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Mass spectrometry

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Intros
Lessons
  1. Using mass spectrometry.
  2. What is mass spectrometry?
  3. Stages of mass spectrometry analysis.
  4. Reading an organic mass spectrum.
  5. Mass spectrum of chlorine, Cl2
  6. Example: Calculating relative atomic mass of boron.
  7. Example 2: Calculating atomic mass of molybdenum.
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Examples
Lessons
  1. The mass spectrum of butane (C4H10) is shown below:
    1. Identify the molecular ion peak (M+) and suggest the identity of the other three major peaks on the spectrum.
    2. Explain why a small peak at m/z = 59 is present in the mass spectrum. Suggest the most likely cause of this peak.
    Topic Notes
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    Introduction to Mass Spectrometry

    Mass spectrometry is a powerful analytical technique in chemistry that plays a crucial role in identifying and quantifying molecules. This spectroscopic method measures the mass-to-charge ratio of ions, providing valuable information about the composition and structure of substances. As one of the most important analytical methods, mass spectrometry finds applications in various fields, including pharmaceuticals, environmental science, and forensics. The introduction video will provide a visual overview of this technique. In this lesson, we will focus on three main objectives: understanding the fundamental principles of how mass spectrometry works, exploring the stages involved in producing a mass spectrum, and learning how to analyze mass spectra for organic structure determination and relative atomic mass calculations. By mastering these concepts, you'll gain essential skills in interpreting mass spectrometric data, a valuable asset in modern chemistry research and industry applications.

    Fundamentals of Mass Spectrometry

    Mass spectrometry is a powerful analytical technique used to identify and quantify molecules based on their mass-to-charge ratio. This method plays a crucial role in various scientific fields, including chemistry, biology, and physics. The primary purpose of mass spectrometry is to determine the molecular mass of compounds, identify isotopes, and calculate relative atomic mass.

    To understand mass spectrometry, it's essential to differentiate between spectroscopy and spectrometry. Spectroscopy involves the study of how matter interacts with electromagnetic radiation, while spectrometry focuses on measuring and analyzing the mass-to-charge ratio of ions. Mass spectrometry falls under the latter category, as it deals with the separation and detection of charged particles.

    One of the key applications of mass spectrometry is determining the mass of unknown compounds. For example, in pharmaceutical research, scientists can use this technique to identify the molecular mass of newly synthesized drugs. By analyzing the mass spectrum, researchers can confirm the structure and purity of their compounds, ensuring the development of safe and effective medications.

    Mass spectrometry is also invaluable in identifying isotopes in elemental samples. Isotopes are atoms of the same element with different numbers of neutrons, resulting in varying atomic masses. By using mass spectrometry, scientists can accurately measure the abundance of different isotopes in a sample. This capability is particularly useful in fields such as geology, where isotope ratios can provide information about the age and origin of rocks and minerals.

    Another significant application of mass spectrometry is calculating relative atomic mass. The relative atomic mass of an element is the weighted average of the masses of its isotopes, taking into account their natural abundance. Mass spectrometry allows for precise measurements of isotope masses and their relative abundances, enabling accurate calculations of relative atomic mass. This information is crucial for understanding the chemical properties of elements and their behavior in various reactions.

    To illustrate these concepts, let's consider an example of carbon isotope analysis. Carbon has three naturally occurring isotopes: carbon-12, carbon-13, and carbon-14. Using mass spectrometry, scientists can determine the exact masses of these isotopes and their relative abundances in a sample. This information is vital in fields such as archaeology, where carbon-14 dating is used to estimate the age of organic materials.

    Mass spectrometry has revolutionized many areas of scientific research by providing accurate and sensitive measurements of molecular mass. In environmental science, for instance, it helps identify and quantify pollutants in air and water samples. In forensic science, mass spectrometry is used to analyze trace evidence, such as drug residues or explosive compounds. The technique's versatility and precision make it an indispensable tool in modern analytical chemistry.

