{"id":4697,"date":"2026-06-01T12:06:17","date_gmt":"2026-06-01T11:06:17","guid":{"rendered":"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-7-modern-analytical-techniques-i\/mass-spectrometry\/"},"modified":"2026-06-28T05:51:22","modified_gmt":"2026-06-28T04:51:22","slug":"mass-spectrometry","status":"publish","type":"page","link":"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-7-modern-analytical-techniques-i\/mass-spectrometry\/","title":{"rendered":"Identifying Compounds from Mass Spectra"},"content":{"rendered":"\n<section class=\"ols-revision-page ols-identifying-compounds-mass-spectra-page\">\n  <style>\n    .ols-revision-page {\n      --navy: #1C244B;\n      --blue: #2563eb;\n      --soft-blue: #eef4ff;\n      --soft-red: #fff7f7;\n      --soft-purple: #f7f0ff;\n      --soft-green: #f0f7f1;\n      --soft-orange: #fff7ed;\n      --gold: #c9973a;\n      --grey-text: #667085;\n      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Techniques I<\/h4>\r\n\r\n    <ul class=\"ols-topic-list\">\r\n\r\n      <li>\r\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-7-modern-analytical-techniques-i\/mass-spectrometry\/\">Mass Spectrometry<\/a>\r\n      <\/li>\r\n\r\n      <li>\r\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-7-modern-analytical-techniques-i\/infrared-spectroscopy\/\">Infrared Spectroscopy<\/a>\r\n\r\n        <ul class=\"ols-subtopic-list\">\r\n          <li>\r\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-7-modern-analytical-techniques-i\/infrared-spectroscopy\/c-h-stretching-absorption-in-alkanes-alkenes-and-aldehydes\/\">C\u2013H Stretching Absorption in Alkanes, Alkenes and Aldehydes<\/a>\r\n          <\/li>\r\n\r\n          <li>\r\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-7-modern-analytical-techniques-i\/infrared-spectroscopy\/c-c-stretching-absorption-in-alkenes\/\">C=C Stretching Absorption in Alkenes<\/a>\r\n          <\/li>\r\n\r\n          <li>\r\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-7-modern-analytical-techniques-i\/infrared-spectroscopy\/o-h-stretching-absorption-in-alcohols\/\">O\u2013H Stretching Absorption in Alcohols<\/a>\r\n          <\/li>\r\n\r\n          <li>\r\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-7-modern-analytical-techniques-i\/infrared-spectroscopy\/c-o-stretching-absorption-in-aldehydes-and-ketones\/\">C=O Stretching Absorption in Aldehydes and Ketones<\/a>\r\n          <\/li>\r\n\r\n          <li>\r\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-7-modern-analytical-techniques-i\/infrared-spectroscopy\/c-o-and-broad-o-h-stretching-absorption-in-carboxylic-acids\/\">C=O Stretching Absorption and Broad O\u2013H Stretching Absorption in Carboxylic Acids<\/a>\r\n          <\/li>\r\n\r\n          <li>\r\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-7-modern-analytical-techniques-i\/infrared-spectroscopy\/n-h-stretching-absorption-in-amines\/\">N\u2013H Stretching Absorption in Amines<\/a>\r\n          <\/li>\r\n        <\/ul>\r\n      <\/li>\r\n\r\n    <\/ul>\r\n  <\/div>\r\n\r\n  <div class=\"ols-topic-group\">\r\n    <h4>Next Topics<\/h4>\r\n\r\n    <ul class=\"ols-topic-list\">\r\n      <li>\r\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/\">Topic 6 Organic Chemistry I<\/a>\r\n      <\/li>\r\n      <li>\r\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-5-formulae-equations-and-amounts-of-substance\/\">Topic 5 Formulae, Equations &amp; Amounts<\/a>\r\n      <\/li>\r\n      <li>\r\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-4-inorganic-chemistry-and-the-periodic-table\/\">Topic 4 Inorganic Chemistry &amp; The Periodic Table<\/a>\r\n      <\/li>\r\n    <\/ul>\r\n  <\/div>\r\n<\/aside>\r\n\r\n<script>\r\n(function() {\r\n  function normalisePath(path) {\r\n    return String(path || '')\r\n      .split('?')