Analysis method for detecting short-chain fatty acid in table salt through headspace arrow-shaped solid phase microextraction-gas chromatography mass spectrometry

Abstract

The invention discloses an analysis method for detecting short-chain fatty acid in table salt by headspace arrow-shaped solid phase microextraction-gas chromatography mass spectrometry, and belongs to the field of analysis and detection. According to the method, firstly, based on a headspace arrow-shaped solid-phase microextraction technology, polar short-chain fatty acids are extracted and enriched by using an extraction head of 100 [mu] m Polyacrylate, and then gas chromatography-mass spectrometry is used for detection, so that qualitative and quantitative detection of nine short-chain fatty acids such as acetic acid, propionic acid, isobutyric acid, butyric acid, 2-methylbutyric acid, valeric acid, 2-methylvaleric acid, 4-methylvaleric acid and hexanoic acid in the table salt can be realized. According to the method, the headspace arrow-shaped solid-phase microextraction technology is used for extracting the short-chain fatty acid in the table salt for the first time, the effects of interference removal, concentration and enrichment are achieved, and the detection limit of the method is reduced by about 2 orders of magnitude compared with that of a headspace-gas chromatography-mass spectrometry method. The method is simple in sample preparation, high in sensitivity, good in recovery rate and stability and suitable for accurate detection of the short-chain fatty acid in the table salt.

Description

Technical Field

[0001] The invention relates to the technical field of analysis and detection, and in particular to an analysis method for detecting short-chain fatty acids in table salt by headspace arrow-shaped solid phase microextraction-gas chromatography-mass spectrometry. Background Art

[0002] Salt is a necessity in daily life. The quality and safety of salt is not only related to the health and life safety of the people, but also to economic development and social stability. Some commercially available salt emits a strong odor similar to foot odor after heating or rubbing with hands, which is called "stinky foot salt". Studies have shown that during the period of salt rock deposition and diagenesis, the organic matter in the salt lake undergoes oxidation decomposition, reduction synthesis, diagenesis and other processes, resulting in some organic matter remaining in the salt mine. If the deodorization process is not appropriate during the salt production process, the refined salt product may have a significant odor. Feng Feng, Zhang Jing and others detected volatile odor substances in "stinky foot salt" mainly as short-chain fatty acids such as propionic acid, butyric acid, and isovaleric acid, and believed that short-chain fatty acids are the main cause of odor. Some studies have reported that short-chain fatty acids are closely related to schizophrenia and autism. Wang et al. found that the total amount of short-chain fatty acids in the feces of autistic children was significantly higher than that of the control group. Li Huihui et al. found that the total amount of short-chain fatty acids, acetic acid, isovaleric acid and hexanoic acid in the feces of first-episode schizophrenia patients were higher than those in healthy controls. Salt is an indispensable condiment, so it is necessary to establish a detection method for short-chain fatty acids in salt that requires simple pre-treatment, high sensitivity and accuracy.

[0003] It is reported that the detection methods of short-chain fatty acids mainly include gas chromatography, gas chromatography-mass spectrometry, liquid chromatography-mass spectrometry, etc. Among them, the method of detecting short-chain fatty acids by gas chromatography-mass spectrometry is mainly applied to biological samples and dairy products. For example, the Chinese patent application with publication number CN116124905A discloses a method for rapid detection of short-chain fatty acids in mouse plasma, feces and tissue samples based on gas chromatography-mass spectrometry. Fresh samples are taken, acetonitrile is added to extract short-chain fatty acids, and the detection is carried out after centrifugation. Nine kinds of short-chain fatty acids can be detected at the same time; the Chinese patent application with publication number CN10670711A discloses a method for determining free medium and short-chain fatty acids in milk / dairy products, which uses headspace solid phase microextraction and gas chromatography-mass spectrometry to determine free medium and short-chain fatty acids in milk / dairy products. Biological samples and dairy products are different from edible salt sample matrices, so the sample pretreatment conditions are quite different. Such sample pretreatment methods are more complicated and cumbersome, and are not suitable for edible salt samples.

