The Kendrick mass is defined by setting the mass of a chosen molecular fragment, typically CH2, to an integer value in amu (atomic mass units). It is different from the IUPAC definition, which is based on setting the mass of 12C isotope to exactly 12 amu. The Kendrick mass is often used to identify homologous compounds differing only by a number of base units in high resolution mass spectra.[1][2] This definition of mass was first suggested in 1963 by chemist Edward Kendrick,[1] and it has been adopted by scientists working in the area of high-resolution mass spectrometry, environmental analysis,[3][4][5][6]proteomics, petroleomics,[2]metabolomics,[7] polymer analysis,[8] etc.
Other groups of atoms in addition to CH2 can be used define the Kendrick mass, for example CO2, H2, H2O, and O.[12][14][15] In this case, the Kendrick mass for a family of compounds F is given by
.
For the hydrocarbon analysis, F=CH2.
As an example, Kendrick analysis has been used for visualizing families of halogenated compounds of environmental interest that differ only by the number of chlorine, bromine or fluorine substitutions.[4][5]
A recent publication has suggested that Kendrick mass be expressed in Kendrick units with symbol Ke.[16]
In recent years the equation has changed due to rounding errors to:
The members of an alkylation series have the same degree of unsaturation and number of heteroatoms (nitrogen, oxygen and sulfur) but differ in the number of CH2 units. Members of an alkylation series have the same Kendrick mass defect.
The abbreviations KM and KMD have been used for Kendrick mass and Kendrick mass defect, respectively.[20]
Kendrick mass analysis
Plot of Kendrick mass defect as function of Kendrick mass; horizontal lines indicate common repeat units. Each dot in the plot corresponds to a peak measured in a mass spectrum.
In a Kendrick mass analysis, the Kendrick mass defect is plotted as function of nominal Kendrick mass for ions observed in a mass spectrum.[11] Ions of the same family, for example the members of an alkylation series, have the same Kendrick mass defect but different nominal Kendrick mass and are positioned along a horizontal line on the plot. If the composition of one ion in the family can be determined, the composition of the other ions can be inferred. Horizontal lines of different Kendrick mass defect correspond to ions of different composition, for example degree of saturation or heteroatom content.
A Kendrick mass analysis is often used in conjunction with a Van Krevelen diagram, a two- or three- dimensional graphical analysis in which the elemental composition of the compounds are plotted according to the atomic ratios H/C, O/C, or N/C.[12][21]
Kendrick mass defect analysis of polymers and alternative base units
Because Kendrick mass defect analysis can be carried out by substituting any repeating unit for CH2, KMD analysis is particularly useful for the visualizing the data from polymer mass spectra.[8][22] For example, a Kendrick mass defect plot of an ethylene oxide/propylene oxide copolymer can be created by using ethylene oxide (C2H4O) as the base unit and calculating the Kendrick mass as:
where 44.02621 is the calculated IUPAC mass for C2H4O. Alternatively, a KMD plot can be constructed for the same copolymer by using propylene oxide as the base unit.
Polymer mass spectra containing multiple charge ions exhibit isotopic splitting.[23]
Fractional base units and referenced KMD plots
Kendrick mass defect plots created by using fractional base units exhibit enhanced resolution.[24] Referenced Kendrick mass defect plots (KMD plots referenced to the terminal group and adduct composition) with fractional base units can be used to obtain an overview of copolymer composition.[25]
1 2 3 Kendrick, Edward (1963), "A mass scale based on CH2 = 14.00000 for high resolution mass spectrometry of organic compounds", Anal. Chem., 35 (13): 2146–2154, doi:10.1021/ac60206a048.
↑ Ortiz, Xavier; Jobst, Karl J.; Reiner, Eric J.; Backus, Sean M.; Peru, Kerry M.; McMartin, Dena W.; O’Sullivan, Gwen; Taguchi, Vince Y.; Headley, John V. (2014-08-05). "Characterization of Naphthenic Acids by Gas Chromatography-Fourier Transform Ion Cyclotron Resonance Mass Spectrometry". Analytical Chemistry. 86 (15): 7666–7673. doi:10.1021/ac501549p. ISSN0003-2700. PMID25001115.