[0]\r\n      .split('#')[0]\r\n      .replace(\/\\\/+$\/, '')\r\n      .toLowerCase();\r\n  }\r\n\r\n  function highlightActive() {\r\n    var sidebar = document.querySelector('.ols-sidebar');\r\n    if (!sidebar) return false;\r\n\r\n    var currentPath = normalisePath(window.location.pathname);\r\n    var links = 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href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-7-modern-analytical-techniques-i\/\">Topic 7 Modern Analytical Techniques I<\/a> \/\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-7-modern-analytical-techniques-i\/mass-spectrometry\/\">Mass Spectrometry<\/a> \/\n        <span>Identifying Compounds from Mass Spectra<\/span>\n      <\/nav>\n\n      <header class=\"ols-title-card\">\n        <h1>Identifying Compounds from Mass Spectra<\/h1>\n        <p class=\"ols-page-intro\">A concise revision guide to using the molecular ion peak and peak pattern in a mass spectrum to help identify an unknown compound.<\/p>\n\n        <div class=\"ols-badges\">\n          <div class=\"ols-badge\">Paper 2<\/div>\n          <div class=\"ols-badge\">Topic 7: Modern Analytical Techniques I<\/div>\n          <div class=\"ols-badge\">9CH0\/02<\/div>\n        <\/div>\n\n        <div class=\"ols-author\">\n\n    <img decoding=\"async\"\n      class=\"ols-author-avatar-img\"\n      src=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/2026\/05\/Author-Profile.jpeg\"\n      alt=\"Dr. Mohammed Al-Fatah\"\n    >\n\n    <div class=\"ols-author-content\">\n\n      <h2 class=\"ols-author-title\">\n        Written by: Dr. Mohammed Al-Fatah\n      <\/h2>\n\n      <p class=\"ols-author-description\">\n        Chemistry specialist revision notes for A Level Chemistry.\n      <\/p>\n\n      <a class=\"ols-linkedin-pill\" href=\"https:\/\/www.linkedin.com\/in\/doctormohammedfatah\/\" target=\"_blank\" rel=\"noopener noreferrer\">\n\n        <svg class=\"ols-linkedin-icon\" viewBox=\"0 0 24 24\" fill=\"currentColor\" aria-hidden=\"true\">\n          <path d=\"M4.98 3.5C4.98 4.88 3.86 6 2.48 6S0 4.88 0 3.5 1.12 1 2.48 1s2.5 1.12 2.5 2.5zM.5 8h4V24h-4V8zm7 0h3.8v2.2h.1c.5-.9 1.8-2.2 3.9-2.2 4.2 0 5 2.8 5 6.4V24h-4v-7.6c0-1.8 0-4.2-2.6-4.2s-3 2-3 4v7.8h-4V8z\"\/>\n        <\/svg>\n\n        View LinkedIn Profile\n\n      <\/a>\n\n    <\/div>\n\n  <\/div>\n      <\/header>\n\n      <article class=\"ols-note-card soft\">\n        <div class=\"ols-note-title\"><div class=\"ols-note-icon\">1<\/div><h2>What Does Identifying a Compound Mean?<\/h2><\/div>\n        <p>Mass spectrometry can be used to help <strong>identify unknown compounds<\/strong> by analysing the pattern of peaks in their spectra.<\/p>\n        <p>The most important starting point is often the <strong>molecular ion peak<\/strong>, also called the <strong>M<sup>+<\/sup> peak<\/strong>. This peak is caused by the molecular ion formed when one electron is removed from the molecule.<\/p>\n        <div class=\"ols-definition-box\">\n          <p><strong>Molecular ion:<\/strong> the positive ion formed when a molecule loses one electron, usually written as M<sup>+<\/sup>.<\/p>\n        <\/div>\n        <div class=\"ols-key-box\"><p><strong>Key idea:<\/strong> for a 1+ ion, the m\/z value of the molecular ion peak is equal to the relative molecular mass of the compound.<\/p><\/div>\n      <\/article>\n\n      <article class=\"ols-note-card\">\n        <div class=\"ols-note-title\"><div class=\"ols-note-icon\">2<\/div><h2>Use the Molecular Ion Peak to Find Molecular Mass<\/h2><\/div>\n        <p>When a sample is bombarded with electrons in the mass spectrometer, some molecules lose an electron and form molecular ions.