A Method for High Throughput Free Fatty Acids Determination in a Small Section of Bovine Liver Tissue Using Supercritical Fluid Extraction Combined with Supercritical Fluid Chromatography-Medium Vacuum Chemical Ionization Mass Spectrometry

A novel ionization technique named medium vacuum chemical ionization (MVCI) mass spectrometry (MS), which is a chemical ionization using oxonium (H3O+) and hydroxide (OH-) formed from water, has excellent compatibility with the supercritical fluid extraction (SFE)/supercritical fluid chromatography (SFC). We have studied a method to determine free fatty acids (FFAs) in a small section of bovine liver tissue using SFE/SFC-MVCI MS analysis without further sample preparation. A series of FFA molecules interact with the C18 stationary phase, exhibiting broad chromatographic peaks when using a non-modified CO2 as the mobile phase. It can be optimized by adding a small content of methanol to the mobile phase as a modifier; however, it may dampen the ionization efficiency of MVCI since the proton affinity of methanol is slightly higher than water. We have carefully evaluated the modifier content on the ion detection and column efficiencies. The obtained result showed that an optimized performance was in the range of 1 to 2% methanol-modified CO2 mobile phase for both column efficiency and peak intensity. Higher methanol content than 2% degrades both peak intensity and column efficiency. Using optimized SFC conditions, a section of bovine liver tissue sliced for 14 µm thickness by 1 mm square, which is roughly estimated as about 3300 hepatocytes, was applied to determine 18 FFAs amounts for carbon chains of C12-C24. An amount of each tested FFA was estimated as in the range of 0.07 to 2.6 fmol per cell.

Localization of Multiple O-Linked Glycans Exhibited in Isomeric Glycopeptides by Hot Electron Capture Dissociation

We describe a method to obtain a comprehensive profile of multiple glycosylations in glycopeptide isoforms. We detected a wide range of abundances of various O-glycoforms in isomeric glycopeptides using hot electron capture dissociation (hot ECD) in liquid chromatography-tandem mass spectrometry. To capture low abundant glycosylated species, a prototype of a ZenoTOF 7600 system incorporating an efficient electron-activated dissociation device to perform hot ECD was operated in targeted or scheduled high-resolution multiple reaction monitoring workflows. In addition, Zeno trap pulsing was activated to enhance the sensitivity of the time-of-flight mass spectrometer. Sixty-nine O-glycopeptides of the long O-glycopeptides in tryptic bovine fetuin digest were obtained with a relative abundance range from 100 to 0.2%, which included sialylated glycans with Neu5Ac and Neu5Gc.

Microencapsulated Vitamin A Palmitate Degradation Mechanism Study To Improve the Product Stability

By using a high-resolution mass spectrometer, four vitamin A palmitate (VAP) degradants were identified from microencapsulated VAP degradation samples. Based on the degradants, VAP first breaks down into anhydroretinol (ANHR) and palmitic acid (PA) through ester thermal elimination (ETE). Sequentially, the formed ANHR reacts with remaining VAP to ANHR-VAP and with a second ANHR to ANHR-ANHR. The migration of H⁺ in the transition state predicts that the H⁺ concentration in media will affect the ETE. Based on the degradation mechanism discovered from this study, a new product was developed and its media pH changed from 4.2 to 6.2. The new microencapsulated VAP degraded from 22.3% to 4.8% on an annualized basis. In the VAP degradation, no oxidized apo-carotenoids were found. The oxidized apo-carotenoids were detected in the degradation of β-carotene, a pro-vitamin A, through natural oxidation by oxygen in air. This indicated that, in ambient and dry conditions on its own, VAP decay was unlike that of β-carotene through natural oxidation.

A Method for Expanding Mass Range on a Multi-Turn Time-of-Flight Mass Spectrometer by a Lap Superimposed Spectrum

A time-of-flight mass spectrometer that uses a closed-orbit flight path can achieve a high mass resolving power and a high mass accuracy with a small instrument footprint. It has long been known that a drawback to a closed flight path is an obtained spectrum may contain peaks by ions at a different number of laps. A lower m/z ion may overtake higher m/z ions, resulting in the peak being superimposed on an acquired mass spectrum; therefore, such a mass bandwidth of the analyzer is limited to a narrow range given the current situation. However, recent research has documented a solution to the problem based on careful study of the equation of motion of an ion in a closed-path analyzer. All of the ions in the analyzer remain in motion in orbit by the nature of the closed flight path, thus resulting in a superimposed spectrum with the width of the orbital period of the highest mass in the sample matrix, which contains several different lap numbers. When target ions for the sample are known in advance, the time-of-flight for a given m/z can be determined regardless of the lap number under given analyzer conditions, and peak assignment can be self-validated by comparison to a mass spectrum acquired at a different lap condition. Furthermore, the m/z value for an unknown ion can also be determined by comparing time-of-flight values on spectra acquired at different lap conditions.

