CN115684325A - Ultrahigh-resolution mass spectrometry method for dissolving organic carbon and application thereof - Google Patents
Ultrahigh-resolution mass spectrometry method for dissolving organic carbon and application thereof Download PDFInfo
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Abstract
The invention discloses an ultrahigh resolution mass spectrometry method for dissolving organic carbon and application thereof. The mass spectrometry method comprises the following steps: injecting the treated sample into an ESI ion source of a mass spectrum in a negative ion mode, wherein the electrospray voltage is 2800V-3400V, and the sheath gas: the auxiliary airflow ratio is 28 5 ～1×10 6 The temperature of an ion transmission pipe is 275-325 ℃, the resolution is 240000-500000, the flow rate of sample injection is 5-8 mul/min, and the volume ratio of a sample injection solvent is acetonitrile water solution or methanol water solution of 1; and finally, analyzing the mass spectrum data. According to the invention, the optimal parameters in the ultrahigh resolution mass spectrometry are determined through research, so that the DOC mass spectrometry result is optimal, the number of DOC molecules is increased, the response intensity is increased, and the signal-to-noise ratio is reduced, thereby providing a more accurate and convenient analysis method for the DOC detection and analysis.
Description
Technical Field
The invention belongs to the field of mass spectrometry and chemical analysis, and particularly relates to an ultrahigh-resolution mass spectrometry method for dissolving organic carbon and application thereof.
Background
In natural water, organic carbon can be generally divided into a dissolved state and a particle state. The basis for the classification is that the Organic Carbon in the water body can pass through a membrane filter with the pore diameter of 0.45 μm, namely Dissolved Organic Carbon (DOC). DOC is an important chemical component in natural water and mainly contains C, H and O elements and a small amount of heteroatom elements such as N, P, S and the like. DOC is widely available and is generally the natural decomposition of animal and plant residues under the action of microorganisms, wherein humus is the main component of DOC (Wufengchang, queening, living, zhangyu, friedel-crafts, liaohaiqing, baiying minister, guo Jianyang, wangjing, natural organic matter and its importance in surface environment [ J ] lake science, 2008 (01): 1-12.). DOC participates in a large number of biogeochemical cycle processes in water widely, and plays a significant role in all links of an ecosystem. DOC is an important component of global carbon cycle, and DOC in seawater is an important dynamic carbon reservoir in global carbon cycle. Therefore, the research on DOC composition in different water body environments has important significance.
DOC comprises thousands of compounds including organic compounds containing different elements such as DOC, dissolved Organic Nitrogen (DON), dissolved Organic Sulfur (DOS), etc. In the past 30 years, different technologies have been used to characterize DOC, a huge carbon reservoir. The total attribute characterization of the DOC is realized through optical means such as ultraviolet absorption and fluorescence spectrum analysis, but the technology cannot meet the requirement of scientists on deep knowledge of the DOC, cannot analyze the composition characteristics of the DOC from a molecular level, and further hinders the research on the migration and transformation mechanism of the DOC.
The rise of ultra-high resolution mass spectrometry has been widely used in DOC research for the last decade. The high-resolution mass spectrum has high sensitivity when scanning the compound, can obtain accurate molecular weight information of the compound, and can effectively distinguish the molecular composition of different compounds in DOC. Currently, fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) is the best technique for analyzing DOC composition because it is high in accuracy, resolution and sensitivity, but it is expensive and thus not widely used. Electrostatic field Orbitrap mass spectrometry (Orbitrap MS), although less accurate, resolution and sensitivity than FT-ICR-MS, is relatively inexpensive and meets the analytical requirements for most compounds in the DOC (DOI: 10.1021/acs. Analchem.6b01624.). The knowledge of the DOC molecular composition is greatly broken through, and the extremely rich DOC molecular composition information is provided.
However, when the DOC molecular composition is analyzed and characterized by using the high-resolution mass spectrum, the experimental conditions and the setting of mass spectrum parameters have certain influence on the data result obtained by analysis (DOI: 10.1021/acs. Analchem.7b04159). Therefore, before the high-resolution mass spectrometry sample injection analysis is applied, the setting of the parameters needs to be optimized. In the existing research, kido Soule et al (2010) test the influence of instruments and experimental parameters on the stability of DOC in the natural water body determined by FT-ICR MS. Related parameters of ion accumulation time, detection time and resolution ratio under two different data acquisition modes of full scanning and selective ion monitoring are optimized, and the repeatability of ion detection and the repeatability of mass spectrum peak height under the two data acquisition modes are evaluated by applying the optimal instrument conditions. In addition, the commonly used sample injection solvent for the ultra-high resolution mass spectrometry of DOC at present is methanol, methanol is used as the sample injection solvent, so that methyl esterification is easily generated between DOC molecules and methanol, and the methanol has strong elution capability, so that impurities of an ion source can be eluted together to enter mass spectrometry, and the reproducibility of a measurement result is influenced; some researchers also use a mixed solvent of methanol and water with a volume ratio of 1.