1 2 Ubukata, Masaaki; Jobst, Karl J.; Reiner, Eric J.; Reichenbach, Stephen E.; Tao, Qingping; Hang, Jiliang; Wu, Zhanpin; Dane, A. John; Cody, Robert B. (2015). "Non-targeted analysis of electronics waste by comprehensive two-dimensional gas chromatography combined with high-resolution mass spectrometry: Using accurate mass information and mass defect analysis to explore the data". Journal of Chromatography A. 1395: 152–159. doi:10.1016/j.chroma.2015.03.050. PMID25869800.
↑ Jobst, Karl J.; Shen, Li; Reiner, Eric J.; Taguchi, Vince Y.; Helm, Paul A.; McCrindle, Robert; Backus, Sean (2013-04-01). "The use of mass defect plots for the identification of (novel) halogenated contaminants in the environment". Analytical and Bioanalytical Chemistry. 405 (10): 3289–3297. doi:10.1007/s00216-013-6735-2. ISSN1618-2642. PMID23354579. S2CID26310076.
1 2 Ohta, Daisaku; Kanaya, Shigehiko; Suzuki, Hideyuki (2010), "Application of Fourier-transform ion cyclotron resonance mass spectrometry to metabolic profiling and metabolite identification", Current Opinion in Biotechnology, 21 (1): 35–44, doi:10.1016/j.copbio.2010.01.012, PMID20171870
↑ Mopper, Kenneth; Stubbins, Aron; Ritchie, Jason D.; Bialk, Heidi M.; Hatcher, Patrick G. (2007), "Advanced Instrumental Approaches for Characterization of Marine Dissolved Organic Matter: Extraction Techniques, Mass Spectrometry, and Nuclear Magnetic Resonance Spectroscopy", Chemical Reviews, 107 (2): 419–42, doi:10.1021/cr050359b, PMID17300139
1 2 Headley, John V.; Peru, Kerry M.; Barrow, Mark P. (2009), "Mass spectrometric characterization of naphthenic acids in environmental samples: A review", Mass Spectrometry Reviews, 28 (1): 121–34, Bibcode:2009MSRv...28..121H, doi:10.1002/mas.20185, PMID18677766
1 2 3 Reemtsma, Thorsten (2009), "Determination of molecular formulas of natural organic matter molecules by (ultra-) high-resolution mass spectrometryStatus and needs", Journal of Chromatography A, 1216 (18): 3687–701, doi:10.1016/j.chroma.2009.02.033, PMID19264312
↑ Panda, Saroj K.; Andersson, Jan T.; Schrader, Wolfgang (2007), "Mass-spectrometric analysis of complex volatile and nonvolatile crude oil components: a challenge", Analytical and Bioanalytical Chemistry, 389 (5): 1329–39, doi:10.1007/s00216-007-1583-6, PMID17885749, S2CID44948146
↑ Kim, Sunghwan; Kramer, Robert W.; Hatcher, Patrick G. (2003), "Graphical Method for Analysis of Ultrahigh-Resolution Broadband Mass Spectra of Natural Organic Matter, the Van Krevelen Diagram", Analytical Chemistry, 75 (20): 5336–44, doi:10.1021/ac034415p, PMID14710810
↑ Junninen, H.; Ehn, M.; Petäjä, T.; Luosujärvi, L.; Kotiaho, T.; Kostiainen, R.; Rohner, U.; Gonin, M.; Fuhrer, K.; Kulmala, M.; Worsnop, D. R. (2010), "A high-resolution mass spectrometer to measure atmospheric ion composition", Atmospheric Measurement Techniques, 3 (4): 1039, Bibcode:2010AMT.....3.1039J, doi:10.5194/amt-3-1039-2010
↑ Hughey CA, Hendrickson CL, Rodgers RP, Marshall AG, Qian K (October 2001), "Kendrick mass defect spectrum: a compact visual analysis for ultrahigh-resolution broadband mass spectra", Anal. Chem., 73 (19): 4676–81, doi:10.1021/ac010560w, PMID11605846.