    In conclusion, mass spectrometry is a fundamental technique in analytical chemistry that offers unparalleled capabilities in determining molecular mass, identifying isotopes, and calculating relative atomic mass. Its applications span across various scientific disciplines, from drug discovery to environmental monitoring. By understanding the principles of mass spectrometry, researchers can harness its power to unlock new insights into the composition and behavior of matter at the molecular level.

    The Mass Spectrometer: Components and Process

    A mass spectrometer is a sophisticated analytical instrument that plays a crucial role in identifying and quantifying molecules in a sample. At its core, this device operates on the principle of separating ions based on their mass-to-charge ratio (m/z). Let's dive into the components and process of a mass spectrometer, focusing on the widely used electron impact method.

    The journey of a molecule through a mass spectrometer can be likened to an obstacle course, with four main stages: ionization, acceleration, deflection, and detection. Each stage serves a specific purpose in transforming and analyzing the sample.

    1. Ionization: The first step in the mass spectrometry process is ionization. In the electron impact method, the sample molecules are bombarded with high-energy electrons. This collision causes the molecules to lose electrons, turning them into positively charged ions. Imagine this stage as a game of molecular dodgeball, where the sample molecules are the players, and the high-energy electrons are the balls. When a molecule gets hit, it loses an electron and becomes "tagged" as an ion.

    2. Acceleration: Once ionized, the particles enter the acceleration stage. Here, an electric field gives these ions a boost, propelling them forward at high speeds. This acceleration is crucial for the next stage of the process. Think of this step as the ions lining up at the starting line of a race, then being launched forward by a powerful starting gun.

    3. Deflection: The accelerated ions now enter the deflection chamber, which is the heart of the mass spectrometer. This chamber contains a strong magnetic field that curves the path of the ions. The amount of deflection depends on the mass-to-charge ratio (m/z) of each ion. Lighter ions or those with higher charges will be deflected more than heavier or less charged ions.

    To better understand this concept, imagine leaves blowing in the wind. Lighter leaves (like small ions) will be carried further by the wind, while heavier leaves (like large ions) will not travel as far. The wind in this analogy represents the magnetic field in the mass spectrometer.

    4. Detection: The final stage is detection. After being separated based on their m/z ratios, the ions strike a detector. This detector measures the number of ions at each m/z value, creating a mass spectrum. This spectrum is like a fingerprint for the molecule, showing peaks at different m/z values that correspond to different fragments of the original molecule.

    The mass-to-charge ratio (m/z) is the cornerstone of mass spectrometry. It's calculated by dividing the mass of an ion by its charge. This ratio is crucial because it determines how the ion behaves in the magnetic field. Ions with the same m/z will follow the same path through the spectrometer, regardless of their individual masses or charges.

    To illustrate, consider two scenarios: an ion with a mass of 20 and a charge of +1, and another ion with a mass of 40 and a charge of +2. Both would have an m/z of 20 and would follow the same path through the spectrometer. This principle allows the mass spectrometer to separate and identify ions with incredible precision.

    The electron impact method, while powerful, does have its limitations. It tends to cause significant fragmentation of the original molecules, which can make it challenging to determine the mass of the intact molecule. However, this fragmentation pattern is also valuable, as it provides structural information about the molecule.

    In conclusion, the mass spectrometer is a remarkable instrument that transforms a complex mixture of molecules into a detailed mass spectrum. By understanding its components and process - from ionization through electron impact, to acceleration, magnetic deflection based on mass-to-charge ratio, and finally detection - we can appreciate the intricate dance of ions that allows scientists to unravel the composition of matter at a molecular level. This technology continues to be indispensable in fields ranging from pharmaceutical research to environmental monitoring, showcasing the power of physics and chemistry in action.

    Interpreting Mass Spectra

    Mass spectrometry is a powerful analytical technique used to identify and quantify molecules based on their mass-to-charge ratio. Interpreting a mass spectrum is a crucial skill for chemists and biochemists. This guide will walk you through the process of reading and understanding a mass spectrum, focusing on its key components and what they reveal about the molecule under analysis.

