Introduction

Mass spectrometry (MS) is a highly effective qualitative and quantitative analytical technique used to identify and quantify a wide range of clinically relevant analytes.[1] Mass spectrometers expand analytical capabilities to various clinical applications when coupled with gas or liquid chromatography.[2] In addition, mass spectrometry is an essential analytical tool in proteomics due to its ability to identify and quantify proteins.[3]

Most mass spectrometry data are presented in units of the mass-to-charge ratio (m/z), where m is the molecular weight of the ion (in daltons), and z is the number of charges present on the measured molecule.[4] For small molecules (<1000 Da), there is typically only a single charge; therefore, the m/z value is the same as the mass of the molecular ion.[5] However, when larger molecules such as proteins or peptides are measured, they typically carry multiple ionic charges, and, therefore, the z-value is an integer greater than 1. The m/z value is a fraction of the ion's mass in these cases.[6]

Sample preparation is crucial for successful mass spectrometry, particularly when analyzing complex matrices commonly encountered in clinical chemistry. This process typically involves one or more of the following steps—protein precipitation followed by centrifugation or filtration, solid-phase extraction, liquid-liquid extraction, affinity enrichment, or derivatization.[7] Derivatization is the process of chemically modifying the target compounds to make them more suitable for analysis by mass spectrometry.[8] This process typically involves the addition of some well-defined functional groups.[9] The goals of derivatization vary depending on the application but typically include increased volatility, greater thermal stability, modified chromatographic properties, greater ionization efficiency, favorable fragmentation properties, or a combination of these.[10]

Mass spectrometers convert molecules into ions, which are then manipulated using electric and magnetic fields.[11] This process requires 3 main components as follows:

• Ion source: A sample is placed into the mass spectrometer, which is then ionized by the apparatus.[12]
• Mass analyzer: Ions are sorted in the device based on their mass-to-charge ratio (m/z). 
• Detector: Ions are measured and displayed on the mass spectrum chart. 

Atoms and molecules must first be ionized before being accelerated through the mass spectrometer and detected.[13] The sample molecule introduced into the mass spectrometer first gets a positive charge from an ionization source. This positive charge is achieved by removing a valence electron. Alternatively, protons can also be added to create a positive electrical charge. Once ionized, the molecule breaks apart into smaller fragments, then separated according to their mass-to-charge ratio in the mass analyzer.[1] Of note, only the cationic fragments are separated. The neutral species in the mass spectrometer go undetected as they are either absorbed by the apparatus or removed by a vacuum. After the ions are separated, the detector quantifies the ions.[11] 

A chart is generated to analyze the mass spectrometer's results, with the mass-to-charge ratio (m/z) on the x-axis and the relative intensity on the y-axis. [12] For a given sample, the most abundant ion in the sample molecule is known as the base peak.[14] This ion is set to 100% on the y-axis for its relative intensity, and all the remaining ion peaks are generated relative to this value. The molecular ion peak is known as the parent peak because it corresponds to the molecular weight of the sample.[15] For example, if the specimen in the mass spectrometer is hexane, the m/z is 86, as the molecular weight of hexane is 86 g/mol. In addition, if there is a peak at m/z=87, this is classified as the m+1 peak because all atoms have various isotopes.[11]

Specimen Requirements and Procedure

Before using the mass spectrometer, a sample must be prepared for ionization, typically by converting it into either a liquid or gaseous phase using chromatography techniques. The 2 types of chromatography procedures that are used to prepare the sample are gas chromatography and liquid chromatography.[16]

Gas Chromatography

Gas chromatography separates components of a mixture of gases and filters the passage of these molecules based on physical characteristics such as shape, size, molecular weight, and boiling point. The sample is diluted and vaporized in the chromatograph, where it is separated. After separation, the gases enter the mass spectrometer for analysis. Notably, a gas chromatography sample must be volatile, meaning it must be capable of entering the gas phase without breaking down in the mass spectrometer.[17] 

Liquid Chromatography

Liquid chromatography separates samples based on interactions with the mobile and stationary phases, often depending on polarity. If a component's polarity differs from that of the mobile phase, it migrates more quickly through the chromatography column. The sample is separated into bands of individual components that can be further analyzed in mass spectrometry.[18] Other techniques used for sample preparation include electrospray ionization, which uses high voltages to separate components, and fast atom bombardment, which uses a beam to generate ions from a solid phase.[19][20] The types of samples that can be analyzed within mass spectrometry include proteins, nucleic acids, lipids, and fatty acids.[21]

Testing Procedures

In mass spectrometry, several key components are involved in analyzing a sample.

