Mass Spectrometric Analysis Spectral Data File Utilizing Machine Filing and Manual Searching FRED W. McLAFFERTY’ and ROLAND S. GOHLKE Spectroscopy Laboratory, The Dow Chemical Co., Midland, Mich.
F A new filing system for mass spectra utilizes the unique advantages of the mass spectrometer in mixture identification. N o machine searching of this file is necessary, because all spectra having one of their 15 most significant peaks a t a particular m/e will b e grouped together in probable order of abundance. Each such filed card also shows these significant peaks in order of abundance, making reference to original spectra unnecessary. The original filing of this large amount of data can be done with modern business machines. A second no-band filing system is described.
T
HE rapid
identification of unknowns, usually mixtures, is one of the main problems encountered in mass spectrometry in the chemical industry. Positive identification necessitates comparison with known standards, many of which are now available. To aid in this, tTyo general systems for tabulation of mass spectra have been proposed. Zemany (9) and others (3) have described marginal-hole (Keysort-type) cards sorted by hand manipulation. Kuentzel (6) proposed Hollerith-type cards with the IBM (International Business Machines Corp.) sorting machine (Type 0-80 or 82) and such systems have been developed in several laboratories (6). Certain limitations in these systems have led to the development of the tabulation methods described here. Mass spectrometry is unique in the large number of peaks of precisely determinable mass (more exactly mass to charge ratio, mle) which are possible in the individual spectrum, and the high sensitivity of detecting these peaks (signal to noise ratio commonly 1 to 100,000). Thus, it is possible that some relatively minor peak of a n impurity may provide identification when the major ones are obscured by overlap with peaks of other sample components. To utilize these advantages it mas felt that coding should not be limited to just the six highest peaks (9) or those 1 Present address, Eastern Research Laboratory, The Dow Chemical Go., Framingham, illass.
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ANALYTICAL CHEMISTRY
of abundance of a t least 20% of the highest (5, 6). I n utilizing more peaks, however, a n indication of their relative importance becomes imperative. I n addition, the advent of the heated-inlet mass spectrometer ( 7 ) has made the recording of exact mass numbers instead of ranges of m/e necessary a t much higher masses. The first system described codes for each spectrum the integral mass number through m/e 999 of the ten highest peaks in order of size, plus five other peculiar peaks whose mass numbers might stand out in a mixture. Classification of the latter depends on the types of samples usually encountered by the laboratory, but is generally most useful in prol-iding a means to include weak peaks of high m/e. Figure 1 shows the standard IBM punched card used. I n columns 1 through 4 is placed the serial number of the compound, assigned arbitrarily.
Figure 2.
Completed
IBM
Columns 5, 6, and 7 give the molecular weight, as calculated using the most common isotope of each element as its atomic n eight. i i n X punch in column 5 indicates no appreciable molecular ion in the spectra. Columns 8 and 9 signify the hundreds and tens figure of the boiling point in centigrade. An X punch in the 8 column signifies a negative number, and in 9 a melting point, Columns 10, 11, and 12 are the hundreds, tens, and units figures of the m l e of the base peak-the largest peak in the spectrum. Thus, if 91 is the largest peak. 0, 9, and 1 will be punched in these columns. Similarly, 13 through 15 designate the second highest peak, and 16 through 39 the third through tenth highest. The five peculiar peaks are recorded in similar fashion from mass 40 through mass 54. Columns 55 through 75 are used for recording in order of magnitude the next lower whole mass number of any
card of triphenyl phosphite
peaks
at fractional
nz, e . Thus, a
431/2 peak would be recorded as 043. These fractional mass peaks can be due to either metastable or multiply charged ions. Columns 77 and 78 are punched to indicate the number of chlorine and bromine atoms, respectively. This information was thought useful because of the ease of recognizing these elements from their isotspic distribution. Figure 2 s h o w the completed I B M The card of triphenyl phosphite. proper compound names are placed on each card by IBhf equipment from a second card on which is punched the serial number and name. The information punched in the card is printed by machine across the top of the card Iyith the name. K h e n a master deck of one such card for each spectrum of the standard file has been prepared, 22 duplicate decks are made by an I B M punch. Columns 79 and 80 are then used to designate these decks. Using the I B h l sorter, the first of these duplicate decks is arranged in order of mass number of the strongest peak-i.e., is sorted on columns 10, 11, and 12. Similarly, deck number 2 is sorted for the second highest peak on columns 13 through 15, and the rest of the decks on the succeeding peaks as indicated by the respective group of three columns through column 75. Cards in decks for which there are no corresponding peaks are discarded--e.g., if a compound shorrs
Figure 3.
