A pyrroloquinoline quinone disodium salt crystal and preparation method thereof

Abstract

The present invention proposes a pyrroloquinoline quinone disodium salt crystal and a preparation method thereof. A pyrroloquinoline quinone disodium salt crystal, using Cu Ka radiation to perform X-ray powder diffraction, has characteristic peaks at diffraction angles 2θ of 8.347°, 13.540°, 15.252°, 16.690°, 17.537°, 21.329°, 22.642°, 25.824°, 27.439°, 29.923°, 33.682°, 34.519°, 38.863°, and 47.534°, with an error of ±0.2°. The pyrroloquinoline quinone disodium salt crystal of the present invention has a regular crystal morphology, high purity, high density, and good fluidity; the technical scheme of the present invention can conveniently manufacture pyrroloquinoline quinone disodium salt without using an organic solvent, has a simple process, good reproducibility, and is suitable for large-scale production.

Description

Technical Field

[0001] The invention relates to the field of pyrroloquinoline quinone disodium salt crystals, and in particular to pyrroloquinoline quinone disodium salt crystals and a preparation method thereof. Background Art

[0002] Pyrroloquinolinequinone (PQQ) is widely present in prokaryotic cells and eukaryotic tissues, such as Klebsiella pneumoniae, Methylobacterium extorquens, Pseudomonas aeruginosa, Polyporus versicolor and Rhus vernicifera.

[0003] Studies have shown that PQQ is the third coenzyme of oxidoreductase discovered after nicotinamide and flavin nucleotide. It is a small molecule compound found in microorganisms and is widely distributed in various tissues and organs of the human body. It is called the fourteenth vitamin.

[0004] PQQ has multiple physiological functions and has broad application prospects in the food, medicine, cosmetics and other industries. PQQ can be produced through chemical synthesis and fermentation, and commercialized PQQ products are already on the market.

[0005] The molecular weight of PQQ is 330.2, and its chemical name is: 4,5-Dihydro-4,5-dioxo-1H-pyrrolo[2,3-f]quinoline-2,7,9-tricarboxylicAcid, and its structural formula is as follows:

[0006]

[0007] The structural formula of PQQ disodium salt is as follows:

[0008]

[0009] There are relevant literature reports about PQQ disodium salt crystals:

[0010] The Chinese invention patent with publication number CN109134459A discloses a pyrroloquinoline quinone disodium salt crystal, which uses Cu Ka radiation to perform X-ray powder diffraction, and has characteristic peaks at diffraction angles 2θ of 6.35, 7.87, 8.31, 8.80, 13.48, 14.14, 18.43, 18.80, 25.76, 26.08, 26.43, 27.35, 28.34, 28.99, and 29.56 degrees, with an error of ±0.2°.

[0011] The Chinese invention patent with publication number CN102471336A discloses the crystallization of PQQ disodium salt, and the 2θ peaks obtained using Cu Kα radiation show 9.1°, 10.3°, 13.8°, 17.7°, 18.3°, 24.0°, 27.4°, 31.2°, and 39.5° (all ±0.2°); and its thermal stability is measured, but existing studies have shown that it is easily hygroscopic.

[0012] The Chinese invention patent with publication number CN102942567A discloses crystals A and B of PQQ disodium salt and measures their hygroscopicity;

[0013] The X-ray powder diffraction pattern of Crystal A obtained by Cu-Kα ray diffraction has diffraction peaks at the following 2θ angles: 9.6±0.2°, 11.6±0.2°, 14.9±0.2°, 16.0±0.2°, 18.8±0.2°, 19.4±0.2°, 20.4±0.2°, 21.9±0.2°, 22.7±0.2°, 23.2±0.2°, 25.6±0.2°, 33.7±0.2°, 35.0±0.2°, 35.8±0.2°, 36.7±0.2°, 38.0±0.2°, 38.6±0.2

[0014] The X-ray powder diffraction pattern of crystal B obtained by Cu-Kα ray diffraction has diffraction peaks at the following 2θ angles: 8.1±0.2°, 9.0±0.2°, 10.1±0.2°, 13.7±0.2°, 16.4±0.2°, 17.6±0.2°, 18.2±0.2°, 23.9±0.2°, 25.8±0.2°, 27.2±0.2°, 31.0±0.2°, and 39.5±0.2°.