[0004] Dong Ronggui et al. published a study on the determination of fatty acid composition in peculiar-smelling salt by SPME-GC / MS. They established a method for determining fatty acid composition in peculiar-smelling salt by combining SPME with GC / MS. The method used full scan mode, qualitative analysis by NIST 2.2 spectral library, and quantitative analysis by area normalization method, and a total of 27 fatty acids were detected in peculiar-smelling salt. Although this method is aimed at the determination of fatty acid components in peculiar-smelling salt, it is mainly qualitative analysis and screening. The quantitative analysis by area normalization method cannot determine the accurate content of various short-chain fatty acids, and the sensitivity is relatively low. Summary of the invention

[0005] Technical problem to be solved: In view of the current situation that the sensitivity of accurate detection of short-chain fatty acids, which are odorous substances in table salt, is insufficient, the present invention provides an analytical method for detecting short-chain fatty acids in table salt by headspace arrow-shaped solid phase microextraction-gas chromatography-mass spectrometry. The method is simple to operate and has high sensitivity. It can accurately detect the content of short-chain fatty acids in ordinary table salt and table salt with odor, and has good application prospects.

[0006] Technical solution: A headspace arrow-shaped solid phase microextraction-gas chromatography-mass spectrometry analysis method for detecting short-chain fatty acids in table salt, the steps are as follows:

[0007] Step 1: Sample preparation: Weigh the salt sample to be tested and place it in a container, add phosphoric acid solution, seal it, and shake to mix;

[0008] Step 2: Extract and enrich the sample after shaking and mixing by using headspace arrow-shaped solid phase microextraction technology, wherein the extraction head used for headspace arrow-shaped solid phase microextraction is 100 μm Polyacrylate; sample incubation temperature: 40°C; incubation time: 20min; stirring speed: 1000r / min: extraction temperature: 40°C; extraction time: 30min; analysis time: 5min;

[0009] Step 3: gas chromatography-mass spectrometry was used for qualitative analysis using the NIST (National Institute of Standards and Technology) database and quantitative analysis was performed using the external standard method based on the standard curve.

[0010] The short-chain fatty acids in the table salt are 9 kinds of short-chain fatty acids, namely acetic acid, propionic acid, isobutyric acid, butyric acid, 2-methylbutyric acid, valeric acid, 2-methylvaleric acid, 4-methylvaleric acid and hexanoic acid.

[0011] The present invention extracts and enriches short-chain fatty acids in table salt based on headspace arrow-shaped solid phase microextraction technology, and then uses gas chromatography-mass spectrometry for detection. This technology can be used for qualitative and quantitative detection of nine short-chain fatty acids in table salt, including acetic acid, propionic acid, isobutyric acid, butyric acid, 2-methylbutyric acid, valeric acid, 2-methylvaleric acid, 4-methylvaleric acid and hexanoic acid.

[0012] Preferably, in step 1, the salt sample to be tested is weighed and placed in a headspace bottle, and a 0.2% phosphoric acid solution by volume is added and then sealed, and the ratio of the mass of the salt sample to be tested to the volume of the 0.2% phosphoric acid solution by volume is 4g:50μL.

[0013] Furthermore, the salt sample to be tested is common salt without peculiar smell or peculiar salt with obvious odor.

[0014] Preferably, the gas chromatography conditions in step three are as follows: chromatographic column: Agilent HP-INNOWAX (30m×0.32mm×0.25μm); carrier gas: helium (purity of 99.999%), flow rate of 1.0mL / min; injection mode: non-split mode injection; injection port temperature: 250°C; transmission line temperature: 280°C; heating program: initial temperature 60°C maintained for 2min, increased to 200°C at 10°C / min and maintained for 5min, then increased to 250°C at 10°C / min and maintained for 2min.

[0015] Preferably, the mass spectrometry conditions in step three are as follows: ion source: electron bombardment ion source, temperature 230° C.; electron energy: 70 eV; quadrupole temperature: 150° C.; scanning mode: selected ion scanning SIM.

