After adding 100 uL water to lyophilized peptide, final volume was LESS than 100 uL -- is this possible?
why not Adam B Shapiro if the question was for anhydrous silica gel or anhydrous copper sulphate the molecules would adsorb some water to become solvated with only a small increase in size of the salt but the volume of free water would diminish.
Interesting question. I work with proteins for 20 years and I never see that .
Perhaps there are specialized peptides that acts as water absorbents, as Paul Rutland suggests. I tend to think of peptides as simple solutes that add to the volume of water when dissolved. Nevertheless, the total volume of the solution (or suspension, more likely), including the absorbent peptide, would be larger than the volume of the added water because the absorbent would swell when it took up the water. Check to see if there is any solid material left behind after the water was added, which might be the swollen but undissolved peptide.
I have not seen this effect in biological materials either but the question intrigued me. I do like the idea of swollen peptide still coating the tube wall though. As a further thought if the volumes were measured with a pipette and bearing in mind the concept of material remaining on the tube perhaps the viscosity of the solution is very high making it impossible to take up the full 100ul by suction and the rest is still sticking to the tube as you say Adam B Shapiro
Centrifuging the container is a good way to get all the material adhering to the walls to settle to the bottom. This should be done carefully to avoid breaking the container, especially if it is glass. Practice with a similar empty container first to establish the right speed.
40 uL less seems like a bit too much, does not it? I believe You made sure that there is no undissolved material left, you tried centirfugation to bring all the liquid to the bottom of the container and you made sure the pipette you are using is calibrated properly.
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