A new instrument that combines ion mobility spectrometry (IMS) separations with tandem mass spectrometry (MS n ) is described. Ion fragmentation is achieved with vacuum ultraviolet photodissociation (VUV PD) and/or collision-induced dissociation (CID). The instrument is comprised of an approximately 1 m long drift tube connected to a linear trap that has been interfaced to a pulsed F 2 laser (157 nm). Ion gates positioned in the front and the back of the primary drift region allow for mobility selection of specific ions prior to their storage in the ion trap, mass analysis, and fragmentation. The ion characterization advantages of the new instrument are demonstrated with the analysis of the isomeric trisaccharides, melezitose and raffinose. Mobility separation of precursor ions provides a means of separating the isomers and subsequent VUV PD generates unique fragments allowing them to be distinguished.

A new method is presented for constructing ion mobility distributions of precursor ions based upon the extraction of drift time distributions that are monitored for selected fragment ions. The approach is demonstrated with a recently designed instrument that combines ion mobility spectrometry (IMS) with ion trap mass spectrometry (MS) and ion fragmentation, as shown in a recent publication [J. Am. Soc. Mass Spectrom. 22 (2011) 1477–1485]. Here, we illustrate the method by examining selected charge states of electrosprayed ubiquitin ions, an extract from diesel fuel, and a mixture of phosphorylated peptide isomers. For ubiquitin ions, extraction of all drift times over small mass-to-charge (m/z) ranges corresponding to unique fragments of a given charge state allows the determination of precursor ion mobility distributions. A second example of the utility of the approach includes the distinguishing of precursor ion mobility distributions for isobaric, basic components from commercially available diesel fuel. Extraction of data for a single fragment ion is sufficient to distinguish the precursor ion mobility distribution of cycloalkyl-pyridine derivatives from pyrindan derivatives. Finally, the method is applied for the analysis of phosphopeptide isomers (LFpTGHPESLER and LFTGHPEpSLER) in a mixture. The approach alleviates several analytical challenges that include separation and characterization of species having similar (or identical) m/z values within complex mixtures.

Twenty singly-charged dipeptide ions with N-terminal arginine were photodissociated using 157 nm light in both a linear ion-trap mass spectrometer and a MALDI-TOF-TOF mass spectrometer. Analogous to previous work on dipeptides containing C-terminal arginine, this set of samples enabled insights into the photofragmentation propensities associated with individual residues. In addition to familiar products such as a-, d-, and immonium ions, m2 and m2+13 ions were also observed. Certain side chains tended to cleave between their β and γ carbons without necessarily forming d- or w-type ions, and a few other ions were produced by the high-energy fragmentation of multiple bonds.

Twenty singly-charged dipeptide ions with C-terminal arginine were photodissociated with 157 nm light and their tandem mass spectra recorded. Many of the small product ions that were observed are standard peptide fragments that have been commonly seen in VUV photodissociation studies. However, the study of a library of dipeptides containing all 20 N-terminal amino acids enabled the recognition of trends associated with the occurrence of w-, v-, and immonium ions, the observation of competition between forming N- and C-terminal fragments in dipeptide RR, and the identification of some unusual fragment ions appearing at masses of 183, 187, 196, and 197 Da. A highly accurate internal calibration of the photodissociation TOF-TOF data enabled molecular formulae for these four product ions to be derived. Their proposed structures reflect the rather high-energy nature of this fragmentation phenomenon.

Ketogenic contest preparation has become more prevalent in the bodybuilding community. However, few studies have explored the effect of minor nutrient fluctuations on daily blood and breath ketone values during prolonged in-season dieting. PURPOSE: To evaluate acute relationships between diet and ketone levels in a competitive bodybuilder. METHODS: We tracked an IFBB professional female bodybuilder for 75 consecutive days of ketogenic contest preparation. Independent variables were daily kcals consumed, proportions of fat, protein, and carbohydrate, amounts of sodium and potassium, total fluid volume, and coffee intake. We also estimated daily caloric expenditure using a FitBit Charge 3 activity tracker. Dependent variables were blood ketones measured with a Keto-Mojo device and breath ketones measured with a Ketonix Professional Breath Ketone Analyzer. We collected a fasted test each morning and repeated testing at night. Linear regressions evaluated relationships between independent and dependent variables. The prior day's behaviors served as predictors for fasted ketones; the same day's behaviors were used to predict nighttime values.