[0016] Preferably, the ion scanning SIM acquisition mode is: quantitative ion m / z: acetic acid 43, propionic acid 73, isobutyric acid 43, butyric acid 60, 2-methylbutyric acid 74, valeric acid 60, 2-methylvaleric acid 74, 4-methylvaleric acid 57, hexanoic acid 60; qualitative ion m / z: acetic acid 60,45, propionic acid 73,45, isobutyric acid 73,41, butyric acid 73,41, 2-methylbutyric acid 57,87, valeric acid 73,41, 2-methylvaleric acid 87,43, 4-methylvaleric acid 74,73, hexanoic acid 73,87; retention time: acetic acid 6.86min, propionic acid 7.94min, isobutyric acid 8.30min, butyric acid 9.00min, 2-methylbutyric acid 9.49min, valeric acid 10.27min, 2-methylvaleric acid 10.57min, 4-methylvaleric acid 10.97min, hexanoic acid 11.43min.

[0017] Preferably, the quantification by external standard method according to the standard curve in step 3 is as follows:

[0018] S1. A series of mixed standard solutions containing 9 short-chain fatty acids at different concentrations were added to sodium chloride, and headspace arrow-shaped solid phase microextraction-gas chromatography-mass spectrometry was performed. The concentrations of the 9 short-chain fatty acids were used as the abscissa and the peak area of ​​the target compound was used as the ordinate to draw a standard curve, and the corresponding linear regression equation was obtained. The linear ranges of propionic acid, isobutyric acid and valeric acid were 12.5-250 μg / kg, the linear ranges of hexanoic acid, 2-methylbutyric acid, 4-methylvaleric acid and 2-methylvaleric acid were 2.50-250 μg / kg, the linear range of butyric acid was 6.25-250 μg / kg, and the linear range of acetic acid was 125-2500 μg / kg.

[0019] S2. Substitute the test results of step 3 into the corresponding linear regression equation in S1 for calculation to obtain the contents of 9 short-chain fatty acids.

[0020] Headspace solid phase microextraction technology is a sample analysis and preparation technology that integrates purification, enrichment, and concentration. Compared with conventional solid phase microextraction technology, the solid phase microextraction arrow used in the present invention has a larger extraction surface area and a faster speed. When used in conjunction with gas chromatography-mass spectrometry, it has the advantages of simple operation, rapidity, high sensitivity, and no solvent. The present invention combines solid phase microextraction technology with gas chromatography-mass spectrometry, optimizes the solid phase microextraction conditions, and establishes a method for detecting short-chain fatty acids in edible salt by headspace arrow solid phase microextraction-gas chromatography-mass spectrometry for the first time. The method is simple to operate and highly sensitive, and can be used for the rapid differentiation of odorous salt samples and the precise detection of short-chain fatty acids in edible salt.

[0021] Beneficial effects:

[0022] (1) The present invention uses a 100 μm Polyacrylate extraction head for extraction and adopts headspace arrow-shaped solid phase microextraction technology. Compared with other extraction heads in the prior art (100 μm PDMS, 120 μm Carbon WR / PDMS, 120 μm DVB / PDMS, 120 μm DVB / Carbon WR / PDMS), the extraction effect is better and the detection sensitivity is higher;

[0023] (2) The headspace arrow-shaped solid phase microextraction technology proposed in the present invention optimizes the extraction conditions and can greatly improve the extraction efficiency, thereby achieving the effects of removing interference and concentrating and enriching;

[0024] (3) The method of headspace arrow-shaped solid phase microextraction-gas chromatography-mass spectrometry established in the present invention for detecting short-chain fatty acids in edible salt has a detection limit that is about 2 orders of magnitude lower than that of the existing headspace-gas chromatography-mass spectrometry method. In addition, the method has simple sample preparation, high sensitivity, good recovery rate and stability, and is suitable for the accurate detection of short-chain fatty acids in edible salt.