The DOC molecules obtained from the existing ultrahigh resolution mass spectrometry result are fewer, the response intensity is lower, the signal-to-noise ratio is high, and the blank background is higher.
To sum up, the sampling conditions (sampling solvent and sampling amount, etc.) and the instrument parameters (mass resolution, signal response value, scanning number, AGC number, etc.) of the ultra-high resolution mass spectrometry (Orbitrap) need to be optimized to improve the analysis capability of the ultra-high resolution mass spectrometry on the DOC, and form a set of analysis technical scheme for system optimization.
Disclosure of Invention
The invention aims to overcome the defect of DOC analysis by the existing ultrahigh resolution mass spectrum and provides an ultrahigh resolution mass spectrum analysis method for dissolving organic carbon and application thereof.
The invention aims to provide an ultrahigh resolution mass spectrometry method for dissolving organic carbon.
The invention also aims to provide the application of the ultrahigh-resolution mass spectrometry method in dissolved organic carbon analysis.
The above object of the present invention is achieved by the following technical means:
a method for analyzing the mass spectrum of dissolved organic carbon with ultrahigh resolution includes such steps as dissolving organic carbon in water,
s1, sample treatment
Dissolving the enriched and eluted dissolved organic carbon sample in methanol, drying, and preparing a sample injection sample with the concentration of 0.05-0.2 mg/mL by using a sample injection solvent; the sample injection solvent is acetonitrile water solution or methanol water solution with the volume ratio of 1;
s2, injecting the sample obtained in the step S1 into an ESI ion source of the ultra-high resolution mass spectrum in a negative ion mode, wherein the electrospray voltage (ESV) is 2800V-3400V, and the sheath gas: auxiliary airflow ratio 28 5 ～1×10 6 (2.0e5-1.0e6), the temperature (ITT) of an ion transmission tube is 275-325 ℃, the resolution is 240000-500000, the flow rate of sample injection is 5-8 mu l/min, and the scanning range is 100-1000 m/z in a full scanning mode;
and S3, acquiring and analyzing data.
Preferably, in step S1, a sample injection sample with a concentration of 0.1mg/mL is prepared by using a sample injection solvent.
Preferably, in step S1, the injection solvent is an acetonitrile aqueous solution with a volume ratio of 1.
Preferably, in step S2, the electrospray voltage (ESV) is 3200V to 3400V.
Further preferably, in step S2, the electrospray voltage (ESV) is 3200V.
Preferably, in step S2, the sheath gas: the auxiliary airflow ratio is 28.
Further preferably, in step S2, the sheath gas: the auxiliary airflow ratio was 28.
Preferably, in step S2, the Automatic Gain Control (AGC) is 5 × 10 5 ～1×10 6 (5.0e5～1.0e6)。
Further preferably, in step S2, the Automatic Gain Control (AGC) is 5 × 10 5 (5.0e5)。
Preferably, in step S2, the ion transfer tube temperature (ITT) is 275 ℃ to 300 ℃.
Further preferably, in step S2, the ion transfer tube temperature (ITT) is 300 ℃.
Preferably, in step S2, the resolution is 240000.
Preferably, in step S2, the flow rate of the sample injection is 8 μ l/min.
As a specific example of the above method, an ultra-high resolution mass spectrometry method of dissolving organic carbon comprises the steps of,
s1, sample treatment
Dissolving the enriched and eluted Yangtze river mouth dissolved organic carbon sample in methanol, taking 0.2mL of sample methanol solution, drying by using soft nitrogen, and preparing a sample introduction sample with the concentration of 0.1mg/mL by using a solution with the volume ratio of acetonitrile to water being 1;
s2, injecting the sample obtained in the step S1 into an ESI ion source of an ultrahigh-resolution mass spectrum in a negative ion mode, wherein the electrospray voltage (ESV) is 3200V, and the sheath gas: the auxiliary airflow ratio is 28, the Automatic Gain Control (AGC) is 5.0e5, the temperature of an Ion Transmission Tube (ITT) is 300 ℃, the resolution is 240000, the sampling flow rate is 8 mu l/min, acetonitrile water solution with the volume ratio of 1.
