Manganese (II) phosphate isn't very soluble, at neutral pH values, so when manganese (II) chloride to PBS, manganese (II) phosphate forms and precipitates. If the presence of small quantity of EDTA is not a problem in our systems, you could dissolve your manganese (II) chloride in an equimolar solution of EDTA, this should produce the soluble EDTA manganese chelate. Your cells should be able to access the manganese in this form without problem.

To dissolve Manganese(II) chloride tetrahydrate into phosphate-buffered saline (PBS), you can follow these steps:

1. Prepare the PBS solution: Start by preparing the PBS solution by dissolving the appropriate amount of PBS powder or tablets in distilled water according to the manufacturer's instructions. Typically, PBS is available in pre-weighed sachets or tablets for easy preparation.

2. Weigh the Manganese(II) chloride tetrahydrate: Using a balance, measure the desired amount of Manganese(II) chloride tetrahydrate. Ensure that you handle the compound with proper safety precautions, such as using gloves and a fume hood if necessary.

3. Add the Manganese(II) chloride tetrahydrate: Carefully add the weighed Manganese(II) chloride tetrahydrate to the prepared PBS solution. Stir the solution gently with a glass rod or magnetic stir bar to aid dissolution.

4. Monitor and assist dissolution: Manganese(II) chloride tetrahydrate may take some time to dissolve completely. If necessary, you can apply mild heat or increase the stirring speed to facilitate dissolution. However, avoid excessive heating, as it may alter the properties of the solution.

5. Adjust the final volume and pH if needed: Once the Manganese(II) chloride tetrahydrate has dissolved completely, check the final volume of the solution. If the volume has decreased due to evaporation or incomplete dissolution, add distilled water to reach the desired volume. Additionally, verify the pH of the solution and adjust it if required using acid or base solutions.

6. Filter or clarify (optional): Depending on your specific application, you may want to filter the solution to remove any undissolved particles or debris. This step helps ensure a clear solution, especially if the presence of particulate matter might interfere with your experiment or downstream applications.

7. Store the solution: Transfer the dissolved Manganese(II) chloride tetrahydrate in PBS to a suitable container, such as a glass bottle or sterile plastic container. Properly label the container with the contents, concentration, and date of preparation. Store the solution as recommended, either at room temperature or refrigerated, and protect it from light if necessary.

Remember to consult the safety data sheet (SDS) and follow all safety guidelines and laboratory practices when working with chemicals.

Or, consider changing to a phosphate-free buffer, e.g., Tris-HCl, MOPS, etc.

I am tending to stick to Philip answer. pH is a real problem with Mn(II) as manganese tends to disproportionate generating Mn(III) oxide which are white beige and insoluble in water after pH 7.5-8. Any lower pH limit you can go with your PBS solution, say 6.5-7? this range is safer. Phosphate is also detrimental. Other Buffers possible?

I quite agree with Philip's view, however Thomas suggestion may be an option