[0015] The Chinese invention patent with publication number CN103619842A discloses the crystal forms 1 and 2 of PQQ disodium salt, and measures its dispersibility index and skin penetration test, wherein Example 5 shows that crystal form 1 will transform into crystal form 2 at 180°C, and crystal form 2 will absorb moisture after standing at 30°C for a period of time.

[0016] Patent publication number WO2015159236A1 discloses PQQ disodium salt crystal forms 3, 4, 5, 6 and 7, but does not provide any effect experimental data.

[0017] Patent publication number WO2017050171A1 discloses the crystalline form I, crystalline form II and crystalline form III of PQQ disodium salt, and determines their hygroscopicity.

[0018] The Chinese invention patent with publication number CN115716825A discloses a pyrroloquinoline quinone disodium salt crystal, and the X-ray powder diffraction pattern with Cu-Kα as the diffraction source has characteristic peaks at at least the following 2θ angles: 9.05°, 9.42°, 10.24°, 11.49°, 13.67°, 15.18°, 16.29°, 18.97°, 24.40°, 26.25°, 26.92°, 28.06°, 29.09°, 31.72°, wherein the error of the 2θ angle is ±0.2°.

[0019] The Chinese invention patent with publication number CN112125899A discloses a pyrroloquinoline quinone disodium salt crystal, a preparation method thereof and a composition containing the same. The diffraction pattern obtained by X-ray powder diffraction of the pyrroloquinoline quinone disodium salt crystal using Cu--Kα radiation has characteristic peaks: 9.4°, 11.8°, 13.6°, 15.1°, 16.1°, 18.9°, 20.0°, 23.8°, 26.5°, 27.5°, 28.5°, wherein the error of the 2θ angle is ±0.2°, and there is no characteristic peak between 16.1° and 18.9°.

[0020] The above documents respectively give different crystal forms of pyrroloquinoline quinone disodium salt and their XRD derivative characteristics. Studies have shown that each crystal form and its preparation method have certain shortcomings. Summary of the invention

[0021] The main purpose of the present invention is to provide a pyrroloquinoline quinone disodium salt crystal and a preparation method thereof, which has the characteristics of a new crystal structure and high density, and solves the problem in the prior art that the pyrroloquinoline quinone disodium salt has low density and leads to insufficient processability.

[0022] The technical solution of the present invention is achieved in this way:

[0023] The invention firstly proposes a pyrroloquinoline quinone disodium salt crystal, and uses Cu Ka radiation to perform X-ray powder diffraction, and has characteristic peaks at diffraction angles 2θ of 8.347°, 13.540°, 15.252°, 16.690°, 17.537°, 21.329°, 22.642°, 25.824°, 27.439°, 29.923°, 33.682°, 34.519°, 38.863° and 47.534°, with an error of ±0.2°.

[0024] Further, X-ray powder diffraction was performed using Cu Ka radiation, and no characteristic peaks were found between diffraction angles 2θ of 0° to 8.347° and 8.347° to 13.540°.

[0025] Furthermore, X-ray powder diffraction using Cu Ka radiation showed no characteristic peaks within the diffraction angle 2θ range of 17.537° to 21.329°.

[0026] The X-ray powder diffraction pattern of the pyrroloquinoline quinone disodium salt crystal of the present invention is as follows: Figure 1 .

[0027] The 2θ, d and relative intensity data of the X-ray powder diffraction of the pyrroloquinoline quinone disodium salt crystal of the present invention are as follows:

[0028]

[0029] The present invention further proposes a method for preparing pyrroloquinoline quinone disodium salt crystals, comprising the following steps:

[0030] (1) Dissolving: Add free pyrroloquinoline quinone or pyrroloquinoline quinone alkali metal salt to purified water, control the temperature to 20-35° C., add alkali to adjust the pH to 6.0-7.0 while stirring, stir until all dissolved, and filter;

[0031] (2) Acidification and salt crystallization: under stirring conditions, maintaining the temperature at 20-35°C, adding phosphate buffer containing NaCL to adjust the pH to 2.5-3.0;

[0032] (3) Cooling and crystal cultivation: Slowly cool to 6-15°C and then slowly stir to cultivate the crystal;

[0033] (4) Separation and drying: Filter the crystalline product, wash with acid water, and vacuum dry the filter cake to obtain the final product.

