Principles Of Calibration; Double Known Addition (Dka) - Thermo Scientific Orion 2117HL User Manual

General Information
Principles of
Calibration
Double Known
Addition (DKA)
Flow Cell Volume for DKA
Thermo Scientific Orion 2117HL High Level Chloride Analyzer User Guide
Calibration procedures for analytical instruments are important and must
be performed carefully. The calibration procedure used in the Thermo
Scientific Orion 2117HL analyzer is a variation of Double Known
Addition (DKA) using advanced electrode and flow cell technology. This
method has the distinct advantages of being fast, easy and accurate.
Before calibration begins, the diverter valve is pushed in to divert flow from
the measure drain, allowing the flow cell to fill.
At the beginning of the DKA calibration the actual concentration in the
sample is unknown. The analyzer measures the potential (E
this value in the microprocessor. A known amount of standard 1 solution
is added to the flow cell, which increases the concentration (C
corresponding known amount (dC
into the flow cell, thoroughly mixing sample and standard in a closed-
loop system. The new potential (E
when stability is reached. Adding standard 2, preferably 10 times more
concentrated than standard 1, increases the concentration (dC
sample reservoir. Again, the new potential (E
when the reading is stable. Now, we have the following three unknowns:
E =E
s
E =E
1
E =E
2
S is the Slope at 25 °C (298.15 K)
T is the temperature in Kelvin, measured when the potential E is measured.
E , E , E
s 1 2
microprocessor solves these three equations, to obtain the values of S
and E . The calibration result is stored for use during online monitoring
o
to convert the measured potential and temperature in the sample into
concentration values in either ppm or ppb.
When the calibration is complete the flow cell drains as the sample flow
Figure I-2
returns. The flow cell volume returns to the measurement level. After
allowing approximately 30 minutes for concentrated calibration solution
to be flushed from the system, the 2117HL analyzer can begin sample
measurement again.
In addition to Double Known Addition (DKA), the 2117HL analyzer also
allows the operator the ability to perform an offline calibration.
+ S(T /298.15) log (C
o s
+ S(T /298.15) log [(C
o 1
+ S(T /298.15) log [(C
o 2
have been determined during the calibration procedure. The
). During this process, air is pumped
1
) is measured and stored automatically
1
) is measured and stored
2
/C )
s iso
+ dC )/C ]
s 1 iso
+ dC + dC )/C ]
s 1 2 iso
) and stores
s
) with a
s
) in the
2
I-5