A method for determining volatile components in Liubao tea using ion source low energy mode

Abstract

The invention discloses a method for determining volatile substance components in Liubao tea in an ion source low-energy mode, and belongs to the technical field of tea component determination. The determination method can accurately determine whether a Liubao tea sample contains volatile substance components in a volatile substance database, and the determination method has good anti-interference performance, fast determination speed and strong specificity. The Liubao tea sample is extracted with a solvent, adsorbed by a solid phase microextraction needle, and then placed in a gas chromatography-tandem quadrupole time-of-flight mass spectrometer to obtain a spectrum for determination, and then the spectrum is matched with data in the volatile substance database to obtain a determination result. The determination in the gas chromatography-tandem quadrupole time-of-flight mass spectrometer includes gas chromatography determination and mass spectrometry determination, and the ion source is in a low-energy mode when performing the mass spectrometry determination.

Description

Technical Field

[0001] The invention relates to the technical field of tea component determination, and more specifically, to a method for determining volatile components in Liubao tea using an ion source low energy mode. Background Art

[0002] Liubao tea made with modern technology has a dark brown appearance, a bright red soup, a mellow and smooth taste, and a pure aroma. In particular, it has the characteristic of becoming more fragrant as it ages. The storage years have a great influence on the aroma, flavor, and taste of Liubao tea, and the storage years have become an important factor affecting the price of Liubao tea in the market. Studies have shown that different storage years will affect the quality of Liubao tea, as well as tea polyphenols, amino acids, theaflavins, thearubigins, theabrownins, and volatile components.

[0003] The volatile substances in Liubao tea are the characteristic components of Liubao tea, which play an important role in the taste and aroma of tea. Therefore, how to effectively determine the volatile substances contained in Liubao tea has become an important factor in evaluating the quality of Liubao tea. The traditional determination method is to adsorb and enrich the volatile components of Liubao tea through solid phase microextraction, desorb the components enriched on the solid phase microextraction needle through the gas phase inlet, and determine the volatile components through gas chromatography tandem quadrupole time-of-flight mass spectrometry and standard ion source energy mode.

[0004] The ion source energy used in the traditional determination method is 70eV, but most substances in nature cannot obtain the molecular ion peak of the substance at this energy, resulting in too many fragments, and the molecular weight of the substance cannot be judged by the molecular ion, resulting in a large error in determining the volatile substance composition, and the determination time is long. The traditional determination method for the qualitative characterization of the volatile substance requires the use of standard substances to characterize the retention time of the chromatographic peak, and it is difficult to separate the target peak and the impurity peak in the complex matrix of tea. Therefore, it is urgent to invent a method that can effectively determine the volatile substance composition in Liubao tea, so as to more quickly and accurately determine the volatile substance composition contained in Liubao tea, so as to better evaluate the quality of Liubao tea. Summary of the invention

[0005] The purpose of the present invention is to provide a method for determining volatile substance components in Liubao tea in low energy mode of an ion source. The determination method can be used to accurately determine whether a Liubao tea sample contains volatile substance components in a volatile substance database. The determination method has good anti-interference ability, fast determination speed and strong specificity.

[0006] The technical solution of the present invention is as follows:

[0007] A method for determining volatile components in Liubao tea using an ion source low-energy mode comprises the following steps: extracting a Liubao tea sample with a solvent, adsorbing the sample using a solid phase microextraction needle, and then placing the sample in a gas chromatography-tandem quadrupole time-of-flight mass spectrometer to obtain a spectrum, and then matching the spectrum with data in a volatile substance database to obtain a determination result; the determination in the gas chromatography-tandem quadrupole time-of-flight mass spectrometer comprises gas chromatography determination and mass spectrometry determination, and the ion source is in low-energy mode when performing the mass spectrometry determination.

[0008] Furthermore, 1-2 g of Liubao tea sample was placed in a 20 mL headspace bottle, 5-8 mL of deionized water was added, the bottle was sealed with a cover, placed under a heating device for heating, and a solid phase microextraction needle was inserted for adsorption.

