Method for detecting residual mineral oil in edible oil

Abstract

The application relates to the technical field of food analysis, and specifically discloses a detection method for residual mineral oil in edible oil. The application comprises extraction, purification, concentration, detection and analysis steps, specifically: the eluent after purification is subjected to freezing pretreatment, addition of toluene, rotary evaporation concentration under mild conditions and nitrogen blowing concentration in sequence. The application can simultaneously realize accurate quantification of saturated hydrocarbon mineral oil (MOSH) in edible oil and accurate tracing of pollution sources such as kerosene and diesel oil through one-time detection, and has the advantages of low cost, easy popularization and high accuracy.

Description

Technical Field

[0001] This application relates to the technical field of food analysis, and in particular to a method for detecting residual mineral oil in edible oils. Background Technology

[0002] Edible oils pose a risk of mineral oil contamination during production and transportation, including contamination of raw materials, leakage during processing, contamination of packaging materials, and contamination caused by improper handling during transportation. Mineral oils may pose potential threats to human health, including digestive system disorders, nervous system damage, and endocrine disruption. Methods for detecting mineral oils in edible oils mainly include qualitative and quantitative methods. The existing quantitative method is EN 16995-2017 "Foodstuffs - Vegetable oils and foodstuff on basis of vegetable oils - Determination of mineral oil saturated hydrocarbons (MOSH) and mineral oil aromatic hydrocarbons (MOAH) with on-line HPLC-GC-FID". This method, applicable to the quantitative detection of C10-C50 saturated hydrocarbon mineral oil (MOSH) and mineral oil aromatic hydrocarbon (MOAH) in vegetable oils, utilizes HPLC separation followed by GC-FID analysis. For samples with significant interference, activated alumina is used to adsorb n-alkanes or epoxidized unsaturated hydrocarbons to remove impurities. The method is more accurate when the MOSH content is higher than 10 mg / kg, making it the most advanced mineral oil detection method currently available. However, it requires an online HPLC-GC-FID system, which is dedicated to mineral oil detection and is expensive (each unit costs over 1.5 million RMB). It cannot be used for other tests, and due to market size limitations, it struggles to meet the urgent market demand during food safety incidents.

[0003] Furthermore, both qualitative and quantitative methods face a common technical challenge in the concentration step of sample pretreatment: trace mineral oils in edible oils, especially components with low boiling points (such as C10-C14 alkanes), are easily lost through volatilization during conventional nitrogen blowing or rotary evaporation concentration processes. These low-carbon components are key characteristic indicators for identifying light mineral oil contamination such as kerosene and diesel oil; their loss directly leads to lower detection results and seriously affects the accuracy of pollution source tracing analysis.

[0004] Therefore, there is an urgent need in this field for a detection method that is cost-effective, easy to promote, and can effectively solve the problem of loss of trace and volatile mineral oil components during the concentration process, so as to achieve highly sensitive quantification and accurate traceability of residual mineral oil in edible oils. Summary of the Invention

[0005] In a first aspect, this application provides a method for detecting residual mineral oil in edible oil, comprising the following steps: 1) Extraction: Weigh the edible oil and dissolve it to obtain an extract containing mineral oil; 2) Purification: Transfer the extract obtained in step 1) to a purification column and elute the purification column to obtain the eluent; 3) Concentration: The eluent collected in step 2) is subjected to freeze pretreatment, rotary evaporation and nitrogen blowing in sequence to obtain a concentrated solution; 4) Detection: The concentrated solution obtained in step 3) was detected by gas chromatography-flame ionization detector to obtain a spectrum; 5) Analysis: Based on the spectrum obtained in step 4), perform source tracing analysis of mineral oil and quantitative analysis of saturated hydrocarbon mineral oil; Before the rotary evaporation concentration begins, 50-150 μL of toluene is added to the pretreated eluent.

[0006] Optionally, the freezing pretreatment is as follows: the eluent is frozen in an environment of -25°C to -15°C for 10-30 minutes, and then heated to 0-4°C at a rate of 0.5-1°C / min under stirring and held for 5-10 minutes.

[0007] Optionally, in the freezing pretreatment step, after the temperature is raised to 0-4°C, a stabilizer is added to the eluent, wherein the stabilizer is a hexane solution of tert-butylhydroquinone.