And S3, acquiring and analyzing data.
The application of the ultra-high resolution mass spectrometry method in the analysis of dissolved organic carbon is also within the protection scope of the invention.
Preferably, the dissolved organic carbon is derived from natural water or soil.
Preferably, the dissolved organic carbon is from a natural water body.
Compared with the prior art, the invention has the following beneficial effects:
the invention researches electrospray voltage and sheath gas in ultrahigh resolution mass spectrometry: the optimal parameters are determined by the influence of parameters such as auxiliary airflow ratio, automatic gain control, ion transmission tube temperature, resolution ratio, sample injection flow rate, sample injection solvent and the like on DOC analysis, so that the DOC mass spectrometry result is optimal, the number of DOC molecules is increased, the response intensity is increased and the signal-to-noise ratio is reduced. The ultrahigh resolution mass spectrometry method provides a more accurate and convenient analysis method for the detection and analysis of the Dissolved Organic Carbon (DOC).
Drawings
FIG. 1 shows the response results of mass spectrum peaks after changing the injection concentration in example 1 of the present invention.
FIG. 2 shows the effect of varying sample concentration on molecular SNR in example 1 of the present invention.
FIG. 3 shows the response of mass spectrum peak after changing the flow rate of the sample injection in example 2 of the present invention.
FIG. 4 is the response result of mass spectrum peak after changing the ratio of the injected solvent in example 3 of the present invention.
FIG. 5 shows the effect of varying the ratio of the injected solvent on the molecular signal-to-noise ratio in example 3 of the present invention.
FIG. 6 shows the response of mass spectrum peak after changing the injected solvent in example 3.
FIG. 7 shows the effect of changing the injection solvent on the molecular SNR in example 3 of the present invention.
FIG. 8 shows the results of mass peak responses after changing gas parameters in example 4 of the present invention.
FIG. 9 shows the effect of varying gas parameters on molecular SNR in example 4 of the present invention.
FIG. 10 shows the results of mass peak responses after changing the instrument parameters in example 5 of the present invention.
FIG. 11 shows the effect of changing the parameters of the apparatus on the molecular SNR in example 5 of the present invention.
Fig. 12 shows the detection results of DOC in the near-shore and far-shore samples of the estuary in example 6 of the present invention, where a is the response intensity and B is the signal-to-noise ratio.
FIG. 13 shows the measurement results of lipids, proteinoids, amino acids, tannins, lignins, and black char compounds in the samples near and far from the estuary in example 6 of the present invention.
Detailed Description
The present invention will be further described with reference to the following specific examples, which are not intended to limit the invention in any manner. Reagents, methods and apparatus used in the present invention are conventional in the art unless otherwise indicated.
Unless otherwise indicated, reagents and materials used in the following examples are commercially available.
Experimental reagents and materials:
the Suwanne River Fulvic Acid (SRFA; suwanne River Fulvic Acid Standard II,2S 101F) used in this experiment was from the International humus society; methanol and acetonitrile were both LC grade, purchased from Merck KGaA (Darmstadt, germany); the ultrapure water system used in the experiments was manufactured by Xiamen Rische scientific instruments Ltd (model: unique-R10).
The invention tests the influence of various factors on mass spectrum data, including DOC concentration and sample injection reagent contained in a sample injection. Before sample injection, the SRFA stock solution needs to be diluted according to the sample injection concentration and the sample injection reagent designed by experiments.
Example 1 Effect of sample concentration on DOC Mass Spectrometry detection
1. Sample processing
Dissolving a standard sample SRFA in ultrapure water to prepare a stock solution of 0.4mg/mL, and refrigerating at 4 ℃ in the dark.
2. Conditions of the experiment
The analysis was performed using a ThermoFisher Scientific Orbitrap Fusion MS.
Before sample introduction, the instrument is corrected by using the instrument negative source correction liquid under the negative ion mode. The SRFA sample was diluted and the ESI ion source was injected using a syringe pump. Diluting the SRFA sample by using a methanol water solution to obtain sample introduction samples with sample introduction concentrations of 0.05mg/mL, 0.1mg/mL and 0.2mg/mL, wherein the volume percentage of the sample introduction solvent methanol water solution in the sample introduction samples is 50% (v/v).
