Study on adsorption of a weakly basic compound to glass vials

Author / 1,2 Hu Rong 1 Hol drum Drum Song Xuezhi before the 1 tour Jinsong 1 – The new 1, 2

【Abstract】Borosilicate glass is a widely used packaging material and solution container in the pharmaceutical industry. Although it has the characteristics of high resistance, such as smooth, corrosion resistance and wear resistance, the metal ions and silanol groups contained in borosilicate glass may still interact with drugs. In the analysis of chemical drugs by high performance liquid chromatography (HPLC), the typical injection vial is borosilicate glass. By investigating the effect of HPLC glass vials of three brands on the stability of solifenacin succinate which is a weak alkaline compound, it was found that the adsorption to the alkaline drugs existed in the glass vials produced by different manufacturers. The adsorption was mainly caused by the interaction of protonated amino and dissociative silanol group, and the presence of succinate promoted it. The addition of hydrochloric acid could desorb the drug or adding appropriate proportion of organic solvents could prevent adsorption. The purpose of this paper is to remind the drug testing enterprises to pay attention to the interaction between alkaline drugs and glass, and to reduce the data deviation and the investigation work of deviation caused by the lack of knowledge of the adsorption characteristics of glass bottles in the process of drug analysis.
Key words: Solifenacin succinate, amino group, HPLC glass vials, adsorb

Glass as a packaging material has the advantages of smoothness, easy elimination and corrosion resistance.Corrosion, wear resistance, volume stability and other advantages, so it is widely used in the pharmaceutical application. Medicinal glass is divided into sodium calcium glassand borosilicate glass, according to the different components it contains. Among them, soda lime glass contains 71%~75%SiO2, 12%~15% Na2O, 10%~15% CaO; borosilicate glass contains 70%~80% SiO2, 7%~13%B2O3, 4%~6% Na2O and K2O and 2%~4% Al2O3 . Borosilicate glass has excellent chemicalresistance due to the use of B2O3 instead of most of Na2O and CaO
Because of its scientific nature, it was chosen as the main container for the liquid medicine. However, boronSilicone glass, even with its high resistance, may still interact with drugs, There are four common reaction mechanisms as follows [1]:
1)Ion exchange: Na+ , K+ , Ba2+, Ca2+ in the glass undergo ion exchange with H3O+ inthe solution, and there is a reaction between the exchanged ions and the drug;
2)Glass dissolution: Phosphate, oxalate,Citrates and tartrates will accelerate the dissolution of glass and cause silicides. and Al3+ is released into solution;
3)Corrosion: EDTA present in the drug solution(EDTA) may complex with divalent ions or trivalent ions in the glass
4)Adsorption: There is a broken Si-O bond on the glass surface, which can adsorb H+

The formation of OH- can form hydrogen bonds with certain groups in the drug, resulting in the drug being adsorbed to the glass surface.
Most chemicals contain weakly basic amine groups, When analyzing chemical drugs with high performance liquid chromatography (HPLC), the commonly used HPLC autosampler vial which is made of borosilicate glass, and the presence of SiO- on the glass surface will interact with protonated amine group, allowing the drug density decreases, the analysis results will be inaccurate, and laboratory OOS (Out of Specification). In this report, the weak basic (pKa is 8.88[2]) drug solifenacin succinate (structural formula is shown in Figure 1) is used as the research object, and the influence of several amber borosilicate glass injection vials on the market on drug analysis is investigated. , and from an analytical point of view to find a solution to the adsorption of such drugs on glass.

1.Test part
1.1Materials and equipment for experiments
1.1.1 Equipment: Agilent High Efficiency with UV Detector
Liquid chromatography
1.1.2 Experimental materials: Solifenacin succinate API was produced by Alembic
Pharmaceuticals Ltd. (India). Solifenacin standard (99.9% purity) was purchased from USP. ARgrade potassium dihydrogen phosphate, triethylamine, and phosphoric acid were purchased from China Xilong Technology Co., Ltd. Methanol and acetonitrile (both HPLC grade) were purchasedfrom Sibaiquan Chemical Co., Ltd. Polypropylene (PP) bottles were purchased from ThermoScientific (US), and 2ml amber HPLC glass bottles were purchased from Agilent Technologies(China) Co., Ltd., Dongguan Pubiao Laboratory Equipment Technology Co., Ltd., and Zhejiang Hamag Technology Co., Ltd. (A, B, C are used below to represent different sources of glass vials, respectively).