↑ Panda, Saroj K.; Andersson, Jan T.; Schrader, Wolfgang (2007), "Mass-spectrometric analysis of complex volatile and nonvolatile crude oil components: a challenge", Analytical and Bioanalytical Chemistry, 389 (5): 1329–1339, doi:10.1007/s00216-007-1583-6, PMID17885749, S2CID44948146
↑ Reemtsma, Thorsten (2009), "Determination of molecular formulas of natural organic matter molecules by (ultra-) high-resolution mass spectrometry Status and needs", Journal of Chromatography A, 1216 (18): 3687–3701, doi:10.1016/j.chroma.2009.02.033, PMID19264312
↑ Wu, Zhigang; Rodgers, Ryan P.; Marshall, Alan G. (2004), "Two- and Three-Dimensional van Krevelen Diagrams: A Graphical Analysis Complementary to the Kendrick Mass Plot for Sorting Elemental Compositions of Complex Organic Mixtures Based on Ultrahigh-Resolution Broadband Fourier Transform Ion Cyclotron Resonance Mass Measurements", Analytical Chemistry, 76 (9): 2511–6, doi:10.1021/ac0355449, PMID15117191
↑ Cody, Robert B.; Fouquet, Thierry (2017). "Paper spray and Kendrick mass defect analysis of block and random ethylene oxide/propylene oxide copolymers". Analytica Chimica Acta. 989: 38–44. doi:10.1016/j.aca.2017.08.005. PMID28915941.
↑ Fouquet, T.; Cody, R. B.; Sato, H. (2017-09-01). "Capabilities of the remainders of nominal Kendrick masses and the referenced Kendrick mass defects for copolymer ions". Journal of Mass Spectrometry. 52 (9): 618–624. Bibcode:2017JMSp...52..618F. doi:10.1002/jms.3963. ISSN1096-9888. PMID28670698.
Related Research Articles
Mass spectrometry (MS) is an analytical technique that is used to measure the mass-to-charge ratio of ions. The results are presented as a mass spectrum, a plot of intensity as a function of the mass-to-charge ratio. Mass spectrometry is used in many different fields and is applied to pure samples as well as complex mixtures.
An ion source is a device that creates atomic and molecular ions. Ion sources are used to form ions for mass spectrometers, optical emission spectrometers, particle accelerators, ion implanters and ion engines.
Tandem mass spectrometry, also known as MS/MS or MS2, is a technique in instrumental analysis where two or more stages of analysis using one or more mass analyzer are performed with an additional reaction step in between these analyses to increase their abilities to analyse chemical samples. A common use of tandem MS is the analysis of biomolecules, such as proteins and peptides.
Gas chromatography–mass spectrometry (GC–MS) is an analytical method that combines the features of gas-chromatography and mass spectrometry to identify different substances within a test sample. Applications of GC–MS include drug detection, fire investigation, environmental analysis, explosives investigation, food and flavor analysis, and identification of unknown samples, including that of material samples obtained from planet Mars during probe missions as early as the 1970s. GC–MS can also be used in airport security to detect substances in luggage or on human beings. Additionally, it can identify trace elements in materials that were previously thought to have disintegrated beyond identification. Like liquid chromatography–mass spectrometry, it allows analysis and detection even of tiny amounts of a substance.
In mass spectrometry, matrix-assisted laser desorption/ionization (MALDI) is an ionization technique that uses a laser energy-absorbing matrix to create ions from large molecules with minimal fragmentation. It has been applied to the analysis of biomolecules and various organic molecules, which tend to be fragile and fragment when ionized by more conventional ionization methods. It is similar in character to electrospray ionization (ESI) in that both techniques are relatively soft ways of obtaining ions of large molecules in the gas phase, though MALDI typically produces far fewer multi-charged ions.
Electron-capture dissociation (ECD) is a method of fragmenting gas-phase ions for structure elucidation of peptides and proteins in tandem mass spectrometry. It is one of the most widely used techniques for activation and dissociation of mass selected precursor ion in MS/MS. It involves the direct introduction of low-energy electrons to trapped gas-phase ions.
In a chemical analysis, the internal standard method involves adding the same amount of a chemical substance to each sample and calibration solution. The internal standard responds proportionally to changes in the analyte and provides a similar, but not identical, measurement signal. It must also be absent from the sample matrix to ensure there is no other source of the internal standard present. Taking the ratio of analyte signal to internal standard signal and plotting it against the analyte concentrations in the calibration solutions will result in a calibration curve. The calibration curve can then be used to calculate the analyte concentration in an unknown sample.