[0008] Optionally, the purification column, from bottom to top, consists of: glass wool, anhydrous sodium sulfate, neutral silica gel, silica gel sulfate, an equal mass mixture, and anhydrous sodium sulfate; the equal mass mixture is composed of anhydrous sodium sulfate and silica gel sulfate.

[0009] Optionally, the rotary evaporation is performed at an endpoint pressure of 300-330 hPa and a water bath temperature of 35-40℃ for concentration.

[0010] Optionally, the nitrogen blowing is: when the volume is concentrated to less than 1 mL by rotary evaporation, nitrogen blowing is used to obtain the concentrate at room temperature.

[0011] Optionally, the mineral oil in the traceability analysis in step 5) is selected from kerosene or diesel.

[0012] In summary, this application includes at least one of the following beneficial technical effects: 1. Significantly improves the recovery rate and detection sensitivity of trace and volatile mineral oil components: This application utilizes the synergistic effect of "freezing pretreatment" and "addition of toluene protectant" to achieve near-complete retention of the target analyte; 2. Accurate source tracing analysis of light mineral oil pollution sources has been achieved: Because this application has specially optimized the retention capacity of C10-C14 characteristic components, it can clearly and completely obtain the chromatographic fingerprints of light mineral oils such as kerosene and diesel (including "bulging peaks" and characteristic n-alkane peaks). 3. Combining multifunctionality and high efficiency: This application can simultaneously complete two key tasks through one sample pretreatment and one GC-FID injection: first, to accurately quantify saturated hydrocarbon mineral oil (MOSH); and second, to qualitatively identify the pollution sources of mineral oil (such as kerosene and diesel). Attached Figure Description

[0013] Figure 1 The image shown is a gas chromatogram of a diesel sample from this invention. Figure 2 The image shows a superimposed gas chromatogram of a soybean oil sample contaminated with diesel oil (top) and a blank sample (bottom) according to the present invention. Figure 3 The image shown is a gas chromatogram of the kerosene sample of this invention. Figure 4 The image shown is a superimposed gas chromatogram of a soybean oil sample (top) contaminated with kerosene and a blank sample (bottom) according to the present invention. Detailed Implementation

[0014] To provide a clearer understanding of the technical features, objectives, and beneficial effects of the present invention, the technical solution of the present invention will now be described in detail with reference to the following specific embodiments and accompanying drawings. However, this should not be construed as limiting the scope of implementation of the present invention.

[0015] Material

[0016] Hexane (pesticide residue grade, Xingke), anhydrous sodium sulfate (superior grade, Sinopharm), concentrated sulfuric acid (superior grade, Leybold), silica gel for chromatography column packing (70 mesh–230 mesh), glass wool (CNW), n-alkane standard (C 10 -C 40 1000 μg / mL in cyclohexane, Tanmo quality inspection), toluene (pesticide residue grade, Shanghai Xingke High Purity Solvent Co., Ltd.).

[0017] Example 1 Detection Method

[0018] 1.1 Extraction Use a Bass dropper to draw 0.5 g of edible oil into a nitrogen blow-off tube, add a small amount of n-hexane to dissolve it completely to obtain an n-hexane extract.

[0019] 1.2 Purification Take a glass chromatography column with a stopcock and add glass wool, 1 g of anhydrous sodium sulfate, 2 g of neutral silica gel, 10 g of 33% sulfuric acid silica gel, a mixture of 2 g of anhydrous sodium sulfate and 33% sulfuric acid silica gel of equal mass, and 1 g of anhydrous sodium sulfate in sequence. Dry pack the column and activate it with 20 mL of n-hexane. When the liquid level drops to 2 mm from the top of the packing material, close the stopcock and prepare for sample loading. Use a Bath dropper to transfer the n-hexane extract to the purification column. Wash the nitrogen blow-off tube with 1 mL of n-hexane each time, for a total of 3 times. Transfer all the washing solution to the purification column. Connect a 250 mL pouch to the end and elute with 30 mL of n-hexane at a flow rate of 2 mL / min (a flow rate of 2 mL / min achieves the optimal balance between elution effect, column efficiency, and reagent usage). The sulfuric acid silica gel is prepared by removing background from neutral silica gel at 550℃ for 4 hours, then adding analytical grade concentrated sulfuric acid at 0.5 times the mass of the silica gel. The anhydrous sodium sulfate is activated at 550℃ for 4 hours. If silica gel and anhydrous sodium sulfate are not cleaned with n-hexane and activated at high temperature, the impurities they contain will interfere with the spectrum.

