 0.07 CsFi,N 375,980704 CzoF34N3 921.954896 9.42 C7F16 368,976033 915.954896 CigF34Ns 7.94 C6F13 318,979228 Ci9F33N3 896.956493 0.06 C6Fll 280.982424 889.958092 CzoF3zN3 0.51 CGFION 215.987095 CisF3zN3 877,958092 0.23 CsFii 268,982424 CisFazN3 865.958092 100.00 CsFg 230.985619 CisFaiN3 846.959689 CsFsN 225.990291 0.16 CisF3 oN3 821.961287 0.44 C4Fs 218,985619 CnF3oNa 815.961287 0.88 C4F7 180,988815 CisFzsN3 189.964483 0.05 GFiN 175.993487 Ci7FzsN3 777.964483 0.08 C3F1 168.988815 CI~FZDNZ 770.959811 4.85 C84N 137.996682 c 1fiFZsN3 765.964483 0.12 C3F5 130.992010 751.961409 CieFzsNz 0.04 C3FaN 125.996682 Ci6Fz7N-i 732.963007 0.18 CZF5 118.992010 Ci6Fz6N3 721.967678 C3FzNz 102.002952 0.06 Ci5FnNz 720.963007 0.14 C2F4 99.993609 CI~FZ~N~ 715.967678 0.07 CzFzN 75.999878 Ci5Fz5N3 696.969276 68.995207 0.04 CF3 Ci~FzaN3 677.970874 49.996805 0.08 CFz CF 30.998402 Theoretical values using C = 12.oooO00, F = 18.9984022, N = 14.0030738. Note: A metastable ion, corresponding to the transition C18F3zN3++ C16FzsNz+ C2F3Nis present at m/e 686.4.
Relative sensitivity 0.18 0.28 0.11 0.72 1.24 0.26 1.39 1.41 0.88 0.28 0.50 4.04 0.42 5.12 0.13 0.48 1.21 0.92 1.39 0.92 0.76 1.28 2.18 1.28 15.03 7.00 19.12 9.42 24.68 1.51 5.30 13.81 79.65 0.85 1.49
+
VOL. 40, NO. 12, OCTOBER 1968
1917
~
Table II. Examples of Mass Measurements Reference peak 613.96473~ 865.9581
Mass ratio
Measured mass
Theoretical mass
1.255709 1.410430 1.013857 1.057735 1.071596 1.115476 1.230938 1.346417
770.9610 865.9542 877.9581 915.9541 927,9572 965.9555 1065.9407 1165.9407
770.9598 865,9581 877.9581 915,9549 927.9549 965.9517 1065.9453 1165.9389
A , ppm 1.6 4.3 0.0 0.9 2.5 3.9 4.3 1.5
AvA,ppm: 2.4 a
From heptacosaperfluorotertiarybutylamineused as an external reference standard,
stable ion at mje 686.4, as shown in Table I. The highest mass ion with only one N atom occurs at m / e 376, due probably to a similar process subsequent to the loss, by 0cleavage, of the second sidechain. As a completely fluorinated material, perffuorotriheptyltriazine does not yield ions that interfere with hydrocarbon ions. It is a liquid at room temperature, and may be easily introduced in any mass spectrometer. It may be used for the precise mass measurement of ions of m / e values up to 1600 with the Nier peak matching system which allows one to measure accurately peaks of mass 40 per cent higher than that of the reference peak, and up to m / e 1185 with a computerized data acquisition system, which requires that ion standards bracket sample ions.
This standard, together with the now commercially available insertion probes, should be of considerable aid in the mass spectral analysis of very heavy molecular weight materials. In these laboratories it was used for the mass measurement of organic (not halogenated) materials up to molecular weight 1200. The mass spectrometer was an Associated Electrical Industries, Ltd. model MS 9 high resolution instrument. ACKNOWLEDGMENT The perfluoroheptyltriazine used in this work was prepared and furnished by courtesy of Peninsular Chemresearch, Inc., of Gainesville, Fla. RECEIVED for review April 12, 1968. Accepted May 31, 1968.
Ultrasonic Nebulizer for Easily Changing Sample Solutions J. M. Mermet and J. P. Robin Service de Chimie IndustrieIIe et AnaIytique, Institut National des Sciences AppliquPes, 20, Avenue A . Einstein-VILLEURBANNE (%&e) France
PRODUCING AN AEROSOL raises some problems which have been solved by using a pneumatic nebulizer. The use of ultrasonic spraying has been discussed by several authors (1-14), for general and medical research and for spectroscopic purposes (flame photometry, atomic absorption spectrophotometry, induction-coupled plasma, etc . . . ). This spraying process has numerous advantages, particularly increased output due to the good quality of the fog.
(1) K. Bisa, K. Dirnagl, and R. Esche, Siemens Z., 8, 341 (1954). (2) H. Dunken, G. Pforr, and W. Mikkeleit, Z . Chem., 3, 196 (19631. ( 3 j Zbik, 4,237 (1964). (4) H. Dunken, G. Pforr, W. Mikkeleit, and K. Geller, Spectrochim. Acra, 20, 1531 (1964). (5) E. L. Gershenzon and-0. K. Eknadiosyants, Soviet Phys.Acousr. (English Transl.), 10, 127 (1964). (6) P. Herzog, 0. P. Nordlander, and C. G. Engstrom, Acra Anaesthesiol. Scand., 8, 79 (1964). (7) H. C. Hoare and R. A. Mostyn, ANAL.CHEM., 39,1153 (1967). (8) H. C . Hoare, R. A. Mostyn, and B. T. N. Newland, Anal. Chim. A m , 40, 181 (1968). (9) W. J. Kirsten and G. 0. B. Bertilsson, ANAL.CHEM., 38, 648 (1966). (10) R. H. Wendt and V. A. Fassel, ibid., 37,920(1965). (11) C. D. West and D. N. Hume, ibid., 36, 412 (1964). (12) C. D. West, ibid., 40, 253 (1968). (13) J. Spitz and G. Uny, Appl. Opt., 7 , 1345 (1968). (14) M. E. Ropert, Mithodesphysiques d'analyses, (GAMS), 4,231 (1968).
1918
ANALYTICAL CHEMISTRY
Pneumatic spraying, in the case of aqueous solutions, has a yield of about 10%. That is, only 10% of the nebulized solution constitutes a fine aerosol which can leave the cell where it is generated and, for instance, enter a flame. Indeed, whatever the type of spraying, it has been ascertained that the diameter of the droplets going through the flame is approximately identical. Such is the case with ultrasonic spraying when a suitable frequency is used. This explains the stability of the fog and also the good spraying yield. Consequently, analyses can be made with smaller quantities. It is also possible to get a spray rate independent of the gaseous flow rate. This may be advantageous for the study of some physical parameters of flames or plasmas. At first, we studied the works of West and Hume ( I I ) and Wendt and Fassel (IO) in order to design an accessory which would feed an H F induction-coupled plasma. Our aim was to devise an apparatus that would allow samples to be changed without interrupting the plasma discharge. Several kinds of ultrasonic generators are available; they operate with or without a liquid transmitter. After some testing, we chose the first type which appeared to us as the most suitable to solve our problem. To introduce and remove the sample, several authors (7, 12) have worked with this kind of generator by changing spraying cells. For our part, we think that this method has some drawbacks, especially in building cells of identical characteristics. Therefore, we use a motionless vessel combined with a reversible pump.
