TCA is not very quantitative for low concentrations of proteins. That's why
its use is often recommended with carrier protein. I don't think this person
wants to contaminate their prep with BSA or some such. If she can, the
gentlest way to concentrate a prep is akin to the PEG method just suggested,
but instead of PEG, use dry Sephadex. In other words, put the sample into a
dialysis bag, and cover with dry sephadex. The sephadex will swell using the
water (and dialysable salts) from the sample. Moreover she can recover the
sephadex by washing and drying. Good luck.
jw
