Method for determining 15N isotope abundance of ammonium salt by using high-resolution liquid chromatograph-mass spectrometer

Abstract

The invention relates to a method for determining 15N isotope abundance of ammonium salt by using a high-resolution liquid chromatograph-mass spectrometer, which comprises the following steps: converting 15N-labeled ammonium nitrogen in a 15N-labeled ammonium salt sample into a 15N-labeled organic matter by using a derivatization reagent, and detecting the 15N in-situ abundance by using the high-resolution liquid chromatograph-mass spectrometer. Compared with the prior art, the method can be used for in-situ abundance detection of the 15N labeled ammonium salt inorganic sample, and has the advantages of simplicity, convenience, high applicability, accuracy and the like.

Description

Technical Field

[0001] The present invention relates to stable isotopes 15 The technical field of N labeling rate detection is particularly related to a method for determining ammonium salts using a high-resolution liquid chromatography-mass spectrometry instrument. 15 N isotope abundance method. Background Art

[0002] Ammonium salts are composed of ammonium ions (NH4 + ) and acid ions (such as Cl - 、SO4 2- 、NO3 - The salt compounds formed by the combination of nitrogen and other substances can be used as fertilizers to provide nitrogen nutrition and improve the activity of soil microorganisms; they are also used in food industries such as fermentation; at the same time, their excessive presence can cause toxicity to aquatic organisms and eutrophication of water bodies, and ammonium ions in water bodies need to be regularly tested. With the continuous development of stable isotope technology, 15 As tracers, N-labeled ammonium salt reagents are gradually used in agriculture, biological nitrogen fixation, drug synthesis and other fields. 15 The N circulation and reaction process are used to explore the mechanisms of soil nitrogen transformation, nitrogen fixation, drug molecular reaction, etc. Therefore, the relevant ammonium salt reagents 15 The evaluation of N isotope abundance is crucial to the accuracy and stability of tracing results.

[0003] Commonly used methods for determining isotope abundance include nuclear magnetic resonance spectroscopy and mass spectrometry. 13 C. Abundance detection of deuterium-labeled chemicals. Invention patent CN 112305007 A discloses a method for determining the deuterium isotope abundance of deuterium-labeled compounds using nuclear magnetic resonance hydrogen spectrum or deuterium spectrum. The internal standard method is used to measure the hydrogen content in the deuterium-labeled compound by the peak area of ​​the spectrum, thereby obtaining the isotope abundance of the deuterium-labeled compound and also obtaining the information of the deuterium labeling site. The method is simple to operate and the detection data is accurate. Invention patent CN 116879341A discloses a method for determining the deuterium isotope abundance of deuterium-labeled compounds using nuclear magnetic resonance carbon spectrum. 13 The isotope abundance of C-labeled compounds is determined by deconvoluting the carbon spectrum and integrating the peak area. 13 C isotope abundance. This method has the advantages of wide application range, simple operation process and high accuracy.

[0004] Mass spectrometry mainly includes gas isotope mass spectrometry, "mass cluster" method and high resolution mass spectrometry. Gas isotope mass spectrometry is to convert the sample into gas for detection. Invention patent CN 111983007 A discloses a method for determining nitric acid or nitrate 15A method or device for determining the abundance of N isotopes, wherein a sample, an oxide and a reducing agent are added to a reaction tube, vacuumed and sealed, and heated to generate 15 N-labeled nitrogen is then introduced into a gas isotope mass spectrometer and the relative intensities of the peaks are calculated. 15 The "mass cluster" method uses a chromatographic-mass spectrometer to obtain the mass spectrum data of the target object, and analyzes the mass spectrum data through the classification calculation method of the "mass cluster" to achieve the D, 13 C or 15 Isotope abundance detection of N-labeled organic compounds. Invention patent CN104122339 A discloses a method for isotope abundance detection based on high performance liquid chromatography-mass spectrometry and the "mass cluster" method. Invention patent CN 104330515A discloses a method for determining 13 The method for determining the isotopic abundance and chemical purity of C-labeled linear fatty acids uses the ratio of isotope peak clusters to calculate the isotopic abundance value of the labeling reagent, which can be achieved 13 Accurate calculation of isotope abundance and chemical purity of C-labeled fatty acids. High-resolution mass spectrometry has ultra-high resolution and high sensitivity, and can directly detect organic compounds in different labeling states, so it has great advantages in isotope abundance detection. Invention patent CN 112630345 A discloses a method for detecting the isotope distribution and abundance of deuterium-labeled compounds based on a high-resolution mass spectrometer. The method is for deuterium-labeled compounds, and its sampling method is flow injection sampling. Multiple mass spectra are collected and the deuterium isotope abundance is calculated according to the formula. Invention patent CN 116482256A discloses a method for measuring the isotope distribution and abundance of deuterium-labeled compounds using a high-resolution liquid chromatography-mass spectrometer. 15 N. 13 Compared with the gas isotope method, the C-labeled isotope abundance method of organic compounds can achieve the determination of two isotope abundances with a single injection. This method is simple to operate, requires less sample, and has high accuracy and stability.