A mass chromatogram is a representation of mass spectrometry data as a chromatogram, where the x-axis represents time and the y-axis represents signal intensity. The source data contains mass information; however, it is not graphically represented in a mass chromatogram in favor of visualizing signal intensity versus time. The most common use of this data representation is when mass spectrometry is used in conjunction with some form of chromatography, such as in liquid chromatography–mass spectrometry or gas chromatography–mass spectrometry. In this case, the x-axis represents retention time, analogous to any other chromatogram. The y-axis represents signal intensity or relative signal intensity. There are many different types of metrics that this intensity may represent, depending on what information is extracted from each mass spectrum.
In mass spectrometry, direct analysis in real time (DART) is an ion source that produces electronically or vibronically excited-state species from gases such as helium, argon, or nitrogen that ionize atmospheric molecules or dopant molecules. The ions generated from atmospheric or dopant molecules undergo ion-molecule reactions with the sample molecules to produce analyte ions. Analytes with low ionization energy may be ionized directly. The DART ionization process can produce positive or negative ions depending on the potential applied to the exit electrode.
The mass recorded by a mass spectrometer can refer to different physical quantities depending on the characteristics of the instrument and the manner in which the mass spectrum is displayed.
Mass spectrometry imaging (MSI) is a technique used in mass spectrometry to visualize the spatial distribution of molecules, as biomarkers, metabolites, peptides or proteins by their molecular masses. After collecting a mass spectrum at one spot, the sample is moved to reach another region, and so on, until the entire sample is scanned. By choosing a peak in the resulting spectra that corresponds to the compound of interest, the MS data is used to map its distribution across the sample. This results in pictures of the spatially resolved distribution of a compound pixel by pixel. Each data set contains a veritable gallery of pictures because any peak in each spectrum can be spatially mapped. Despite the fact that MSI has been generally considered a qualitative method, the signal generated by this technique is proportional to the relative abundance of the analyte. Therefore, quantification is possible, when its challenges are overcome. Although widely used traditional methodologies like radiochemistry and immunohistochemistry achieve the same goal as MSI, they are limited in their abilities to analyze multiple samples at once, and can prove to be lacking if researchers do not have prior knowledge of the samples being studied. Most common ionization technologies in the field of MSI are DESI imaging, MALDI imaging, secondary ion mass spectrometry imaging and Nanoscale SIMS (NanoSIMS).
Sample preparation for mass spectrometry is used for the optimization of a sample for analysis in a mass spectrometer (MS). Each ionization method has certain factors that must be considered for that method to be successful, such as volume, concentration, sample phase, and composition of the analyte solution. Quite possibly the most important consideration in sample preparation is knowing what phase the sample must be in for analysis to be successful. In some cases the analyte itself must be purified before entering the ion source. In other situations, the matrix, or everything in the solution surrounding the analyte, is the most important factor to consider and adjust. Often, sample preparation itself for mass spectrometry can be avoided by coupling mass spectrometry to a chromatography method, or some other form of separation before entering the mass spectrometer. In some cases, the analyte itself must be adjusted so that analysis is possible, such as in protein mass spectrometry, where usually the protein of interest is cleaved into peptides before analysis, either by in-gel digestion or by proteolysis in solution.
Matrix-assisted laser desorption electrospray ionization (MALDESI) was first introduced in 2006 as a novel ambient ionization technique which combines the benefits of electrospray ionization (ESI) and matrix-assisted laser desorption/ionization (MALDI). An infrared (IR) or ultraviolet (UV) laser can be utilized in MALDESI to resonantly excite an endogenous or exogenous matrix. The term ‘matrix’ refers to any molecule that is present in large excess and absorbs the energy of the laser, thus facilitating desorption of analyte molecules. The original MALDESI design was implemented using common organic matrices, similar to those used in MALDI, along with a UV laser. The current MALDESI source employs endogenous water or a thin layer of exogenously deposited ice as the energy-absorbing matrix where O-H symmetric and asymmetric stretching bonds are resonantly excited by a mid-IR laser.