<\/p>\n\n        <div class=\"ols-formula-box\">\n          <p>Molecule + electron beam &rarr; M<sup>+<\/sup> + e<sup>&#8211;<\/sup><\/p>\n          <small>The molecular ion normally has a single positive charge, so m\/z matches the molecular mass.<\/small>\n        <\/div>\n\n        <p>In a mass spectrum, the molecular ion peak is usually the peak with the <strong>highest significant m\/z value<\/strong>. Small M+1 peaks may appear just above it because of naturally occurring isotopes such as carbon-13, so these are usually ignored when finding the main molecular mass.<\/p>\n\n        <div class=\"ols-key-box\"><p><strong>Exam focus:<\/strong> use the highest significant molecular ion peak, not a small M+1 isotope peak, when identifying the molecular mass.<\/p><\/div>\n      <\/article>\n\n      <article class=\"ols-note-card purple\">\n        <div class=\"ols-note-title\"><div class=\"ols-note-icon\">3<\/div><h2>Read the Axes Before Interpreting the Spectrum<\/h2><\/div>\n        <p>The <strong>x-axis<\/strong> in a mass spectrum shows the mass-to-charge ratio, written as <strong>m\/z<\/strong>. The <strong>y-axis<\/strong> shows the relative abundance of ions, often expressed as a percentage.<\/p>\n        <p>For most introductory A Level examples, the ions are assumed to have a <strong>1+ charge<\/strong>. This means the m\/z value can be interpreted directly as the mass of that ion.<\/p>\n\n        <div class=\"ols-table-wrap\">\n          <table class=\"ols-table\">\n            <thead>\n              <tr>\n                <th>Feature<\/th>\n                <th>Meaning<\/th>\n                <th>How it helps identify a compound<\/th>\n              <\/tr>\n            <\/thead>\n            <tbody>\n              <tr>\n                <td data-label=\"Feature\">m\/z value<\/td>\n                <td data-label=\"Meaning\">Mass-to-charge ratio of an ion<\/td>\n                <td data-label=\"How it helps identify a compound\">For 1+ ions, it gives the mass of the ion.<\/td>\n              <\/tr>\n              <tr>\n                <td data-label=\"Feature\">Relative abundance<\/td>\n                <td data-label=\"Meaning\">How common each ion is compared with the others<\/td>\n                <td data-label=\"How it helps identify a compound\">The peak pattern can support a suggested structure.<\/td>\n              <\/tr>\n              <tr>\n                <td data-label=\"Feature\">M<sup>+<\/sup> peak<\/td>\n                <td data-label=\"Meaning\">Peak caused by the molecular ion<\/td>\n                <td data-label=\"How it helps identify a compound\">Its m\/z value gives the relative molecular mass.<\/td>\n              <\/tr>\n            <\/tbody>\n          <\/table>\n        <\/div>\n      <\/article>\n\n      <article class=\"ols-note-card orange\">\n        <div class=\"ols-note-title\"><div class=\"ols-note-icon\">4<\/div><h2>Worked Example: Identifying Ethanol<\/h2><\/div>\n        <p>The mass spectrum of an unknown alcohol shows a molecular ion peak at <strong>m\/z 46<\/strong>. Assuming the molecular ion has a 1+ charge, this means the relative molecular mass of the compound is <strong>46<\/strong>.<\/p>\n\n        <div class=\"ols-worked-grid\">\n          <div class=\"ols-worked-step\">\n            <h3>Step 1: Find the molecular ion peak<\/h3>\n            <p>The molecular ion peak is at m\/z 46, so the compound has M<sub>r<\/sub> = 46.<\/p>\n          <\/div>\n          <div class=\"ols-worked-step\">\n            <h3>Step 2: Compare with possible alcohols<\/h3>\n            <p>Ethanol has formula C<sub>2<\/sub>H<sub>5<\/sub>OH, or C<sub>2<\/sub>H<sub>6<\/sub>O.