[0034] Furthermore, in step (1), the free state of pyrroloquinoline quinone is pyrroloquinoline quinone acid, the alkali metal salt of pyrroloquinoline quinone is pyrroloquinoline quinone monosodium salt, disodium salt or trisodium salt, and the free state of pyrroloquinoline quinone or the alkali metal salt of pyrroloquinoline quinone is 0.5-15 g / L.

[0035] Furthermore, in step (1), the alkali is sodium carbonate or sodium bicarbonate aqueous solution with a concentration of 5-20%.

[0036] Furthermore, in step (2), the phosphate concentration in the phosphate buffer containing NaCL is: 0.18-0.22 mol / L, the NaCL concentration in the phosphate buffer containing NaCL is: 18-22% (w / v), and the pH of the phosphate buffer containing NaCL is: 1.0-1.8.

[0037] Furthermore, in step (2), the addition time of the phosphate buffer containing NaCL is 1-4 hours.

[0038] Furthermore, in step (3), the cooling rate is controlled at 2-6°C / h, the slow stirring speed is 20-150 rpm, and the stirring crystal growing time is 3-10 hours.

[0039] Furthermore, in step (4), the pH of the acid water used for washing is 2.5-3.0, and the acid used is hydrochloric acid or sulfuric acid; the vacuum drying temperature is 45-65° C., and the drying time is 4-15 hours.

[0040] The invention has the following beneficial effects: 1. The pyrroloquinoline quinone disodium salt crystal of the invention has a regular crystal morphology, high purity, high density and good fluidity; 2. The technical scheme of the invention can conveniently manufacture pyrroloquinoline quinone disodium salt without using an organic solvent, has a simple process, good crystal form reproducibility and is suitable for large-scale production; 3. According to the properties of pyrroloquinoline quinone, weakly alkaline alkali salts such as sodium carbonate or sodium bicarbonate used in the invention and the pH value during dissolution are controlled, so that the risk of degradation and discoloration of pyrroloquinoline quinone under alkaline conditions is effectively reduced, and the content and purity of the product are improved; 4. Sodium chloride added during crystallization can effectively promote the formation of the crystal form of the invention; 5. The cooling rate and crystal growing operation are controlled, so that the particle size of the crystal is effectively increased, which is beneficial to the subsequent product filtration, the filtration rate is increased, and the fluidity of the product is improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0042] Figure 1 is an X-ray powder diffraction pattern of the pyrroloquinoline quinone disodium salt crystal of the present invention;

[0043] Figure 2 The X-ray powder diffraction spectrum of the crystal obtained in Comparative Example 1;

[0044] Figure 3 The X-ray powder diffraction spectrum of the crystal obtained in Comparative Example 2;

[0045] Figure 4 The X-ray powder diffraction spectrum of the crystal obtained in Comparative Example 3;

[0046] Figure 5 The X-ray powder diffraction spectrum of the crystal obtained in Comparative Example 4 is shown. DETAILED DESCRIPTION

[0047] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0048] Example 1

[0049] Reference Figure 1-2 , a pyrroloquinoline quinone disodium salt crystal, which performs X-ray powder diffraction using Cu Ka radiation, and has characteristic peaks at diffraction angles 2θ of 8.347°, 13.540°, 15.252°, 16.690°, 17.537°, 21.329°, 22.642°, 25.824°, 27.439°, 29.923°, 33.682°, 34.519°, 38.863°, and 47.534°, with an error of ±0.2°.

[0050] Further, X-ray powder diffraction was performed using Cu Ka radiation, and no characteristic peaks were found between diffraction angles 2θ of 0° to 8.347° and 8.347° to 13.540°.

[0051] Furthermore, X-ray powder diffraction using Cu Ka radiation showed no characteristic peaks within the diffraction angle 2θ range of 17.537° to 21.329°.

[0052] The pyrroloquinoline quinone disodium salt crystal of the present invention has regular crystal morphology, high purity, high density and good fluidity.