1.2HPLC analysis method
1.2.1Solifenacin succinate and solifenacin free base: the chromatographic column isphenomenex luna®C18 (2), 4.6 mm × 100 mm, 3 µm. With phosphate buffer (weigh 4.1 g ofpotassium dihydrogen phosphate, weigh 2 ml of triethylamine, add it to 1 L of ultrapure water, stir to dissolve, usephosphoric acid(pH was adjusted to 2.5)-acetonitrile-methanol (40:30:30) as the mobile phase,

Figure 1 Structural formula of solifenacin succinate

Figure 2 Comparison of peak areas of the same solution of solifenacin succinate in PP vials and glass vials from three manufacturers A, B, and C

the column temperature was 30°C, the flow rate was 1.0 mL/min, and the injection volume was 50 mL,The detection wavelength is 220 nm.
1.2.2 Succinic acid sample: using YMC-PACK ODS-A 4.6 mm × 150 mm, 3 µm column, 0.03 mol/L phosphate buffer (adjusted to pH 3.2 withphosphoric acid)-methanol (92:8) as mobile phase, flow rate 1.0 mL/min, column temperature 55 °C, and the injection volume was 90 mL. Chromatograms were acquired at 204 nm.
1.3 ICP-MS analysis method
The elements in the solution were analyzed using an Agilent 7800 ICP-MS system, the analysis mode was He mode (4.3mL/min), the RF power was 1550W, the plasma gasflow rate was 15L/min, and the carrier gas flow rate was 1.07mL/min. The fog room temperaturewas 2°C, the peristaltic pump lifting/stabilizing speed was 0.3/0.1 rps, the sample stabilizationtime was 35 s, the sample lifting time was 45 s, and the collection depth was 8 mm.

Sample preparation

Solifenacin succinate solution: prepared with ultrapure water, theconcentration is 0.011 mg/mL.
1.4.2 Succinic acid solution: prepared with ultrapure water, the concentration is 1mg/mL.
1.4.3 Solifenacin solution: dissolve solifenacin succinate in water, sodium carbonate was added, and after the solution changed from colorless tomilky white, ethyl acetate was added. The ethyl acetate layer was then separated and thesolvent was evaporated to give solifenacin. Dissolve an appropriate amount of solifenacin inethanol (ethanol accounts for m 5% in the final solution), and then dilute with water to preparea solution with a concentration of 0.008 mg/mL solifenacin (with the solifenacin succinate solution contained in the solution same as solifenacin concentration).

Results and Discussion

2.1 Adsorption capacity of HPLC vials of different brands
Dispense the same aqueous solution of solifenacin succinate into PP vials and 3 brands of autosampler vials were injected at intervals in the same environment, andthe peak area of the main peak was recorded. From the results in Figure 2, it can be seenthat the peak area of the PP vials is stable, and there is almost no change after 44 h.While the peak areas of the three brands of glass vials at 0 h were smaller than PP bottle, and the peak area continues to decrease during storage.

Figure 3 Changes in peak areas of solifenacin, succinic acid, and solifenacin succinate aqueous solutions stored in glass vials and PP vials

To further study this phenomenon, solifenacin, succinate acid, Aqueous solutions of solifenacin acid and succinate in glass vials of manufacturer Band PP bottles to investigate the change of peak area with time, and at the same time the glass
Three solutions in vials were inductively coupled using an Agilent 7800 ICP-MSPlasma mass spectrometer for elemental analysis. The data in Figure 3 show that inGlass vials in aqueous medium did not adsorb succinic acid, but adsorbed solifenacinFree base and solifenacin succinate. Glass vials adsorb succinate. The extent of linacin is stronger than that of solifenacin free base, at the initial momentSolifenacin succinate and solifenacin free base in glass vials. The ratios of the peak areas of the solutions contained in the PP bottles were 0.94 and 0.98, respectively.
It is generally believed that the surface of silicate glass can absorb some water, which some water combines with Si4+ in the form of OH groups to form silanol groups In the composition of oxide glass, polyvalent ions can hardly move, but alkali metal (such as Na+ ) and alkaline earth metal ions (such as Ca2+) can move when conditions permit, especially alkali metal ions are easy toflow, can exchange with H+ adsorbed on the glass surface andTransfer to the glass surface to form silanol groups [3-4]. Therefore, the H+ concentration ofThe increase can promote ion exchange to increase the silanol groups on the glass surface. by table1 shows that the content of B, Na, and Ca in the solution varies from high to low. are succinic acid, solifenacin succinate and solifenacin.

sample B (μg/L) Na(μg/L) Ca(μg/L) Al(μg/L) Si(μg/L) Fe(μg/L)
water 2150 3260 20 No Detection 1280 4520
Succinic acid solution 3380 5570 400 429 1450 139720
Solifenacin Succinate Solution 2656 5130 380 No Detection 2250 2010
solifenacin solution 1834 2860 200 No Detection 2460 No Detection