[0009] Furthermore, the heating temperature range of the heating device is 70 to 90° C., and the adsorption time is 30 to 45 minutes.

[0010] Furthermore, the chromatographic column in the gas chromatography determination is a non-polar column, the stationary phase is 5% phenyl-methylpolysiloxane, the specifications are 30m×0.25mm, 0.25μm; the injection port temperature is 250-280°C; the septum purge is 3-5mL / min; the split ratio is 7-10:1; the chromatographic column flow He is 1mL / min; the quenching gas He is 2.25mL / min; the collision gas N2 is 1.5mL / min; the interface temperature is 280-300°C; the programmed temperature is adopted, the temperature is directly increased to 40°C and maintained for 3min, and then the temperature is increased to 300°C at a heating rate of 5°C / min and maintained for 5min, and then the column oven temperature is maintained at 310°C and operated for 2min, and the chromatographic column flow He is 2mL / min.

[0011] The mass spectrometry conditions are:

[0012] The ion source is a high-sensitivity ion source equipped with a low-energy mode; the solvent delay time is 3 min; the scanning range is 30-500 m / z; the ion source energy is 5-15 eV, and the data acquisition mode is a centroid map and a contour map.

[0013] Furthermore, the specific steps of matching the spectrum obtained by the gas chromatography-tandem quadrupole time-of-flight mass spectrometer with the data in the volatile substance database are as follows:

[0014] (1) Performing primary mass spectrum matching on the obtained centroid map and contour map with the material component data in the volatile material database one by one. If the molecular ion peak matching degree of the material component in the matching result reaches 90 points or more, proceed to the next step. Otherwise, it is considered that the material does not exist and the primary mass spectrum matching of the next material component is performed;

[0015] (2) Perform secondary ion matching on the obtained centroid map and contour map and the material component data in the volatile substance database. If the deviation of the secondary ions in the matching result is less than or equal to 10 ppm, it is determined that the material component is present. Otherwise, it is considered that the material does not exist and the process returns to step (1) to perform primary mass spectrum matching on the next material component.

[0016] Furthermore, the volatile substance database stores data information such as the Chinese and English names, molecular formulas, CAS numbers, precise molecular weights and mass losses of various volatile substances.

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] The invention discloses a method for determining volatile substance components in Liubao tea by using an ion source low-energy mode. The method comprises the following steps: extracting a Liubao tea sample by solvent, adsorbing the sample by using a solid phase microextraction needle, and then placing the sample in a gas chromatography-tandem quadrupole time-of-flight mass spectrometer to obtain a spectrum, and then matching the spectrum with data in a volatile substance database to obtain a determination result. Determination in the gas chromatography-tandem quadrupole time-of-flight mass spectrometer includes gas chromatography determination and mass spectrometry determination. When performing mass spectrometry determination, the ion source is in a low-energy mode. The method uses the low-energy mode to obtain a high-resolution spectrum. The high-resolution spectrum monitors the precise mass-to-charge ratio of the substance being measured, and thus the method has good anti-interference performance. The method can quickly perform qualitative analysis by using the precise mass-to-charge ratio without separating a target substance from an impurity peak in the sample, and the resolution of the substance components is higher and the specificity is strong. DETAILED DESCRIPTION

[0019] The technical solution of the present invention is further described in detail below in conjunction with specific implementation methods, but does not constitute any limitation to the present invention.

[0020] The invention discloses a method for determining volatile components in Liubao tea using an ion source low-energy mode, which comprises extracting a Liubao tea sample with a solvent, adsorbing the sample using a solid phase microextraction needle, and then placing the sample in a gas chromatography-tandem quadrupole time-of-flight mass spectrometer to obtain a spectrum, and then matching the spectrum with data in a volatile substance database to obtain a determination result. The determination in the gas chromatography-tandem quadrupole time-of-flight mass spectrometer includes gas chromatography determination and mass spectrometry determination, and the ion source is in a low-energy mode when performing the mass spectrometry determination.