3. Instrument parameter setting
A negative ion mode; electrospray voltage (ESV) 3200V; the sheath gas flow rate was 5arb; the auxiliary airflow rate is 2arb; the tail blowing gas flow rate was 0arb (sheath gas: auxiliary gas: tail blowing gas flow rate ratio 5; the sheath gas, the auxiliary gas and the tail blowing gas are all nitrogen; the sample injection flow rate is 5 mu L/min, and the sample injection solvent methanol: water =1 (v: v); an ion transport tube temperature (ITT) of 300 ℃; resolution 240000, integration time 100ms; the lens voltage is 70V; automatic gain control (AG)C) The number of (2.0 e5) is 2.0 × 10 5 (ii) a The maximum ion implantation time is 100ms; and in a full scanning mode, the scanning range is 100-1000 m/z. And changing to sample introduction samples with different concentrations for testing.
4. Data acquisition and processing
Mass spectrum data obtained after sample injection is derived from Xcalibur 3.0, preliminary treatments such as mass spectrum peak molecular formula distribution and the like are carried out in formula software, and Excel (Microsoft, 2007) is used for carrying out subsequent data statistics and analysis. When mass spectrum peaks are matched, the matching error is less than 5ppm, simultaneously, after field blank and operation blank are deducted, mass spectrum peaks of all signal-to-noise ratios (S/N > 6) in mass spectrum original signals are selected and molecular formula distribution is carried out, and the analysis principle is as follows: up to no more than 30 12C,60 1H,20 1O, 3 14N,1 32S,1 13C,1 18O and 1 34S in DOC molecular formula. The molecular formulas containing isotopes (e.g., 13c,18o and 34S) are not discussed. Furthermore, the resolved molecular formulae all follow the following three principles: (1) the number of H is at least one-third of the number of C, and the number may not exceed 2C + N +2; (2) the total number of N and H atoms must be even (N criterion); (3) the number of N or O atoms does not exceed the total number of C atoms.
5. Results
(1) The results of mass spectrum peak responses after changing the sample concentration are shown in FIG. 1.
The results in FIG. 1 show that the response intensity (intensity) gradually increases with increasing sample concentration.
(2) The results of the effect of varying the sample concentration on the number of the molecular formula are shown in table 1,
TABLE 1
| Number of molecular formula | |
| 0.05mg/mL | 1767 |
| 0.10mg/mL | 2029 |
| 0.20mg/mL | 2305 |
| Three samples at different concentrations share a peak | 1369 |
The results in Table 1 show that the amount of the identified compound formula significantly increased as the feed concentration increased from 0.05mg/mL to 0.20 mg/mL.
(3) The effect of varying sample concentration on molecular signal-to-noise ratio is shown in FIG. 2
The results in FIG. 2 show that as the concentration of the sample is increased, the signal-to-noise ratio is reduced, indicating that the noise is gradually increased as the concentration is increased.
As can be seen, the mass spectrometry ion source is more likely to become dirty as the concentration of the injected sample increases and the more compounds enter. When the sample injection concentration is 0.10mg/mL, the ideal number and response intensity of molecules are ensured, and the ion source is not easy to become dirty.
Example 2 influence of sample injection flow Rate on DOC Mass Spectrometry detection
1. Sample processing
The same as in example 1.
2. Conditions of the experiment
The same as in example 1.
3. Instrument parameter setting
A negative ion mode; electrospray voltage (ESV) 3200V; the sheath gas flow rate was 5arb; the auxiliary airflow rate is 2arb; the tail-blowing gas flow rate was 0arb (sheath gas: auxiliary gas flow rate ratio 5; the sheath gas, the auxiliary gas and the tail blowing gas are all nitrogen; the sample injection concentration is 0.1mg/mL, and the sample injection solvent methanol: water =1 (v: v); an ion transport tube temperature (ITT) of 300 ℃; resolution 240000, cumulative time 100ms;the lens voltage is 70V; the number of Automatic Gain Controls (AGC) is 2.0 x 10 5 (ii) a The maximum ion implantation time is 100ms; and in a full scanning mode, the scanning range is 100-1000 m/z. Only the flow rate of the sample injection was changed, and the flow rates of the sample injection were set to 5. Mu.L/min, 8. Mu.L/min, and 10. Mu.L/min, respectively, for analysis.
4. Data acquisition and processing
The same as in example 1.
5. Results
(1) The results of mass spectrum peak responses after changing the injection flow rate are shown in FIG. 3.