[0053] Example 2

[0054] A method for preparing pyrroloquinoline quinone disodium salt crystals comprises the following steps:

[0055] (1) Dissolving: Add free pyrroloquinoline quinone or pyrroloquinoline quinone alkali metal salt to purified water, control the temperature to 20-35° C., add alkali to adjust the pH to 6.0-7.0 while stirring, stir until all dissolved, and filter;

[0056] (2) Acidification and salt crystallization: under stirring conditions, maintaining the temperature at 20-35°C, adding phosphate buffer containing NaCL to adjust the pH to 2.5-3.0;

[0057] (3) Cooling and crystal cultivation: Slowly cool to 6-15°C and then slowly stir to cultivate the crystal;

[0058] (4) Separation and drying: Filter the crystalline product, wash with acid water, and vacuum dry the filter cake to obtain the final product.

[0059] Wherein, in step (1), the free state of pyrroloquinoline quinone is pyrroloquinoline quinone acid, the alkali metal salt of pyrroloquinoline quinone is pyrroloquinoline quinone monosodium salt, disodium salt or trisodium salt, and the free state of pyrroloquinoline quinone or the alkali metal salt of pyrroloquinoline quinone is 0.5-15 g / L.

[0060] Wherein, in step (1), the alkali is sodium carbonate or sodium bicarbonate aqueous solution with a concentration of 5-20%.

[0061] Wherein, in step (2), the phosphate concentration in the phosphate buffer containing NaCL is: 0.18-0.22 mol / L, the NaCL concentration in the phosphate buffer containing NaCL is: 18-22% (w / v), and the pH of the phosphate buffer containing NaCL is: 1.0-1.8.

[0062] Wherein, in step (2), the addition time of the phosphate buffer containing NaCL is 1-4 hours.

[0063] Wherein, in step (3), the cooling rate is controlled at 2-6°C / h, the slow stirring speed is 20-150 rpm, and the stirring crystal growing time is 3-10 hours.

[0064] Wherein, in step (4), the pH of the acid water used for washing is 2.5-3.0, and the acid used is hydrochloric acid or sulfuric acid; the vacuum drying temperature is 45-65° C., and the drying time is 4-15 hours.

[0065] The technical scheme of the present invention can conveniently manufacture pyrroloquinoline quinone disodium salt without using an organic solvent, has a simple process, good crystal form reproducibility, and is suitable for large-scale production; according to the properties of pyrroloquinoline quinone, weakly alkaline salts such as sodium carbonate or sodium bicarbonate used in the present invention and the pH value during dissolution are controlled, so that the risk of degradation and discoloration of pyrroloquinoline quinone under alkaline conditions is effectively reduced, and the content and purity of the product are improved; sodium chloride added during crystallization can effectively promote the formation of the crystal form of the present invention; and the cooling rate and crystal growing operation are controlled to effectively increase the particle size of the crystal, which is beneficial to the subsequent product filtration, increases the filtration rate, and improves the fluidity of the product.

[0066] Example 3

[0067] Add 15 g of pyrroloquinoline quinone acid to 1.5 L of water, dissolve under stirring at 25°C, adjust the pH to 6.3 with 10% sodium carbonate solution, dissolve completely, and filter;

[0068] 700 ml of phosphate buffer (containing 135 g of NaCL and 0.21 mol / L of phosphate) with a pH of 1.2 was added for 2.5 hours until the pH reached 2.6 at the end of the addition.

[0069] Cool down to 8°C at a rate of 2°C / h, continue stirring and heat preservation for 5 hours, stirring speed 50 rpm;

[0070] Filter, wash the wet product with hydrochloric acid solution with a pH of 3.0, and vacuum dry at 50°C for 6 hours to obtain 13.5g of crystals. The obtained crystals were tested, and the purity was 99.83% by HPLC; the Na ion content was 12.2%; the mass ratio of PQQ to Na contained in the crystals was PQQ:Na=1:1.98, indicating that the crystals were PQQ disodium salt; the X-ray powder diffraction test results showed that the crystals were new crystal forms. The powder diffraction spectrum of the crystals is shown in Figure 1 .