<\/p>\n          <\/div>\n          <div class=\"ols-worked-step\">\n            <h3>Step 3: Calculate the relative molecular mass<\/h3>\n            <p>(2 &times; 12.0) + (6 &times; 1.0) + 16.0 = <strong>46.0<\/strong><\/p>\n          <\/div>\n        <\/div>\n\n        <div class=\"ols-formula-box\">\n          <p>M<sub>r<\/sub> of ethanol = 46.0<\/p>\n          <small>This matches the molecular ion peak at m\/z 46.<\/small>\n        <\/div>\n\n        <div class=\"ols-figure-card\">\n          <div class=\"ols-figure-image\">\n            <a class=\"ols-lightbox-link\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/2026\/05\/Mass-spectrometry-analysis-of-ethanol.png\" aria-label=\"Open mass spectrometry analysis of ethanol image full screen\">\n              <img decoding=\"async\" class=\"ols-zoomable-img ols-lightbox-target\" src=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/2026\/05\/Mass-spectrometry-analysis-of-ethanol.png\" alt=\"Mass spectrometry analysis of ethanol showing the molecular ion peak used to identify the compound\">\n            <\/a>\n          <\/div>\n          <div class=\"ols-figure-caption\">\n            <p>The molecular ion peak at m\/z 46 matches the relative molecular mass of ethanol, C<sub>2<\/sub>H<sub>5<\/sub>OH.<\/p>\n          <\/div>\n        <\/div>\n      <\/article>\n\n      <article class=\"ols-note-card\">\n        <div class=\"ols-note-title\"><div class=\"ols-note-icon\">5<\/div><h2>Use the Peak Pattern to Support the Identity<\/h2><\/div>\n        <p>The molecular ion peak gives the molecular mass, but a mass spectrum usually contains other peaks as well. These arise from <strong>fragment ions<\/strong>, produced when the molecular ion breaks apart.<\/p>\n        <p>Fragment peaks can help distinguish compounds with the same molecular mass. For example, different alcohols may produce different fragment ion patterns even if they have the same molecular formula.<\/p>\n        <div class=\"ols-key-box\"><p><strong>Key idea:<\/strong> molecular ion peak first, then peak pattern. The molecular ion peak gives molecular mass, while fragment peaks help support the identity or structure.<\/p><\/div>\n      <\/article>\n\n      <article class=\"ols-note-card purple\">\n        <div class=\"ols-note-title\"><div class=\"ols-note-icon\">6<\/div><h2>Common Exam Points<\/h2><\/div>\n        <p>These points help avoid common mistakes when interpreting mass spectra of unknown compounds.<\/p>\n\n        <div class=\"ols-rule-list\">\n          <div class=\"ols-rule-item\"><h3>Do not confuse the base peak with the molecular ion peak<\/h3><p>The base peak is the tallest peak. The molecular ion peak is the peak caused by the whole molecule after losing one electron. They are not always the same peak.<\/p><\/div>\n          <div class=\"ols-rule-item\"><h3>Use the highest significant m\/z value<\/h3><p>The molecular ion peak is usually at the highest significant m\/z value. Small M+1 peaks can occur due to carbon-13 and should not normally be used as the main molecular mass.<\/p><\/div>\n          <div class=\"ols-rule-item\"><h3>State the charge assumption<\/h3><p>For a 1+ molecular ion, m\/z is equal to the molecular mass. If the charge were different, the relationship would change.<\/p><\/div>\n          <div class=\"ols-rule-item\"><h3>Show the molecular mass calculation<\/h3><p>When suggesting a compound, calculate its M<sub>r<\/sub> and compare it directly with the molecular ion peak.<\/p><\/div>\n        <\/div>\n      <\/article>\n\n      <section class=\"ols-h5p-card\">\n        <h2>Check Your Understanding<\/h2>\n        <p>Use these short tasks to test how the molecular ion peak and peak pattern are used to identify unknown compounds from mass spectra.