The results in FIG. 3 show that as the sample flow rate increases, more compounds enter the mass spectrum, so the response intensity (intensity) increases gradually, and the next part of low flow rate can be detected after the flow rate increases because of low ionization efficiency or because of low concentration of non-captured ions; as the amount of sample introduction increases, the ion detection signal increases, and the compounds with high ionization efficiency are more competitive, so the response signal increases exponentially. However, the sample introduction flow rate is increased, and mass substances entering the mass spectrometer are increased, so that the ion source is easily polluted.
(2) The results of varying the injection flow rate on the number of the molecules are shown in table 2,
TABLE 2
| Number of molecular formula | |
| 5μL/min | 2572 |
| 8μL/min | 2537 |
| 10μL/min | 2605 |
| Three samples at different flow rates share a peak | 1588 |
Table 2 in conjunction with fig. 3 shows that as the injection flow rate is increased from 5 μ L/min to 8 μ L/min, the amount of the identified compound molecular formula does not increase significantly, but the response intensity increases significantly; when the flow rate was increased to 10 μ L/min, the number of identified compound molecular formulas increased significantly, while the response intensity of the compound doubled. When the flow rate is increased to 10 mu L/min, the response intensity is increased too fast, which indicates that the compound has stronger competitive ionization, the characterization of the compound difficult to ionize is influenced, and meanwhile, the pollution of the ion source can be accelerated if the sample injection flow rate is too high.
Therefore, the mass spectrum peak response signal and the identified compound molecular formula number are combined, and 8 μ L/min is most suitable as the injection flow rate.
Example 3 Effect of sample injection solvent on DOC Mass Spectrometry detection
1. Sample processing
The same as in example 1.
2. Conditions of the experiment
The same as in example 1.
3. Instrument parameter setting
A negative ion mode; electrospray voltage (ESV) 3200V; the sheath gas flow rate was 5arb; the auxiliary airflow rate is 2arb; the tail-blowing gas flow rate was 0arb (sheath gas: auxiliary gas flow rate ratio 5; the sheath gas, the auxiliary gas and the tail blowing gas are all nitrogen; the sample injection concentration is 0.1mg/mL; the sample injection flow rate is 5 mul/min; an ion transport tube temperature (ITT) of 300 ℃; resolution 240000, cumulative time 100ms; the lens voltage is 70V; the number of Automatic Gain Controls (AGC) is 2.0 x 10 5 (ii) a The maximum ion implantation time is 100ms; and in a full scanning mode, the scanning range is 100-1000 m/z. The sample injection solvents were set to 1. And alsoA1.
4. Data acquisition and processing
The same as in example 1.
5. As a result, the
(1) The response results of mass spectrum peaks after changing the solvent ratio of the injection sample are shown in FIG. 4.
The results in fig. 4 show that the increase of methanol ratio in the injection solvent makes it easier to remove the solvent during the ionization process, and the ionization efficiency is higher, so that more compounds are detected and the response signal is multiplied.
(2) The results of the effect of changing the ratio of the injection solvent on the number of the molecular formula are shown in Table 3, the results of the effect of changing the ratio of the injection solvent on the signal-to-noise ratio of the molecular formula are shown in FIG. 5,
TABLE 3
| Number of |
|
| 1 | 1885 |
| 1, methanol water (v: v) | 2029 |
| 3 | 2947 |
| Three samples with different ratios of solvents share a common peak | 1600 |
The results in table 3 and fig. 5 show that as the methanol ratio in the injected solvent increases, the number of the identified compound molecular formula increases and the signal-to-noise ratio also gradually increases; the volume ratio of methanol to water is increased from 1.
As the methanol fraction in the injected solvent increases, methanol tends to form adducts with the compounds and their fragments, and may increase the molecular formula number, forming more adduct peaks than the compound peaks in the DOC.
Thus, the response signal of the mass spectrum peak and the number of identified compound molecular formulas were combined, and the injection solvent methanol: the water content is 1 (v: v).
(3) The response results of mass spectrum peaks after changing the injected solvent are shown in FIG. 6.
The results in FIG. 6 show that the response intensity of the mass spectrum peak detected with acetonitrile water as the injection solvent is much higher than that detected with methanol water as the injection solvent. Because the viscosity coefficient (2.02 mPas) of the methanol is far higher than that (0.98 mPas) of the acetonitrile, the boiling point of a sample injection solvent of the acetonitrile and water is lower, the sample injection solvent is easier to volatilize, the ionization efficiency of the compound is higher, and the influence strength of the compound is higher.