[0005] Among the existing isotope abundance detection methods, nuclear magnetic resonance spectroscopy is mainly used to 13 C. Abundance detection of deuterium-labeled chemicals; Gas isotope mass spectrometry is to convert all samples into gas for detection, which is only suitable for the detection of reagents with higher purity, and the pre-treatment steps are cumbersome; The "mass cluster" method uses low-resolution mass spectrometry and deconvolution methods to process low-resolution mass spectrometry data, but when faced with organic compounds with a large number of labels, each measured data must be converted into an equation group and then calculated, which is relatively inefficient; High-resolution mass spectrometry can directly detect the isotope distribution of samples under different labeling states, and then directly derive the isotope abundance. It is often used for isotope abundance detection of organic compounds. Therefore, the above method is not suitable for inorganic compounds. 15 The detection of N isotope abundance has certain limitations. Summary of the Invention

[0006] The purpose of the present invention is to provide a method for determining ammonium salts by high resolution liquid chromatography-mass spectrometry. 15 The N isotope abundance method can be used to 15 Isotopic abundance detection of N-labeled ammonium salt inorganic samples.

[0007] The purpose of the present invention can be achieved by the following technical solutions: a method for determining the ammonium salt by high resolution liquid chromatography-mass spectrometry 15 The method of N isotope abundance is to firstly convert the 15 N-labeled ammonium salt samples 15 N-labeled ammonium nitrogen is converted to 15 N-labeled organic matter was then detected by high-resolution liquid chromatography-mass spectrometry. 15 N isotope abundance.

[0008] The invention converts the organic matter into organic matter by adding a derivatization reagent and then uses a high-resolution liquid chromatography-mass spectrometer for detection, and has a small sample dosage, simple steps and good accuracy.

[0009] Preferably, the 15 The N-labeled ammonium salt sample was 15 N-labeled ammonium salt inorganic sample.

[0010] Preferably, the 15 The N-labeled ammonium salt sample was 15 N-labeled ammonium sulfate, 15 N-labeled ammonium nitrate or 15 N-labeled ammonium chloride.

[0011] In the present invention, 15 The N-labeled ammonium salt sample was 15 N-labeled ammonium sulfate, 15 N-labeled ammonium nitrate or 15 N marks ammonium chloride and other ammonium-containing compounds.

[0012] Preferably, the derivatization reagent is a derivatization condensation reagent.

[0013] More preferably, the derivatization agent is formaldehyde.

[0014] In the present invention, the ammonium nitrogen in the ammonium salt sample is converted into organic matter by a derivatization reagent.

[0015] Preferably, the 15 N-labeled ammonium salt samples 15 N-labeled ammonium nitrogen is converted to 15 The specific steps for N labeling of organic matter include:

[0016] Take 0.1-5mg 15The N-labeled ammonium salt sample was placed in a centrifuge tube, diluted sulfuric acid solution was added to dissolve it, and then the derivatization reagent was slowly added dropwise, vortexed and allowed to stand, and then an organic solvent was added, shaken and allowed to stand, the supernatant was taken and filtered with a filter membrane to obtain a test solution containing 15 N marks organic matter.

[0017] More preferably, 0.2-1.5 mg 15 N-labeled ammonium salt samples were placed in centrifuge tubes.

[0018] Further preferably, the concentration of the dilute sulfuric acid solution is 0.1-5 mol / L.

[0019] In the present invention, the pH of the original solution should be acidic after adding the dilute sulfuric acid solution.