no multiply-charged ions, its cards in deck 16 through 22 are unnecessary. These sorted decks are then combined, using the I B M split sequence collator or statistical sorter, SO that cards sorted for each mass number in each respective deck are grouped together, These are placed in order under each mass number-e.g., the deck 1 cards of all compounds having their strongest peak a t m/e 100 are followed immediately by all cards of deck 2 having their second strongest peak a t 100, etc. Each deck is printed on different colored cards so that these divisions stand out in the file. Decks 16 through 22 are filed separately, because they represent recognizably different m/e’s. An alternate simpler sorting method requires three additional columns of the card. I n these are duplicated the mass number by which each individual card nil1 be filed-e.g., all deck 1 cards will have columns 10, 11, and 12 duplicated in these columns. Sorting all of the cards on these three columns and then on 79 and 80 will yield the file in final arrangement. Thus, t o identify the compound causing a particular peak in the mass spectrum of a mixture, the cards filed under that m/e are inspected. Those cards are composed of all spectra containing that particular peak in their ten highest and in five additional peaks. These spectra can then be compared with the unknown in order of highest probability
of finding the compound. Thus, to identify an unknown 181 peak, the cards shown in Figure 3 would be among those compared with unknown spectrum. Chlorodiisopropylbenzene would be compared first, because it has 181 as its base peak. Because all the significant peaks of the spectrum in relative order of magnitude are s h o w on the filed card, referral to the original spectrum is usually unnecessary for compound verification and is done when quantitative calculations are to be performed using the identified compound. This is not possible in other systems (6, 6). A similar procedure can be carried out to identify a peak a t a fractional m/e by employing the smaller file of these cards. No machine searching has been necessary, though this could then be done on such a discrete mass group for an additional characteristic, as a certain boiling range or additional peak. DISCUSSION
Such a file in this laboratory currently encodes 4000 spectra, requiring 72,000 IBh4 cards housed in 24 card drawers of 26-inch depth. This file has been used successfully on thousands of unknown identifications over the last five years. This experience has shown that the coding of the fractional mass peaks, columns 55 through 75, and the number of chlorine and bromine atoms, 77 and 78, have been used to a very
Cards removed from file to indentify unknown m/e 181 peak VOL. 31, NO. 7, JULY 1959
1161
Figure 4.
Coding necessary for 1,2,3,4-tetrabromobutclne in no-band system
limited extent. For them could be substituted in columns 55 through 74 a chemical structure code similar to those in Kuentzel-type systems (5, 6). Colunins 75 through 77 could be used for the simpler sorting method suggested above. An X piinch to indicate peaks of >20% magnitude has been added, thus making available the no-band (1) information described later. The large number of cards makes hand filing laborious, so that new spectra are accumulated for periodic machine filing. This also corrects any interim misplacements. I n practice, it has been simpler to prepare a new file from the master deck containing the old and new spectra. Although this is done mainly by machine, the difficulty of new filing is probably the most serious disadvantage. M’ith this system, for any compound present in a complex mixture there are available on its I B M card 15 whole mass peaks (unless there are not this many peaks altogether in the spectrum), a n y one of which could aid in identification of the compound even if the rest of the peaks are obscured by other components. If an arbitrary limit is set up for the intensity of the peaks included, i t is possible to have only one peak coded. Using a limit of 20%, this would be true for the triphenyl phosphite, Figure 2. B u t here peaks as m/e 217 and 310, which are only a few per cent of the base peak, are still strong enough to make possible identification of triphenyl phosphite when the concentration is less than 1%. This file of punched cards also has proved useful for correlations of mass spectra, which are necessary for identification of compounds for which no reference spectrum is available. An obvious use is to determine if a particular peak is typical of any certain type of 1 162
ANALYTICAL CHEMISTRY
