Hach-Lange LUMISTOX 300 LPV321 User Manual - Manual (Page 34)

LUMIStox 300 Operating Manual Dr. Bruno Lange GmbH
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Page: 34
4 Appendix:
4.1 Sample preparation for the luminescent bacteria test
For reasons connected with the biology of the luminescent bacteria and the measuring
technology, the luminescent bacteria test requires a sample preparation step to be
carried out.
Adjusting the salt content of the sample to 2% NaCl
Luminescent bacteria are marine organisms and therefore have to be kept in an
environment with an adequate salt content. The salt content of the sample is therefore
increased to 2% by adding solid NaCl (p.a. quality).
For example, 2 g NaCl need to be dissolved in 100 ml sample, or 0.3 g NaCl in 15 ml
sample.
No salt should be added to samples that have a salt content of about 2 to 4%. The
luminescence of the bacteria is inhibited at salt concentrations of more 4%.
Setting the pH of the sample
DIN 38412 L 34/341 for the luminescent bacteria test requires the pH of wastewater
samples to be set to 7 to prevent any inhibition of luminescence due to differences in
pH. The pH is adjusted with NaOH or HCl in such a way as to cause the least possible
change in the sample concentration.
For example, 1 mol/l NaOH or HCl can be added.
It is not usual to adjust the pH when single substances are being studied.
Elution of solid samples
Solid samples (contaminated soil, earth, compost, sludge) can be studied with the
luminescent bacteria test by preparing an eluate to be used as the sample in the test.
Dr. Lange supplies the LUMISterra (LYW429) set for the preparation of solid samples
for the luminescent bacteria test.