Ionization

During ionization, atoms are ionized by removing an electron, producing a positive ion known as a cation. Mass spectrometers only analyze positive ions. Cations are formed regardless of the present state of the atoms. For example, this is true even if there is initially a negative ion in the sample, such as fluoride, or an element that does not form ions, such as neon.[22] Inside the mass spectrometer, an electrical field is generated that emits electrons. These electrons return to the electron trap, forming collisions to knock off the electrons to create cations.[23]

The most common form of ionization used in gas chromatography/mass spectrometry (GC/MS) is electron ionization. This method requires a source of electrons in the form of a filament to which an electric potential is applied, typically at 70 eV.[24] The molecules in the source are bombarded with high-energy electrons, resulting in the formation of charged molecular ions and fragments. Molecules break down into characteristic fragments according to their molecular structure.[25] The resulting ions and their relative proportions are reproducible, enabling the qualitative identification of compounds.[26]

Unlike electron ionization in GC/MS, most liquid chromatography/mass spectrometry (LC/MS) ionization techniques are conducted at atmospheric pressure. Electrospray ionization and atmospheric pressure chemical ionization are soft ionization techniques that leave the molecular ion largely intact in the source.[27] Many LC/MS techniques use technologies after the source, in the mass analyzer, to fragment molecules and generate the daughter or fragment ions used in identification.[28] However, ionization techniques in LC/MS produce fragments and, therefore, mass spectra that are somewhat less reproducible between instruments compared to the electron ionization method used in gas GC/MS.[29]

Electrospray ionization uses a combination of voltage, heat, and air to produce successively smaller droplets from the liquid, eluting off a chromatographic column.[30] As the solvent evaporates, the droplets become more concentrated, significantly increasing charge per unit volume. Ions accumulated at the droplet surface desorb from the liquid into the gas phase, allowing these gas phase ions to enter the mass spectrometer for analysis.[31] In addition, complete evaporation of the solvent liberates large ions, such as proteins, producing the necessary gas phase ions for analysis.[32] Atmospheric pressure chemical ionization produces ions using a combination of heat to completely vaporize the sample and plasma produced by an electrical discharge, commonly referred to as a corona discharge.[33] The corona discharge ionizes the evaporated solvent, and through physical interaction with gaseous sample components, including the analytes of interest, positive or negative ions are formed.[34]

Acceleration

All ions undergo acceleration to achieve the same amount of kinetic energy. Cations pass through slits in the mass spectrometer apparatus and accelerate into the ion beam, allowing the mass analyzer to start separating the ions based on the mass-to-charge ratio.[35]

Deflection

A magnetic field deflects the cations based on their mass and charge. Mass and deflection are inversely proportional, whereas charge and deflection are directly proportional. Therefore, ions with a lower mass are deflected more, and ions with a higher positive charge experience greater deflection.[36] This process allows the apparatus to determine the mass-to-charge ratio. The mass-to-charge ratio is denoted by m/z. For example, if an ion has a mass of 120 and a charge of 3+, the m/z ratio is 40. Notably, most ions passing through the mass spectrometer carry a charge of 1+, meaning their mass (or molecular weight) is typically equivalent to the m/z value.[37]

Detection

In mass spectrometry, a detector quantifies the ions and removes certain ones. Positive ions are detected using the apparatus, whereas neutral ions are removed by the vacuum.[38] The most common detection method is the electron multiplier.[39] In this detector, a series of dynodes with increasing potentials are linked. When ions strike the first dynode surface, electrons are emitted. These electrons are attracted to the next dynode, where more secondary electrons are emitted due to the higher potential of subsequent dynodes. A cascade of electrons is formed by the end of the chain of dynodes, resulting in overall signal amplification on the order of 1 million or greater.[40]

Vacuum

Mass spectrometers operate at low pressure, which creates a vacuum effect as there is less probability that ions collide with one another in the apparatus. This environment facilitates the proper separation of cations from the neutral ions, as the vacuum removes the neutral molecules.[41]