[0020] 1.3 Concentration A. Freezing pretreatment: Add 50 μL of 80 μg / mL tert-butylhydroquinone (TBHQ) n-hexane solution to the collected approximately 30 mL eluent and freeze at -20 °C for 20 minutes; then, with magnetic stirring, program the temperature to 2 °C at a rate of 0.8 °C / min and maintain at that temperature for 8 minutes; B. Rotary evaporation concentration: Accurately add 100 μL of toluene to the pretreated eluent. Then, perform rotary evaporation concentration on the eluent with added toluene at an initial pressure of 500 hPa, an end pressure of 330 hPa, and a water bath temperature of 40°C until the remaining volume is approximately 500 μL. C. Nitrogen blowing concentration: Transfer the above concentrate to a KD concentration tube with a 0.1 mL graduation, slowly blow nitrogen to below 100 μL at room temperature, and then bring the volume to 0.1 mL with n-hexane.

[0021] 1.4 Detection Detection was performed using a gas chromatography-flame ionization detector (GC-FID).

[0022] Gas chromatography conditions: Column: DB-5ms, 30 m × 0.25 mm × 0.25 μm or equivalent column; Temperature program: Initial temperature 50 ℃, ramp to 60 ℃ at 2.5 ℃ / min, ramp to 280 ℃ at 22 ℃ / min, ramp to 315 ℃ at 25 ℃ / min, hold for 16 min; Injector temperature: 300 ℃; Injection volume: 1 μL; Injection method: splitless injection.

[0023] Flame ionization detection conditions: detector temperature 340℃, high-purity nitrogen gas, flow rate 1.5 mL / min.

[0024] 1.5 Source Tracing Analysis When edible oils are contaminated with mineral oil, the potential source of contamination can be determined by comparing the standard gas chromatograms of kerosene and diesel oil. Soybean oil samples contaminated with mineral oil are compared with standard gas chromatograms of mineral oil. Kerosene and diesel oil can be qualitatively identified based on the characteristic peaks and bulging peaks of n-alkanes.

[0025] 1.6 Quantitative Analysis Saturated hydrocarbon mineral oils appear as bulging peaks (UCM) in the spectrum. Mineral oils contaminating edible vegetable oils are almost entirely composed of branched alkanes and cycloalkanes. Sharp peaks are generally considered to be normal alkanes, terpenes, squalene and their isomerization products, as well as sterenes and alkenes with carotenoid structures. Therefore, the content of saturated hydrocarbon mineral oils is quantified using the external standard method by measuring the area of ​​the bulging peak. The bulging peak area equals the total area within the range minus the area of ​​the sharp peak. (Using C...) 10 -C 40 The average response factor is used to plot a standard curve, and the calculation formula is as follows: ; In the formula: X — The content of saturated hydrocarbon mineral oil in the sample, expressed in milligrams per kilogram (mg / kg). c1—The concentration corresponding to the total area in the sample solution obtained from the standard curve, in micrograms per milliliter (μg / mL). c2 — The concentration of the sharp peak in the sample solution obtained from the standard curve, in micrograms per milliliter (μg / mL). V—the final volume of the sample solution, in milliliters (mL); m — Sample mass, in grams (g).

[0026] Example 2 Detection Results

[0027] 2.1 Limit of Quantitation and Limit of Detection Saturated hydrocarbon mineral oils are a series of compounds whose quantity and composition are unknown. These compounds are characterized by being alkanes (including chain and cyclic hydrocarbons). Due to their similar properties and diverse types, they cannot be effectively separated in spectra, overlapping to form a cluster of peaks resembling bulges. Quantitative analysis requires summing the peak areas of all peaks within the range. Interference peaks not originating from the sample, including stray peaks from the GC system and reagents, may be included in the bulge peaks representing saturated hydrocarbon mineral oils during data processing, altering the results. These stray peaks can be considered as background in the blank. Following Appendix A of HJ 168-2020 regarding the detection of the target analyte in the blank test, with the permissible difference between any measured values ​​within the range of "mean of blank test measured value ± 1 / 2 of the estimated detection limit," nine blank tests were performed according to the quantitative analysis method of Example 1. To rigorously evaluate blank interference, the blank test spectra were analyzed at C... 10 -C 40 The peaks and baseline bulges within the range were summed, and the detection limit was calculated using the following formula: ; In the formula, MDL is the method detection limit, and t (n-1,0.99) Let S be the t-distribution value with n-1 degrees of freedom and 99% confidence level, and S be the standard deviation of n parallel determinations. Referring to the t-value table, when n=9, the degrees of freedom are 8, and t=2.896. The calculated method detection limit is 3.12 μg / mL. When the sample size is 0.5g and the final volume is 0.1 mL, the method detection limit (LOD) is 0.5 mg / kg, and the method quantitation limit (LOQ, calculated as 3 times the LOD) is 1.5 mg / kg.

