Hach-Lange LUMISTOX 300 LPV321 User Manual - Manual (Page 16)

LUMIStox 300 Operating Manual Dr. Bruno Lange GmbH
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Page: 16
2.6 Determining the EC value
The EC value is the concentration of a sample that causes 20% (EC20) or 50% (EC50)
inhibition in the luminescent bacteria test (EC = effective concentration). A dilution
series of no less than 3 and no more than 9 dilution levels, for double determinations, is
used to determine these values. The LUMIStox 300 can only calculate an EC value if
the value lies within the concentrations for which 10 to 90% inhibition are measured in
the test. A single luminescent bacteria test can be used to determine EC values for up
to three incubation periods, e.g. for 5, 15 and 30 minutes. The control solution and 9
samples (dilutions) can be measured with one LUMIStherm.
Incorrect individual measurements of initial or final luminescence can be annulled
immediately with <C> and carried out again.
Work steps
1. Prepare and dilute the sample(s).
2. Pipette 1.5 ml sample (dilution) into measuring cuvettes and bring to the correct
temperature in row A of the LUMIStherm. The highest sample concentration
should be positioned on the extreme right.
3. Bring 1.5 ml control solution (2% NaCl solution) to the correct temperature in
position A1 of the LUMIStherm.
4. Reactivate the preserved bacteria as described in the package circular.
5. Pipette 0.5 ml bacteria suspension into measuring cuvettes (2 per sample
dilution) and leave to stand for 15 minutes in rows B and C of the LUMIStherm to
acquire the correct temperature.
6. Select evaluation mode <EC> and the required luminescent bacteria test, e.g.
<480> for LCK480, on the LUMIStox 300.
7. Enter the initial settings for the test into the LUMIStox 300.
8. Measure the initial luminescence of the bacteria at the specified time intervals.
9. Immediately after each measurement, pipette 0.5 ml control solution or sample
dilution from the corresponding position in row A into the bacteria suspension in
row B or C. Wait for the residual incubation time to elapse.
10. Measure the final luminescence of the control and test solutions for each of the
specified time intervals.
11. Record or print the results.