Interfering Factors

The primary sources of interference in mass spectrometry typically occur during sample preparation and the measurement of separated ions within the spectrometer. Interference can occur due to inaccurate sample handling when acquiring from patients or improper quality control.[42] Interference alters the concentration of the molecules, which can result in the inaccuracy of the mass spectrometer graph due to potential contaminants or other ions appearing.[43]

Results, Reporting, and Critical Findings

Mass spectrometry produces results for the mass-to-charge ratio of ions in a compound.[2] The results are reproduced on a graph known as a mass spectrum, which plots the relative abundance of ions versus the mass-to-charge ratio.[3] The spectra showcase elements and isotopes to configure a given compound's chemical identity and structure.[14] The graph should be analyzed to deduce the structural quality of the compound based on the mass spectrometer. The graph consists of 3 main components and an additional component depending on the isotopes present in the sample, which are relevant for determining the structure.

• Molecular ion peak (or parent peak): This is the second-highest peak that corresponds directly to the compound in question. The m/z ratio directly correlates to the molecular weight. For example, if hexane is the compound, the m/z ratio is 86, reflecting its molecular weight of 86 g/mol.[44]
• Base peak: This is the ion with the highest relative abundance in the compound out of all the ions in the given sample. The relative intensity of this ion is set to 100%, and all other ion peaks are set relative to this value.[45] 
• M+1 peak: This smaller peak corresponds to an isotope in the sample. For example, if the molecular weight of the specimen is 96 g/mol, the m/z ratio is 96. Thus, the m+1 peak is at an m/z of 97. Although it may seem confusing for an ion to have a mass greater than the compound itself, this occurs due to isotopes of elements, such as carbon and hydrogen, contributing to the formation of the m+1 peak.[46] 
• M+2 peak: This is another small peak similar to the m+1 peak. Certain elements, such as chlorine and oxygen, have multiple isotopes, which is why these elements in a given compound can result in an m+2 peak.[46]

Clinical Significance

Mass spectrometry is applicable across diverse fields, including forensic toxicology, metabolomics, proteomics, pharma/biopharma, and clinical research. Specific applications of mass spectrometry include drug testing and discovery, food contamination detection, pesticide residue analysis, isotope ratio determination, protein identification, and carbon dating.[47] 

Applications of Mass Spectrometry in the Diagnosis of Disease

Mass spectrometers are primarily used in clinical settings to diagnose diseases due to biomarkers. Biomarkers are used in diagnoses, prognoses, and treatment.[48] For example, the enzyme amylase can be used as a biomarker for pancreatitis in disease diagnosis. Similarly, natriuretic peptides are monitored in patients with cardiovascular diseases to predict patient outcomes. Mass spectrometry can be used to examine the metabolic profile of pharmacologic agents to monitor the efficacy of certain therapies.[49]

Mass spectrometers can measure biomarkers, ranging in size from small molecules to large macromolecules.[50] The principle of mass spectrometers also applies to human body samples such as plasma and serum blood, urine, saliva, sweat, and skin secretions.[2] Using liquid or gas chromatography allows for biomarkers to be separated and analyzed in smaller pieces, which optimizes the sensitivity and specificity of the spectrometer. Thus, mass spectrometers thereby improve clinical decision-making.[6] Mass spectrometers analyze a sample and its biomarker profile to diagnose disease. Of note, 2 critical biomarkers are proteins and lipids.[13] In earlier examples, it was stated that enzymes, which are proteins, can be used to detect diseases. Similarly, a lipid panel has often been used to diagnose diseases such as metabolic syndrome.[1]

If the biomarker is a protein, the principles of proteomics can be applied to mass spectrometry.[13] Mass spectrometry has been used to quantify differences between 2 biological states of proteomes, a set of proteins produced in a specific organism. A protein sample is placed into the spectrometer, and the mass of the individual components of the protein is tagged based on the isotopes generated through spectral analyses.[2] The mass spectrometer is useful in this setting because it generates spectral data for proteomes, allowing the human body to analyze proteins in urine and serum.[3]