[0020] More preferably, the mixture is vortex-mixed and then allowed to stand for 4-6 minutes.

[0021] More preferably, the organic solvent is one or more organic reagents that are insoluble in water.

[0022] More preferably, the organic solvent is dichloromethane, chloroform or diethyl ether.

[0023] More preferably, the mixture is allowed to stand for 4-6 minutes after shaking.

[0024] More preferably, the 15 The mass volume ratio of the N-labeled ammonium salt sample to the dilute sulfuric acid solution is 0.1-5 mg:1-2 mL.

[0025] More preferably, the 15 The mass volume ratio of the N-labeled ammonium salt sample to the derivatization reagent is 0.1-5 mg: 2-3 mL.

[0026] More preferably, the 15 The mass volume ratio of the N-labeled ammonium salt sample to the organic solvent is 0.1-5 mg:3-4 mL.

[0027] Further preferably, the pore size of the filter membrane is 0.20-0.24 μm.

[0028] More preferably, the 15 N-labeled ammonium salt samples 15 N-labeled ammonium nitrogen is converted to 15 The specific steps of N labeling organic matter include:

[0029] Take 0.1-5mg 15Place the N-labeled ammonium salt sample in a 10 mL centrifuge tube, add 1-2 mL of dilute sulfuric acid solution to dissolve it, then slowly add 2-3 mL of the derivatization reagent dropwise, vortex to mix, and let it stand for 5 minutes; then add 3-4 mL of organic solvent, shake, and let it stand for 5 minutes. Remove the supernatant and filter it with a 0.22 μm filter membrane to obtain the test solution.

[0030] Preferably, in the high-resolution liquid chromatography-mass spectrometry instrument, the mass detection deviation of the high-resolution mass spectrometer is less than 5 ppm.

[0031] Preferably, in the high-resolution liquid spectrometer, the chromatographic conditions are as follows:

[0032] The chromatographic column was a C18 column, the mobile phase A was a 0.1% formic acid aqueous solution, the mobile phase B was methanol, the flow rate was 0.3 mL / min, the elution condition was 90% B isocratic elution for 4-5 min, and the column temperature was 30-40°C.

[0033] Preferably, in the high-resolution liquid chromatography-mass spectrometry instrument, the mass spectrometry conditions are as follows:

[0034] The ion source is ESI; the electrospray voltage is 3000-3800 V; the nebulizing gas is 2-6 L / min; the auxiliary gas is 0-10 L / min; the ion transfer tube temperature is 300-350°C; the scanning mode is positive and negative ion scanning in full scan mode; the resolution is 60000-120000; and the scanning mass-to-charge ratio range is 40-600 m / z.

[0035] Preferably, the 15 The calculation formula for N isotope abundance is:

[0036]

[0037] Where E is the amount of ammonium salt in the sample 15 N isotope abundance, in 15 Atom% N 15 N); I 145.102 is the mass spectrometry signal intensity of the molecular ion peak at 145.102; I 144.105 is the mass spectrometry signal intensity of the molecular ion peak at 144.105; I 143.108 is the mass spectrometry signal intensity of the molecular ion peak at 143.108; I 142.111 is the mass spectrometry signal intensity of the molecular ion peak at 142.111; I 141.113 is the mass spectrometry signal intensity of the molecular ion peak at 141.113.

[0038] Further preferably, the mass spectrum signal intensities of the molecular ion peaks 145.102, 144.105, 143.108, 142.111, and 141.113 are the superimposed mass spectrum signal intensities within the peak time window in the extracted ion current graph.

[0039] For 15 Currently, the only method for detecting the isotopic abundance of N-labeled ammonium salts in inorganic samples is gas isotope mass spectrometry, which converts the ammonium in the sample into nitrogen gas by adding sodium hypobromite. However, this method is quite limited and only works with reagents containing only high-purity ammonium ions. Furthermore, the sample must undergo a complex and time-consuming pretreatment process before injection. The method described in the present invention is simple, highly applicable, and accurate.

[0040] Compared with the prior art, the present invention has the following beneficial effects:

[0041] 1. The present invention can be used for 15 The isotopic abundance detection method of N-labeled ammonium salt inorganic samples is simple, highly applicable and accurate;

[0042] 2. This invention significantly shortens detection time and improves detection efficiency. This method does not require lengthy pre-treatment steps such as vacuuming and gas conversion, but instead separates the sample after derivatization, making it simpler and more convenient than existing methods.

