Model 6500/5 Kinetics Mode

Rate studies involve the measurement of the change in concentration of a participant in the reaction as a function of time. Spectrometric rate measurement involves the measurement of a fall or rise in absorption at a fixed wavelength. The most widely encountered application of spectrometric rate measurements is for the study of enzymes (proteins that are present in all living tissue). Enzymes cannot be measured directly, but their catalytic properties allow their estimation from the speed of the reactions which they catalyze.

This operating mode allows kinetics rate measurements to be made - a change in absorbance at a constant wavelength over a given period of time. The photometrics value - as either %Transmittance or Absorbance - versus time is plotted graphically on the LCD. The user can enter any kinetics lag time (between 0 and 9999 seconds) and run time (between 10 and 9999 seconds). Alternatively, the kinetics run time can be set to commence when the absorbance or transmittance exceeds or falls below a user set level.

The y-axis limits can be set manually or they can be automatically re-scaled to the most appropriate values on completion of a kinetics run.

A variety of parameters will influence the rate of reaction. The majority of these (i.e., substrate concentration, enzyme concentration and pH) have to be accounted for in the chemistry. However, one of the most important is temperature and it is important to control the temperature of the sample and reagents precisely immediately prior to and during measurement. For this requirement, a whole range of thermostatted cell holders and temperature control systems is available.

After a kinetics run has been completed, a number of analysis tools are available. A line of best fit can be calculated from the acquired data points over the whole kinetics run or just between a user set portion of the kinetics run. The statistics available from a kinetics run are:

Initial Value the photometrics value of the very first point obtained in the kinetics run

Delta the slope of the line created by taking the first and last points of the kinetics run in isolation

Concentration the result of the Delta calculation multiplied by the user set factor value

Best Fit Line the equation of the form y = mx + c of the calculated line of best fit between the user selectable points.