    The mass spectrum is a two-dimensional plot with the x-axis representing the mass-to-charge ratio (m/z) and the y-axis showing the relative abundance of ions. The mass-to-charge ratio is calculated by dividing the mass of an ion by its charge. In most cases, the charge is +1, so the m/z value directly corresponds to the mass of the ion. The relative abundance indicates the quantity of each ion detected, with the tallest peak (base peak) assigned a value of 100% and other peaks scaled accordingly.

    When interpreting a mass spectrum, it's essential to understand the three main types of peaks: the molecular ion peak, isotope peaks, and fragment ion peaks. Let's explore each of these using the example of an organic molecule, such as ethanol (CH3CH2OH).

    The molecular ion peak is typically the rightmost significant peak in the spectrum and represents the unfragmented molecule that has lost one electron. For ethanol, this peak would appear at m/z 46, corresponding to its molecular mass. The molecular ion peak is crucial as it provides the molecular mass of the compound, a vital piece of information for structure determination.

    Isotope peaks appear next to the molecular ion peak and result from the natural abundance of isotopes in the molecule. For ethanol, you might observe a small peak at m/z 47, representing molecules containing a 13C atom or 2H (deuterium) instead of the more common 12C or 1H. The pattern and intensity of isotope peaks can provide valuable information about the elemental composition of the molecule.

    Fragment ion peaks are the most numerous in a mass spectrum and occur at lower m/z values than the molecular ion peak. These peaks result from the molecule breaking apart during the ionization process. For ethanol, you might see peaks at m/z 31 (loss of a methyl group), m/z 29 (loss of OH), and m/z 15 (CH3+ fragment). The fragmentation pattern is like a fingerprint for the molecule and provides crucial structural information.

    To identify the molecular mass from a mass spectrum, locate the molecular ion peak, which is often (but not always) the highest m/z peak with significant intensity. Confirm this by looking for isotope peaks that match the expected pattern for the suspected molecular formula. The m/z value of the molecular ion peak corresponds to the molecular mass of the compound.

    Extracting structural information requires careful analysis of the fragmentation pattern. Start by identifying the molecular ion peak and then work your way down the spectrum, noting significant peaks and their m/z differences. These differences often correspond to common functional groups or structural units. For example, a difference of 15 m/z units often indicates the loss of a methyl group (CH3).

    Look for characteristic fragmentation patterns associated with specific functional groups. For instance, alcohols like ethanol often show a prominent peak at M-1 (where M is the molecular mass) due to the loss of a hydrogen atom from the OH group. Aromatic compounds typically have a strong molecular ion peak due to their stability.

    Pay attention to the relative intensities of peaks. More stable fragments tend to produce more intense peaks. The base peak (the most intense peak in the spectrum) often corresponds to a particularly stable fragment or the molecular ion itself.

    Consider the nitrogen rule: if a molecule contains an odd number of nitrogen atoms, its molecular ion will have an odd m/z value. This can help in determining whether nitrogen is present in the compound.

    Utilize the concept of isotope patterns to confirm the presence of certain elements. For example, the presence of chlorine or bromine in a molecule results in a distinctive isotope pattern due to their natural isotopic abundances.

    Remember that interpreting mass spectra becomes easier with practice and familiarity with common fragmentation patterns. It's often helpful to compare the spectrum of an unknown compound with spectra of known compounds or to

    Isotopes and Mass Spectrometry: The Chlorine Example

    Mass spectrometry is a powerful analytical technique that provides crucial information about isotopes, and chlorine serves as an excellent example to demonstrate this capability. Chlorine, with its two naturally occurring isotopes, 35Cl and 37Cl, offers a clear illustration of how mass spectrometry can reveal isotopic information and aid in calculating relative atomic mass.

    When examining the mass spectrum of elemental Cl2, we observe distinct peaks corresponding to different isotopic combinations. The most prominent peaks appear at mass-to-charge (m/z) ratios of 70, 72, and 74. These peaks represent the molecular ions of Cl2 with different isotopic compositions: 35Cl-35Cl, 35Cl-37Cl, and 37Cl-37Cl, respectively.

