Standard Reference Material 2881 - National Institute of Standards ...

Here Q is a function of all the experimental conditions: the instrument parameters, thesample concentrations, and the sample preparation method. In the experimental proceduredescribed later, once the instrument parameters and experimental preparation methods areoptimized, every attempt is made to keep them constant to insure experimentalreproducibility. Later is will be shown how variation in the machine parameters can affect thevariation of Q and thus the Type B uncertainty. It should be noted that Q is a function of M 0 ,and is sometimes designated as Q(M 0 ).We shall now explore equation [6.5] and see how small linear shifts of the calibrationconstant Q over limited mass ranges effects quantities derivable from MALDI-TOF MS data.First we shall explore quantities like the total signal, the total detected mass, and the massratios of mixtures and see how these quantities relate to the true MMD of the polymer.The total signal (S T ) from the polymer is given by:∑∑0S = S = k n + Q(M − M )Tiioino∑ini[6.6]while the total mass of polymer detected (G T ) is given by:∑∑00 0G = m S = k M n + QM ( M − M )Tiiioniinno∑ini[6.7]where M 0 n and M 0 w are defined in equations 4.1 and 4.2, and are the true number average andmass average relative molecular masses. By multiplying equations 4.1 and 4.2 together wehave:∑M M = m n /wni2ii∑ini[6.8]16