Method for determining the content of dmpp in compound fertilizer

Abstract

The application discloses a method for determining the content of DMPP in compound fertilizer, comprising the following steps: S1, standard working solution preparation; S2, sample pretreatment; S3, chromatography-mass spectrometry detection; S4, quantitative analysis. In view of the quantitative error caused by the matrix effect, the application proposes to prepare a gradient standard working solution by using a blank fertilizer matrix extract, to eliminate the physical and chemical property difference between the sample and the standard product through matrix matching, and to improve the accuracy of the calibration curve. Secondly, in order to strengthen the purification effect of the complex matrix sample, a C18 solid-phase extraction column is introduced to combine with a methanol-water system for elution, and the activation and redissolution conditions are optimized, so that the non-polar interferents such as lipids and pigments are effectively removed, the NY / T3423-2019 water extraction system is compatible, the ESI + / MRM mode is adopted, and the sensitivity and anti-interference ability are significantly better than those of HPLC-UV; the method is suitable for research / internal control / confirmation, and if used for supervision sampling / arbitration, method verification and recognition need to be completed in advance.

Description

Technical Field

[0001] This invention belongs to the field of chemical detection technology, specifically relating to a method for determining the DMPP content in compound fertilizer. Background Technology

[0002] DMPP (dimethylpyrazole phosphate), as a highly efficient nitrification inhibitor, is widely used in compound fertilizer production. It improves fertilizer utilization and reduces nitrogen loss by inhibiting the activity of nitrifying bacteria in the soil and delaying the conversion of ammonium nitrogen to nitrate nitrogen. However, the amount of DMPP added to compound fertilizers is usually low (generally 0.5-1.5% w / w), and the fertilizer matrix composition is complex, potentially containing pigments, residual organic solvents, or other interfering substances, making accurate quantitative analysis challenging.

[0003] Currently, most methods for detecting DMPP employ high-performance liquid chromatography (HPLC) or liquid chromatography-mass spectrometry (LC-MS / MS). However, traditional methods have the following limitations: First, they do not fully consider the influence of matrix effects, and directly using a pure solvent standard curve may lead to quantitative deviations. Second, the pretreatment steps are simple and difficult to effectively remove interfering components in complex matrices, especially for liquid fertilizers or samples containing surfactants, which can easily cause ion inhibition or peak tailing. Third, the mass spectrometry parameters are not optimized enough, the qualitative basis is singular, and false positive results may occur. Therefore, we propose a method for determining the DMPP content in compound fertilizers. Summary of the Invention

[0004] The purpose of this invention is to provide a method for determining the DMPP content in compound fertilizers. To address quantitative errors caused by matrix effects, a gradient standard working solution is prepared using a blank fertilizer matrix extract. Matrix matching eliminates the differences in physicochemical properties between the sample and the standard, improving the accuracy of the calibration curve. Secondly, to enhance the purification effect on complex matrix samples, a C18 solid-phase extraction column combined with a methanol-water elution system is introduced, and activation and reconstitution conditions are optimized to effectively remove non-polar interfering substances such as lipids and pigments.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A method for determining the DMPP content in compound fertilizer, comprising the following steps:

[0007] S1. Preparation of standard working solutions: Using blank fertilizer matrix extract as solvent, prepare matrix-matched standard working solutions with DMPP concentration gradients of 0.01, 0.05, 0.1, 0.5, and 1.0 mg / L.

[0008] S2. Sample pretreatment:

[0009] For solid fertilizer, weigh 2 parts by weight of sample, add 20 parts by weight of primary water, extract by shaking at 25±2℃ for 30 minutes, centrifuge at 10000r / min for 10 minutes, and take the supernatant.

[0010] For liquid fertilizer, take 2 parts by weight of the sample, add 18 parts by weight of primary water to dilute, shake for 10 minutes, centrifuge and take the supernatant;

[0011] For complex matrix samples, the supernatant was passed through an activated C18 solid-phase extraction column. The activation conditions were: sequential washing with 5 parts by mass of methanol and 5 parts by mass of primary water. The methanol eluent was collected, blown dry under nitrogen, and then reconstituted with 1 part by mass of primary water.