[0025] (4) Compared with the existing SPME-GC / MS technology for determining the fatty acid composition in odorous salt (Dong Ronggui et al.), the present invention adopts arrow-shaped solid phase microextraction, while the prior art adopts conventional solid phase microextraction. Compared with conventional solid phase microextraction technology, the arrow-shaped solid phase microextraction has a larger extraction surface area, faster speed and higher sensitivity. In addition, the DVB / CAR on PDMS coating extraction head used in the prior art is suitable for volatile and semi-volatile C3-C20 flavor substances, while the Polyacrylate coating extraction head used in the present invention is suitable for polar semi-volatile compounds, and the extraction effect of several short-chain fatty acids involved in the present invention is significantly enhanced. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 Bar graph showing the effect of different types of solid phase microextraction tips on the extraction efficiency of short-chain fatty acids;

[0027] Figure 2 The line graphs show the effects of extraction temperature (A), extraction time (B) and incubation time (C) on the extraction efficiency of nine short-chain fatty acids.

[0028] Figure 3 This is the total ion current diagram of the gas chromatography-mass spectrometry of 9 short-chain fatty acids, including: 1. acetic acid; 2. propionic acid; 3. isobutyric acid; 4. butyric acid; 5. 2-methylbutyric acid; 6. valeric acid; 7. 2-methylvaleric acid; 8. 4-methylvaleric acid; 9. hexanoic acid. DETAILED DESCRIPTION

[0029] The present invention is further described in detail below in conjunction with the accompanying drawings and specific examples, but it should not be construed as limiting the present invention. Without departing from the spirit and essence of the present invention, the modification or replacement of the method, steps or conditions of the present invention all belongs to the scope of the present invention. The experimental methods and reagents without specifying the specific conditions in the examples are all in accordance with the conventional conditions in the art.

[0030] The present invention aims at short-chain fatty acids, which are odorous substances that may exist in table salt, and uses solid phase microextraction technology in combination with gas chromatography-mass spectrometry to optimize the solid phase microextraction conditions and establish a method for detecting short-chain fatty acids in table salt by headspace arrow-shaped solid phase microextraction-gas chromatography-mass spectrometry.

[0031] Example 1: Determination of the content of 9 short-chain fatty acids in salt samples:

[0032] 1. Instrument

[0033] Agilent 8890-5977B gas chromatograph-mass spectrometer (Agilent Technologies, USA); HP-INNOWAX capillary column (30 m × 0.32 mm × 0.25 μm, Agilent Technologies, USA); Milli-Q IQ7000 ultrapure water system (Merck, Germany); ML304T electronic balance (precision 0.1 mg, Mettler-Toledo Instruments (Shanghai) Co., Ltd.), MCA225S-2CCN-I electronic balance (precision 0.01 mg, Sartorius, Germany).

[0034] 2. Raw materials and reagents:

[0035] Salt control samples were purchased from local supermarkets, including well salt, lake salt, sea salt, bamboo salt, and odorous salts were commissioned by the market. Acetic acid standards, propionic acid, isobutyric acid, butyric acid, 2-methylbutyric acid, valeric acid, 2-methylvaleric acid, 4-methylvaleric acid, and caproic acid (Shanghai Anpu Cuishi Standard Technology Service Co., Ltd.); phosphoric acid and sodium chloride (Sinopharm Chemical Reagent Co., Ltd.).

[0036] 3. Analysis methods:

[0037] Step 1: First weigh 4 g of salt sample into a 20 mL headspace sample bottle, add 50 μL of 0.2% (V / V) H3PO4 solution into the sample bottle, tighten the bottle cap, vortex to mix, and then load it onto the instrument for extraction and detection.

[0038] Step 2: Place the sample in the headspace bottle into the sample tray, and use the headspace arrow-shaped solid phase microextraction technology to extract and enrich the sample after shaking and mixing. The specific solid phase microextraction conditions are as follows:

[0039] Extraction head: 100μm Polyacrylate;

[0040] Sample incubation temperature: 40°C; incubation time: 20 min; stirring speed: 1000 r / min:

[0041] Extraction temperature: 40℃; extraction time: 30min;

[0042] Analysis time: 5 minutes.

