Heelo Tomasz Spietz ,

They look like crystals as they seem very sharp on the picture.

What was the concentration of your buffer?

3 months is a long time to keep a buffer in stock I would suggest to keep it for less than a month.

Also, it can be common to develop contamination from spores or bacteria, resulting in small fibrous structures developing in the bottom of the container.

Poor lab practice (such as returning unused buffer back to the container, or inserting reusable pipettes) can also accelerate contamination.

Best regards,

Marie B.

There is an easy solution to come up with a better guess. Put the container on sonication bath for 10 min, if "crystals" dissolve, they are most likely not SiO2 or contamination but just a complex compound of salts.

Thanks for the answers.

Marie Berthuel , the buffer was: 3,876 g of sodium bicarbonate and 5,709 g of sodium carbonate. I thought that buffer solutions are quite stable, especially these not including ammonia salts. I'll take your advice into consideration. I'm going to condcut simple experiment - I'll prepare the fresh carbonate buffer in bottle washed with nitric acid and I'll see what will happen in a few months.

Iman Roohani - unfortunately I've already discarded this buffer. I'm going to check it next time.

Best Regards