<\/p>\n\n        <div class=\"ols-h5p-grid\">\n          <div class=\"ols-h5p-frame\"><div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-255\" class=\"h5p-iframe\" data-content-id=\"255\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"T2.2.4.1 Drag: Identifying Compounds from Mass Spectra Key Concepts\"><\/iframe><\/div><\/div>\n          <div class=\"ols-h5p-frame\"><div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-256\" class=\"h5p-iframe\" data-content-id=\"256\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"T2.2.4.2 MCQ: Molecular Ion Peak and Molecular Mass\"><\/iframe><\/div><\/div>\n          <div class=\"ols-h5p-frame\"><div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-257\" class=\"h5p-iframe\" data-content-id=\"257\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"T2.2.4.3 MCQ: Identifying Ethanol from a Mass Spectrum\"><\/iframe><\/div><\/div>\n          <div class=\"ols-h5p-frame\"><div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-258\" class=\"h5p-iframe\" data-content-id=\"258\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"T2.2.4.4 MCQ: Base Peak and Molecular Ion Peak\"><\/iframe><\/div><\/div>\n        <\/div>\n      <\/section>\n\n      <section class=\"ols-quicksnap-card\">\n        <h2>QuickSnap Summary<\/h2>\n        <p>Identifying a compound from a mass spectrum starts with the molecular ion peak, then uses the wider peak pattern to support the proposed identity.<\/p>\n\n        <div class=\"ols-snap-list\">\n          <div class=\"ols-snap-item\"><div class=\"ols-snap-number\">1<\/div><p>Find the molecular ion, M<sup>+<\/sup>, peak in the spectrum.<\/p><\/div>\n          <div class=\"ols-snap-item\"><div class=\"ols-snap-number\">2<\/div><p>For a 1+ ion, use the m\/z value of the molecular ion peak as the molecular mass.<\/p><\/div>\n          <div class=\"ols-snap-item\"><div class=\"ols-snap-number\">3<\/div><p>Compare the molecular mass with possible compounds by calculating their M<sub>r<\/sub> values.<\/p><\/div>\n          <div class=\"ols-snap-item\"><div class=\"ols-snap-number\">4<\/div><p>Use fragment peaks and the overall peak pattern as supporting evidence for the proposed compound.<\/p><\/div>\n        <\/div>\n      <\/section>\n\n\n\n      \n\n      <section class=\"ols-faq-card\">\n        <h2>FAQs<\/h2>\n        <p>These questions focus on the main exam points for identifying compounds from mass spectra.<\/p>\n\n        <div class=\"ols-faq-list\">\n          <div class=\"ols-faq-item\">\n            <h3>What is the molecular ion peak?<\/h3>\n            <p>The molecular ion peak is the peak caused by the whole molecule after it has lost one electron. It is often written as the M<sup>+<\/sup> peak.<\/p>\n          <\/div>\n          <div class=\"ols-faq-item\">\n            <h3>How does the molecular ion peak identify molecular mass?<\/h3>\n            <p>If the molecular ion has a 1+ charge, the m\/z value of the molecular ion peak is equal to the relative molecular mass of the compound.<\/p>\n          <\/div>\n          <div class=\"ols-faq-item\">\n            <h3>Why might there be a small peak after the M<sup>+<\/sup> peak?<\/h3>\n            <p>A small M+1 peak can occur because of naturally occurring heavier isotopes, such as carbon-13. This should not normally be used as the main molecular ion peak.<\/p>\n          <\/div>\n          <div class=\"ols-faq-item\">\n            <h3>Why is ethanol identified from a molecular ion peak at m\/z 46?<\/h3>\n            <p>Ethanol has formula C<sub>2<\/sub>H<sub>5<\/sub>OH. Its relative molecular mass is (2 &times; 12.0) + (6 &times; 1.0) + 16.0 = 46.0, matching the molecular ion peak at m\/z 46.<\/p>\n          <\/div>\n          <div class=\"ols-faq-item\">\n            <h3>Are fragment peaks useful for identification?