Page 125 - Illustrated Pocket Dictionary of Chromatography

124 MATRIX BLANK

transfer in a stagnant phase are contributors to zone spreading
(increased peak width) and are captured as the C term in the van
Deemter and Knox equations.

matrix blank A sample that contains all the components of a
sample, in concentrations that are expected in the sample, except for
the compounds that are to be analyzed. A matrix blank is used to
determine whether or not there are any matrix components that will
ultimately interfere with the analysis (e.g., coelute).

McReynolds phase constants Developed to establish a
systematic ordering of GC stationary phases with respect to
specific solute interactions. This can then be used to predict the
change in the retention index, DI, for the tested phase with respect to
squalene:

DI = aX¢ + bY¢ + cZ¢ + dU¢ + eS¢

where a, b, c, d, and e are assigned constant values associated with a
specific test probe molecule (e.g., benzene, nitropropane, etc) and X¢,
Y¢, Z¢, U¢, and S¢ refer to a molecule’s aromaticity, proton donor/accep-
tor characteristics, proton acceptor characteristics, dipole interac-
tions, and strong proton acceptor characteristics, respectively. Tables
of the values for each of these constants were generated for a wide
range of nonpolar to very polar stationary phases.

mean, x The mean value for any set of related data is the best esti-
mate of the value of the results and is mathematically determined by:

x = Â x n
i
where S represents the summation of all data points 1–n and x i is the
value of the ith datum in the set of n data points. For example, for
the set of data 6.1, 6.4, 6.2, 6.2, and 6.1, x is 6.2 [i.e., (6.1 + 6.4 + 6.2 +
6.2 + 6.1)/5].

median The middle value in a set of rank-ordered data. For
example, for the set of data 6.1, 6.4, 6.2, 6.2, and 6.1, the rank order is
6.1, 6.1, 6.2, 6.2, 6.4 and the median is 6.2.

mesh and mesh sizes A mesh is used to sieve particles having a
wide size distribution. The mesh size is determined by the number of
meshes in the sieve and is characterized with respect to the largest