50
Standard Operations
5.5.3 Take a US Pharmacopoeia color measurement
The LICO 500 method of determining color in accordance with the
U.S. Pharmacopoeia corresponds to the specifications in Chapter
631 "Color and Achromicity " and Chapter 1061 "Color -
Instrumental measurement ". A total of 20 color reference solutions
(identified sequentially by the letters A to T) are defined in the U.S.
Pharmacopoeia. The color of the measured sample is automatically
correlated to the color reference solutions. This means that the
color reference solution that is closest to the sample (i.e. the
reference solution with the smallest color difference
Δ
E* to the color
of the sample) is displayed. The
Δ
L*,
Δ
a* and
Δ
b* values give the
quantitative differences between the L*,a* and b* values of the
sample and those of the displayed USP solutions.
The measurements can be carried out with cuvettes/sample cells
with a path length of 10 mm,11 mm or 50 mm. The use of a longer
path lengths increase the accuracy associated with the
measurement.
The CIE L*a*b* values depend on the path length and are always
related to the type of cuvette/sample cell used.
1.
Select
US Pharmacopeia
.
2.
Insert the sample cuvette/cell.
3.
The result of the color calculation is displayed.
The
Δ
Lab* - values shows the color difference of the measured
sample in relation to the nearest USP - Color standard which is
shown above the color difference values (here color standard L).
The
Δ
E* - value shows the three dimensional color difference of the
measured sample in relation to the USP Color standard L.
The touch-sensitive area around the matching result
(touch-sensitive area 8) is active.
4.
Press the area around the matching result. The color axis a*, b*
and the loci of the sample (+) is displayed as well as the USP
color standards.
5.
Press
Printer
for printout or
Return
for exit the window.
5.5.4 Determine the Iodine color value
DIN 6162 defines the Iodine color value as mg of iodine per 100 mL
of potassium iodide solution. Color matching with the Iodine color
determines the depth of color of clear liquids like solvents,
plasticisers, resins, oils and fatty acids, whose color is similar to
that of a solution of iodine and potassium iodide of the same
thickness.