[0012] S3, Chromatography-Mass Spectrometry Detection:

[0013] Chromatographic conditions: Mobile phase A, an aqueous solution containing 0.1 parts by mass of formic acid; Mobile phase B, acetonitrile;

[0014] Gradient elution program: 0-2 min B phase accounts for 20%, 5 min increases to 80%, maintains until 7 min, 7.1 min recovers to 20% and equilibrates until 10 min;

[0015] Chromatographic column: C18 reversed-phase column, 2.1 mm × 100 mm, particle size 1.8-2.6 μm, flow rate 0.3 mL / min, injection volume 5 μL;

[0016] Mass spectrometry conditions, ion source, electrospray ionization positive ion mode (ESI) + Monitoring mode: Multiple reaction monitoring (MRM), precursor ion m / z 186.1, quantitative daughter ion m / z 139.0, collision energy 18 eV, qualitative daughter ion m / z 122.0, collision energy 15 eV;

[0017] S4. Quantitative Analysis: Establish a matrix-matched standard curve R using the aforementioned gradient concentration standard working solutions. 2 ≥0.995, the DMPP content in the sample was calculated using the external standard method, and the method detection limit was ≤0.005 mg / kg and the quantitation limit was ≤0.015 mg / kg.

[0018] Preferably, the qualitative daughter ions include m / z 122.0±0.1 and m / z 93.0±0.1, with collision energies of 15±1 eV and 25±1 eV, respectively; the abundance of m / z 93.0 daughter ions must be ≥ 30% of the abundance of m / z 122.0 daughter ions, otherwise it is judged as a false positive.

[0019] Preferably, in the gradient elution process, the formic acid content of mobile phase A is 0.099-0.101 parts by mass per 100 parts of aqueous solution, and mobile phase B is acetonitrile with a purity ≥99.9%.

[0020] Preferably, the eluent reconstituted solution for SPE purification of the complex matrix sample is a primary aqueous solution containing 0.24-0.26 parts by mass of methanol.

[0021] Preferably, in the oscillation extraction step, 0.05-0.1 parts by weight of sodium dodecyl sulfate, SDS, and C are added to the solid sample. 12 H 25 SO4Na;

[0022] After centrifugation, the supernatant needs to be pre-filtered with a 0.45 μm filter membrane, which is pre-wetted with 5 parts by mass of methanol and 10 parts by mass of primary water.

[0023] Preferably, deuterated DMPP internal standard d3-DMPP is added to the analyte before mass spectrometry detection. 2 H3]C5H8N2 + , concentration 0.05 parts by mass / 1000 parts solution.

[0024] Preferably, the mass spectrometer source temperature is 148-152℃, the desolvation gas temperature is 345-355℃, and the gas flow rate is 785-815L / h.

[0025] Preferably, the nitrogen blowing reconstitution step is carried out at a constant temperature of 45±2℃, with a nitrogen flow rate of 2.5-3.0L / min, and evaporation is carried out until the residual liquid is ≤0.05 parts by mass.

[0026] Preferably, when preparing the matrix-matched standard working solution, 0.01 parts by weight of potassium dihydrogen phosphate (KH2PO4) is added to every 100 parts of solution.

[0027] The technical effects and advantages of this invention are as follows:

[0028] By limiting the parent ion m / z to 186.1 and specific daughter ion pairs, the quantitative (139.0) and qualitative (122.0) values ​​are used to solve the problem of isomer interference in fertilizers; the use of blank matrix to match standard solutions is forced to eliminate the matrix inhibition effect of complex fertilizer systems.

[0029] Using a binary gradient system of 0.1 parts by mass formic acid aqueous solution / acetonitrile, formic acid enhances the ionization efficiency of DMPP in positive ion mode and optimizes the peak shape, with a tailing factor of <1.2.