    The relative heights of these peaks provide valuable information about the natural abundance of chlorine isotopes. The peak at m/z 70 (35Cl-35Cl) is the tallest, followed by the peak at m/z 72 (35Cl-37Cl), and finally, the smallest peak at m/z 74 (37Cl-37Cl). This pattern reflects the fact that 35Cl is more abundant in nature than 37Cl.

    To calculate the relative atomic mass of chlorine using isotopic abundances, we need to consider the mass and abundance of each isotope. The relative atomic mass is the weighted average of the isotopic masses, where the weights are the fractional abundances. For chlorine, the calculation would be:

    Relative atomic mass = (mass of 35Cl × abundance of 35Cl) + (mass of 37Cl × abundance of 37Cl)

    The natural abundances of chlorine isotopes are approximately 75.76% for 35Cl and 24.24% for 37Cl. Using these values and the exact masses of the isotopes, we can calculate the relative atomic mass of chlorine to be about 35.45 amu.

    The concept of probability of isotopic combinations plays a crucial role in predicting the ratios of different isotopic combinations in molecules like Cl2. The probability of forming each isotopic combination can be calculated using the individual isotope abundances. For Cl2, we have three possible combinations:

    1. 35Cl-35Cl: Probability = 0.7576 × 0.7576 = 0.5740 (57.40%)
    2. 35Cl-37Cl: Probability = 2 × (0.7576 × 0.2424) = 0.3671 (36.71%)
    3. 37Cl-37Cl: Probability = 0.2424 × 0.2424 = 0.0588 (5.88%)

    Note that for the 35Cl-37Cl combination, we multiply by 2 to account for both possible arrangements (35Cl-37Cl and 37Cl-35Cl). These probabilities directly correspond to the relative intensities of the peaks in the mass spectrum of Cl2.

    Understanding these probabilities is essential for interpreting mass spectra of more complex molecules containing multiple chlorine atoms. As the number of chlorine atoms increases, the isotope pattern becomes more complex, with a characteristic distribution often referred to as the "chlorine isotope cluster."

    Mass spectrometry's ability to reveal isotopic information extends far beyond chlorine. This technique is invaluable in various fields, including environmental science, forensics, and archaeology. For instance, it can be used to determine the origin of samples, track pollutants, or date ancient materials through isotope ratio analysis.

    In conclusion, the chlorine example vividly demonstrates how mass spectrometry provides detailed isotopic information. By analyzing the mass spectrum of Cl2, we can directly observe the presence of different isotopes, calculate their relative abundances, and use this information to determine the element's relative atomic mass. The probability of isotopic combinations further enhances our understanding of molecular composition and helps predict spectral patterns for more complex molecules.

    Calculating Relative Atomic Mass from Mass Spectra

    Relative atomic mass is a fundamental concept in chemistry that represents the weighted average mass of an element's isotopes. Mass spectrometry provides precise data on isotopic masses and abundances, allowing for accurate calculations of relative atomic mass. This article will explain the process using boron as an example, discuss the general equation, and demonstrate its application to more complex elements like transition metals.

    Let's begin with boron, which has two naturally occurring isotopes: boron-10 and boron-11. Mass spectrometry data reveals their exact masses and relative abundances. The equation for calculating relative atomic mass is:

    Relative Atomic Mass = Σ(Isotopic Mass × Fractional Abundance)

    For boron:

    Boron-10: Mass = 10.0129 u, Abundance = 19.9%
    Boron-11: Mass = 11.0093 u, Abundance = 80.1%

    Calculating:

    Relative Atomic Mass of Boron = (10.0129 × 0.199) + (11.0093 × 0.801)
    = 1.9926 + 8.8184
    = 10.811 u

    This result closely matches the standard relative atomic mass of boron (10.81) found in periodic tables.

    The process becomes more intricate for elements with multiple isotopes, particularly transition metals. These elements often have several naturally occurring isotopes, each contributing to the overall relative atomic mass. The same equation applies, but with more terms to account for additional isotopes.