compound. The illustration of the cards filed under m/e 181 shon s several perfluoro compounds (due to their CZ,-ion), so an unidentifiable 181 peak might be checked for the possibility of arising from a perfluoro compound. A more common case is a peak such as m/e 45, for which 561 standards in this file give significant peaks. Of these, 73% are compounds containing oxygen, in which the 45 peaks commonly represent ions such as -C2H40H and -CHZOCHs. Another 16% of the compounds a t m/e 45 contain sulfur. Thus, the IBM file shows there is a high probability that a n unidentified 45 peak is due to an oxygenated, or less probably, a sulfur inipurity. It is planned to publish a table of individual mass numbers showing the significant compound types yielding each m/e, as is illustrated above. This should be applicable to mass spectral identifications in the same way that the Colthup chart ( 2 ) has been used for infrared spectra. Tabulations of the most probable peaks from the master deck of punched cards can aid in spectral correlations. For instance, I B M machines can prepare a list of the numerical difference betm-een the parent peak and each of the peaks included on the cards for alkyl chlorinated compounds. Such a list shows differences as 35, 71, 15, etc., indicating the strong tendency of such compounds to lose a chlorine atom, HC12-, and a methyl group. For this correlation work chemical structure codings (6, 6) mould be most useful. I n principle, this file is a n extension of the classical coding system for x-ray diffraction data (4) in which the three strongest lines are manually filed according to n a v e length. Recently a
similar system for mass spectra has been proposed utilizing the three highest peaks (8). NO-BAND SYSTEM
A second system was developed concurrently with this one. I n addition to sorting for the particular m,’c of the unidentified peak, it also uses the information on masses !There there are no significant peaks. This second system is a n extension of the one described by Baker, Wright, and Opler (1) for infrared spectra. Only the modifications of their method are described, because their theory, discussions, and equipment apply to the present system. The coding necessary for 1, 2, 3, 4tetrabromobutane is shoivn in Figure 4. The compound serial number is indicated in columns 1 through 4. Only the X and 9 rons are used for columns 5 through 78. Each is used to indicate a specific peak present in the mass spectrum in intensity of a t least 20% of the highest peak. Thus a 9 punch in column 5 s h o m a significant peak below mass 12 in the spectrum, a 9 in column 6 a t peak a t m/e 12, and the 9 row in columns 7 through 78 indicates masses 13 through 84, respectively. Similarly, a n X punch in columns 5 through 78 indicates masses of 85 through 158, respectively. If there are significant peaks above mass 84, a 9 punch is placed in column 79. I n the same way a n X punch in 79 indicates peaks above m/e 158 with an intensity of 20% or greater of that of the highest peak. The significant peaks over mass 84 are also punched in a second card t o obtain overlap in the information. Here the 9 roTT of columns 5 throuqh
79 is a duplicate of the X row, of the first card. Masses from 159 to 232
are shown in the X row, with column 79 indicating significant peaks over 232. Similar cards are prepared for the maw intervals of 159 through 306, 233 through 380, 307 through 454, 381 through 528, 455 through 602, etc. Column 80 is used to designate which of these mass intervals is represented on the card. After preparation, the cards are separated by this number in column 80 into separate decks. The data at the top of the card are taken from the master deck of the first tabulation system described. Thus, these data usually include additional peaks to those punched in the card, and indicate the relative order of magnitude of these. It is possible to punch the cards of this system directly from the cards of the first system using appropriate IBRI machines. The two decks of cards whose m ' e range includes t h a t of the peak sought are searched by the I B M collator utilizing also as no-band peaks all peaks in this range of iiiagnitude less than 20%
of the sought peak. It is usually necessary to search only one deck, especially if no punch is required in X79 of this deck. The principal advantage (1) of this second method is the large statistical leverage of including the no-band peaks. Often the sort can demand that the cards selected have no peak at more than 100 individual m/e positions. It is especially advantageous if the unidentifiable peak is a t such a common m/e that the first system contains a large number of cards filed at this mass. However, the first method has been more widely used in this laboratory because no machine searching is necessary, the 15 coded peaks almost always include all those of significance, and the selected standard spectra are arranged in order of peak magnitude. These advantages should make this method applicable to other fields of spectroscopy.