If the biomarker is a lipid, the principles of lipidomics can be applied to generate a clinical profile for the patient using mass spectrometry.[21] Lipidomics consists of the lipid profile and set of reactions generated within biology. Lipids are used for energy storage and assist in the endocrine regulation of the body system.[51] Mass spectrometry has been used to characterize masses of important ingredients in lipid oxidation reactions, helping quantify the various molecules of lipid reactions and, thus, their biological properties within the human body.[52]

Applications of Mass Spectrometry in COVID-19

During the peak of the coronavirus pandemic, many countries were hindered by inadequate testing due to supply chain shortages and inconsistencies in mass-produced testing kits. Clinical laboratories thus created a method to use mass spectrometry. Nasal swab samples of patients were analyzed using mass spectrometry, and the pattern generated by the spectrum was used to categorize patients if they were COVID-19 positive or negative.[53]

Applications of Mass Spectrometry in Pharmaceuticals

Mass spectrometry plays a crucial role in the analysis of pharmaceutical drugs. The ionization process within the apparatus helps differentiate the molecules that create the drugs. This capability is essential for conducting faster and more accurate screenings during clinical analysis of patient samples, leading to improved drug monitoring and safety.[54]

Applications of Mass Spectrometry in the Analysis of Glycans

Oligosaccharides are molecules formed by associating several monosaccharides linked through glycosidic bonds. Determining the complete structure of oligosaccharides is more complex compared to that of proteins or oligonucleotides. This process involves the determination of additional components as a consequence of the isomeric nature of monosaccharides and their capacity to form linear or branched oligosaccharides.[55] Knowing the structure of an oligosaccharide requires not only the determination of its monosaccharide sequence and its branching pattern but also the isomer position and the anomeric configuration of each of its glycosidic bonds.[56] Advances in glycobiology involve a comprehensive study of the structure, biosynthesis, and biology of sugars and saccharides. Mass spectrometry is emerging as an enabling technology in the field of glycomics and glycobiology.[57]

Applications of Mass Spectrometry in the Analysis of Oligonucleotides

Oligonucleotides, DNA or RNA, are linear polymers of nucleotides. These nucleotides are composed of a nitrogenous base, a ribose sugar, and a phosphate group.[58] Oligonucleotides may undergo several natural covalent modifications, which are commonly present in transfer RNA and ribosomal RNA, or unnatural ones resulting from reactions with exogenous compounds.[59] Mass spectrometry plays a vital role in identifying these modifications and determining their structure and position in the oligonucleotide. This technique allows the determination of the molecular weight of oligonucleotides and, directly or indirectly, their sequences.[60]

Applications of Mass spectrometry in Environmental Analysis

Drinking water testing, pesticide screening and quantitation, soil contamination assessment, monitoring carbon dioxide levels and pollution and conducting trace elemental analysis of heavy metals leaching.[61]

Applications of Mass Spectrometry in Forensic Analysis

In forensic science, mass spectrometry is used to analyze trace evidence, such as fibers from carpets and polymers found in paints. Mass spectrometry is also essential in arson investigations to detect fire accelerants, confirm drug abuse, and identify explosive residues in bombing investigations.[62]

Quality Control and Lab Safety

When working in the laboratory, it is crucial to exercise caution while preparing samples before introducing the compound into the mass spectrometer for analysis. For example, using the proper measuring tools for accuracy during chromatography is essential.[63] If quality control is not used, resultant peaks may form in the mass spectrum, which does not correspond to ions within the sample.[64] 

Operating the mass spectrometer requires safety to be taken into consideration. The mass spectrometer apparatus can have high temperatures, resulting in burns. Thus, it is important not to touch any part of the apparatus while the spectral data is generated. In addition, ionization occurs within the device, so it is essential to be cautious when running a mass spectrometer. Lastly, the samples placed in the spectrometer could be hazardous upon exposure to the skin or inhalation.[65] Thus, wearing the appropriate personal protective equipment, such as safety glasses, long pants, closed-toed shoes, a long lab coat, and gloves, is highly recommended.[66]

Enhancing Healthcare Team Outcomes

Interprofessional communication is essential when using mass spectrometers. For example, if a patient presents to the emergency department after ingesting an unknown compound, lab technicians and pathologists can analyze the patient's sample to identify the components present in the substance. This collaboration enables laboratory professionals to support healthcare workers, including nurses and physicians, in hospital or clinic settings.