Ion mobility spectrometry–mass spectrometry (IMS-MS) is an analytical chemistry method that separates gas phase ions based on their interaction with a collision gas and their masses. In the first step, the ions are separated according to their mobility through a buffer gas on a millisecond timescale using an ion mobility spectrometer. The separated ions are then introduced into a mass analyzer in a second step where their mass-to-charge ratios can be determined on a microsecond timescale. The effective separation of analytes achieved with this method makes it widely applicable in the analysis of complex samples such as in proteomics and metabolomics.
Capillary electrophoresis–mass spectrometry (CE–MS) is an analytical chemistry technique formed by the combination of the liquid separation process of capillary electrophoresis with mass spectrometry. CE–MS combines advantages of both CE and MS to provide high separation efficiency and molecular mass information in a single analysis. It has high resolving power and sensitivity, requires minimal volume and can analyze at high speed. Ions are typically formed by electrospray ionization, but they can also be formed by matrix-assisted laser desorption/ionization or other ionization techniques. It has applications in basic research in proteomics and quantitative analysis of biomolecules as well as in clinical medicine. Since its introduction in 1987, new developments and applications have made CE-MS a powerful separation and identification technique. Use of CE–MS has increased for protein and peptides analysis and other biomolecules. However, the development of online CE–MS is not without challenges. Understanding of CE, the interface setup, ionization technique and mass detection system is important to tackle problems while coupling capillary electrophoresis to mass spectrometry.
Ambient ionization is a form of ionization in which ions are formed in an ion source outside the mass spectrometer without sample preparation or separation. Ions can be formed by extraction into charged electrospray droplets, thermally desorbed and ionized by chemical ionization, or laser desorbed or ablated and post-ionized before they enter the mass spectrometer.
In mass spectrometry, resolution is a measure of the ability to distinguish two peaks of slightly different mass-to-charge ratios ΔM, in a mass spectrum.
Isobaric labeling is a mass spectrometry strategy used in quantitative proteomics. Peptides or proteins are labeled with chemical groups that have identical mass (isobaric), but vary in terms of distribution of heavy isotopes in their structure. These tags, commonly referred to as tandem mass tags, are designed so that the mass tag is cleaved at a specific linker region upon high-energy CID (HCD) during tandem mass spectrometry yielding reporter ions of different masses. The most common isobaric tags are amine-reactive tags. However, tags that react with cysteine residues and carbonyl groups have also been described. These amine-reactive groups go through N-hydroxysuccinimide (NHS) reactions, which are based around three types of functional groups. Isobaric labeling methods include tandem mass tags (TMT), isobaric tags for relative and absolute quantification (iTRAQ), mass differential tags for absolute and relative quantification, and dimethyl labeling. TMTs and iTRAQ methods are most common and developed of these methods. Tandem mass tags have a mass reporter region, a cleavable linker region, a mass normalization region, and a protein reactive group and have the same total mass.
Laser ablation electrospray ionization (LAESI) is an ambient ionization method for mass spectrometry that combines laser ablation from a mid-infrared (mid-IR) laser with a secondary electrospray ionization (ESI) process. The mid-IR laser is used to generate gas phase particles which are then ionized through interactions with charged droplets from the ESI source. LAESI was developed in Professor Akos Vertes lab by Dr. Peter Nemes in 2007 and it was marketed commercially by Protea Biosciences, Inc until 2017. Fiber-LAESI for single-cell analysis approach was developed by Dr. Bindesh Shrestha in Professor Vertes lab in 2009. LAESI is a novel ionization source for mass spectrometry (MS) that has been used to perform MS imaging of plants, tissues, cell pellets, and even single cells. In addition, LAESI has been used to analyze historic documents and untreated biofluids such as urine and blood. The technique of LAESI is performed at atmospheric pressure and therefore overcomes many of the obstacles of traditional MS techniques, including extensive and invasive sample preparation steps and the use of high vacuum. Because molecules and aerosols are ionized by interacting with an electrospray plume, LAESI's ionization mechanism is similar to SESI and EESI techniques.
Petroleomics is the identification of the totality of the constituents of naturally occurring petroleum and crude oil using high resolution mass spectrometry. In addition to mass determination, petroleomic analysis sorts the chemical compounds into heteroatom class, type. The name is a combination of petroleum and -omics.
This page is based on this Wikipedia article Text is available under the CC BY-SA 4.0 license; additional terms may apply. Images, videos and audio are available under their respective licenses.
