Thermo Scientific Orion 2110XP Ammonia Analyzer

General InformationPrinciples ofCalibrationDouble KnownAddition (DKA)Calibration procedures for analytical instruments are important and mustbe performed carefully. The calibration procedure used in the ThermoScientific Orion 2110XP is a variation of Double Known Addition (DKA)using advanced electrode and flow cell technology in combination with thepassive diffusion system. This method has the distinct advantages of beingfast, easy, and accurate.Before calibration begins, the diverter valve is pushed in to divert flow fromthe measure drain, allowing the flow cell to fill.At the beginning of the DKA calibration the actual concentration in thesample is unknown. The analyzer measures the potential (E s ) and storesthis value in the microprocessor. A known amount of standard 1 solutionis added to the flow cell, which increases the concentration (C s ) with acorresponding known amount (dC 1 ). During this process, air is pumpedinto the flow cell, thoroughly mixing sample and standard in a closedloopsystem. The new potential (E 1 ) is measured and stored automaticallywhen stability is reached. Adding standard 2, preferably 10 times moreconcentrated than standard 1, increases the concentration (dC 2 ) in thesample reservoir. Again, the new potential (E 2 ) is measured and storedwhen the reading is stable. Now, we have the following three unknowns:E s =E o + S(T s /298.15) log (C s /C iso )E 1 =E o + S(T 1 /298.15) log [(C s + dC 1 )/C iso ]E 2 =E o + S(T 2 /298.15) log [(C s + dC 1 + dC 2 )/C iso ]S is the Slope at 25 °C (298.15 K)T is the temperature in Kelvin, measured when the potential E is measured.Figure I-2Flow Cell Volume for DKAE s , E 1 , E 2 have been determined during the calibration procedure. Themicroprocessor solves these three equations, to obtain the values of Sand E o . The calibration result is stored for use during online monitoringto convert the measured potential and temperature in the sample intoconcentration values in either ppm or ppb.When the calibration is complete the flow cell drains as the sample flowreturns. The flow cell volume returns to the measurement level. Afterallowing approximately 30 minutes for concentrated calibration solutionto be flushed from the system, the 2110XP analyzer can begin samplemeasurement again.In addition to Double Known Addition (DKA), the 2110XP analyzer alsoallows the operator the ability to perform an offline calibration.Thermo Scientific Orion 2110XP Ammonia Analyzer User GuideI-5