[0030] Adding sodium dodecyl sulfate (SDS) as a surfactant during the solid sample extraction stage enhances the desorption efficiency of the target analyte from the surface of solid particles.

[0031] In the mass spectrometry detection process, in addition to the conventional quantitative ions, m / z 93.0±0.1 is added as an auxiliary qualitative ion, and true positive signals are screened by an abundance ratio threshold of ≥30% to avoid false positive judgments caused by co-eluent impurities.

[0032] The concentration range of formic acid in mobile phase A was defined as 0.099-0.101% w / w to stabilize ionization efficiency, and the purity of acetonitrile was limited to ≥99.9% to reduce background noise. The nitrogen blowing conditions were optimized to maintain a constant temperature of 45±2℃ and a flow rate of 2.5-3.0 L / min to ensure controllable residual liquid. Deuterated internal standard d3-DMPP was added to correct injection errors and improve data reliability. Detailed Implementation

[0033] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0034] This invention provides a feasible and operational procedure for the LC-MS / MS quantification and confirmation of DMPP (3,4-dimethylpyrazole phosphate) in fertilizers, compatible with the NY / T3423-2019 water extraction system, and employs ESI. + / MRM mode offers significantly better sensitivity and anti-interference capabilities than HPLC-UV; it is suitable for R&D / internal control / validation. If used for surveillance sampling / arbitration, method validation and approval must be completed first.

[0035] The method for determining the DMPP content in compound fertilizers includes the following steps:

[0036] S1. Preparation of standard working solutions: Using blank fertilizer matrix extract as solvent, prepare matrix-matched standard working solutions with DMPP concentration gradients of 0.01, 0.05, 0.1, 0.5, and 1.0 mg / L; when preparing matrix-matched standard working solutions, add 0.01 parts by mass of potassium dihydrogen phosphate (KH2PO4) to every 100 parts of solution.

[0037] S2. Sample pretreatment:

[0038] For solid fertilizer, weigh 2 parts by weight of sample, add 20 parts by weight of primary water, extract by shaking at 25±2℃ for 30 minutes, centrifuge at 10000r / min for 10 minutes, and take the supernatant.

[0039] For liquid fertilizer, take 2 parts by weight of the sample, add 18 parts by weight of primary water to dilute, shake for 10 minutes, centrifuge and take the supernatant;

[0040] For complex matrix samples, the supernatant was passed through an activated C18 solid-phase extraction column. The activation conditions were: sequential washing with 5 parts by mass of methanol and 5 parts by mass of primary water. The methanol eluent was collected, nearly dried under nitrogen, and then reconstituted with 1 part by mass of primary water. The reconstituted eluent for complex matrix samples purified by SPE was a primary aqueous solution containing 0.24-0.26 parts by mass of methanol.

[0041] In the shaking extraction step, 0.05-0.1 parts by weight of sodium dodecyl sulfate, SDS, and C2O2 need to be added to the solid sample. 12 H 25 SO4Na;

[0042] After centrifugation, the supernatant needs to be pre-filtered with a 0.45 μm filter membrane, which is pre-wetted with 5 parts by mass of methanol and 10 parts by mass of primary water.

[0043] S3, Chromatography-Mass Spectrometry Detection:

[0044] Chromatographic conditions: Mobile phase A, an aqueous solution containing 0.1 parts by mass of formic acid; Mobile phase B, acetonitrile;

[0045] Gradient elution program: 0-2 min B phase accounts for 20%, 5 min increases to 80%, maintains until 7 min, 7.1 min recovers to 20% and equilibrates until 10 min;

[0046] Chromatographic column: C18 reversed-phase column, 2.1 mm × 100 mm, particle size 1.8-2.6 μm, flow rate 0.3 mL / min, injection volume 5 μL;

[0047] Mass spectrometry conditions, ion source, electrospray ionization positive ion mode (ESI) + The monitoring mode is Multiple Reaction Monitoring (MRM). The precursor ion is m / z 186.1, the quantitative daughter ion is m / z 139.0 with a collision energy of 18 eV, and the qualitative daughter ion is m / z 122.0 with a collision energy of 15 eV. The qualitative daughter ions include m / z 122.0 ± 0.1 and m / z 93.0 ± 0.1, with collision energies of 15 ± 1 eV and 25 ± 1 eV, respectively. The abundance of the m / z 93.0 daughter ion must be ≥ 30% of the abundance of the m / z 122.0 daughter ion; otherwise, it is considered a false positive. The mass spectrometry source temperature is 148-152℃, the desolvation gas temperature is 345-355℃, and the gas flow rate is 785-815 L / h.

