Applications of Modern Mass Spectrometry

The importance of quantifying ruminal microbial crude protein synthesis has promoted the development and comparison of several different methods for precise determination of both the amount and rate of synthesis. One major challenge is in estimating and differentiating protein in the rumen between microbial, dietary, and endogenous fractions, and to correctly isolate the solid and liquid microbial fraction of the rumen contents. This is further complicated by the goal of using non-invasive methods as much as is feasible, such as avoiding the use of fistulated animals; the selection of an appropriate microbial marker, specifically one that behaves similarly in the solid-associated and liquid-associated microbial fractions. It is also vital to be able to accurately estimate the contribution of microbial protein to overall nitrogen used by the animal, which can be accomplished by the use of 15N labeled, as assimilated by ruminal bacteria, and by the quantification of labeled nitrogen via mass spectrometry (15N/14N). This review focuses on challenges regarding accurate quantification of microbial crude protein synthesis in the rumen, as well as providing the methodology for quantification using the 15N marker. This review is based on the collection of scientific papers from the main research groups in feed and animal nutrition in ruminants.

LC-MS combines high separation ability of liquid chromatography with strong mass spectrometric structure identification. The advantages of LC-MS include high sensitivity and selectivity, minimal sample throughput, fast analysis speed and extensive structural information. It has been widely used in many fields, such as natural product analysis, pharmaceutical and food analysis, and environmental analysis.

In recent years, a great deal of researches have been conducted on the qualitative and quantitative aspects of food proteins and peptides. A variety of qualitative analyses of food proteins and peptides have been performed by LC-MS, such as accurate analysis of relative molecular weight, primary structural sequence, disulfide bond position, post-translational modifications (PTMs), etc. The quantitative analysis of proteins and peptides by LC-MS has been mainly achieved by two methods, i.e., label-free methods (peak intensities approach and spectral counting approach) and labeled methods (chemical labeling, metabolic labeling and enzymatic labeling methods). This chapter focuses on the application of qualitative and quantitative analysis of proteins and peptides in food sources.

Because of its unique capabilities, mass spectrometry is an indispensable part of life science research. In this chapter, a review is made on aids of chemometrics in life sciences applications of mass spectrometry. Because of the increasing complexity of biological samples and ongoing technological enhancements of mass spectrometers, huge sum of data are provided for each biological sample. If the routine exploratory tools are used for data exploration, much of the information is not extractable and hence it gets lost. However, chemometrics helps to explore data thoroughly and extract maximum amount of information. The most common aids of chemometrics in bio-based mass spectrometry data is for experimental design, noise reduction, classification, library search, identification of biomolecules, finding the biomarkers, data compression and data mining.

This chapter is focused on the different aspects of using chemometrics for the analysis of mass spectrometry data in omics and biomedical images. In the first part, chemometrics applications for mass data in omics sciences (metabolomics and proteomics) are revealed. The mass data in omics are mainly provided by hyphenation of mass spectrometry with chromatographic techniques, i.e., gas chromatography (GC), liquid chromatography (LC) and electrophoretic techniques. In the second part of the chapter, the benefits of using chemometrics for mass spectrometry images are revealed. The data of these images are gathered by mass spectrometer itself or hyphenation with chromatographic techniques. Since, hyphenated methods are used for both omics and biomedical imaging, some of the chemometrics methodologies used in these two disciplines may be the same.

Heavy metal ions are basic elements of earth crust. These metal ions are non-biodegradable in nature and tend to accumulate in our ecosystem in due course of time. Some of the most toxic heavy metal ions include arsenic, mercury, cadmium, lead, nickel etc. The toxicity level depends on density for any biological system. Due to increasing applications of heavy metal ion compounds in industrial, agricultural and medical fields, water pollution induced by excess levels of heavy metal ion becomes a big crisis for us. As such, detection of heavy metal ions in water is an important issue for us. Mass spectroscopy methods are the most conventionally applied methods for the detection of heavy metal ions in water. Some of the mass spectroscopic methods are atomic absorption spectroscopy, inductively coupled plasma mass spectroscopy, graphite furnace atomic absorption spectroscopy etc. These methods have well detection capability of heavy metal ions in water with good selectivity and sensitivity. Along with mass spectroscopic methods, the use of optical fiber technology for heavy metal ions detection is remarkable. Optical fiber based sensors system for the detection of heavy metal ions basically works by changing the effective refractive index of its surroundings. For selective binding of heavy metal ions, sensitive layers are coated on optical fiber probe. Laser or light emitting diode is used as a light source in an optical fiber sensor for signal purpose. Accordingly, output response for various heavy metal ions is recorded on an optical spectrometer. From their output response, we can determine the concentration of metal ions present in water. It is noticed that optical fiber sensor can also have good sensitivity and selectivity towards the detection of heavy metal ions as mass spectroscopy methods.

In forensic analytical chemistry, chemical investigation of the liquid/gas/solid evidences from the crime scene after the explosion (soil, water, concrete/glass/ wood pieces, metal, clothes taken from suspects, etc.) and reliable identification of explosive residues on such evidences remain an active area of research due to increased demand for homeland security against terrorist and warfare threats, as well as environmental monitoring. GC-MS, LC-MS, and LC-MS/MS offer distinct advantages for laboratory analysis of explosives in post-blast samples, including soil/ water/plant matrices, etc. Time-of-Flight, Ion-Trap, and Orbitrap technologies provide high resolution, better analyte identification, and accurate mass information at sub-ppm levels. Direct analysis techniques, such as ambient MS has a wider range of applications and offer high sensitivity/selectivity and direct analysis from the surface of interest. Techniques like Direct Analysis In Real Time (DART) and Desorption electrospray ionization (DESI), which can ionize substances directly on surfaces, offer new opportunities for security screening of explosives. Orbitrap MS was also used together with Raman microscopy for detailed molecular-level characterization of explosives and the chemical analysis of latent fingerprints. Electro-flow focusing ionization with in-source collision-induced dissociation can be used for MS detection and chemical imaging for speciation of the signatures of explosive devices and to detect proper spatial discrimination of explosive traces. Miniaturization to be used infield analysis with low cost is a technique work on currently. Multi-analyte detection with high selectivity/sensitivity to be able to use in as many different matrices and to be able to analyze without or with a very short and simple sample preparation methods are targeted for future analyses. Despite other reviews focussing on a certain group of techniques, this chapter summarizes some important developments in the standard MS techniques and ambient MS techniques used in laboratory, on-site, and miniaturized mass spectrometric analysis of high energetic materials in the last two decades, mostly conducted in the last decade.