(4) The results of the effect of varying the injection solvent on the number of molecular formulas are shown in table 4,
TABLE 4
| Number of |
|
| 1 | 2733 |
| 1, methanol water (v: v) | 3345 |
| Two samples of different solvents share a peak | 2015 |
The results in Table 4 show that methanol water as solvent is about 20% more than acetonitrile water as solvent can identify the molecular formula of the compound, which indicates that methanol water as solvent can detect more compound than acetonitrile water as solvent, and the solvent containing methanol is easier to form adduct with the compound and its fragments in DOC, thus increasing the molecular formula amount of the compound detected by mass spectrometry.
(5) The effect of changing the injection solvent on the molecular signal-to-noise ratio is shown in FIG. 7
FIG. 7 shows that the signal-to-noise ratio of the compounds detected with methanol water as the solvent and acetonitrile water as the solvent is not very different.
Taken together, therefore, the response signals of the mass spectral peaks and the identified number of compound formulae, acetonitrile: water 1.
Example 4 Effect of sheath and supporting gases on DOC Mass Spectrometry detection
1. Sample processing
The same as in example 1.
2. Conditions of the experiment
The same as in example 1.
3. Instrument parameter setting
A negative ion mode; electrospray voltage (ESV) 3200V; the sample injection concentration is 0.1mg/mL; sampling a solvent methanol: water =1 (v: v); the ion transport tube temperature (ITT) is 300 ℃; high resolution 240000, cumulative time 100ms; the lens voltage is 70V; the number of Automatic Gain Controls (AGC) is 2.0 x 10 5 (ii) a The maximum ion implantation time is 100ms; and in a full scanning mode, the scanning range is 100-1000 m/z. Only the sheath gas and the auxiliary gas are changed, the sample injection flow rate is 5 mu L/min, and the sheath gas: the auxiliary airflow ratio is 4; the sample introduction flow rate is 8 muL/min, and the sheath gas: the auxiliary airflow ratio is 15, 28. Are respectively divided intoAnd (6) analyzing. The sheath gas and the auxiliary gas are both nitrogen.
4. Data acquisition and processing
The same as in example 1.
5. As a result, the
(1) The results of the mass spectral peak response after changing the gas parameters are shown in FIG. 8.
The results in FIG. 8 show that at a sample flow rate of 5. Mu.L/min, the response intensity of the sheath gas and auxiliary gas flow rate ratio of 4 is significantly reduced compared to the response intensity of the flow rate ratio of 4; the response intensity for a flow rate ratio of 15.
When the sample injection flow rate is 5 muL/min, the response intensity of the flow rate ratio of 15; the response intensity for a flow rate ratio of 15.
When the sample injection flow rate is 8 mu L/min, the response intensity of the flow rate ratio of 28; the response intensity for a flow rate ratio of 28.
The sheath gas is unchanged, and the mass spectrum peak response intensity of the identified compound is reduced due to the increase of the auxiliary gas; the auxiliary gas is unchanged, the sheath gas is properly increased, and the mass spectrum peak response intensity of the compound which is helpful for identification is increased.
(2) The results of the effect of varying the gas parameters on the number of molecular formulas are shown in table 5,
TABLE 5
The results in table 5 show that, in the flow rate ratio of sheath gas to auxiliary gas at a flow rate of 5 μ L/min, the number of the formula having a flow rate ratio of 4; the number of molecular formulas with a flow rate ratio of 5; however, the number of molecular formulas with a flow rate ratio of 15. It can be seen from the response intensity of the mass spectrum peak in fig. 4 that the sheath gas is increased to a certain extent, and the increase of the assisting gas helps to increase the number of the identified molecular compounds.
When the flow rate of the sample is 8 μ L/min, the mass spectrum peak response intensity is slightly reduced when the ratio of the sheath gas flow rate to the auxiliary gas flow rate is 28.
(3) The effect of varying gas parameters on molecular signal-to-noise ratio results are shown in figure 9,
FIG. 9 shows that at a sample injection flow rate of 5 μ L/min, the ratio of sheath gas to auxiliary gas flow rate is 4; the flow ratio is 5; the flow rate ratio 15.
When the sample injection flow rate is 5 muL/min, compared with the signal-to-noise ratio of 4, the signal-to-noise ratio of 15; the signal-to-noise ratio of 15 for flow rate ratio 5 is significantly higher than that of 5 for flow rate ratio.
When the sampling flow rate is 8 muL/min, compared with the signal-to-noise ratio of 15, the signal-to-noise ratio of the flow rate is 28; the response intensity for a flow rate ratio of 28.