[0048] Before mass spectrometry detection, deuterated DMPP internal standard d3-DMPP is added to the analyte solution. 2 H3]C5H8N2 + 0.05 parts by mass per 1000 parts of solution;

[0049] S4. Quantitative Analysis: Establish a matrix-matched standard curve R using the aforementioned gradient concentration standard working solutions. 2≥0.995, calculate the DMPP content in the sample using the external standard method, and meet the method detection limit ≤0.005mg / kg and quantitation limit ≤0.015mg / kg; in the gradient elution program, the formic acid content of mobile phase A is 0.099-0.101 parts by mass / 100 parts of aqueous solution, and mobile phase B is acetonitrile with a purity ≥99.9%.

[0050] Based on the above, the following embodiments are possible:

[0051] Example 1

[0052] Instructions: Prepare the standard working solution by adding 0.01 parts by mass of KH2PO4 to every 100 parts of solution using the blank fertilizer matrix extract as the solvent to prepare a matrix-matched standard solution with a DMPP concentration gradient of 0.01-1.0 mg / L.

[0053] For sample pretreatment, for solid fertilizer, weigh 2g of sample, add 20mL of primary water and 0.05g of SDS, extract by shaking at 25℃ for 30min, and take the supernatant after centrifugation.

[0054] For complex matrix samples, the supernatant was purified by C18 column (methanol activation → 5% methanol-water rinsing → methanol elution) and then reconstituted by nitrogen blowing.

[0055] Chromatography-mass spectrometry was used for detection. The mobile phases were A (0.1% formic acid water) and B (acetonitrile). The gradient elution program was set as follows: 0-2 min B phase 20%, 5 min to 80%, maintained until 7 min, 7.1 min to 20% and equilibrated until 10 min.

[0056] Mass spectrometry parameters: precursor ion m / z 186.1, quantitative daughter ion m / z 139.0 (18 eV), qualitative daughter ion m / z 122.0 (15 eV).

[0057] Quantitative analysis was performed, with the content calculated using the external standard method, and the standard curve R² ≥ 0.995.

[0058] The efficacy was verified, and the recovery rate was 92.3±1.8% for solid fertilizer (n=6) and 89.5±2.3% for liquid fertilizer.

[0059] The sensitivity is 0.004 mg / kg, the detection limit is 0.012 mg / kg, and the quantitation limit is 0.012 mg / kg, which meets the requirements for trace analysis.

[0060] The false positive rate, relying solely on m / z122.0 for qualitative analysis, was 5.2%.

[0061] Example 2

[0062] The difference from Example 1 lies in the following steps:

[0063] The standard working solution was prepared in the same manner as in Example 1, but with the addition of an internal standard of 0.05 g / L d3-DMPP.

[0064] Sample pretreatment: The pretreatment of solid / liquid fertilizers is the same as in Example 1, but the supernatant after centrifugation needs to be filtered through a 0.45μm filter membrane soaked in methanol-water.

[0065] When reconstituted SPE eluent for complex matrix samples, use primary water containing 0.25% methanol (to avoid adsorption of the target analyte).

[0066] Chromatography-mass spectrometry detection was performed, with the addition of a m / z 93.0 daughter ion (collision energy 25 eV) as a mass spectrometry parameter, and a positive threshold was set for its abundance ≥ 30% of m / z 122.0.

[0067] Quantitative analysis was performed using the internal standard method combined with the external standard curve to correct for matrix effects.