    Let's consider molybdenum, a transition metal with seven naturally occurring isotopes. Here's a worked example using approximate values:

    Mo-92: Mass 91.91 u, Abundance 14.84%
    Mo-94: Mass 93.91 u, Abundance 9.25%
    Mo-95: Mass 94.91 u, Abundance 15.92%
    Mo-96: Mass 95.90 u, Abundance 16.68%
    Mo-97: Mass 96.91 u, Abundance 9.55%
    Mo-98: Mass 97.91 u, Abundance 24.13%
    Mo-100: Mass 99.91 u, Abundance 9.63%

    Applying the equation:

    Relative Atomic Mass of Mo = (91.91 × 0.1484) + (93.91 × 0.0925) + (94.91 × 0.1592) + (95.90 × 0.1668) + (96.91 × 0.0955) + (97.91 × 0.2413) + (99.91 × 0.0963)

    = 13.64 + 8.69 + 15.11 + 15.99 + 9.25 + 23.63 + 9.62
    = 95.93 u

    This calculated value aligns closely with the standard relative atomic mass of molybdenum (95.95) found in periodic tables.

    The accuracy of these calculations depends on the precision of mass spectrometry data. Modern instruments can measure isotopic masses to several decimal places and abundances to fractions of a percent. This level of precision is crucial for elements with many isotopes or those with isotopes of similar abundances.

    For transition metals and other elements with numerous isotopes, this method is invaluable. It accounts for all naturally occurring isotopes and their specific contributions to the element's overall mass. This is particularly important for

    Conclusion

    In this lesson, we explored the fundamental principles of mass spectrometry, a powerful analytical technique in chemistry. We learned how to interpret mass spectra, identifying molecular ions, fragment ions, and isotope peaks. The calculation of relative atomic mass using isotopic abundance data was also covered. Mass spectrometry's significance in analytical chemistry cannot be overstated, as it enables precise determination of molecular structures and isotopic compositions. This technique finds applications across various scientific fields, from environmental analysis to pharmaceutical research. The introduction video provided a visual understanding of these concepts, and we encourage you to review it for reinforcement. By mastering mass spectrometry, chemists can unlock valuable insights into molecular composition and structure, advancing our understanding of chemical systems. Remember, the ability to analyze mass spectra is a crucial skill in modern analytical chemistry, opening doors to exciting research opportunities and technological advancements.

    Using Mass Spectrometry: What is Mass Spectrometry?

    Step 1: Introduction to Mass Spectrometry

    Mass spectrometry is a powerful analytical technique used in chemistry to measure the mass of molecules. The name itself provides a clue to its function: "mass" refers to the measurement of mass, and "spectrometry" refers to the method of measurement. This technique is essential for identifying the composition of a sample by analyzing the mass of its molecules or fragments.

    Step 2: Understanding the Objectives of Mass Spectrometry

    The primary objectives of mass spectrometry include understanding how the technique works, the stages involved in producing a mass spectrum, and analyzing the resulting data. A mass spectrum is the graphical representation of the data obtained from the mass spectrometer, which provides evidence for the molecular structure and relative atomic mass of the sample being analyzed.

    Step 3: The Process of Mass Spectrometry

    Mass spectrometry involves several stages to produce a mass spectrum. Initially, the sample is introduced into the mass spectrometer. The sample molecules are then ionized, causing them to break into fragments. These ionized fragments are separated based on their mass-to-charge ratio (m/z) and detected to produce a mass spectrum. This spectrum is then analyzed to determine the mass of the molecules and their fragments.

    Step 4: Analyzing Mass Spectra

    Once the mass spectrum is obtained, it can be analyzed to find evidence of organic structures and calculate the relative atomic mass. The mass spectrum provides peaks that correspond to the mass of different fragments of the molecule. By interpreting these peaks, chemists can deduce the structure of the molecule and identify unknown compounds. Additionally, the presence of isotopes in elemental samples can be detected, which is useful for understanding the composition of elements like chlorine.