Table 1 Elemental concentrations of solifenacin succinate, solifenacin and succinic acid aqueous solutions stored in glass vials for 8 days

In addition, it can be seen from the data in Table 2 that after storage in glass bottles for 24 h, the dissolved The pH of the liquid has risen. This phenomenon is very close to the above theory

Vial No. Recovery rate after storage in glass for 71 h
(%) Recovery rate after PH adjusted
Vial 1 97.07 100.35
Vial 2 98.03 100.87
Vial 3 87.98 101.12
Vial 4 96.96 100.82
Vial 5 98.86 100.57
Vial 6 92.52 100.88
Vial 7 96.97 100.76
Vial 8 98.22 101.37
Vial 9 97.78 101.31
Table 3 Desorption situation of solifenacin succinate after acid addition

Since the Si-OH on the glass surface can be dissociated into SiO-[5] between pH 2~12, while solifenacin occurs N in an acidic environment Protonation (measured pH of aqueous solution of solifenacin succinate is 5.34, the pH value of solifenacin solution is 5.80), and the difference between the two Hydrophilic interactions lead to drug adsorption on the glass surface (Fig. 3), solifenacin was adsorbed more and more over time.
In addition, Bacon and Raggon [6] also found that in neutral solution, hydroxy acids with a hydroxyl group in the position relative to the carboxyl group Salt solutions can extract oxidized silicion. In the molecular structure of solifenacin succinate, there is a hydroxyl group relative to the position of the carboxylate,which will attack on the glass, SiO2 is extracted and the glass is eroded. Therefore, after salt formation with succinic acid, the adsorption of solifenacin in water is even more obvious.

2.2 Methods to avoid adsorption
Storage time pH
0h 5.50
24h 6.29
48h 6.24
Table 2 pH changes of aqueous solutions of solifenacin succinate in glass bottles

Although PP vials do not adsorb solifenacin succinate, But during the storage of the solution in the PP vial, other impurity peaks are generated and The prolongation of the storage time gradually increase the impurity peak area, which caused interference to the detection of the main peak.
Therefore, it is necessary to explore a method that can prevent glass adsorption.
Take 1.5 mL of solifenacin succinate aqueous solution in a glass vial. After being placed in the solution for 71 h, the recovery rates were all low. Add 0.1M hydrochloric acid, adjust the pH to about 2.3, from the data in Table 3. It can be seen that the recovery rates all returned to normal levels, indicating that the adsorption storagetime reaction can be inhibited at lower pH.

Another way is to reduce adsorption by adding organic solvents. Make 10%, 20%, 30%, 50% methanol, ethanol, isopropanol, acetonitrile was prepared at a concentration of 0.01 mg/mL in Solifenacin succinate liquid. The above solutions were put into glass vials and PP vials, respectively. At room temperature Its stability was studied shows. The investigation found that too little organic solvent could not prevent adsorption, while organic solvent too much solvent will lead to abnormal peak shape of main peak due to solvent effect. Only moderate organic solvents can be added to effectively prevent succinic acid Solifenacin is adsorbed on glass, add 50% methanol or ethanol or 30%~50% acetonitrile can overcome the weak interaction between the drug and the surface of the vial.

  PP vials Glass Vials Glass Vials Glass Vials Glass Vials
Storage time 0h 0h 9.5h 17h 48h
30% acetonitrile 823.6 822.5 822 822.6 823.6
50% acetonitrile 822.1 826.6 828.9 830.9 838.5
30% isopropanol 829.2 823.1 821.2 820 806.9
50% ethanol 828.6 825.6 831.4 832.7 830.4
50% methanol 835.8 825 825.6 825.8 823.1
Table 4 Effects of different organic solvents on the adsorption of glass bottles

that solifenacin succinate is preferentially retained in solution. Table 4 numbers
It has been shown that when solifenacin succinate is stored in a glass vials, use
After the organic solvent solution of the above example is diluted,the succinate in the glass vials. The peak area of linacin within 48h is the same as the peak area of PP vial at 0h. Between 0.98 and 1.02, the data is stable.

3.0 conclusion:
Different brands of glass vials for weak base compound succinic acid Solifenacin will produce different degrees of adsorption, the adsorption is mainly is caused by the interaction of protonated amine groups with free silanol groups. Therefore, this article reminds drug testing companies that during liquid storage or analysis, be sure to pay attention to the loss of drug, the appropriate diluent pH or suitable diluent pH can be investigated in advance. Example so for oganic solvents to avoid the interaction between basic drugs and glass, so as to reduce data bias during drug analysis and the resulting bias on investigation.

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Figure 4. Interaction between the protonated amino group of solifenacin and dissociated silanol groups on the glass surface

Post time: May-26-2022