In the emergency room, clinicians play a crucial role in fostering this interprofessional environment by sharing the patient's medical history and physical examination findings. This information can help narrow the possible compounds in the patient's sample, facilitating a more accurate and timely diagnosis and treatment plan.

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References

1.

Király M, Dalmadiné Kiss B, Vékey K, Antal I, Ludányi K. [Mass spectrometry: past and present]. Acta Pharm Hung. 2016;86(1):3-11. [PubMed: 27295872]

2.

Matthiesen R, Bunkenborg J. Introduction to mass spectrometry-based proteomics. Methods Mol Biol. 2013;1007:1-45. [PubMed: 23666720]

3.

Zhang G, Annan RS, Carr SA, Neubert TA. Overview of peptide and protein analysis by mass spectrometry. Curr Protoc Protein Sci. 2010 Nov;Chapter 16:Unit16.1. [PubMed: 21104985]

4.

Urban PL. Quantitative mass spectrometry: an overview. Philos Trans A Math Phys Eng Sci. 2016 Oct 28;374(2079) [PMC free article: PMC5031646] [PubMed: 27644965]

5.

Sugai T. Mass and Charge Measurements on Heavy Ions. Mass Spectrom (Tokyo). 2017;6(3):S0074. [PMC free article: PMC5745234] [PubMed: 29302406]

6.

Domon B, Aebersold R. Mass spectrometry and protein analysis. Science. 2006 Apr 14;312(5771):212-7. [PubMed: 16614208]

7.

Wilschefski SC, Baxter MR. Inductively Coupled Plasma Mass Spectrometry: Introduction to Analytical Aspects. Clin Biochem Rev. 2019 Aug;40(3):115-133. [PMC free article: PMC6719745] [PubMed: 31530963]

8.

Finoulst I, Pinkse M, Van Dongen W, Verhaert P. Sample preparation techniques for the untargeted LC-MS-based discovery of peptides in complex biological matrices. J Biomed Biotechnol. 2011;2011:245291. [PMC free article: PMC3238806] [PubMed: 22203783]

9.

Guerrasio R, Haberhauer-Troyer C, Steiger M, Sauer M, Mattanovich D, Koellensperger G, Hann S. Measurement uncertainty of isotopologue fractions in fluxomics determined via mass spectrometry. Anal Bioanal Chem. 2013 Jun;405(15):5133-46. [PubMed: 23559335]

10.

Vilbaste M, Tammekivi E, Leito I. Uncertainty contribution of derivatization in gas chromatography/mass spectrometric analysis. Rapid Commun Mass Spectrom. 2020 Aug 30;34(16):e8704. [PubMed: 31845399]

11.

Haag AM. Mass Analyzers and Mass Spectrometers. Adv Exp Med Biol. 2016;919:157-169. [PubMed: 27975216]

12.

Olshina MA, Sharon M. Mass Spectrometry: A Technique of Many Faces. Q Rev Biophys. 2016 Jan;49 [PMC free article: PMC5238952] [PubMed: 28100928]

13.

Bantscheff M, Schirle M, Sweetman G, Rick J, Kuster B. Quantitative mass spectrometry in proteomics: a critical review. Anal Bioanal Chem. 2007 Oct;389(4):1017-31. [PubMed: 17668192]

14.

Alexandrov T, Chernyavsky I, Becker M, von Eggeling F, Nikolenko S. Analysis and interpretation of imaging mass spectrometry data by clustering mass-to-charge images according to their spatial similarity. Anal Chem. 2013 Dec 03;85(23):11189-95. [PubMed: 24180335]

15.

Buchberger AR, DeLaney K, Johnson J, Li L. Mass Spectrometry Imaging: A Review of Emerging Advancements and Future Insights. Anal Chem. 2018 Jan 02;90(1):240-265. [PMC free article: PMC5959842] [PubMed: 29155564]

16.

Bourgogne E, Wagner M. [Sample preparation and bioanalysis in mass spectrometry]. Ann Biol Clin (Paris). 2015 Jan-Feb;73(1):11-23. [PubMed: 25582719]

17.