[0021] This method uses solid phase microextraction technology combined with gas chromatography-tandem time-of-flight mass spectrometry and a self-built volatile substance database to screen and characterize a variety of volatile characteristic components in Liubao tea. Its advantage is that the method uses a low energy mode to obtain a high-resolution spectrum. High-resolution mass spectrometry monitors the precise mass-to-charge ratio of the substance being measured. High-resolution mass spectrometry has a good anti-interference effect on the qualitative characterization of volatile components in the Liubao tea matrix. The traditional low-resolution gas-mass spectrometry method requires the use of standard substances to characterize the retention time of the chromatographic peaks for the qualitative characterization of such substances. It is difficult to separate the target peaks and impurity peaks in the complex matrix of tea. Due to the low resolution, low-resolution mass spectrometry is easily interfered by co-eluting substances during the determination process. It takes a long time to separate these co-eluting substances from the target substance. Due to the differences in different Liubao tea matrices, when using low-resolution gas-mass spectrometry, it is necessary to conduct certain preliminary experiments on the sample to be measured, and determine the programmed temperature gradient method to completely separate the substances before formal detection can be carried out. This method can quickly identify the target substance and impurity peaks in the sample through accurate mass-to-charge ratio without separating them, with higher resolution and stronger specificity. This method can also be used to detect volatile components in tea samples other than Liubao tea.

[0022] Among them, the dissolution, extraction and adsorption process of Liubao tea samples is to put 1-2g of Liubao tea samples into a 20mL headspace bottle, add 5-8mL of deionized water, seal it with a cover, place it under a heating device for heating, and insert a solid phase microextraction needle for adsorption. The heating temperature range of the heating device is 70-90℃, and the adsorption time is 30-45min. After dissolving, extracting and adsorbing the Liubao tea samples according to this requirement, more complete volatile substance components can be adsorbed, so that the subsequent detection can obtain more accurate results.

[0023] The chromatographic column in the gas chromatography determination is a non-polar column, the stationary phase is 5% phenyl-methylpolysiloxane, the specifications are 30m×0.25mm, 0.25μm; the injection port temperature is 250-280°C; the septum purge is 3-5mL / min; the split ratio is 7-10:1; the chromatographic column flow He is 1mL / min; the quenching gas He is 2.25mL / min; the collision gas N2 is 1.5mL / min; the interface temperature is 280-300°C; the temperature is programmed to directly increase to 40°C and hold for 3min, then increase to 300°C at a heating rate of 5°C / min and hold for 5min, then maintain the column oven temperature at 310°C and run for 2min, and the chromatographic column flow He is 2mL / min.

[0024] The mass spectrometry conditions are:

[0025] The ion source is a high-sensitivity ion source equipped with a low-energy mode; the solvent delay time is 3 min; the scanning range is 30-500 m / z; the ion source energy is 5-15 eV, and the data acquisition mode is a centroid map and a contour map.

[0026] The specific steps for matching the spectrum obtained by gas chromatography-tandem quadrupole time-of-flight mass spectrometry with the data in the volatile substance database are as follows:

[0027] (1) Performing primary mass spectrum matching on the obtained centroid map and contour map with the material component data in the volatile material database one by one. If the molecular ion peak matching degree of the material component in the matching result reaches 90 points or more (primary mass spectrum matching, deviation is less than or equal to 10 ppm), proceed to the next step. Otherwise, it is considered that the material does not exist, and the primary mass spectrum matching of the next material component is performed;

[0028] (2) Perform secondary ion matching on the obtained centroid map and contour map and the material component data in the volatile substance database. If the deviation of the secondary ions in the matching result is less than or equal to 10 ppm, it is determined that the material component is present, and the method returns to step (1) to perform primary mass spectrum matching on the next material component. Otherwise, the method is deemed not to exist, and the method returns to step (1) to perform primary mass spectrum matching on the next material component.