[0043] Step 3: Use gas chromatography-mass spectrometry to perform qualitative analysis using the NIST database and perform quantitative analysis using the external standard method based on the standard curve. The gas chromatography-mass spectrometry detection conditions are as follows:

[0044] (1) Chromatographic conditions

[0045] Chromatographic column: Agilent HP-INNOWAX (30m×0.32mm×0.25μm);

[0046] Carrier gas: helium (purity 99.999%), flow rate 1.0 mL / min;

[0047] Injection mode: splitless mode injection;

[0048] Inlet temperature: 250°C;

[0049] Transmission line temperature: 280°C;

[0050] Heating program: initial temperature 60°C, hold for 2 min, increase to 200°C at 10°C / min, hold for 5 min, then increase to 250°C at 10°C / min, hold for 2 min.

[0051] (2) Mass spectrometry conditions

[0052] Ion source: electron bombardment ion source, ion source temperature 230℃;

[0053] Electron energy: 70eV;

[0054] Quadrupole temperature: 150°C

[0055] Scanning mode: selected ion scanning (SIM), the retention time, quantitative ion, and qualitative ion parameters of the nine short-chain fatty acids are shown in Table 1;

[0056] Solvent delay: 5 min.

[0057] Table 1 Retention time, quantitative ion and qualitative ion of 9 short-chain fatty acids

[0058]

[0059]

[0060] The specific details of the quantification using the external standard method according to the standard curve are as follows:

[0061] S1. A series of mixed standard solutions of 9 short-chain fatty acids with different concentrations were added to sodium chloride, and headspace arrow-shaped solid phase microextraction-gas chromatography-mass spectrometry was performed. The concentrations of the 9 short-chain fatty acids were used as the horizontal coordinates and the peak areas of the target compounds were used as the vertical coordinates to draw a standard curve, and the corresponding linear regression equation was obtained. The linear ranges of propionic acid, isobutyric acid and valeric acid were 12.5-250 μg / kg, the linear ranges of hexanoic acid, 2-methylbutyric acid, 4-methylvaleric acid and 2-methylvaleric acid were 2.50-250 μg / kg, the linear range of butyric acid was 6.25-250 μg / kg, and the linear range of acetic acid was 125-2500 μg / kg.

[0062] S2. Substitute the test results of step 3 into the corresponding linear regression equation in S1 for comparison to obtain the contents of 9 short-chain fatty acids.

[0063] The preparation of the series of concentration mixed standard solutions in this embodiment is as follows: accurately weigh 9 kinds of short-chain fatty acid standards, dissolve and fix the volume with ultrapure water, and prepare 9 single standard solutions. Take an appropriate volume of the single standard solution respectively, dilute it with ultrapure water to obtain a mixed standard stock solution, wherein the concentration of acetic acid is 5 mg / mL, the concentration of propionic acid and isobutyric acid is 2.5 mg / mL, and the concentration of butyric acid, 2-methylbutyric acid, valeric acid, 2-methylvaleric acid, 4-methylvaleric acid and hexanoic acid is 0.5 mg / mL. Before the test, the mixed standard stock solution is gradient 4 to 2000 times with ultrapure water to prepare a series of concentration mixed standard solutions.