[0068] The efficacy was verified, and the recovery rate of solid fertilizer increased to 96.5±0.9%, while that of liquid fertilizer reached 94.2±1.5% (the internal standard effectively offset matrix interference).

[0069] Precision, RSD decreased from 3.2% in Example 1 to 1.8% (n=6).

[0070] The false positive rate was reduced to 3.8% by screening for the m / z 93.0 / 122.0 abundance ratio.

[0071] Example 3

[0072] Based on Examples 1-2, the steps are explained as follows:

[0073] The standard working solution was prepared based on Example 2, with the formic acid content of mobile phase A strictly limited to 0.100% (w / w) and the acetonitrile purity ≥99.9%.

[0074] For sample pretreatment, the amount of SDS added during solid fertilizer extraction was increased to 0.1g, and the micelle concentration was >8mM to fully release the hydrophobic DMPP.

[0075] The nitrogen blowing conditions for the C18 column eluent were optimized to a constant temperature of 45℃, a nitrogen flow rate of 2.8L / min, and a residual liquid of ≤0.05g.

[0076] Chromatography-mass spectrometry detection, mass spectrometry source temperature 150℃, desolvation gas temperature 350℃, gas flow rate 800L / h, to maximize ion transport efficiency.

[0077] The system flushing solution is 70% methanol-water containing 0.05% formic acid to reduce instrument residue.

[0078] Quantitative analysis was performed, and the internal standard and matrix were matched with a standard curve to ensure a linear relationship R² ≥ 0.999.

[0079] The efficacy was verified, and the recovery rates of both solid and liquid fertilizers were >98% (RSD < 1%), while the recovery rate of complex matrix samples reached 95.7 ± 0.6%.

[0080] The sensitivity is excellent, with a detection limit as low as 0.002 mg / kg and a quantitation limit of 0.007 mg / kg, which is superior to industry standards.

[0081] It has strong anti-interference capabilities, with a false positive rate of only 1.5%, and no column clogging occurs even after 100 consecutive injections (due to the synergistic protection of the filter membrane and rinsing solution).

[0082] The effects of the above embodiments are compared in the following table:

[0083] Table 1 Comparison of Results

[0084]

[0085] Alternatively, the specific operation of the above-mentioned determination method is as follows:

[0086] 1. Sample Preparation (following NY / T3423-2019, accurate weighing): For solid samples, reduce to approximately 100g, grind through a 0.5mm sieve, weigh 2.00g (accurate to 0.001g) into a 50mL centrifuge tube, and add 20mL of primary water. For liquid samples, shake well, take 2.00mL into a 50mL centrifuge tube, and dilute with 18mL of primary water.

[0087] 2. Extraction: Shake at 25℃ for 30 min (solid) / 10 min (liquid) to ensure complete dissolution.

[0088] 3. Centrifugation and preliminary purification: Centrifuge at 10000r / min for 10min and collect the supernatant; for simple matrices, directly filter through a 0.22μm aqueous filter membrane for testing; for complex matrices (organic fertilizer / humic acid fertilizer), purify according to step 4.

[0089] 4. Complex matrix SPE purification (C18 column):

[0090] Activation: 5 mL methanol → 5 mL primary water;

[0091] Load the sample by taking 5 mL of the supernatant from centrifugation and loading it onto the column, discarding the initial flow.

[0092] Rinse with 5 mL of 5% methanol-water solution, then discard the rinse solution.

[0093] Elute with 5 mL of methanol, collect the eluent; blow with nitrogen to near dryness, reconstitute with 1 mL of primary water, and filter through a 0.22 μm aqueous filter membrane for analysis.

[0094] 5. Preparation of standard curve and quality control samples:

[0095] Matrix-matched external standard method: Dilute the stock solution with blank matrix extract to prepare a series of 0.01, 0.05, 0.1, 0.5, and 1.0 mg / L solutions, with R² ≥ 0.995.