[0029] The identification points of secondary ions are calculated according to Table 5 of the EU Non-mandatory Directive 2002-657-EC. When the identification points reached are greater than or equal to 4, it can be confirmed that the sample contains this compound. The identification points are calculated as follows: the identification point of the parent ion is 2, and the identification point of each product ion (daughter ion) obtained by parent ion conversion is 2.5. According to the qualitative requirements, the high-resolution mass spectrum contains at least one parent ion and one product ion (daughter ion) converted from the parent ion.

[0030] The volatile substance database contains the Chinese and English names, molecular formulas, CAS numbers, accurate molecular weights and mass loss information of various volatile substances. The volatile substance components stored in the volatile substance database are shown in Table 1.

[0031] Table 1 Volatile substance composition

[0032]

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[0039]

[0040]

[0041]

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[0050]

[0051] The above description is only a preferred embodiment of the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for determining volatile components in Liubao tea using an ion source low energy mode, characterized in that: The Liubao tea sample is extracted with a solvent, adsorbed with a solid phase microextraction needle, and then placed in a gas chromatography-tandem quadrupole time-of-flight mass spectrometer to obtain a spectrum, and then the spectrum is matched with the data in the volatile substance database to obtain a measurement result. The measurement in the gas chromatography-tandem quadrupole time-of-flight mass spectrometer includes gas chromatography measurement and mass spectrometry measurement, and the ion source is in low energy mode when performing mass spectrometry measurement; The chromatographic column in the gas chromatography determination is a non-polar column, the stationary phase is 5% phenyl-methyl polysiloxane, the specification is 30m×0.25mm, 0.25μm; the injection port temperature is 250-280°C; the septum purge is 3-5mL / min; the split ratio is 7-10:1; the chromatographic column flow He is 1mL / min; the quenching gas He is 2.25mL / min; the collision gas N2 is 1.5mL / min; the interface temperature is 280-300°C; the temperature is programmed to directly increase to 40°C and hold for 3min, then increase to 300°C at a heating rate of 5°C / min and hold for 5min, then keep the column oven temperature at 310°C and run for 2min, the chromatographic column flow He is 2mL / min; The mass spectrometry conditions are: The ion source was a high-sensitivity ion source equipped with a low-energy mode; the solvent delay time was 3 min; the scanning range was 30-500 m / z; the ion source energy was 5-15 eV, and the data acquisition mode was centroid and contour plots; The specific steps for matching the spectrum obtained by gas chromatography-tandem quadrupole time-of-flight mass spectrometry with the data in the volatile substance database are as follows: (1) Perform primary mass spectrum matching on the obtained centroid map and contour map with the material component data in the volatile substance database one by one. If the molecular ion peak matching degree of the material component in the matching result reaches 90 points or more, proceed to the next step. Otherwise, it is considered that the material does not exist and the primary mass spectrum matching of the next material component is performed; (2) Perform secondary ion matching on the obtained centroid map and contour map and the material component data in the volatile material database. If the deviation of the secondary ions in the matching result is less than or equal to 10 ppm, it is determined that the material component is present. Otherwise, it is considered that the material does not exist and the process returns to step (1) to perform primary mass spectrum matching on the next material component.

2. The method for determining volatile components in Liubao tea using an ion source low energy mode according to claim 1, characterized in that: Put 1-2g of Liubao tea sample into a 20mL headspace bottle, add 5-8mL of deionized water, cover and seal, place under a heating device to heat, and insert a solid phase microextraction needle for adsorption.

3. The method for determining volatile components in Liubao tea using an ion source low energy mode according to claim 2, characterized in that: The heating temperature range of the heating device is 70 to 90° C., and the adsorption time is 30 to 45 minutes.

4. The method for determining volatile components in Liubao tea using an ion source low energy mode according to claim 1, characterized in that: The volatile substance database stores data information such as the Chinese and English names, molecular formulas, CAS numbers, precise molecular weights and mass losses of various volatile substances.

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