In my opinion, one can choose either a strategy to extract the API or a strategy to remove unwanted impurities. In the first case, it probably makes sense to try to select a sufficiently selective extractant based on the properties of API.

If the second strategy is followed, it is necessary to get rid of the polymers.

To remove hypromellose, the literature suggests heating the sample to 70 degrees Celsius, then filtering the hot solution (hypromellose at this temperature forms clots and remains on the filter). If for some reason this method is not suitable or effective enough for you, I would recommend preliminary separation of the hypromellose by planar thin layer chromatography.

Polyethylene oxide is more difficult..... You may find the approaches of these authors helpful.

Davidson A, Morisseau E, Li A, Joseph S, Johnson M. Challenges in sample preparation for swellable core technology tablets: Approaches for the removal of polyethylene oxide and optimization of API recovery. J Pharm Biomed Anal. 2023 Sep 5;233:115492. doi: 10.1016/j.jpba.2023.115492. Epub 2023 May 27. PMID: 37269578.

They used two modes of extraction as sample preparation

To extract the API and related substances from a sample with Polyox or HPMC, use solvents like water, methanol, or ethanol that can dissolve both the polymer and the active ingredients. You may need to heat or sonicate the mixture to help with extraction. Afterward, filter or centrifuge to remove any remaining solid particles, leaving you with the API and related substances for analysis.

Extracting the Active Pharmaceutical Ingredient (API) and related substances from a sample matrix containing polymers like Polyox or HPMC can be challenging due to the complex nature of the matrix. Here are some general steps you can follow:

*1. Sample Preparation:*

- *Weighing* : Accurately weigh the sample matrix.

- *Homogenization* : Homogenize the sample to ensure uniformity.

*2. Solvent Selection:*

- Choose a suitable solvent that can dissolve the API and related substances but not the polymer matrix. Common solvents include methanol, ethanol, acetonitrile, or a mixture of these.

*3. Extraction:*

- *Liquid-Liquid Extraction (LLE)* : Mix the sample with the solvent and perform liquid-liquid extraction to separate the API and related substances from the polymer.

- *Solid-Phase Extraction (SPE)* : Use SPE cartridges or disks to selectively adsorb the API and related substances from the sample matrix.

*4. Filtration:*

- Filter the extract to remove any undissolved particles or polymer residues.

*5. Concentration:*

- Concentrate the extract by evaporating the solvent under reduced pressure or using a rotary evaporator.

*6. Analysis:*

- Analyze the concentrated extract using techniques such as High-Performance Liquid Chromatography (HPLC), Gas Chromatography (GC), or Mass Spectrometry (MS) to quantify the API and related substances.

*7. Validation:*

- Validate the method to ensure accuracy, precision, specificity, and reproducibility.

Extracting the active pharmaceutical ingredient (API) and related substances from a sample matrix containing polymers like Polyox (polyethylene oxide) or HPMC (hydroxypropyl methylcellulose) can be challenging due to the complex nature of these polymers. However, with the right approach, it is possible to achieve effective separation and quantification. Below is a step-by-step guide to help you design an extraction protocol:

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### **1. Understand the Sample Matrix**

- **Polymer Characteristics**: Polyox and HPMC are water-soluble polymers that can form viscous solutions or gels, which may interfere with extraction.

- **API and Related Substances**: Identify the physicochemical properties of the API and related substances (e.g., solubility, polarity, stability) to guide the extraction process.

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### **2. Sample Preparation**

- **Dissolution**: Dissolve the formulation in a suitable solvent. For water-soluble polymers, water or a water-miscible solvent (e.g., methanol, acetonitrile) is often used.

- If the API is not water-soluble, consider using a mixture of water and an organic solvent (e.g., water:methanol or water:acetonitrile).

- **Dilution**: Dilute the sample to reduce viscosity and improve handling.

- **Filtration**: Use a syringe filter (e.g., 0.22 µm or 0.45 µm) to remove undissolved polymer or particulate matter. Ensure the filter material is compatible with your solvent system.

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### **3. Extraction Techniques**

Depending on the nature of the API and related substances, you can use one or more of the following techniques:

#### **a. Liquid-Liquid Extraction (LLE)**

- Suitable for APIs that are more soluble in organic solvents than in water.

- Add an immiscible organic solvent (e.g., ethyl acetate, dichloromethane) to the aqueous sample and shake vigorously.

- Separate the organic layer, which should contain the API and related substances, while the polymer remains in the aqueous phase.

- Evaporate the organic solvent to concentrate the analytes.

#### **b. Solid-Phase Extraction (SPE)**

- Use SPE cartridges to selectively retain the API and related substances while allowing the polymer to pass through.

- Choose an appropriate SPE sorbent (e.g., C18 for non-polar analytes, ion exchange for charged analytes).

- Wash the cartridge to remove the polymer, then elute the analytes with a suitable solvent.

#### **c. Protein Precipitation (for polymers that behave similarly to proteins)**

- Add a precipitating agent (e.g., acetonitrile, methanol) to the sample to precipitate the polymer.

- Centrifuge the sample to separate the precipitate from the supernatant, which contains the API and related substances.

- Filter the supernatant to remove any remaining polymer.

#### **d. Dialysis**

- Use dialysis membranes with a specific molecular weight cutoff to separate the API and related substances (typically smaller molecules) from the polymer (larger molecules).

- This method is slower but effective for removing high-molecular-weight polymers.

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### **4. Analytical Techniques for Quantification**

After extraction, analyze the API and related substances using appropriate techniques:

- **HPLC/UPLC**: Use reverse-phase or ion-exchange chromatography with UV, PDA, or MS detection.

- **GC-MS**: For volatile or semi-volatile analytes.

- **LC-MS/MS**: For sensitive and selective quantification of related substances.

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### **5. Method Development and Validation**

- **Optimization**: Optimize the extraction conditions (e.g., solvent composition, pH, extraction time) to maximize recovery of the API and related substances.

- **Recovery Studies**: Perform recovery experiments to ensure the extraction method is efficient and reproducible.

- **Matrix Effects**: Evaluate potential matrix effects from residual polymer or other excipients.

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### **6. Specific Considerations for Polyox and HPMC**

- **Polyox**: This polymer can form gels at higher concentrations. Use dilution or organic solvents to reduce viscosity.

- **HPMC**: This polymer is less viscous than Polyox but can still interfere with extraction. Consider using SPE or protein precipitation for effective removal.

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### **Example Protocol**

1. Dissolve the formulation in a water:methanol (50:50) mixture.

2. Dilute the sample to reduce viscosity.

3. Filter the solution through a 0.22 µm nylon filter.

4. Perform SPE using a C18 cartridge:

- Condition the cartridge with methanol and water.

- Load the sample onto the cartridge.

- Wash with water to remove the polymer.

- Elute the API and related substances with methanol.

5. Analyze the eluate using HPLC-MS.