Fothergill WT. Gas chromatography. Technique. Proc R Soc Med. 1968 May;61(5):525-8. [PMC free article: PMC1902480] [PubMed: 5655250]

18.

Rappold BA. Review of the Use of Liquid Chromatography-Tandem Mass Spectrometry in Clinical Laboratories: Part I-Development. Ann Lab Med. 2022 Mar 01;42(2):121-140. [PMC free article: PMC8548246] [PubMed: 34635606]

19.

Meher AK, Chen YC. Electrospray Modifications for Advancing Mass Spectrometric Analysis. Mass Spectrom (Tokyo). 2017;6(Spec Iss):S0057. [PMC free article: PMC5448333] [PubMed: 28573082]

20.

Hemling ME. Fast atom bombardment mass spectrometry and its application to the analysis of some peptides and proteins. Pharm Res. 1987 Feb;4(1):5-15. [PubMed: 3334162]

21.

Züllig T, Köfeler HC. HIGH RESOLUTION MASS SPECTROMETRY IN LIPIDOMICS. Mass Spectrom Rev. 2021 May;40(3):162-176. [PMC free article: PMC8049033] [PubMed: 32233039]

22.

Lin JL, Chu ML, Chen CH. A portable multiple ionization source biological mass spectrometer. Analyst. 2020 May 18;145(10):3495-3504. [PubMed: 32186555]

23.

Huang MZ, Cheng SC, Cho YT, Shiea J. Ambient ionization mass spectrometry: a tutorial. Anal Chim Acta. 2011 Sep 19;702(1):1-15. [PubMed: 21819855]

24.

Maciel EVS, Pereira Dos Santos NG, Vargas Medina DA, Lanças FM. Electron ionization mass spectrometry: Quo vadis? Electrophoresis. 2022 Aug;43(15):1587-1600. [PubMed: 35531989]

25.

Margolin Eren KJ, Elkabets O, Amirav A. A comparison of electron ionization mass spectra obtained at 70 eV, low electron energies, and with cold EI and their NIST library identification probabilities. J Mass Spectrom. 2020 Dec;55(12):e4646. [PubMed: 32996658]

26.

Famiglini G, Palma P, Termopoli V, Cappiello A. The history of electron ionization in LC-MS, from the early days to modern technologies: A review. Anal Chim Acta. 2021 Jul 04;1167:338350. [PubMed: 34049632]

27.

Commisso M, Anesi A, Dal Santo S, Guzzo F. Performance comparison of electrospray ionization and atmospheric pressure chemical ionization in untargeted and targeted liquid chromatography/mass spectrometry based metabolomics analysis of grapeberry metabolites. Rapid Commun Mass Spectrom. 2017 Feb 15;31(3):292-300. [PubMed: 27935129]

28.

Tian H, Bai J, An Z, Chen Y, Zhang R, He J, Bi X, Song Y, Abliz Z. Plasma metabolome analysis by integrated ionization rapid-resolution liquid chromatography/tandem mass spectrometry. Rapid Commun Mass Spectrom. 2013 Sep 30;27(18):2071-80. [PubMed: 23943328]

29.

Berisha A, Dold S, Guenther S, Desbenoit N, Takats Z, Spengler B, Römpp A. A comprehensive high-resolution mass spectrometry approach for characterization of metabolites by combination of ambient ionization, chromatography and imaging methods. Rapid Commun Mass Spectrom. 2014 Aug 30;28(16):1779-91. [PubMed: 25559448]

30.

Tycova A, Prikryl J, Kotzianova A, Datinska V, Velebny V, Foret F. Electrospray: More than just an ionization source. Electrophoresis. 2021 Jan;42(1-2):103-121. [PubMed: 32841405]

31.

Wilm M. Principles of electrospray ionization. Mol Cell Proteomics. 2011 Jul;10(7):M111.009407. [PMC free article: PMC3134074] [PubMed: 21742801]

32.

Wilm M. Principles of electrospray ionization. Mol Cell Proteomics. 2011 May 19; [PubMed: 21597042]

33.

Pitman CN, LaCourse WR. Desorption atmospheric pressure chemical ionization: A review. Anal Chim Acta. 2020 Sep 15;1130:146-154. [PubMed: 32892934]

34.