[0028] 2.2 Detection of Mineral Oil Recovery Rate in Edible Oils According to the detection method in Example 1, sunflower seed oil was spiked with 100 mg / kg kerosene and diesel oil, respectively, and the recovery rates after deducting background were 95% and 91%.

[0029] 2.3 Source Tracing Analysis Figure 1 This is the gas chromatogram of a diesel sample, with the peak range C. 10 -C 28 And has obvious C 13 -C 17 Characteristic peaks of n-alkanes. Figure 2 This is a superimposed gas chromatogram of a soybean oil sample contaminated with diesel oil (top) and a blank sample (bottom) according to the present invention, showing obvious C... 13 -C 17 The presence of n-alkane characteristics (not found in soybean oil), along with the simultaneous appearance of bulging peaks at the corresponding positions, indicates that the sample is contaminated with diesel fuel.

[0030] Figure 3 This is the gas chromatogram of a kerosene sample, with the peak range C. 10 -C 14 And has obvious C 11 -C 14 Characteristic peaks of n-alkanes. Figure 4 This is a superimposed gas chromatogram of a soybean oil sample contaminated with kerosene (top) and a blank sample (bottom) according to the present invention, showing obvious C... 11 -C 14 If the sample exhibits a characteristic (not present in soybean oil) and a bulging peak appears simultaneously at the corresponding position, it can be determined that the sample is contaminated with kerosene.

[0031] Example 3 Comparison of different concentration methods

[0032] To compare the effects of different concentration methods on the detection method of this application, an experimental control group with different concentration steps was designed as shown below (except for the concentration steps, the sample pretreatment (extraction, purification) and subsequent detection and analysis steps were consistent with those in Example 1). Soybean oil samples spiked with 10 mg / kg kerosene (characteristic peaks C10-C14) were treated to examine the overall kerosene recovery rate.

[0033] Experimental group: The concentration steps of Example 1 were used (freezing pretreatment + TBHQ + 100 μL toluene + optimized rotary evaporation). Control Group 1: A. Freezing Pretreatment: The collected eluent (approximately 30 mL) was frozen at -20°C for 20 minutes; subsequently, the temperature was programmed to rise to 2°C at a rate of 0.8°C / min under magnetic stirring and held at this temperature for 8 minutes; B. Rotary Evaporation Concentration: 100 μL of toluene was accurately added to the pretreated eluent. The eluent containing toluene was then concentrated by rotary evaporation at an initial pressure of 500 hPa, an final pressure of 330 hPa, and a water bath temperature of 40°C until the remaining volume was approximately 500 μL; C. Nitrogen Blowing Concentration: The concentrated solution was transferred to a KD concentration tube with a 0.1 mL graduation and slowly blown with nitrogen to a mark below 100 μL at room temperature. The volume was then adjusted to 0.1 mL with n-hexane.

[0034] Control Group 2: A. Freezing Pretreatment: Add 50 μL of 80 μg / mL tert-butylhydroquinone (TBHQ) n-hexane solution to approximately 30 mL of collected eluent, and freeze at -20°C for 20 minutes; subsequently, with magnetic stirring, program the temperature to 2°C at a rate of 0.8°C / min and maintain at this temperature for 8 minutes; B. Rotary Evaporation Concentration: The pretreated eluent was concentrated by rotary evaporation at an initial pressure of 500 hPa, an final pressure of 330 hPa, and a water bath temperature of 40°C until the remaining volume was approximately 500 μL; C. Nitrogen Blowing Concentration: Transfer the concentrated solution to a KD concentration tube with a 0.1 mL graduation, and slowly blow nitrogen to below 100 μL at room temperature, then bring the volume to 0.1 mL with n-hexane.

