Samples should be sent in several aliquots (at least 4) of 30-40 ul of protein concentration of 5mg/ml or more. All aliquots should be prepared from the same batch of purification. One aliquot each will be used for NS-EM and the three attemps of cryo-EM. 

Along with the sample, a gel-filtration profile of a freeze-thaw sample is necessary to prove the stability (solubility and oligomerization) of the sample doesn't change due to flash-freezing after purification/concentration.

Buffer conditions: preferably no glycerol or upto a maximum of 4%; low salt, preferably 300mM but should not exceed 500mM NaCl. Should discuss with the local contacts in case of unusual buffer conditions, including Imidazole, sugars, or mild detergents, etc.