Byrdwell WC. Atmospheric pressure chemical ionization mass spectrometry for analysis of lipids. Lipids. 2001 Apr;36(4):327-46. [PubMed: 11383683]

35.

Lee JK, Banerjee S, Nam HG, Zare RN. Acceleration of reaction in charged microdroplets. Q Rev Biophys. 2015 Nov;48(4):437-44. [PMC free article: PMC5446060] [PubMed: 26537403]

36.

Nier KA. Dempster's descendants-The core of the development of mass spectrometry. J Mass Spectrom. 2020 Aug;55(8):e4353. [PubMed: 30900786]

37.

Budzikiewicz H, Grigsby RD. Mass spectrometry and isotopes: a century of research and discussion. Mass Spectrom Rev. 2006 Jan-Feb;25(1):146-57. [PubMed: 16134128]

38.

Elliott AG, Merenbloom SI, Chakrabarty S, Williams ER. Single Particle Analyzer of Mass: A Charge Detection Mass Spectrometer with a Multi-Detector Electrostatic Ion Trap. Int J Mass Spectrom. 2017 Mar;414:45-55. [PMC free article: PMC5676562] [PubMed: 29129967]

39.

Shan L, Gao H, Zhang J, Li W, Su Y, Guo Y. Plasma and serum exosome markers analyzed by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry coupled with electron multiplier. Talanta. 2022 Sep 01;247:123560. [PubMed: 35623246]

40.

Tsybin YO, Witt M, Baykut G, Håkansson P. Electron capture dissociation Fourier transform ion cyclotron resonance mass spectrometry in the electron energy range 0-50 eV. Rapid Commun Mass Spectrom. 2004;18(14):1607-13. [PubMed: 15282786]

41.

Guo C, Diao Z, Liu J, Yang B, Zhang J. Quantification and evaluation of ion transmission efficiency in two-stage vacuum chamber miniature mass spectrometer. J Mass Spectrom. 2022 Mar;57(3):e4816. [PubMed: 35229406]

42.

Keller BO, Sui J, Young AB, Whittal RM. Interferences and contaminants encountered in modern mass spectrometry. Anal Chim Acta. 2008 Oct 03;627(1):71-81. [PubMed: 18790129]

43.

Kim BK, Gwon MR, Kang WY, Lee IK, Lee HW, Seong SJ, Cho S, Yoon YR. Rapid Interference-free Analysis of β-Lapachone in Clinical Samples Using Liquid Chromatography-Mass Spectrometry for a Pharmacokinetic Study in Humans. Anal Sci. 2021 Aug 10;37(8):1105-1110. [PubMed: 33390413]

44.

Goraczko AJ. Molecular mass and location of the most abundant peak of the molecular ion isotopomeric cluster. J Mol Model. 2005 Sep;11(4-5):271-7. [PubMed: 15928922]

45.

Steeves JB, Gagne HM, Buel E. Normalization of residual ions after removal of the base peak in electron impact mass spectrometry. J Forensic Sci. 2000 Jul;45(4):882-5. [PubMed: 10914589]

46.

Grange AH, Donnelly JR, Sovocool GW, Brumley WC. Determination of elemental compositions from mass peak profiles of the molecular ion (m) and the m + 1 and m + 2 ions. Anal Chem. 1996 Feb 01;68(3):553-60. [PubMed: 21619089]

47.

Zhang XW, Li QH, Xu ZD, Dou JJ. Mass spectrometry-based metabolomics in health and medical science: a systematic review. RSC Adv. 2020 Jan 16;10(6):3092-3104. [PMC free article: PMC9048967] [PubMed: 35497733]

48.

Furlani IL, da Cruz Nunes E, Canuto GAB, Macedo AN, Oliveira RV. Liquid Chromatography-Mass Spectrometry for Clinical Metabolomics: An Overview. Adv Exp Med Biol. 2021;1336:179-213. [PubMed: 34628633]

49.

Heaney LM, Jones DJ, Suzuki T. Mass spectrometry in medicine: a technology for the future? Future Sci OA. 2017 Aug;3(3):FSO213. [PMC free article: PMC5583653] [PubMed: 28884010]

50.