[0071] Example 4

[0072] Add 10 g of pyrroloquinoline quinone trisodium salt to 1.0 L of water, dissolve under stirring at 28°C, adjust pH to 6.6 with 10% sodium bicarbonate, dissolve completely, and filter;

[0073] 500 ml of phosphate buffer (containing 90 g of NaCL and 0.20 mol / L of phosphate) with a pH of 1.5 was added for 3 hours until the pH reached 2.75 at the end of the addition;

[0074] Cool down to 10°C at a rate of 4°C / h, continue stirring and heat preservation for 8 hours, stirring speed 100 rpm;

[0075] Filter by suction, wash the wet product with hydrochloric acid solution with a pH of 2.85, and vacuum dry at 55°C for 8 hours to obtain 10.5 g of crystals. The obtained crystals were tested, and the purity was 99.56% by HPLC; the Na ion content was 12.42%; the mass ratio of PQQ to Na contained in the crystals was PQQ:Na=1:2.02, indicating that the crystals were PQQ disodium salt; the X-ray powder diffraction test results showed that the crystals were new crystal forms. The crystal powder diffraction spectrum was the same as that in Example 1.

[0076] Example 5

[0077] Add 10 g of pyrroloquinoline quinone monosodium salt to 1.0 L of water, dissolve under stirring at 33°C, adjust pH to 6.9 with 10% sodium bicarbonate, dissolve completely, and filter;

[0078] 500 ml of phosphate buffer (containing 90 g of NaCL and 0.20 mol / L of phosphate) with a pH of 1.6 was added for 4 hours until the pH reached 2.9 at the end of the addition.

[0079] Cool down to 12°C at a rate of 5°C / h, continue stirring and heat preservation for 9 hours, stirring speed 150 rpm;

[0080] Filter by suction, wash the wet product with sulfuric acid solution with a pH of 2.75, and vacuum dry at 60°C for 7 hours to obtain 9.5g of crystals. The obtained crystals were tested, and the purity was 99.80% by HPLC; the Na ion content was 12.46%; the mass ratio of PQQ to Na contained in the crystals was PQQ:Na=1:2.03, indicating that the crystals were PQQ disodium salt; the X-ray powder diffraction test results showed that the crystals were new crystal forms. The crystal powder diffraction spectrum was the same as that in Example 1.

[0081] Comparative Example 1

[0082] According to the method of the embodiment of the patent with publication number CN102471336A and EP2455379B1, PQQ disodium salt crystals were prepared: 12g PQQ trisodium salt was completely dissolved in 1000mL deionized water, 1000mL ethanol was added to the solution, the pH was adjusted to 3.2 with 10% hydrochloric acid, and then stirred at room temperature for 1h, filtered, and vacuum dried at room temperature for 10h to obtain PQQ disodium salt crystals. The X-ray powder diffraction spectrum of the obtained crystals was consistent with that of CN102471336A, such as Figure 2 .

[0083] Comparative Example 2

[0084] According to the preparation method of the patent with publication number CN109134459A, 10g of pyrroloquinoline quinone acid was prepared by controlling the temperature at 25°C, adding sodium hydroxide solution to adjust the pH to 7.5 while stirring, and stirring until it was completely dissolved; adjusting the pH to 3.2 with 10% hydrochloric acid; the feed liquid was desalted by nanofiltration, and washed with purified water until the conductivity of the effluent was ≤50μS / cm; the desalted feed liquid was vacuum concentrated and crystallized, the crystal product was filtered, washed with water, and the filter cake was vacuum dried to obtain 7.5g of the final product; and X-ray powder diffraction analysis was performed on it, which was consistent with the X-ray diffraction of CN109134459A, such as Figure 3 .

[0085] Comparative Example 3

[0086] According to the method of Example 1 of the patent with publication number CN102942567A, PQQ disodium salt crystals were prepared: 10 g of PQQ disodium salt was taken, stirred and balanced with 1000 ml of acetonitrile at 26°C for 6 days, then the solution was filtered and dried in air for 60 minutes to obtain PQQ disodium salt crystals, which were subjected to X-ray powder diffraction analysis, and the X-ray diffraction was consistent with that of CN102942567A; Figure 4 .

[0087] Comparative Example 4

[0088] According to the method of Example 12 of the patent with publication number WO2017050171A1, PQQ disodium salt crystals were prepared: 10 g of PQQ trisodium salt was dissolved in 1 L of water and 3 L of ethanol, the temperature was raised to 50°C, and the mixture was stirred for 30 min. The mixture was filtered and cooled to 20°C, and the pH was adjusted to 3.6. The mixture was stirred, filtered, and vacuum dried at 25°C to obtain PQQ disodium salt crystals. The X-ray powder diffraction spectrum of the obtained crystals was consistent with that of WO2017050171A1 crystal form III, as shown in FIG. Figure 5 .