[0043] 3. The sample amount of the present invention is only 0.1-5 mg, and the sample amount is small;

[0044] 4. The method of the present invention, combined with a high-resolution mass spectrometer, has ultra-high resolution and can detect the exact mass of the compound. It has a significant advantage in isotope abundance detection. Compared with gas isotope mass spectrometry, it has higher detection sensitivity, precision and accuracy, and the detection time is short, and multiple measurements can be performed.

[0045] 5. The method of the present invention is time-consuming, the sample does not need to be subjected to solid phase extraction, the recovery rate is high, the mass spectrometry signal intensity can be ensured, and it is applicable to some 15 N isotope labeling. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 This is embodiment 1 of the present invention 15 High-resolution mass spectrum of N2-ammonium sulfate sample after conversion;

[0047] Figure 2 This is embodiment 2 of the present invention 15 High-resolution mass spectrum after N-ammonium chloride conversion;

[0048] Figure 3 This is embodiment 3 of the present invention 15High-resolution mass spectrum of N-ammonium nitrate after conversion. DETAILED DESCRIPTION

[0049] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments. This embodiment is implemented based on the technical solution of the present invention, and provides a detailed implementation method and specific operation process, but the protection scope of the present invention is not limited to the following embodiments.

[0050] Unless otherwise specified, the reagents, methods, instruments and equipment used in the present invention are conventional reagents, methods, instruments and equipment in the art. Unless otherwise specified, the reagents and materials used in the following examples are commercially available.

[0051] Example 1

[0052] 15 N-labeled ammonium sulfate isotope abundance detection

[0053] Take 0.2mg 15 Dissolve N2-ammonium sulfate in a 10mL centrifuge tube with 1mL of 4mol / L dilute sulfuric acid. Next, add 2mL of formaldehyde solution, vortex to mix, and let stand for 5 minutes. Then, add 4mL of ether, shake, and let stand for 5 minutes. Remove the supernatant and filter through a 0.22μm filter to obtain the test solution.

[0054] High-resolution liquid spectrometry was used for detection, and calibration was performed before detection. The mass detection deviation was less than 5ppm.

[0055] Chromatographic conditions were as follows: chromatographic column: Hypersil GOLD VANQUISH column (100 mm × 2.1 mm, 1.9 μm); mobile phase: mobile phase A was 0.1% formic acid in water, mobile phase B was methanol; elution conditions: 90% B isocratic elution for 5 min; flow rate: 0.3 mL / min; injection volume (i.e., the injection volume of the solution to be tested): 1 μL.

[0056] The mass spectrometry conditions were as follows: ion source: ESI; electrospray voltage (Ion Sray Voltage): 3400 V; sheath gas (Sheath Gas): 5.34 L / min; auxiliary gas (Aux Gas): 9.35 L / min; ion transfer tube temperature: 320°C; scan mode: positive ion scan in full scan mode; resolution: 120,000; scanning mass-to-charge ratio range: 40-500 m / z.

[0057] The obtained high-resolution mass spectrum is as follows Figure 1 shown.

[0058] The mass spectrometry signal intensities of the molecular ion peaks 145.102, 144.105, 143.108, 142.111, and 141.113 were extracted. The results are as follows. The relative intensities are 100, 2.99, 0.03, 0, and 0.01, which are substituted into the formula:

[0059]

[0060] The calculated isotopic abundance is 99.25atom% 15 N, with 15 The N2-ammonium sulfate isotope abundance values ​​are consistent.

[0061] Example 2

[0062] 15 Isotopic abundance detection of N-labeled ammonium chloride

[0063] Take 0.5mg 15 Dissolve N-ammonium chloride in a 10mL centrifuge tube with 1.5mL of 4mol / L dilute sulfuric acid. Next, add 2mL of formaldehyde solution, vortex to mix, and let stand for 5 minutes. Then, add 4mL of dichloromethane, shake, and let stand for 5 minutes. Remove the supernatant and filter through a 0.22μm filter to obtain the test solution.

[0064] High-resolution liquid spectrometry was used for detection, and calibration was performed before detection. The mass detection deviation was less than 5ppm.

