4.2.2 Calculation for Other Pathlengths and for Other Volume
Fractions:
Insert the pathlength (unit: meter) and the volume fraction
(unit
L)
in the equation instead of the figures given above.
4.3
Calculation at Variabl'e Pathlengths (longitudinal
measurement)
Certain (centrifugal) analyzers me a sure
longitudinally
through the cuvettes. The light path thus becomes proportio–
nal to the total assay volume in the cuvette. Dilution of the
assay medium in the cuvettes with an inactive fluid eauses a
corresponding elongation of the light path, and the absorban–
ce remains constant. The net effect is that the calculation
factor becomes proportional to the sample volume and indepen–
dent of the sample volume fraction in the cuvette (34). In
the example below the sample volume is lO pL.
30
Symbols
Typ
e of Quantity
Exarop le
Uni t
a
Area of cuvette end
0.25 x
v
Sample volume
lO
x
i
equals i nerease in absorbance
at 340
Other symbols
i
x a
b
E
x v
i
x
25
b
6300
nm per s
as given above.
i x 0.25 x l0- 4
630 x lO x 10- 6
b
i x 0.003968 x mol x s-l x L-l
b
i x 0.003968 kat/L
b
i x 3968 ykat/L
x
x
10- 4
2 m
10- 6
L
-l
s
-l
2
s
x m
m 2 x mol-l x
L
mol x s-l
L
Calculated for a Measuring Time of 60 s:
b
i x 3968 U/L
b
~
x 66 .13 ykat/L
Klinisk kemi
i
Norden 2: suppl, /990