Caldecourt, Ascher Opler, J. L. Saunderson, and Korman Wright. LITERATURE CITED
(1) Baker,
A. W. Wright, Norman, Opler, Ascher, ANAL.CHEX 25, 1457
(1953). (2) Colthup, N. B., J. O p t . SOC. Am. 40, 397 (1950). (3) Consolidated Electrodynamics Corp., 300 S o . Sierra Madre Blvd., Pasadena, Calif. Keysort File of Mass Spectral
Data. (4) Hanawalt, J. D., Rinn, H. W., Frevel, L. K., IND.ENG.CHEM.,ANAL. ED 10, 457 (1938). 15) . 23, ~, Kuentzel, L. E., A N ~ L CHEJI. 1413 (1951). (6) McCrae, J. hl., Kellogg Co., Jersey City, N. J., private communication. (7) O'Neal, M. J., Jr., )Vier, T. P., ANAL.CHEM.23,830 (1951). (8'1 Iron Hoene, J., Users' Clinic, Consoli-
dated Electrodynamics Corp., New Orleans, La., June 1958. (9) Zemany, P. D., An.4~. CHEM. 22, 920 (1950).
ACKNOWLEDGMENT
The authors appreciate very helpful discussions Kith A. W. Baker, V. J.
RECEIVED for review October 23, 1958. Accepted March 25, 1959. ASTM E-14 Meeting on Mass Spectrometry, New Orleans, La., May 1954.
X-Ray Powder Diffraction Patterns of Strontium Phosphates R. C.
ROPP,M. A. AIA, C. W. W. HOFFMAN, T. J. VELEKER,
and R. W. MOONEY
Chemical & Metallurgical Division, Sylvania Electric Products Inc., Towanda, Pa.
b The x-ray powder patterns of 12 strontium phosphates have been reported for their value in the identification of phosphate materials and in the elucidation of the reactions of strontium phosphates. Chemically, strontium phosphates are similar in their reactions to the calcium phosphates.
T
calcium phosphates are important commercially as fertilizers and mineral supplements. I n contrast, little use has been found for the strontium phosphates. As a result, considerable chemical (19) and x-ray data ( 6 , 8) may be found for the calcium phosphates, whereas the existing data concerning the strontium phosphates are scarce and a t times contradictory. Thilo and Grunze ( I S ) report that the course of dehydration of Sr(H2P04)2 is similar to that of Ca(H2P0&. A phase rule study of the system SrOPzOS-H~Oa t 25" C. was reported by Tartar and Lorah (16). Two modifications of Sr2P207have been prepared and identified by Ranby, Mash, and HE
Henderson (16). A recent paper (9) disclosed the existence of two forms of SrHP04. Little is known structurally of the strontium phosphates. Zachariasen (61) found rhombohedral symmetry for Sr3(PO&, while Klement ( 7 ) found the usual hexagonal structure for strontium hydroxylapatite. Brasseur and Plumier (3) have proposed the existence of a hydrated form of the tristrontium phosphate having the apatite structure. This paper describes methods of preparation of the strontium phosphates and compiles their x-ray powder patterns, many of these for the first time (Tables I and 11). The x-ray powder diffraction method has proved convenient for identifying the crystalline strontium phosphates and for cataloging the reactions which they undergo. The ASTM x-ray powder data file (1) lists four strontium phosphate compounds. Three of these cards, Kos. 1-0512, 2-0761, and 2-0655, agree with the present data and are p-SrHP04, SrdOHMPOda, and SrdP04)2, respectively. Card 2-0744, listed as a
strontium phosphate, is evidently a hydroxyl apatite. The data in Table I1 do not include these results, but only data gathered in the present work. No published x-ray data exist for Sr(HzPO&, SrH2P207, a-, P-, and YSr(POd2. APPARATUS AND TECHNIQUE
The y-rav diffraction patterns were taken on a Norelco unit (Sorth A4merican Philips Co., Inc.) equipped with Geiger-counter diffractometer and using nickel-filtered CuKa: radiation of 1.542 A. wave length. Sample preparations prior to x-ray meswrement and intensity measurement. follo +T the procedure adopted by the National Bureau of Standards (15). The intensity values of each pattern were measured as peak height above background and expressed as percentages of the strongest line. Standard techniques v-ere used in the various chemical preparationq. Differential thermal analyses were taken on an apparatus similar to that described bv Stone 114). Thermogravimetric data were obtained with a recording Stanton thermobalance. VOL. 31, NO. 7, JULY 1959
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