[0035] Control Group 3: A. Rotary evaporation concentration: Accurately add 100 μL of toluene to the pretreated eluent. The eluent with added toluene is then concentrated by rotary evaporation at an initial pressure of 500 hPa, an final pressure of 330 hPa, and a water bath temperature of 40°C until the remaining volume is approximately 500 μL. B. Nitrogen blowing concentration: Transfer the above concentrate to a KD concentration tube with a 0.1 mL graduation. Slowly blow nitrogen at room temperature until the volume is below 100 μL. Then, bring the volume to 0.1 mL with n-hexane.

[0036] Control Group 4: A. Rotary evaporation concentration: The pretreated eluent was concentrated by rotary evaporation at an initial pressure of 500 hPa, an final pressure of 330 hPa, and a water bath temperature of 40°C until the remaining volume was approximately 500 μL; B. Nitrogen blowing concentration: The concentrated solution was transferred to a KD concentration tube with a 0.1 mL graduation and slowly blown with nitrogen at room temperature until the volume was below 100 μL. The volume was then adjusted to 0.1 mL with n-hexane.

[0037] The results are shown in Table 1.

[0038] Table 1 processing method Recovery rate experimental group 98.5% Control group 1 95.0% Control group 2 90.2% Control group 3 88.3% Control group 4 85.1% Results Analysis: In the detection of trace mineral oils in edible oils, low-carbon components (C10-C14) are easily lost during concentration, leading to insufficient sensitivity and inaccurate results in the source tracing analysis of light pollutants such as kerosene and diesel. The above data demonstrates that the combined approach of "freezing pretreatment + TBHQ + toluene protectant" can significantly increase the kerosene recovery rate to 98.5%, fundamentally improving the method's ability to capture the most volatile components, thereby greatly enhancing the accuracy and reliability of source tracing analysis.

[0039] The above are all preferred embodiments of this application, and are not intended to limit the scope of protection of this application. Therefore, all equivalent changes made in accordance with the structure, shape and principle of this application should be covered within the scope of protection of this application.

Claims

1. A method for detecting residual mineral oil in edible oil, characterized in that, Includes the following steps: 1) Extraction: Weigh the edible oil and dissolve it to obtain an extract containing mineral oil; 2) Purification: Transfer the extract obtained in step 1) to a purification column and elute the purification column to obtain the eluent; 3) Concentration: The eluent collected in step 2) is subjected to freeze pretreatment, rotary evaporation and nitrogen blowing in sequence to obtain a concentrated solution; 4) Detection: The concentrated solution obtained in step 3) was detected by gas chromatography-flame ionization detector to obtain a spectrum; 5) Analysis: Based on the spectrum obtained in step 4), perform source tracing analysis of mineral oil and quantitative analysis of saturated hydrocarbon mineral oil; Before the rotary evaporation concentration begins, 50-150 μL of toluene is added to the pretreated eluent.

2. The method for detecting residual mineral oil in edible oil according to claim 1, characterized in that, The freezing pretreatment is as follows: the eluent is frozen in an environment of -25°C to -15°C for 10-30 minutes, and then heated to 0-4°C at a rate of 0.5-1°C / min under stirring and held for 5-10 minutes.

3. The method for detecting residual mineral oil in edible oil according to claim 2, characterized in that, In the freezing pretreatment step, after the temperature is raised to 0-4°C, a stabilizer is added to the eluent, wherein the stabilizer is a hexane solution of tert-butylhydroquinone.

4. The method for detecting residual mineral oil in edible oil according to claim 1, characterized in that, The purification column consists of, from bottom to top: glass wool, anhydrous sodium sulfate, neutral silica gel, silica gel sulfate, an equal mass mixture, and anhydrous sodium sulfate; the equal mass mixture is composed of anhydrous sodium sulfate and silica gel sulfate.

5. The method for detecting residual mineral oil in edible oil according to claim 1, characterized in that, The rotary evaporation is carried out at an endpoint pressure of 300-330 hPa and a water bath temperature of 35-40℃.

6. The method for detecting residual mineral oil in edible oil according to claim 1, characterized in that, The nitrogen blowing is performed by: when the volume of the concentrate is reduced to less than 1 mL by rotary evaporation, nitrogen blowing is then performed at room temperature to obtain the concentrate.

7. The method for detecting residual mineral oil in edible oil according to claim 1, characterized in that, The mineral oil used in the traceability analysis in step 5) is selected from kerosene or diesel.

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