The fact that when the flow rate of the sheath gas is lower (less than or equal to 5), the signal-to-noise ratio of the mass spectrum signal is lower due to the increase of the auxiliary gas; and when the flow rate of the sheath gas is higher (more than or equal to 15), the signal-to-noise ratio of the mass spectrum signal is increased due to the increase of the auxiliary gas.
In conclusion, when the sample injection flow rate is 8 muL/min and the ratio of sheath gas to auxiliary gas flow rate is 28.
Example 5 Effect of instrument parameters on DOC Mass Spectrometry detection
1. Sample processing
The same as in example 1.
2. Conditions of the experiment
The same as in example 1.
3. Instrument parameter setting
A negative ion mode; electrospray voltage (ESV) 3200V; the sheath gas flow rate was 5arb; the auxiliary airflow rate is 2arb; the tail-blowing gas flow rate was 0arb (sheath gas: auxiliary gas flow rate ratio 5; the sheath gas, the auxiliary gas and the tail blowing gas are all nitrogen; the sample injection concentration is 0.1mg/mL; the sample injection flow rate is 5 mu l/min; sampling a solvent acetonitrile: water =1 (v: v); an ion transport tube temperature (ITT) of 300 ℃; high resolution 240000, cumulative time 100ms; the lens voltage is 70V; the number of Automatic Gain Controls (AGC) is 2.0 x 10 5 (2.0e5); the maximum ion implantation time is 100ms; and in a full scanning mode, the scanning range is 100-1000 m/z.
The following parameters were varied and the analysis was performed separately.
(1) Changing AGC
AGC is set to 1.0e5, 2.0e5, 5.0e5, 1.0e6, respectively.
(2) Altering ESV
The ESVs were set to 2800V, 3000V, 3200V, 3400V, respectively.
(3) Altering ITT
ITT was set at 275 deg.C, 300 deg.C, 325 deg.C, respectively.
(4) Resolution ratio
The resolutions were set to 120000, 240000, 500000, respectively.
4. Data acquisition and processing
The same as in example 1.
5. Results
(1) The results of the response of the mass spectrum peaks after changing the instrument parameters are shown in fig. 10, the results of the influence of changing the instrument parameters on the number of the molecular formula are shown in table 6, and the results of the influence of changing the instrument parameters on the molecular formula signal-to-noise ratio are shown in fig. 11.
TABLE 6
The results in fig. 10, 11 and table 6 show that as the Automatic Gain Control (AGC) parameter increases from 1.0e5 to 1.0e6, the intensity of the mass spectrum peak response of the compound gradually decreases, the number of identified compound molecular formulas gradually increases, and the signal-to-noise ratio gradually increases. And comprehensively considering the mass spectrum peak response intensity of the compound and the number of the identified compound molecules, and determining that the optimal AGC is 5.0e5.
As the electrospray voltage (ESV) parameter increased from 2800V to 3400V, there was no significant change in the compound mass spectrum peak response intensity, the number of identified compound molecular formulas increased first and then decreased, and the signal-to-noise ratio also showed a rule of increasing first and then decreasing. When the ESV is 3200V, the number of the identified compound molecular formulas is the largest, and the signal-to-noise ratio is the largest, so that the ESV is determined to be 3200V optimally.
As the ion transport tube temperature (ITT) increased from 275 ℃ to 325 ℃, the compound mass spectral peak response intensity increased slightly, the number of identified compound molecular formulas increased first and then decreased, and there was no significant change in signal-to-noise ratio. When the ITT is 300 ℃, the number of the identified molecular formulas of the compound is the largest, and the mass spectrum peak response intensity is higher, so that the ITT is determined to be the most optimal 300 ℃.
As the resolution parameter is increased from 120000 to 50000, the response intensity of the mass spectrum peak of the compound is slightly reduced, the number of the molecular formulas of the identified compound is obviously increased, the signal-to-noise ratio is gradually reduced, and the noise signal is gradually increased along with the increase of the resolution. When the resolution ratio is increased, the cyclotron time of ions in the electrostatic field orbit ion trap is increased, collisions among the ions are increased, more fragment compounds are generated, and meanwhile, more compounds can be identified along with the increase of the cyclotron time, so that the overall response intensity of the compounds is reduced. And (4) integrating the mass spectrum peak response intensity of the compound and the number of the identified compound molecules, and determining that the optimal resolution is 240000.
By integrating the above optimization analysis experiments, we determined the optimal mass spectrometry sample introduction conditions and instrument parameter settings, negative ion mode, automatic Gain Control (AGC) 5.0e5, electrospray voltage (ESV) 3200, ion transport tube temperature (ITT) 300 ℃, resolution 240000, accumulation time 100ms, sheath gas: the auxiliary gas is 28.