Selective Extraction of a Monoisotopic Ion While Keeping the Other Ions in Flight on a Multi-Turn Time-of-Flight Mass Spectrometer

Using a multi-turn time-of-flight (TOF) mass spectrometer, we have extracted a single xenon isotope ion, ¹²⁹Xe⁺, from its orbit at given a lap number without disturbing the rest of isotopes. After detecting the ¹²⁹Xe⁺ at 20 laps, the rest of the xenon isotope spectrum was obtained at 30 laps, which generated a TOF spectrum where the TOF difference between ¹²⁹Xe⁺ and ¹³⁰Xe⁺ was 87.4 μs while ¹³⁰Xe⁺ and ¹³¹Xe⁺ were 1.03 μs. The time distance between ¹²⁹Xe⁺ and other isotopes can be set by any lap difference that is a factor of 8.7 μs, which depends on the acceleration voltage and the mass of the ion. Method accuracy was verified by comparing the isotopic abundance ratio of the xenon sample after withdrawing one of the ions from the isotope cluster to the abundance ratio obtained from the conventional method. The TOF stability was also evaluated at various lap numbers between 10 to 230.

[Development of a Method for Simultaneous Analysis of Egg and Milk Major Allergens in Beverage Products Using High-Performance Liquid Chromatography-Quadrupole Time-of-Flight Mass Spectrometry]

A method for simultaneous analysis of egg and milk allergens using LC-QTOF-MS was developed. The proteins measured were α-casein, β-lactoglobulin, and ovalbumin, which are the main protein allergens in milk and eggs. The proteins were digested using trypsin, and the digests were analyzed by LC-QTOF-MS. Sixteen peaks were detected that confirmed the amino acid sequences of the digests, and a MRM method with high resolution (MRM-HR) using product ions of these peaks was applied for quantification. Next, validation studies were performed using beverage products to which milk and egg standard protein solutions had been added. Good linearity was achieved over the concentration range of 1.25 to 20 μg/g of milk and egg protein, and acceptable reproducibility and accuracy were obtained at 10 μg/g. Moreover, good agreement was also observed between LC-QTOF-MS and ELISA. These findings suggest that this LC-QTOF-MS method may be useful for determining the milk and egg protein contents of beverages.

A new approach to improving the accuracy of elemental analysis in laser mass spectrometry

It is shown that the main reason affecting the accuracy and reproducibility of the elemental analysis of solids with a laser source of ions is the difference in the ionization cross sections of different elements in the generation of laser plasma. Computer modeling was carried out for the evaporation of the sample and generation of laser plasma at different values of laser power density. The aim of modelling was to determine the cause of the low accuracy of analysis by direct selection of ions from the plasma. The researches have shown that we cannot get satisfactory accuracy of analysis using analytical signal formed only on the base of single-charged ions. At the same time, in the formation of an analytical signal, as a sum of the intensities of the mass peaks of all charges of each element, the accuracy of the analysis does not depend either on the ionization cross section or on the nonreproducibility of the laser radiation power. It is shown that this approach completely eliminates the "matrix effect."

Separation of Isobaric Compounds Using a Spiral Orbit Type Time-of-Flight Mass Spectrometer, MALDI-SpiralTOF

The development of a MALDI-TOF mass spectrometer that utilizes spiral ion trajectory, SpiralTOF, is reported. The total flight path length was 17 m, which is five times longer than that in commonly used reflectron ion optical system. The SpiralTOF reduced the dependence of the mass resolving power on the mass of the analyte, while improving the accuracy of the mass measurements. Furthermore, SpiralTOF has two advantages that can be exploited for the separation of minor abundant isobaric components in mass spectra. One is the reduction in chemical background due to the post source decay (PSD), which is achieved through PSD ion elimination by electrostatic sectors contained within the SpiralTOF. The other is that the stabilities of peak positions are improved during mass spectrum accumulation. The peak drift caused by the fine structure of matrix crystals and the small irregularities on the sample surface can be reduced by extending the flight path. In this study, these advantages are demonstrated via the analysis of a block copolymer and mass spectrometry imaging (MSI) of lipids.

Mass Spectrometry Imaging and Structural Analysis of Lipids Directly on Tissue Specimens by Using a Spiral Orbit Type Tandem Time-of-Flight Mass Spectrometer, SpiralTOF-TOF

In this paper, we report the use of mass spectrometry imaging and structural analysis of lipids directly on a tissue specimen, carried out by means of matrix-assisted laser desorption/ionization tandem time-of-flight mass spectrometry, using a combination of spiral orbit-type and reflectron-type time-of-flight mass spectrometers. The most intense peak observed in the mass spectrum from a brain tissue specimen was confirmed as phosphatidylcholine (34 : 1) [M+K](+), using tandem mass spectrometry. The charge remote fragmentation channels, which are characteristically observed using high-energy collision-induced dissociation, contributed significantly to this confirmation. Accurate mass analysis was further facilitated by mass correction using the confirmed peak. In mass spectrometry imaging, the high resolving power of our system could separate doublet peak of less than 0.1 u difference, which would otherwise be problematic when using a low-resolution reflectron type time-of-flight mass spectrometer. Two compounds, observed at m/z 848.56 and 848.65, were found to be located in complementary positions on a brain tissue specimen. These results demonstrate the importance of a high-performance tandem time-of-flight mass spectrometer for mass spectrometry imaging and analysis of observed compounds, to allow distinction between biological molecules.