Interpretation of Proton Magnetic Resonance Spectra by Computer Program: An Enhanced Elimination Algorithm
Sir: I read with considerable interest the article which Beech, Jones, and Miller ( I ) published in your journal recently. The algorithm suggested falls roughly into three phases: selection from the table of the macrofragments which are consistent with the spectrum provided; elimination of macrofragments which do not comply with the rules given below; and molecule “building” with the remaining macrofragments. This latter state is computationally most complex and so. it is important that the elimination procedure should be as efficient as possible. Below I suggest a number of ways in which the elimination procedure outlined in the paper ( I ) could be considerably enhanced. If a macrofragment [the nomenclature used here is that introduced in ( I ) ] contains s identical peripheral groups (e.g. CH2 with CH and CH as peripheral groups), then the elimination rules for the macrofragments must be extended such that: if the peripheral group is non-proton containing and is of valency n then the group must appear a t least s X ( n - 1)times among the peripherals of the macrofragments derived from other multiplets (the n - 1 rule of ( I ) ) ; if the peripheral group is proton-containing, then it should be present as the middle group in s of the macrofragments derived from other multiplets in which the current middle group is a peripheral group. (And, of course, for a macro-
fragment to be acceptable, all of the peripheral groups must satisfy one of the above conditions.) Given a list of macrofragments, L, the above elimination rules should be applied until no further members of the list are eliminated. The reason for this is that macrofragment A may be retained because macrofragment B and C satisfy its requirements for peripheral groups. However, if B is subsequently eliminated, then A must also be eliminated unless there is another macrofragment to satisfy A’s peripheral groups. The list of macrofragments, L, is rejected if all the macrofragments suggested to explain a particular multiplet are eliminated. This rule should be applied a t the beginning of each elimination cycle.
LITERATURE CITED (1)
G.Beech, R. 1.Jones, and K. Miller, Anal. Chem., 40, 714-718
(1974).
D. H. Sleeman Centre for Computer Studies The University of Leeds Leeds LS2 9JT, England
RECEIVEDfor review December 26, 1974. Accepted February 14,1975.
I AIDS FOR ANALYTICAL CHEMISTS Titanium Sublimation Pump Method for the Determination of Noble Gases in Gas Mixtures R. W. Baker, J. N. Black, E. D. Sengl, and H. A. Woltermann Monsanto Research Corporation, Mound Laboratory, Miamisburg, OH 45342
A titanium sublimation pump (TSP) method has been developed for the determination of noble gases in gas mixtures. Although helium has been utilized for most of this work, the method is equally applicable to other noble gas determinations. Previous work by Stump and Newton has demonstrated the feasibility of this approach ( I , 2 ) . The method evolved as a means for the accurate determination of the 3He decay product in mixtures containing T2 and HT. Development of the T S P method was necessary since mass spectrometry, the usual technique for analysis, is limited by the interference of the Tf ion with the 3He peak. (The mass difference between this pair is only 1 part in 100,000). Equipment and Description. This method utilizes the chemical “gettering” action of titanium to separate chemically active gases from inert gases. A simple PVT calculation is used to determine the mole percent of inert gas present in the mixture. A mass spectrometer is interfaced di-
rectly to this system and provides verification of the composition of the residual inert gas following each determination. The equipment fabricated to accomplish this analysis is shown schematically in Figure 1. This three-liter volume is constructed of 316 stainless steel whose thickness is approximately l/4 in. The interior of the volume is polished and plated with a layer of gold approximately 0.01-in. thick to minimize absorption, adsorption, and exchange effects. A water jacket surrounds the three-liter volume and maintains it to within f0.05 “C of a constant temperature by means of a Lauda TK-30DH constant-temperature circulator. Likewise, the MKS pressure head and the T S P body are thermostated to the same temperature by parallel outlets from this circulator. The titanium sublimation pump consists of a T S P filament cartridge (Varian Model 916-0017) powered by a controller (Varian Model 922-0032) ( 3 ) . Iondevices supplied ANALYTICALCHEMISTRY, VOL. 47,
NO. 8, JULY 1975
1487
