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10 Libra S21/S22, English Issue 02 - 04/2004
Reaction Rate (2.3)
Reagent test kits are routinely used for the enzymatic determination of compounds in
food, beverage and clinical laboratories by measuring NAD / NADH conversion at 340
nm. The change in absorbance over a specified time period can be used to provide
useful information when an appropriate factor, defined in the reagent kit protocol, is
applied.
Note that reaction rate and enzyme activity can be calculated if the factor used takes
account of the absorbance difference per unit time, as opposed to the absorbance
difference per se.
The correlation (quality of line fit) is calculated from 10 equally spaced absorbance /
time points during the course of the experiment. The procedure is as follows:
• Enter appropriate wavelength and press OK (F3)
• Select time units; seconds (1) or minutes (2)
• Enter delay time (or lag time), if applicable and press OK (F3)
• Enter the duration of the assay and press OK (F3)
• Enter factor required to convert slope to meaningful units and press OK (F3)
• Insert reference and press green run key
• This reference value is used for subsequent samples until changed
• Insert samples as required and press (repeat as necessary)
• The assay is shown graphically as it proceeds and reverts to show
• The result (total change in absorbance over the reaction time as defined
by the intercepts multiplied by the factor), slope and the line quality (a
coefficient of determination of > 95 % is expected if the assay was
carried out over a linear section). The slope is always presented as
Abs/min, even in seconds mode
• Start and final absorbances, as well as absorbance difference
• To see the assay on the whole display, press Graph (F3); to return press OK (F3)
• Data points can be viewed by pressing Data (F1) moving the cursor (F2 and F1)
• To go back and change the parameters press Method (F1)
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