6
Methods
COD Reagents
Selecttheappropriatevialforthedesiredrange*:
LR-Range: 0–150mg/l,partnumber251990Y,25count
MR-Range: 0–1500mg/l,partnumber251991Y,25count
HR-Range: 0–15000mg/l,partnumber251992Y,25count
*Reagents are also availble in 150 count packages.
Preparing the Sample
Openareactionvialwithawhitecapandaddthespeciedvolume.
(Ensurethatappropriatepersonnelsafetyequipmentisused.)
LR-/MR: 2 ml water sample
HR: 0.2 ml water sample
Prepareablank(Note1)byusingdeionizedwater(TOC-free)insteadofthesample
(LR/MR: 2 ml, HR: 0.2 ml).
Replacethecaptightly.Invertthevialgentlyseveraltimestomixthecontents(Thevialwillbecome
hotduringmixing!)anddigestthevialsfor120minutesinthereactoratatemperatureof150°C.
Removethevialsfromthereactorandallowthemtocooldownto60°Corless.Mixthecontentsby
invertingeachvialseveraltimeswhilestillwarm.Thenallowthevialstocooltoambienttemperature
beforemeasuring.
Guidelines for photometric measurements
1. Runsamplesandblankswiththesamebatchofvials.
Theblankisstablewhenstoredinthedarkandcanbeusedforfurthermeasurementswithvials
fromthesamebatch.
2. Don‘tplacehotvialsintheadapter.Allowthevialstocooltoroomtemperaturefor
a minimum 45 minutes. It is recommended to leave the vials to cool over night.
3. Suspended solids in the vial lead to incorrect measurements. For this reason it is important to place
thevialscarefullyintheadapter.Theprecipitantatthebottomofthesampleshouldnotbe
suspended.
4. Cleantheoutsideofthevialswithatoweltoremovengerprintsorothermarks
.
5. Avoidspillageofwaterorreagentsolutionintothesamplechamberbecausethiscanleadtoincor-
rect test results.
6. Contaminationofthetransparentcellchambercanresultinincorrectreadings.Checkatregularin-
tervalsand–ifnecessary–cleanthetransparentcellchamberusingamoistclothorcottonswab.
7. Largetemperaturedifferencesbetweentheinstrumentandtheenvironmentcanleadtoerrors–
e.g.duetotheformationofcondensationinthecellchamberoronthevial.
8. Toavoiderrorscausedbystraylightdonotusetheinstrumentinbrightsunlight.