[0096] Quality control samples: low (0.05 mg / L), medium (0.2 mg / L), and high (0.8 mg / L) spiked samples, and blank and parallel samples were prepared in the same batch.

[0097] 6. Chromatographic conditions (UPLC / rapid LC, stable retention time): Column, C18 (2.1mm×100mm, 1.8 / 2.6μm); column temperature 35℃; flow rate 0.3mL / min; injection volume 5μL.

[0098] Gradient elution: 0-2 min 20% B → 5 min 80% B → 7 min 80% B → 7.1 min 20% B → 10 min equilibration.

[0099] 7. Mass spectrometry conditions (ESI) + / MRM, key parameter)

[0100] Ion source, ESI + The parent ion m / z is 186.1 ([M+H]). + ); Quantitative ion 139.0 (CE18eV); Qualitative ion 122.0 (CE15eV); Cone voltage 30V.

[0101] Ion source temperature 150℃; desolvation gas temperature 350℃ / flow rate 800L / h; collision gas is nitrogen.

[0102] 8. On-machine testing and data processing

[0103] The order is: blank → standard curve (low → high) → sample → quality control sample → parallel sample → blank.

[0104] Quantitative analysis was performed using the matrix-matched external standard method, with concentration on the x-axis and peak area of ​​the quantitative ion pair on the y-axis. Results were retained to two decimal places.

[0105] Quality control: recovery rate 85%-115%, RSD ≤ 5%; blank with no interfering peaks, retention time deviation ≤ 0.1 min; LOD ≤ 0.005 mg / kg, LOQ ≤ 0.015 mg / kg;

[0106] The above control requirements are shown in the table below:

[0107] Table 2 Control Requirements Table

[0108]

[0109] In summary, this invention addresses the problem of isomer interference in fertilizers by limiting the parent ion m / z to 186.1 and specific daughter ion pairs, with a quantitative value of 139.0 and a qualitative value of 122.0; and by forcing the use of blank matrix to match the standard solution, it eliminates the matrix inhibition effect of complex fertilizer systems.

[0110] Using a binary gradient system of 0.1 parts by mass formic acid aqueous solution / acetonitrile, formic acid enhances the ionization efficiency of DMPP in positive ion mode and optimizes the peak shape, with a tailing factor of <1.2.

[0111] Adding sodium dodecyl sulfate (SDS) as a surfactant during the solid sample extraction stage enhances the desorption efficiency of the target analyte from the surface of solid particles.

[0112] In the mass spectrometry detection process, in addition to the conventional quantitative ions, m / z 93.0±0.1 is added as an auxiliary qualitative ion, and true positive signals are screened by an abundance ratio threshold of ≥30% to avoid false positive judgments caused by co-eluent impurities.

[0113] The concentration range of formic acid in mobile phase A was defined as 0.099-0.101% w / w to stabilize ionization efficiency, and the purity of acetonitrile was limited to ≥99.9% to reduce background noise. The nitrogen blowing conditions were optimized to maintain a constant temperature of 45±2℃ and a flow rate of 2.5-3.0 L / min to ensure controllable residual liquid. Deuterated internal standard d3-DMPP was added to correct injection errors and improve data reliability.