    Step 5: Applications of Mass Spectrometry

    Mass spectrometry has a wide range of applications in various fields. It is used to identify unknown compounds, determine the structure of molecules, and detect isotopes in elemental samples. This technique is crucial in fields such as pharmaceuticals, environmental science, and forensic analysis, where precise measurement of molecular mass is essential for research and development.

    Step 6: Conclusion

    In summary, mass spectrometry is a vital analytical method in chemistry that measures the mass of molecules and their fragments. By understanding the process and analyzing the resulting mass spectra, chemists can gain valuable insights into the composition and structure of samples. This technique's ability to provide detailed molecular information makes it indispensable in scientific research and various industrial applications.

    FAQs

    1. What is the basic principle of mass spectrometry?

      Mass spectrometry is an analytical technique that measures the mass-to-charge ratio of ions. It involves ionizing chemical compounds to generate charged molecules or molecule fragments and measuring their mass-to-charge ratios. The basic principle is the separation of ions based on their mass and charge in electric and magnetic fields.

    2. How does a mass spectrometer work?

      A mass spectrometer works in four main stages: ionization, acceleration, deflection, and detection. First, the sample is ionized, typically by electron bombardment. Then, the ions are accelerated by an electric field. Next, they are deflected by a magnetic field based on their mass-to-charge ratio. Finally, the deflected ions are detected, and their abundance is measured to produce a mass spectrum.

    3. What information can be obtained from a mass spectrum?

      A mass spectrum provides several key pieces of information: the molecular mass of the compound, its elemental composition, isotopic abundance, and structural information through fragmentation patterns. The molecular ion peak gives the molecular mass, while fragment peaks provide insights into the molecule's structure. Isotope peaks reveal information about the element's isotopic composition.

    4. How is relative atomic mass calculated using mass spectrometry data?

      Relative atomic mass is calculated using the equation: Relative Atomic Mass = Σ(Isotopic Mass × Fractional Abundance). Mass spectrometry provides precise data on isotopic masses and their relative abundances. By multiplying each isotope's mass by its fractional abundance and summing these products, we obtain the weighted average mass, which is the relative atomic mass.

    5. What are some applications of mass spectrometry in chemistry?

      Mass spectrometry has numerous applications in chemistry, including: determining the structure of unknown compounds, analyzing complex mixtures, measuring isotope ratios, quantifying trace elements, studying reaction mechanisms, and identifying biomolecules. It's used in environmental analysis, pharmaceutical research, forensic science, and many other fields where precise molecular identification and quantification are crucial.

    Prerequisite Topics

    Understanding the fundamental concepts that lay the groundwork for mass spectrometry is crucial for students and researchers alike. While there are no specific prerequisite topics provided for mass spectrometry in this case, it's important to recognize that this analytical technique draws upon various scientific disciplines. A strong foundation in chemistry, physics, and mathematics is generally beneficial for those delving into the world of mass spectrometry.

    Mass spectrometry is a powerful analytical tool used to determine the mass-to-charge ratio of ions, providing valuable information about the composition and structure of molecules. To fully grasp the principles and applications of mass spectrometry, students should have a solid understanding of basic chemical concepts, such as atomic structure, molecular bonding, and chemical reactions. These foundational topics help in interpreting the data obtained from mass spectrometers and understanding the behavior of molecules during the ionization and fragmentation processes.

    Physics plays a significant role in mass spectrometry, particularly in understanding how ions move through electric and magnetic fields. Concepts from classical mechanics and electromagnetism are essential for comprehending the principles behind ion separation and detection in mass spectrometers. Students with a strong background in physics will find it easier to grasp the intricacies of different mass analyzer types and their operating principles.

    Mathematics, especially in areas such as calculus and statistics, is invaluable when it comes to data analysis and interpretation in mass spectrometry. The ability to perform complex calculations, understand mathematical models, and apply statistical methods is crucial for processing and interpreting mass spectra accurately. Students proficient in mathematics will be better equipped to handle the quantitative aspects of mass spectrometry and perform advanced data analysis techniques.