[0089] Tap density test

[0090] The tap density of the pyrroloquinoline quinone disodium salt prepared in Example 1, Example 2 and Comparative Example 1 was measured respectively, and the results are shown in the following table:

[0091] Sample source Example 3 Example 4 Comparative Example 1 Tap density g / cm3 0.632 0.648 0.435

[0092] The pyrroloquinoline quinone disodium salt provided by the present invention has a higher density and a stronger fluidity than the pyrroloquinoline quinone disodium salt prepared by the method of Comparative Example 1, and is more conducive to the development and use of solid dosage forms.

[0093] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A pyrroloquinoline quinone disodium salt crystal, characterized in that: X-ray powder diffraction was performed using Cu Ka radiation, and characteristic peaks were found at diffraction angles 2θ of 8.347°, 13.540°, 15.252°, 16.690°, 17.537°, 21.329°, 22.642°, 25.824°, 27.439°, 29.923°, 33.682°, 34.519°, 38.863°, and 47.534°, with an error of ±0.2°.

2. The pyrroloquinoline quinone disodium salt crystal according to claim 1, characterized in that: X-ray powder diffraction using Cu Ka radiation revealed no characteristic peaks within the range of diffraction angles 2θ of 0° to 8.347° and 8.347° to 13.540°.

3. The pyrroloquinoline quinone disodium salt crystal according to claim 2, characterized in that: X-ray powder diffraction using Cu Ka radiation showed no characteristic peaks between diffraction angles 2θ of 17.537° and 21.329°.

4. A method for preparing the pyrroloquinoline quinone disodium salt crystal according to any one of claims 1 to 3, characterized in that: The following steps are involved: (1) Dissolving: Add free pyrroloquinoline quinone or pyrroloquinoline quinone alkali metal salt to purified water, control the temperature to 20-35° C., add alkali to adjust the pH to 6.0-7.0 while stirring, stir until all dissolved, and filter; (2) Acidification and salt crystallization: under stirring conditions, maintaining the temperature at 20-35°C, adding phosphate buffer containing NaCl to adjust the pH to 2.5-3.0; (3) Cooling and crystal cultivation: Slowly cool to 6-15°C and then slowly stir to cultivate the crystal; (4) Separation and drying: Filter the crystalline product, wash with acid water, and vacuum dry the filter cake to obtain the final product.

5. The method for preparing pyrroloquinoline quinone disodium salt crystals according to claim 4, characterized in that: In step (1), the free state of pyrroloquinoline quinone is pyrroloquinoline quinone acid, the alkali metal salt of pyrroloquinoline quinone is pyrroloquinoline quinone monosodium salt, disodium salt or trisodium salt, and the free state of pyrroloquinoline quinone or the alkali metal salt of pyrroloquinoline quinone is 0.5-15 g / L.

6. The method for preparing pyrroloquinoline quinone disodium salt crystals according to claim 4, characterized in that: In step (1), the alkali is sodium carbonate or sodium bicarbonate aqueous solution with a concentration of 5-20%.

7. The method for preparing pyrroloquinoline quinone disodium salt crystals according to claim 4, characterized in that: In step (2), the phosphate concentration in the phosphate buffer containing NaCl is: 0.18-0.22 mol / L, the NaCl concentration in the phosphate buffer containing NaCl is: 18-22% w / v, and the pH of the phosphate buffer containing NaCl is: 1.0-1.

8.

8. The method for preparing pyrroloquinoline quinone disodium salt crystals according to claim 4, characterized in that: In step (2), the addition time of the phosphate buffer containing NaCl is 1-4 hours.

9. The method for preparing pyrroloquinoline quinone disodium salt crystals according to claim 4, characterized in that: In step (3), the cooling rate is controlled at 2-6°C / h, the slow stirring speed is 20-150 rpm, and the stirring crystal growing time is 3-10 hours.

10. The method for preparing pyrroloquinoline quinone disodium salt crystals according to claim 4, characterized in that: In step (4), the pH of the washing acid water is 2.5-3.0, and the acid used is hydrochloric acid or sulfuric acid; The vacuum drying temperature is 45-65°C and the drying time is 4-15 hours.

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