Hach ULTRATURB sc User Manual

24Maintenance5.5 Monitoring test equipmentAs part of a quality assurance system for test equipment monitoring, it isnecessary to check the instrument calibration; this can be performed using aformazine standard series in accordance with DIN EN ISO 7027.You can either make up the formazine solution yourself as per the instructions thatfollow 5.5.1 Preparing formazine solution in accordance with DIN EN ISO 7027 orprocure it from the manufacturer (LCW 813 or Stabl Cal).1. To check the instrument calibration, first thoroughly rinse out the measuringchamber using distilled water.2. Prepare a turbidity series using formazine reference solutions as per DIN ENISO 7027; the measuring series should correspond to the measuring rangeselected. For example, in the measuring range FNU 0–5.0 chose referencesolutions with FNU 0.5–1.0–2.0–3.0–4.0.Note: If there are any variations in the measurements, it is recommendable to measure anew standard preparation prior to changing the instrument calibration! Experience hasshown that the variation in the formazine preparation can be greater than the possible driftin the ULTRATURB instrument.When checking the instruments as per EN 450901 or GLP we thereforerecommend recording the date in an instrument log and checking for any long-term drift. Checks on the operation of the ULTRATURB can in practice also bemade by means of parallel measurements with turbidity photometers designed inaccordance with DIN and ISO.5.5.1 Preparing formazine solution in accordance with DIN EN ISO 7027ChemicalsChemicals of "analysis" purity are used. The chemicals must be stored in hardglass bottles.Water• Place a membrane filter, pore size 0.1 μm (for bacteriologicalexperiments), for 1 hour in 100 mL of distilled water.• Filter 250 mL water through this filter and discard the water.• Then filter 500 mL of distilled water twice through the same filter and usethis water for making up the standard solution.Formazine (C 2 H 4 N 2 ) parent solutionCAUTIONHydrazine sulphate is toxic and possibly carcinogenic• Dissolve 10.0 g of hexamethylentetramine (C 6 H 12 N 4 ) in water and top upto 100 mL (solution A).• Dissolve 1 g of hydrazine sulphate (N2 H 6 SO 4 ) in water and top up to100 mL (solution B).• Mix 5 mL of solution A with 5 mL of solution B.• After 24 hours at 25° C (±3 °C) (77 °F (± 5.4 °F)) top up this solution withwater to 100 mL.