    Additionally, a basic understanding of analytical chemistry techniques and instrumentation can provide valuable context for mass spectrometry. Familiarity with other analytical methods, such as chromatography, can help students appreciate the complementary nature of these techniques when used in conjunction with mass spectrometry.

    While specific prerequisite topics may vary depending on the depth and focus of a mass spectrometry course or research project, a well-rounded scientific background is undoubtedly beneficial. Students who have a solid foundation in chemistry, physics, and mathematics will find themselves better prepared to tackle the complexities of mass spectrometry and its wide-ranging applications in fields such as proteomics, metabolomics, and environmental analysis.

    In conclusion, although there are no explicitly stated prerequisite topics for mass spectrometry in this case, students should strive to build a strong foundation in the fundamental sciences. This interdisciplinary approach will not only enhance their understanding of mass spectrometry but also prepare them for the challenges and opportunities that arise in this dynamic field of analytical chemistry.

    In this lesson, we will learn:

    • How mass spectrometry works and the stages involved in producing a mass spectrum.
    • How to analyze mass spectra to find evidence of organic structure.
    • How to work out relative atomic mass from mass spectrum data.

    Notes:

    • Mass spectrometry is, in a sentence, a weighing scale for molecules. It can produce data for the molecular weight of molecules that are put into it. The process works as follows:
      • Ionization: A pure sample of a substance is placed in the spectrometer and bombarded by high-energy electrons. This causes the molecules to lose an electron and become a positive ion.
        • These ions are highly unstable. Many break up into two fragments: a neutral fragment and a fragment ion. This is important later!

      • Acceleration: the ion fragments are passed through an electric field which causes positively charged ions to accelerate. The higher their charge, the faster they accelerate.
        The neutral radical molecules or any unionized molecules do not accelerate as they are uncharged – they are lost at this point, and removed by vacuum.

      • Deflection: the accelerated ions pass through a magnetic field which causes them to deflect off of a straight path according to their mass and charge:
        • The higher the charge of the ion, the more deflection occurs.
        • The lower the mass of the ion, the more deflection occurs.

      • Detection: The deflection turns the ions towards a detector and by the time they reach it, the ions have separated out and arrive at separate times according to the mass to charge ratio (m/z): The lower the mass-to-charge ratio, the earlier the fragment ion arrives at the detector. The spectrometer can then produce a graph showing the m/z of all the ions and the relative abundance (how much of the sample ions had this m/z). An example of a mass spectrum is below:
        • When ions fragment, they do so because they are unstable. The resulting ions are usually relatively more stable fragments of the hydrocarbon chain (such as CH3+ or C2H5+). With a charge of +1, knowing the mass of these fragments makes identifying these fragments very easy and noticeable on a mass spectrum!

    • A mass spectrum displays an x-axis plotting mass-to-charge ratio (m/z) against a y-axis plotting relative abundance (it is relative – like in other spectroscopy, the y-axis normally isn’t graduated/scaled.) The spectrum itself has some key features:
      • A molecular ion peak (symbol M+). This is the largest m/z peak of significant abundance (not one of the very small peaks) on the x-axis. The molecular ion peak is just the whole molecule intact, but with the electron knocked off of it from the ionization process. This m/z peak is good evidence for the molecular mass of the substance being analyzed. This applies to electron impact (EI) mass spectrometry – other methods have peaks larger than the molecular ion.
      • Isotope peaks – these are most of the small peaks on the spectrum. Mass spectrometry measures molecular mass of individual atoms or molecules. This means that isotopes are fairly easily seen on a mass spectrum – the most obvious ones are the small peaks just after the molecular ion peak. These could be the peaks where one of the hydrogens is 2H, or a carbon atom is 13C.
      • Ion fragments – these are the large peaks throughout the mass spectrum. These are where the molecular ion has fragmented on its way to the detector; into a smaller fragment ion and a neutral fragment that is lost in the spectrometer as it can’t be accelerated or detected.