Carneiro G, Radcenco AL, Evaristo J, Monnerat G. Novel strategies for clinical investigation and biomarker discovery: a guide to applied metabolomics. Horm Mol Biol Clin Investig. 2019 Jan 17;38(3) [PubMed: 30653466]

51.

Han X, Yang K, Gross RW. Multi-dimensional mass spectrometry-based shotgun lipidomics and novel strategies for lipidomic analyses. Mass Spectrom Rev. 2012 Jan-Feb;31(1):134-78. [PMC free article: PMC3259006] [PubMed: 21755525]

52.

Del Carmen Piqueras M. Utility of Moderate and High-Resolution Mass Spectrometry for Class-Specific Lipid Identification and Quantification. Methods Mol Biol. 2017;1609:83-90. [PubMed: 28660576]

53.

SoRelle JA, Patel K, Filkins L, Park JY. Mass Spectrometry for COVID-19. Clin Chem. 2020 Nov 01;66(11):1367-1368. [PMC free article: PMC7543316] [PubMed: 32956447]

54.

Loos G, Van Schepdael A, Cabooter D. Quantitative mass spectrometry methods for pharmaceutical analysis. Philos Trans A Math Phys Eng Sci. 2016 Oct 28;374(2079) [PMC free article: PMC5031633] [PubMed: 27644982]

55.

Zaia J. Mass spectrometry and glycomics. OMICS. 2010 Aug;14(4):401-18. [PMC free article: PMC3133787] [PubMed: 20443730]

56.

Wuhrer M. Glycomics using mass spectrometry. Glycoconj J. 2013 Jan;30(1):11-22. [PMC free article: PMC3547245] [PubMed: 22532006]

57.

Leymarie N, Zaia J. Effective use of mass spectrometry for glycan and glycopeptide structural analysis. Anal Chem. 2012 Apr 03;84(7):3040-8. [PMC free article: PMC3319649] [PubMed: 22360375]

58.

Crain PF, McCloskey JA. Applications of mass spectrometry to the characterization of oligonucleotides and nucleic acids. Curr Opin Biotechnol. 1998 Feb;9(1):25-34. [PubMed: 9503584]

59.

Basiri B, Bartlett MG. LC-MS of oligonucleotides: applications in biomedical research. Bioanalysis. 2014 Jun;6(11):1525-42. [PubMed: 25046052]

60.

Meng Z, Simmons-Willis TA, Limbach PA. The use of mass spectrometry in genomics. Biomol Eng. 2004 Jan;21(1):1-13. [PubMed: 14715314]

61.

Hernández F, Sancho JV, Ibáñez M, Abad E, Portolés T, Mattioli L. Current use of high-resolution mass spectrometry in the environmental sciences. Anal Bioanal Chem. 2012 May;403(5):1251-64. [PubMed: 22362279]

62.

Hoffmann WD, Jackson GP. Forensic Mass Spectrometry. Annu Rev Anal Chem (Palo Alto Calif). 2015;8:419-40. [PubMed: 26070716]

63.

Masson P. Quality control techniques for routine analysis with liquid chromatography in laboratories. J Chromatogr A. 2007 Jul 27;1158(1-2):168-73. [PubMed: 17418222]

64.

Cooper PJ, Charnock DJ, Taylor MJ. The prevalence of bulimia nervosa. A replication study. Br J Psychiatry. 1987 Nov;151:684-6. [PubMed: 3446313]

65.

Bonnel D, Stauber J. Applications of Mass Spectrometry Imaging for Safety Evaluation. Methods Mol Biol. 2017;1641:129-140. [PubMed: 28748461]

66.

Cornish NE, Anderson NL, Arambula DG, Arduino MJ, Bryan A, Burton NC, Chen B, Dickson BA, Giri JG, Griffith NK, Pentella MA, Salerno RM, Sandhu P, Snyder JW, Tormey CA, Wagar EA, Weirich EG, Campbell S. Clinical Laboratory Biosafety Gaps: Lessons Learned from Past Outbreaks Reveal a Path to a Safer Future. Clin Microbiol Rev. 2021 Jun 16;34(3):e0012618. [PMC free article: PMC8262806] [PubMed: 34105993]

Disclosure: Eshita Garg declares no relevant financial relationships with ineligible companies.

Disclosure: Muhammad Zubair declares no relevant financial relationships with ineligible companies.