Concentration is among the essential parameters in chemistry and, by definition, is the ratio of the mass of a particular substance to the total mass of the solution or mixture. Therefore, the least ambiguous way to determine concentration is by dry weight. However we normally determine concentration of biopolymers by other means such as spectrophotometry either directly or after a chromogenic reaction. It is noted, however, that all secondary standards such as A 1%, 1cm are useful only when they are correlated with mass of the substance, and this is where the dry weight method serves best. In conventional dry weight methods, the dried residue has been carefully protected from moist air, using a glass weighing bottle which is far to heavy for a microbalance. I have developed a simple micro method of dry weight determination which requires a minimum of 0.2 mg of biopolymer, if present in a purely aqueous solution, and uses a microbalance of weighing range of 0-200 mg and sensitivity of 1 micron and lightweight drying cups. Since the role of the microbalance is limited to weighing lightweight cups, a more precise microbalance could be used. This method has been tested on some 20 proteins and shown to give consistent results A 1%, 1cm values at 280 nm based on dry weights have shown a generally good agreement with literature values. The method of turbidity correction by linear extension of ln(absorbance) vs ln(wavelength) to obtain uniform absorbance values has been verified by model experiments using synthetic polymer beads (Progress Report 2, 1)) Comparison of color yields in Lowry's reaction among those proteins examined above shows a general agreement with that of BSA within plus or minus 20% for 13 proteins, but two proteins show extremely large deviation of 170-250%, and one protein shows low value of 75% in general agreement with observations by Lowry et al.
