I have a mixture of compounds from which one is forming crystals. From fractional crystallization, I found that the impurities and the crystals dissolve in the same solvents. Also, the crystals are very fine and thin needle shaped. It is difficult to pick or isolate the crystals from the mixture for further processing like crystal cleaning and re-crystallization. Any suggestions?
You may recover the crystals by filtration on filter paper with appropriate porosity. Then you may perform a re-crystallization.
Thank you sir.
But there is a problem. Even for filtration, how do I choose the solvent since both the impurities and the crystal dissolve in the same solvent.
In such case, different solvents and solvent mixtures for crystal growth. Use high quality starting materials for synthesizing product. After reaction wash the material with same solvent. For inclusion free crystal growth, select better quality needle shaped crystals and pick them from growth vessel. Keep it in clean dry place. Grind them and employ them in recrystallization process.
Little can be said; since the crystallized compound was not identified at the query enunciate; except for the shape of the crystals, said to be needle-like. Maybe you can find interesting to check the signalled discussion: https://www.researchgate.net/post/How_to_increase_crystal_size_using_water_as_a_solvent
Other way you can use is HPLC coupled with mass spectrometry. But if in diverse solvents presents the same behavior, it means the chemical structure is similar, it's complex to separate.
Can intent to identify the morphology of both phases visually and characterize individually until to identify two materials differents.
Too use a chiral reactive, forming a complex that it can separate more easy, if it applies. If too hard separete it's necessary study both phases together with other tecniques (UV, infrarred, "mass spectrometry", etc) and construct the structure of the both materials. With the chemical structures can to know more easy how to separate.
You can also try the simple process: after filtration and washing as usual, take the solid containing the crystals in a petry dish, allow to dry in a CaCl2 desiccator for 2-3 days. Now pour the whole mass in a clean white paper and try to pick up the needle shaped crystals with the help of a sharp needle fitted with plastic or wooden handle (bad conducting materials) and a magnified glass. Before you start picking up crystals, rub the needle gently in your hair (oil free) or with a piece silk cloth, as such the crystals will attract and stick to the tip of the needle. In this way you can segregate the crystals from the impurity. Good quality crystals can be screened under a microscope as usual. Point to be noted that crystals should be air stable
I had tried picking the crystals using needle (static charged) as suggested by Mr. Saha, it did not work out. Sir, is there any modifications I need to do?
it is necessary to crystallize the product in ethanol at room temperature then to filter it?
Dear Sanjana Skumar just in case that this is still of interest for you: Thin, needle-shaped crystals are often not really suitable for use e.g. in single-crystal X-ray diffraction. For a crystal structure determination it is normally preferably to have compact, block-like or prism-like crystals. In order to obtain a different crystal shape, you can either use a different solvent (e.g. acetonitrile instead of ethanol) or use a different crystallization technique. For more information please see this useful guide to Growing Quality Crystals
https://web.mit.edu/x-ray/cystallize.html
See this link
https://www.sciencedirect.com/topics/chemistry/needle-like-crystal
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