Numerous low-Mr metabolites--including creatinine, citrate, hippurate, glucose, ketone bodies, and various amino acids--have been identified in 400- and 500-MHz proton nuclear magnetic resonance (1H NMR) spectra of intact human urine. The presence of many of these was related to the specific condition of the donors: humans in different physiological states (resting, fasting, or post-exercise) and pathological conditions (e.g., diabetes mellitus, cadmium-induced renal dysfunction). We have also monitored the metabolism of simple nonendogenous compounds (methanol and ethanol) and of acetaminophen. The pH-dependencies of the NMR chemical shifts of some urine components are reported. Our studies show that high-resolution 1H NMR spectroscopy provides a fast, simple method for "fingerprint" identification of urinary compounds. In some cases, analytes can be quantified by standard additions or by comparing integrated peak areas for the metabolites with those for creatinine. Determinations of creatinine by 1H NMR spectroscopy compared well with those by an independent chemical assay based on the Jaffé reaction.

have similar probability of occurring. Since h'-f*y-h\y*y are all differentiable in a totally symmetric environment, detailed nmr line shape analysis may allow distinction between "helical" movement of the aliene ligand and isomerization via an intermediate configuration having coplanar allenyl methyl groups. Note that this final example has been simplified by assuming that rapid " -rotation" about the metalallene band does not occur.Should such rotation in fact occur, the distinction will be impossible.

THIS paper attempts (i) to review critically some (but not all) of the techniques which have come to be used by organic chemists during the past few years to infer positive ion structures and mechanisms for the production of fragment ions in the mass spectrometer, and (ii) to consider qualitatively some of the factors which determine the nature of mass spectra. The review is not intended by any means to be exhaustive and reference will therefore not be made to much of the earlier fundamentally important work. Rather, we will concentrate upon the possible pitfalls of energetic considerations, aspects of the kinetic approach (metastable characteristics and substituent effects) and the care required in the interpretation of deuterium labelling results. 1 137 * Obviously, since unimolecular decay is involved, not all ions with k 5 lo5 set.-' will give rise to metastables; the probability of a givcn ion with a given rate constant for fragmentation being observed as a daughter, a metastable ion, or as such, is instrument dependent and calculations have been made in some cases-see Fig. 115 in Ref. 20, Fig. 7, in Ref. 2, and Fig. 8 in Ref. 5. t This will not be true if there is a minimum ratezG for the reaction so that kmin > 106 set.-'.The occurrence of minimum rates for fragmentations and their effect on the shape of k vs. Ecurves is an important but largely unexplored problem.21v2G m*

No abstract

The effect of the addition of argon and other gases upon the intensities of negative ion species formed in an electron impact source has been investigated. The negative ion current generated for a series of aromatic compounds has been investigated as a function both of sample and argon pressure in the ion source of a ZAB-ZF mass spectrometer. For all compounds studied, a striking enhancement of molecular negative ion current occurred on increasing either the pressure of the sample or of argon. The results are consistent with thermalization of the 50 eV electrons by collisions with neutral molecules in the high pressure ion source and collisional stabilization of the negative ions initially formed. Analytical applications of the technique are discussed.

Results are presented (relative ion abundances, I.P. and A.P. measurements) to illustrate substituent effects in the mass spectra of some y-and P-substituted methyl butyrates. It is argued that (i) ' sub-decomposition energy ' ions and (ii) competition in the source with fast fragmentation processes are important factors influencing parent/ daughter ion ratios, which are then rationalised in terms of the variation of these two factors with substituent. In certain cases a substituent effect on the energy of activation of the transition state is also invoked. The variation in parent/daughter ratios at different energies is explained in terms of relative A.P.'s and frequency factors. Mechanisms are discussed for the elimination of MeOH from M+ and for the McLafferty rearrangement. Albany, Albany, N.Y. 12203 BURSEY and McLafferty pioneered the study of substituent effects in mass spectrometry and their early work has been summarised.l Recent considerations 2-5of the basic factors involved in the formation, fragmentation, and collection of organic ions at low pressures in a mass spectrometer has led to recognition of complications in the interpretation of decomposition rates in terms of daughter/parent ion ratios. This has resulted in an enumeration of the variables which influence substituent effects, measured in terms of this parameter, in mass spectrometry. The situation is summarised in a recent review .'j

The fundamental processes of protonation and ethylation, occurring in a methane chemical ionization source, have been investigated for a variety of aromatic amines. The positions of protonation and ethylation on the substrate amines were determined by generating isomeric ions either by protonation of neutral ethyl substituted amines or by ethylation of the amines themselves. The product ions were investigated for structural differences via collision induced dissociation and subsequent analysis via mass analysed ion kinetic energy spectrometry. Similarities and differences between mass analysed ion kinetic energy/collision induced dissociation spectra of these isomeric ions were used to determine protonation and ethylation sites for imidazole, benzimidazole, indazole, pyrrole, pyridine and aniline.

Col&sion with neutral molecules is shown to provide a convenient method of adding internal energy to ions in a field-free drift region of the mass spectrometer. The effects on this process of ion accelerating potential, target gas pressure and identity, and precursor ion internal energy and mass have been investigated to optimize experimental conditions. Such collisions cause ion decompositions whose activation energies cover a broad range; for a particular ion such decompositions can be viewed as its "collisional activation (CA) spectrum." CA spectra, which can be obtained for each ion in the normal mass spectrum, and which appear to follow the predictions of the quasi equilibrium theory, show many more of the possible unimolecular ion decomposition reactions for an ion than do unimolecular metastables, and thus provide valuable information for ion reaction mechanisms and molecular structure detemhation. Collisional activation can sometimes yield ion energies which are relatively inaccessible by electron impact. The precursor ion internal energy has a negligible effect on the ion's CA spectrum except for product ions formed through the processes of lowest activation energy. Thus, CA spectra should also be valuable for the characterization of ion structures. he dissociation of a metastable organic ion in a (7) T. Wachs, P. F.