<\/h3>\n            <p>Yes. Fragment peaks help support the proposed structure because different compounds can break into different characteristic ions.<\/p>\n          <\/div>\n        <\/div>\n      <\/section>\n\n      <section class=\"ols-related-card\">\n        <h2>Related Topics<\/h2>\n        <p>Use these related pages to strengthen your understanding of mass spectrometry and isotope analysis.<\/p>\n\n        <div class=\"ols-related-grid\">\n          <a class=\"ols-related-item\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-1-atomic-structure-and-the-periodic-table\/mass-spectrometry\/the-mass-spectrometer\/\">The Mass Spectrometer<\/a>\n          <a class=\"ols-related-item\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-1-atomic-structure-and-the-periodic-table\/mass-spectrometry\/ram-calculations\/\">RAM Calculations<\/a>\n          <a class=\"ols-related-item\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-1-atomic-structure-and-the-periodic-table\/mass-spectrometry\/predicting-diatomic-mass-spectra\/\">Predicting Diatomic Mass Spectra<\/a>\n        <\/div>\n      <\/section>\n<!-- OLS Author Copyright Footprint \/ Attribution Card -->\n      <section class=\"ols-attribution-card\">\n        <style>\n          .ols-attribution-card {\n            background: linear-gradient(135deg, #ffffff, #f8fbff);\n            border: 1px solid rgba(28, 36, 75, 0.14);\n            border-radius: 28px;\n            box-shadow: 0 18px 45px rgba(28, 36, 75, 0.10);\n            padding: 34px;\n            margin-bottom: 24px;\n            overflow: hidden;\n            font-family: Poppins, Arial, sans-serif;\n            box-sizing: border-box;\n          }\n      \n          .ols-attribution-card,\n          .ols-attribution-card * {\n            box-sizing: border-box;\n          }\n      \n          .ols-attribution-card p {\n            margin: 0;\n            font-size: 14px;\n            line-height: 1.65;\n            font-weight: 300;\n            color: #667085;\n          }\n      \n          .ols-attribution-card strong {\n            font-weight: 700;\n            color: #1C244B;\n          }\n      \n          @media (max-width: 760px) {\n            .ols-attribution-card {\n              padding: 24px 18px;\n              border-radius: 22px;\n            }\n          }\n        <\/style>\n      \n        <p><strong>Copyright notice:<\/strong> This OLS revision content, including the explanations, layout, diagrams, tables and embedded learning structure, is authored for Online Learning System by Dr. Mohammed Al-Fatah. It may not be copied, reproduced, redistributed or adapted without written permission.<\/p>\n      <\/section>\n    <\/main>\n\n  <div class=\"ols-lightbox-overlay\" role=\"dialog\" aria-modal=\"true\" aria-label=\"Image lightbox\">\n    <button class=\"ols-lightbox-close\" type=\"button\" aria-label=\"Close image lightbox\">&times;<\/button>\n    <img decoding=\"async\" class=\"ols-lightbox-img\" src=\"\" alt=\"\">\n  <\/div>\n\n  <script type=\"application\/ld+json\">\n{\n  \"@context\": \"https:\/\/schema.org\",\n  \"@graph\": [\n    {\n      \"@type\": \"WebPage\",\n      \"@id\": \"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-7-modern-analytical-techniques-i\/mass-spectrometry\/identifying-compounds-from-mass-spectra\/#webpage\",\n      \"url\": \"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-7-modern-analytical-techniques-i\/mass-spectrometry\/identifying-compounds-from-mass-spectra\/\",\n      \"name\": \"Identifying Compounds from Mass Spectra\",\n      \"description\": \"A Level Chemistry revision notes explaining how to use the molecular ion peak and mass spectrum peak pattern to identify unknown compounds, including ethanol at m\/z 46.