[0065] Chromatographic conditions were as follows: column: BEH C18 column (100 mm×2.1 mm, 1.9 μm); mobile phase: mobile phase A was 0.1% formic acid aqueous solution, mobile phase B was methanol; elution conditions: 90% B isocratic elution for 4 min; flow rate: 0.3 mL / min; injection volume: 1 μL.

[0066] The mass spectrometry conditions were as follows: ion source: ESI; electrospray voltage (Ion Sray Voltage): 3500 V; sheath gas (Sheath Gas): 5.34 L / min; auxiliary gas (Aux Gas): 9.35 L / min; ion transfer tube temperature: 320°C; scan mode: positive ion scan in full scan mode; resolution: 120,000; scanning mass-to-charge ratio range: 40-500 m / z.

[0067] The obtained high-resolution mass spectrum is as follows Figure 2 shown.

[0068] The mass spectrometry signal intensities of the molecular ion peaks 145.102, 144.105, 143.108, 142.111, and 141.113 were extracted. The results are as follows. The relative ratios of their intensities are 100, 1.93, 0.02, 0, and 0.01, which are substituted into the formula:

[0069]

[0070] The calculated isotopic abundance is 99.51atom% 15 N, with 15 The isotope abundance values ​​of N-ammonium chloride are consistent.

[0071] Example 3

[0072] 15 Detection of isotopic abundance of N-labeled ammonium nitrate

[0073] Take 1.5mg 15 N-ammonium nitrate ( 15 N-labeled ammonium ion) was placed in a 10 mL centrifuge tube and fully dissolved in 1.5 mL of 4 mol / L dilute sulfuric acid. Next, 2 mL of formaldehyde solution was added, vortexed to mix, and allowed to stand for 5 minutes. Subsequently, 3 mL of chloroform was added, the mixture was shaken, and allowed to stand for 5 minutes. The supernatant was removed and filtered through a 0.22 μm filter membrane to obtain the test solution.

[0074] High-resolution liquid spectrometry was used for detection, and calibration was performed before detection. The mass detection deviation was less than 5ppm.

[0075] Chromatographic conditions were as follows: column: BEH C18 column (100 mm×2.1 mm, 1.9 μm); mobile phase: mobile phase A was 0.1% formic acid in water, mobile phase B was methanol; elution conditions: 90% B isocratic elution for 5 min; flow rate: 0.3 mL / min; injection volume: 1 μL.

[0076] The mass spectrometry conditions were as follows: ion source: ESI; electrospray voltage (Ion Sray Voltage): 3600 V; sheath gas (Sheath Gas): 5.34 L / min; auxiliary gas (Aux Gas): 9.35 L / min; ion transfer tube temperature: 320°C; scan mode: positive ion scan in full scan mode; resolution: 120,000; scanning mass-to-charge ratio range: 100-600 m / z.

[0077] The obtained high-resolution mass spectrum is as follows Figure 3 shown.

[0078] The mass spectrometry signal intensities of the molecular ion peaks 145.102, 144.105, 143.108, 142.111, and 141.113 were extracted. The results are as follows. The relative ratios of their intensities are 100, 2.86, 0.02, 0, and 0. Substitute them into the formula:

[0079]

[0080] The calculated isotopic abundance is 99.30atom% 15 N, with 15 The isotope abundance values ​​of N-ammonium nitrate are consistent.

[0081] The above description of the embodiments is intended to facilitate understanding and use of the invention by those skilled in the art. It will be apparent that those skilled in the art can readily make various modifications to these embodiments and apply the general principles described herein to other embodiments without requiring inventive effort. Therefore, the present invention is not limited to the above-described embodiments. Improvements and modifications made by those skilled in the art based on the disclosure of the present invention, without departing from the scope of the present invention, should be within the scope of protection of the present invention.

Claims

1. A method for determining ammonium salts using high-resolution liquid chromatography-mass spectrometry 15 The method for determining N isotopic abundance is characterized in that First, derivatize the 15 N-labeled ammonium salt samples 15 N-labeled ammonium nitrogen is converted to 15 N-labeled organic matter was then detected by high-resolution liquid chromatography-mass spectrometry. 15 N isotope abundance.