[0064] By adding a series of short-chain fatty acid mixed standard solutions of different concentrations to 4g of sodium chloride, under the optimized extraction conditions (see step 2 headspace arrow solid phase microextraction conditions), analysis was performed according to the experimental method (chromatographic and mass spectrometry conditions refer to step 3), and the chromatograms of the nine short-chain fatty acids are shown in Figure 3 . With the concentration of short-chain fatty acids as the horizontal axis and the peak area of ​​the target compound as the vertical axis, a standard curve is drawn. The linear equation, correlation coefficient (r), and linear range of the target compound are shown in Table 2. The standard addition method is adopted to add a mixed standard solution to sodium chloride, and the spiked concentration is gradually reduced. The detection is carried out according to the experimental method, and the detection limit (LOD, S / N≥3) is calculated with a signal-to-noise ratio of 3 times. The results show that short-chain fatty acids have good linearity within the corresponding concentration range, the correlation coefficient is greater than 0.995, and the LOD is 0.25-25.00 μg / kg. In the prior art, Feng Feng et al. in "Determination of short-chain fatty acids in well salt by headspace injection-gas chromatography-mass spectrometry" has a detection limit of 10-200 μg / kg (the results are shown in Table 2 Headspace-gas chromatography-mass spectrometry detection limit), and the sensitivity of the technical solution of the present invention can be increased by 20 to 80 times.

[0065] Table 2 Linear equation, correlation coefficient, linear range and detection limit of target compounds

[0066]

[0067]

[0068] 20 μL of mixed standard solutions of short-chain fatty acids at three concentration levels, low, medium and high, were added to 4 g of blank salt sample for spike recovery experiment, where the concentrations of acetic acid were 10 μg / mL, 50 μg / mL and 250 μg / mL, the concentrations of propionic acid and isobutyric acid were 5 μg / mL, 25 μg / mL and 125 μg / mL, the concentrations of butyric acid and valeric acid were 5 μg / mL, 15 μg / mL and 25 μg / mL, and the concentrations of 2-methylbutyric acid, 2-methylvaleric acid, 4-methylvaleric acid and hexanoic acid were 1 μg / mL, 5 μg / mL and 25 μg / mL. Six samples were prepared in parallel for each spike level and analyzed according to the experimental methods of steps one to three above. The recovery rate and relative standard deviation (RSD) were calculated. The results are shown in Table 3. The spike recovery rates of the nine short-chain fatty acids were 92.2% to 100.1%, and the RSD was 1.4% to 9.4%.

[0069] Table 3 Spiked recovery and precision results (n = 6)

[0070]

[0071] Comparative Example 1

[0072] The stationary phase and coating thickness on the surface of the extraction head affect its extraction ability and selectivity for the target. The molecular structure, functional groups, polarity and other characteristics of the stationary phase determine the extraction ability of the extraction head for the target compound. According to the characteristic parameters of the target polarity, key groups, boiling point and distribution coefficient, the sensitivity and selectivity of the method can be improved by selecting a suitable extraction head. The present invention investigates the selectivity and extraction effect of five types of extraction heads, including 100μm Polyacrylate, 100μm PDMS, 120μm Carbon WR / PDMS, 120μm DVB / PDMS, and 120μm DVB / Carbon WR / PDMS, for nine kinds of short-chain fatty acids. As shown in the attached figure Figure 1 As shown in the figure, under the same chromatographic mass spectrometry conditions, the extraction head Polyacrylate 100μm has a good extraction effect on each target, especially acetic acid, propionic acid, butyric acid and isobutyric acid. This is because 100μm Polyacrylate is a polar coating, which is very effective in adsorbing polar substances such as short-chain fatty acids. Therefore, the 100μm Polyacrylate extraction head was selected to extract 9 short-chain fatty acids.

[0073] Comparative Example 2

[0074] The extraction temperature affects the equilibrium speed of the analyte between the gas phase and the liquid phase and the distribution coefficient between the extraction coating and the gas phase space. In the unbalanced state, increasing the extraction temperature can accelerate the release of the target compound from the liquid to the headspace bottle and improve the extraction efficiency. However, if the system temperature is too high, it will also cause the target compound to desorb from the extraction coating.