\",\n      \"isPartOf\": {\n        \"@type\": \"WebSite\",\n        \"name\": \"Online Learning System\",\n        \"url\": \"https:\/\/www.onlinelearningsystem.net\/xyz\/\"\n      },\n      \"about\": [\n        {\n          \"@type\": \"Thing\",\n          \"name\": \"Mass spectrometry\"\n        },\n        {\n          \"@type\": \"Thing\",\n          \"name\": \"Molecular ion peak\"\n        },\n        {\n          \"@type\": \"Thing\",\n          \"name\": \"Identifying unknown compounds\"\n        }\n      ],\n      \"educationalLevel\": \"A Level\",\n      \"inLanguage\": \"en-GB\"\n    },\n    {\n      \"@type\": \"BreadcrumbList\",\n      \"@id\": \"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-7-modern-analytical-techniques-i\/mass-spectrometry\/identifying-compounds-from-mass-spectra\/#breadcrumb\",\n      \"itemListElement\": [\n        {\n          \"@type\": \"ListItem\",\n          \"position\": 1,\n          \"name\": \"Revision Notes\",\n          \"item\": \"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/\"\n        },\n        {\n          \"@type\": \"ListItem\",\n          \"position\": 2,\n          \"name\": \"A Level Chemistry\",\n          \"item\": \"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/\"\n        },\n        {\n          \"@type\": \"ListItem\",\n          \"position\": 3,\n          \"name\": \"Edexcel\",\n          \"item\": \"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/\"\n        },\n        {\n          \"@type\": \"ListItem\",\n          \"position\": 4,\n          \"name\": \"Topic 7 Modern Analytical Techniques I\",\n          \"item\": \"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-7-modern-analytical-techniques-i\/\"\n        },\n        {\n          \"@type\": \"ListItem\",\n          \"position\": 5,\n          \"name\": \"Mass Spectrometry\",\n          \"item\": \"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-7-modern-analytical-techniques-i\/mass-spectrometry\/\"\n        },\n        {\n          \"@type\": \"ListItem\",\n          \"position\": 6,\n          \"name\": \"Identifying Compounds from Mass Spectra\",\n          \"item\": \"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-7-modern-analytical-techniques-i\/mass-spectrometry\/identifying-compounds-from-mass-spectra\/\"\n        }\n      ]\n    },\n    {\n      \"@type\": \"FAQPage\",\n      \"@id\": \"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-7-modern-analytical-techniques-i\/mass-spectrometry\/identifying-compounds-from-mass-spectra\/#faq\",\n      \"mainEntity\": [\n        {\n          \"@type\": \"Question\",\n          \"name\": \"What is the molecular ion peak?\",\n          \"acceptedAnswer\": {\n            \"@type\": \"Answer\",\n            \"text\": \"The molecular ion peak is the peak caused by the whole molecule after it has lost one electron. It is often written as the M+ peak.\"\n          }\n        },\n        {\n          \"@type\": \"Question\",\n          \"name\": \"How does the molecular ion peak identify molecular mass?\",\n          \"acceptedAnswer\": {\n            \"@type\": \"Answer\",\n            \"text\": \"If the molecular ion has a 1+ charge, the m\/z value of the molecular ion peak is equal to the relative molecular mass of the compound.\"\n          }\n        },\n        {\n          \"@type\": \"Question\",\n          \"name\": \"Why might there be a small peak after the M+ peak?\",\n          \"acceptedAnswer\": {\n            \"@type\": \"Answer\",\n            \"text\": \"A small M+1 peak can occur because of naturally occurring heavier isotopes, such as carbon-13. 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