[0114] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for determining the DMPP content in compound fertilizer, characterized in that, Includes the following steps: S1. Preparation of standard working solutions: Using blank fertilizer matrix extract as solvent, prepare matrix-matched standard working solutions with DMPP concentration gradients of 0.01, 0.05, 0.1, 0.5, and 1.0 mg / L. S2. Sample pretreatment: For solid fertilizer, weigh 2 parts by weight of sample, add 20 parts by weight of primary water, extract by shaking at 25±2℃ for 30 minutes, centrifuge at 10000r / min for 10 minutes, and take the supernatant. For liquid fertilizer, take 2 parts by weight of the sample, add 18 parts by weight of primary water to dilute, shake for 10 minutes, centrifuge and take the supernatant; For complex matrix samples, the supernatant was passed through an activated C18 solid-phase extraction column. The activation conditions were: sequential washing with 5 parts by mass of methanol and 5 parts by mass of primary water. The methanol eluent was collected and nearly dried under nitrogen, and then redissolved with 1 part by mass of primary water. The nitrogen redissolution step was carried out at a constant temperature of 45±2℃ and a nitrogen flow rate of 2.5-3.0 L / min, and evaporated until the residual liquid was ≤0.05 parts by mass. S3, Chromatography-Mass Spectrometry Detection: Chromatographic conditions: Mobile phase A, an aqueous solution containing 0.1 parts by mass of formic acid; Mobile phase B, acetonitrile; Gradient elution program: 0-2 min B phase accounts for 20%, 5 min increases to 80%, maintains until 7 min, 7.1 min recovers to 20% and equilibrates until 10 min; Chromatographic column: C18 reversed-phase column, 2.1 mm × 100 mm, particle size 1.8-2.6 μm, flow rate 0.3 mL / min, injection volume 5 μL; Mass spectrometry conditions, ion source, electrospray ionization positive ion mode (ESI) + Monitoring mode: Multiple reaction monitoring (MRM), precursor ion m / z 186.1, quantitative daughter ion m / z 139.0, collision energy 18 eV, qualitative daughter ion m / z 122.0, collision energy 15 eV; S4. Quantitative Analysis: Establish a matrix-matched standard curve R using the aforementioned gradient concentration standard working solutions. 2 ≥0.995, the DMPP content in the sample was calculated using the external standard method, and the method detection limit was ≤0.005 mg / kg and the quantitation limit was ≤0.015 mg / kg.

2. The method for determining the DMPP content in compound fertilizer according to claim 1, characterized in that: The qualitative daughter ions include m / z 122.0±0.1 and m / z 93.0±0.1, with collision energies of 15±1 eV and 25±1 eV, respectively; the abundance of m / z 93.0 daughter ions must be ≥ 30% of the abundance of m / z 122.0 daughter ions, otherwise it is judged as a false positive.

3. The method for determining the DMPP content in compound fertilizer according to claim 1, characterized in that, In the gradient elution process, the formic acid content of mobile phase A is 0.099-0.101 parts by mass per 100 parts of aqueous solution, and mobile phase B is acetonitrile with a purity ≥99.9%.

4. The method for determining the DMPP content in compound fertilizer according to claim 1, characterized in that, The eluent reconstituted solution for SPE purification of the complex matrix sample is a primary aqueous solution containing 0.24-0.26 parts by mass of methanol.

5. The method for determining the DMPP content in a compound fertilizer according to claim 1, characterized in that, In the aforementioned oscillation extraction step, 0.05-0.1 parts by weight of sodium dodecyl sulfate, SDS, and C need to be added to the solid sample. 12 H 25 SO4Na; After centrifugation, the supernatant needs to be pre-filtered with a 0.45 μm filter membrane, which is pre-wetted with 5 parts by weight of methanol and 10 parts by weight of primary water.

6. The method for determining the DMPP content in a compound fertilizer according to claim 1, characterized in that, Before mass spectrometry detection, deuterated DMPP internal standard d3-DMPP is added to the analyte solution. 2 H3]C5H8N2 + , concentration 0.05 parts by mass / 1000 parts solution.

7. The method for determining the DMPP content in a compound fertilizer according to claim 1, characterized in that, The mass spectrometer source temperature is 148-152℃, the desolvation gas temperature is 345-355℃, and the gas flow rate is 785-815L / h.

8. The method for determining the DMPP content in a compound fertilizer according to claim 1, characterized in that, The nitrogen blowing redissolution step was carried out at a constant temperature of 45±2℃, with a nitrogen flow rate of 2.5-3.0L / min, until the residual liquid was ≤0.05 parts by mass.

9. The method for determining the DMPP content in a compound fertilizer according to claim 1, characterized in that, When preparing the matrix-matched standard working solution, add 0.01 parts by weight of potassium dihydrogen phosphate (KH2PO4) to every 100 parts of solution.

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