[0075] The present invention investigated the effect of 100 μm Polyacrylate on the extraction efficiency of short-chain fatty acids at different temperatures such as 35°C, 40°C, 45°C, 50°C, 55°C, and 60°C. The results are shown in the attached Figure 2 As shown in Figure A, when the temperature rises from 35°C to 40°C, except for a slight decrease in the extraction efficiency of 2-methylvaleric acid, the extraction efficiencies of other short-chain fatty acids are significantly increased or remain consistent. When the temperature continues to rise from 40°C, the extraction efficiency of most target substances decreases, especially the extraction efficiencies of 2-methylvaleric acid, isobutyric acid, hexanoic acid and 2-methylbutyric acid are significantly reduced. Taking all factors into consideration, the temperature of the extraction system of the present invention is selected to be 40°C.

[0076] When the extraction system is not in equilibrium, the adsorption amount of the target on the extraction coating will increase as the extraction time is extended. The present invention investigates the effect of extracting 100 μm Polyacrylate with an extraction head for 5 min, 10 min, 15 min, 20 min, 25 min, 30 min, 35 min, and 40 min on the extraction efficiency of short-chain fatty acids at an extraction temperature of 40°C. The results are shown in the attached figure. Figure 2 As shown in Figure B, as the extraction time increases, the peak area of ​​short-chain fatty acids also increases significantly. When the extraction time reaches 30 min, except for acetic acid, propionic acid, and isobutyric acid, the peak areas of the other six targets tend to be stable. When the extraction time reaches 40 min, the peak areas of some targets decrease slightly. Considering the two factors of extraction efficiency and detection time, the extraction time of the present invention is selected to be 30 min.

[0077] The sample is heated and incubated before extraction, which is conducive to releasing the target in the sample into the headspace bottle as much as possible and improving the extraction efficiency. The present invention investigates the effects of different incubation times such as 10min, 15min, 20min, 25min, 30min, 35min, 40min, and 45min on the extraction efficiency of the target. The results are shown in the attached Figure 2 As shown in Figure C, the extraction efficiency of most target substances is less affected by the incubation time, while the peak areas of acetic acid and caproic acid increase slowly before 20 minutes and show a clear downward trend after 20 minutes. Therefore, the incubation time of the present invention is selected to be 20 minutes.

[0078] Application Example 1

[0079] The analytical method established in Example 1 was applied to detect 9 short-chain fatty acids in 25 batches of salt samples purchased from local supermarkets and 2 batches of peculiar salt samples commissioned by the market. As shown in Table 4 below, except for 4-methylpentanoic acid, the other 8 short-chain fatty acids were detected in the 2 batches of peculiar salt samples, among which the acetic acid content was greater than 2 mg / kg, and the propionic acid and valeric acid contents were greater than 0.1 mg / kg. Due to the high sensitivity of the method, trace amounts of target substances were also detected in a few control samples, but the content was significantly lower than that in the peculiar salt samples.

[0080] Table 4 Detection results of 9 short-chain fatty acids in representative controls and odorous salts

[0081]

[0082] Finally, it should be noted that the above implementation modes are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned implementation modes, a person of ordinary skill in the art should understand that the technical solutions described in the aforementioned implementation modes can still be modified, or some or all of the technical features therein can be replaced by equivalents. However, these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the implementation modes of the present invention.

Claims

1. A headspace arrow-shaped solid phase microextraction-gas chromatography-mass spectrometry analysis method for detecting short-chain fatty acids in salt, characterized in that: Here are the steps: Step 1: Sample preparation: Weigh the salt sample to be tested and place it in a container, add phosphoric acid solution, seal it, and shake to mix; Step 2: Extract and enrich the sample after shaking and mixing by using headspace arrow-shaped solid phase microextraction technology, wherein the extraction head used for headspace arrow-shaped solid phase microextraction is 100 μm Polyacrylate; sample incubation temperature: 40°C; incubation time: 20min; stirring speed: 1000r / min: extraction temperature: 40°C; extraction time: 30min; analysis time: 5min; Step 3: gas chromatography-mass spectrometry was used for qualitative analysis using the NIST database and external standard method was used for quantitative analysis based on the standard curve. The short-chain fatty acids in the table salt are 9 kinds of short-chain fatty acids, namely acetic acid, propionic acid, isobutyric acid, butyric acid, 2-methylbutyric acid, valeric acid, 2-methylvaleric acid, 4-methylvaleric acid and hexanoic acid.

