Many thanks for all the responses, I briefly summarized them as follows: 1. Birefringence-on glass coverslip, dim the room and set the polarizers exactly to extinction, then check if the precipitate glows (exception: cubic space group crystal). 2. Streakseeding-if something grows along the line, it is microcrystalline. 3. X-ray screening in situ. 4. Whether the shiny precipitate can be redissolved or not. 5. Whether the shiny precipitate forms a large connected skin which can be revealed if you drag a needle through it. 6. Fluorescent pens? (I am not quite clear about how the fluorescent pens work, is there any literature to resort to?)
Many thanks again to all of you for your nice help! joy 发件人： Emmanuel Saridakis 发送时间： 2010-06-10 17:52:59 收件人： joybeiyang; CCP4BB@JISCMAIL.AC.UK 抄送： 主题： Re: [ccp4bb] How to distinguish microcrystalline, quasicystalline and precipitation? Hi Joy, Yes, I agree that it is very difficult to distinguish those and it is even more difficult to put it in words or in writing: experts have been talking about shininess, transparency (rather than brown colour) and birefringence as far as I know. All these methods have some grain of truth in them, yet none is as simple let alone as accurate as we would like to believe. So, it seems to me that the only way to distinguish is what I would call the "operational" way, i.e. to streak seed from that precipitate into a couple of drops set at very similar conditions but that are just below the spontaneous nucleation level of supersaturation: if something grows along the streak line, the precipitate was microcrystalline. However, if it doesn't, that doesn't mean that it was not microcrystalline? Dilemma? Another interesting question that you are raising is what are quasicrystalline or "ordered precipitates" really worth, in terms of ultimate success near the relevant conditions... Finally, how about these fluorescent pens? I have not had a chance to use one of these, but my feeling is that they would only really work on good-sized crystals. It would be very interesting to hear members' experiences with these on smaller stuff. Best, Emmanuel ----- Original Message ----- From: joybeiyang To: CCP4BB@JISCMAIL.AC.UK Sent: Thursday, June 10, 2010 9:06 AM Subject: [ccp4bb] How to distinguish microcrystalline, quasicystalline and precipitation? Hi everyone, I am preparing a "crystallization manual" for our group, however, I found that it is very difficult to distinguish microcrystalline, quasicrystalline and precipitation, especially when the precipitation was shiny, like the grit on the beach. Is there a way to distinguish the three? Comments and suggestions will be greatly appreciated! Joy