2. according to claim 1, utilize high resolution liquid spectrometer to measure ammonium salt 15 The method for determining N isotopic abundance is characterized in that described 15 The N-labeled ammonium salt sample was 15 N-labeled ammonium sulfate, 15 N-labeled ammonium nitrate or 15 N-labeled ammonium chloride.

3. according to claim 1, utilize high resolution liquid spectrometer to measure ammonium salt 15 The method for determining N isotopic abundance is characterized in that The derivatization agent is formaldehyde.

4. according to claim 1, utilize high resolution liquid spectrometer to measure ammonium salt 15 The method for determining N isotopic abundance is characterized in that By derivatization reagent 15 N-labeled ammonium salt samples 15 N-labeled ammonium nitrogen is converted to 15 The specific steps for N labeling of organic matter include: Take 0.1-5mg 15 The N-labeled ammonium salt sample was placed in a centrifuge tube, diluted sulfuric acid solution was added to dissolve it, and then the derivatization reagent was slowly added dropwise, vortexed and allowed to stand, and then an organic solvent was added, shaken and allowed to stand, the supernatant was taken and filtered with a filter membrane to obtain a test solution containing 15 N marks organic matter.

5. according to claim 4, utilize high resolution liquid spectrometer to measure ammonium salt 15 The method for determining N isotopic abundance is characterized in that The concentration of the dilute sulfuric acid solution is 0.1-5 mol / L; Vortex mix and let stand for 4-6 minutes; The organic solvent is dichloromethane, chloroform or ether; After shaking, let it stand for 4-6 minutes.

6. according to claim 4, utilize high resolution liquid chromatography-mass spectrometry to measure the method for ammonium salt 15 The method for determining N isotopic abundance is characterized in that described 15 The mass volume ratio of N-labeled ammonium salt sample to dilute sulfuric acid solution is 0.1-5 mg:1-2 mL; described 15 The mass volume ratio of N-labeled ammonium salt sample to derivatization reagent is 0.1-5 mg: 2-3 mL; described 15 The mass volume ratio of N-labeled ammonium salt sample to organic solvent is 0.1-5 mg: 3-4 mL; The pore size of the filter membrane is 0.20-0.24 μm.

7. according to claim 1, utilize high resolution liquid spectrometer to measure ammonium salt 15 The method for determining N isotopic abundance is characterized in that In the high-resolution liquid chromatography-mass spectrometry instrument, the mass detection deviation of the high-resolution mass spectrometer is less than 5 ppm.

8. according to claim 1, utilize high resolution liquid spectrometer to measure ammonium salt 15 The method for determining N isotopic abundance is characterized in that In the high-resolution liquid chromatography-mass spectrometry instrument, the chromatographic conditions are as follows: The chromatographic column was a C18 column, the mobile phase A was 0.1% formic acid in water, the mobile phase B was acetonitrile, the elution conditions were 90% B isocratic elution for 5 min, and the column temperature was 30-40°C; Mass spectrometry conditions are as follows: The ion source is ESI; the electrospray voltage is 3000-3800V; the nebulizing gas is 2-6L / min; the auxiliary gas is 0-10L / min; the ion transfer tube temperature is 300-350℃; the scanning mode is positive and negative electron scanning in full scan mode; the resolution is 60000-120000; and the scanning mass-to-charge ratio range is 40-600m / z.

9. according to claim 1, utilize high resolution liquid spectrometer to measure ammonium salt 15 The method for determining N isotopic abundance is characterized in that described 15 The calculation formula for N isotope abundance is: Where E is the amount of ammonium salt in the sample 15 N isotope abundance, in atom% 15 N;I 145.102 is the mass spectrometry signal intensity of the molecular ion peak at 145.102; I 144.105 is the mass spectrometry signal intensity of the molecular ion peak at 144.105; I 143.108 is the mass spectrometry signal intensity of the molecular ion peak at 143.108; I 142.111 is the mass spectrometry signal intensity of the molecular ion peak at 142.111; I 141.113 is the mass spectrometry signal intensity of the molecular ion peak at 141.

113.

10. The method of measuring ammonium salt by high resolution liquid chromatography-mass spectrometry according to claim 9 15 The method for determining N isotopic abundance is characterized in that The mass spectrometry signal intensities of the molecular ion peaks 145.102, 144.105, 143.108, 142.111, and 141.113 are the superimposed mass spectrum signal intensities within the peak time window in the extracted ion chromatogram.

Images