2. The method for analyzing short-chain fatty acids in salt by headspace arrow-shaped solid phase microextraction-gas chromatography-mass spectrometry according to claim 1, characterized in that: In the step 1, the salt sample to be tested is weighed and placed in a headspace bottle, and a 0.2% phosphoric acid solution is added and then sealed. The ratio of the mass of the salt sample to be tested to the volume of the 0.2% phosphoric acid solution is 4g:50μL.

3. The method for analyzing short-chain fatty acids in salt by headspace arrow-shaped solid phase microextraction-gas chromatography-mass spectrometry according to claim 1, characterized in that: The gas chromatography conditions in step three are as follows: chromatographic column: Agilent HP-INNOWAX, specification is 30m×0.32mm×0.25μm; carrier gas: helium, purity is 99.999%, flow rate is 1.0mL / min; injection mode: non-split mode injection; injection port temperature: 250℃; transmission line temperature: 280℃; heating program: initial temperature 60℃, maintain for 2min, increase to 200℃ at 10℃ / min, maintain for 5min, then increase to 250℃ at 10℃ / min, maintain for 2min.

4. The method for analyzing short-chain fatty acids in salt by headspace arrow-shaped solid phase microextraction-gas chromatography-mass spectrometry according to claim 1, characterized in that: The mass spectrometry conditions in step 3 are as follows: ion source: electron bombardment ion source, temperature 230° C.; electron energy: 70 eV; quadrupole temperature: 150° C.; scanning mode: selected ion scanning SIM.

5. The method for analyzing short-chain fatty acids in salt by headspace arrow-shaped solid phase microextraction-gas chromatography-mass spectrometry according to claim 4, characterized in that: The ion scanning SIM acquisition mode was as follows: quantitative ion m / z: acetic acid 43, propionic acid 73, isobutyric acid 43, butyric acid 60, 2-methylbutyric acid 74, valeric acid 60, 2-methylvaleric acid 74, 4-methylvaleric acid 57, hexanoic acid 60; qualitative ion m / z: acetic acid 60,45, propionic acid 73,45, isobutyric acid 73,41, butyric acid 73,41, 2-methylbutyric acid 57,87, valeric acid 73,41, 2-methylvaleric acid 87,43, 4-methylvaleric acid 74,73, hexanoic acid 73,87; retention time: acetic acid 6.86 min, propionic acid 7.94 min, isobutyric acid 8.30 min, butyric acid 9.00 min, 2-methylbutyric acid 9.49 min, valeric acid 10.27 min, 2-methylvaleric acid 10.57 min, 4-methylvaleric acid 10.97 min, hexanoic acid 11.43 min.

6. The method for analyzing short-chain fatty acids in salt by headspace arrow-shaped solid phase microextraction-gas chromatography-mass spectrometry according to claim 1, characterized in that: In the step 3, the quantification by external standard method according to the standard curve is specifically as follows: S1. A series of mixed standard solutions of 9 short-chain fatty acids with different concentrations were added to sodium chloride, and headspace arrow-shaped solid phase microextraction-gas chromatography-mass spectrometry was performed. The concentrations of the 9 short-chain fatty acids were used as the horizontal coordinates and the peak areas of the target compounds were used as the vertical coordinates to draw a standard curve, and the corresponding linear regression equation was obtained. The linear ranges of propionic acid, isobutyric acid and valeric acid were 12.5-250 μg / kg, the linear ranges of hexanoic acid, 2-methylbutyric acid, 4-methylvaleric acid and 2-methylvaleric acid were 2.50-250 μg / kg, the linear range of butyric acid was 6.25-250 μg / kg, and the linear range of acetic acid was 125-2500 μg / kg. S2. Substitute the test results of step 3 into the corresponding linear regression equation in S1 for calculation to obtain the contents of 9 short-chain fatty acids.

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