EXAMPLE 6 determination of DOC in a sample
1. Sample processing
Dissolving the enriched and eluted Yangtze river mouth dissolved organic carbon sample in methanol, taking 0.2mL of sample methanol solution, drying the sample methanol solution by using soft nitrogen, and preparing a sample injection sample with the concentration of 0.1mg/mL by using a solution with the acetonitrile water volume ratio of 1.
2. Experiment of
The analysis was performed using a ThermoFisher Scientific Orbitrap Fusion MS.
Before sample introduction, the instrument is corrected by using the instrument negative source correction liquid under the negative ion mode. The diluted sample was then injected into the ESI ion source using a syringe pump.
The instrument parameters are as follows: negative ion mode, electrospray voltage (ESV) 3200, sheath gas: the auxiliary airflow ratio is 28; and in a full scanning mode, the scanning range is 100-1000 m/z.
3. Results
(1) The detection results of DOC in the near-shore and far-shore samples of the estuary are shown in fig. 12, where a is response intensity and B is signal-to-noise ratio.
FIG. 12 shows that the mass spectrum response intensity of the DOC sample near the Yangtze river estuary is higher than that of the DOC sample far from the Yangtze river estuary, because the near-shore land source input is more and the seawater composition is complex; the signal-to-noise ratio of the DOC sample at the near bank of the Yangtze estuary is higher than that of the DOC sample at the far bank, because the near-bank seawater has complex composition and larger interference on mass spectrum, and the far-bank seawater has single component, so the signal-to-noise ratio is higher. This further illustrates the low signal-to-noise ratio of the detection method of the present invention.
(2) Fig. 13 shows the measurement results of lipids, proteinoids, amino acids, tannins, lignins, and black charcoals in the samples from the near bank and the far bank of the Yangtze river.
Figure 13 shows that lipids, tannins and lignins are decreasing but proteinoid compounds are increasing from the near shore to the far shore sites of the estuary.
The above embodiments are preferred embodiments of the present invention, but the present invention is not limited to the above embodiments, and any other changes, modifications, substitutions, combinations, and simplifications which do not depart from the spirit and principle of the present invention should be construed as equivalents thereof, and all such changes, modifications, substitutions, combinations, and simplifications are intended to be included in the scope of the present invention.
Claims (10)
1. An ultrahigh resolution mass spectrometry method for organic carbon dissolved in natural water is characterized by comprising the following steps,
s1, sample treatment
Dissolving the enriched and eluted dissolved organic carbon sample in methanol, drying, and preparing a sample injection sample with the concentration of 0.05-0.2 mg/mL by using a sample injection solvent; the sampling solvent is acetonitrile water solution or methanol water solution with the volume ratio of 1;
s2, injecting the sample obtained in the step S1 into an ESI ion source of the ultrahigh-resolution mass spectrum in a negative ion mode, wherein the electrospray voltage is 2800V-3400V, and the sheath gas: the auxiliary airflow ratio is 28 5 ～1×10 6 The temperature of the ion transmission tube is 275-325 ℃, the resolution is 240000-500000, the flow rate of sample injection is 5-8 mu l/min, the full scanning mode is adopted, and the scanning range is 100-1000 m/z;
and S3, acquiring and analyzing data.
2. The method of ultra-high resolution mass spectrometry of claim 1, wherein in step S1, the sample injection is prepared with a sample injection solvent at a concentration of 0.1 mg/mL.
3. The method of claim 1, wherein the electrospray voltage is 3200V to 3400V in step S2.
4. The method for ultra-high resolution mass spectrometry of claim 1, wherein in step S2, the sheath gas: the auxiliary airflow ratio is 28.
5. The method for ultra-high resolution mass spectrometry of claim 1, wherein in step S2, the automatic gain control is 5 x 10 5 ～1×10 6 。
6. The method of claim 4, wherein in step S2, the automatic gain control is 5 x 10 5 。
7. The method of claim 1, wherein in step S2, the ion transfer tube temperature is 275 ℃ to 300 ℃.
8. The method of ultra-high resolution mass spectrometry of claim 1, wherein in step S2, the resolution is 240000.
9. The method of ultra-high resolution mass spectrometry of claim 1, wherein in step S2, the flow rate of the sample is 8 μ l/min.
10. Use of the ultra-high resolution mass spectrometry method of claims 1-9 for dissolved organic carbon analysis.
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