Electrochemical detector

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Electrochemical detectors
Our group of experts in HPLC developing a guideline for qualification of HPLC with different detectors. And we are confused with ECD. I am not an expert in this field so I decided to ask you.
We have two methods of ECD qualification - with and without DUMMY CELL. But I think there are two different types of ECD - coulometric and amperometric. The question is - which method corresponds to which of the types of ECD and do we have to mention in description about DUMMY CELL? See the text bellow

ELECTROCHEMICAL DETECTOR

Linearity, noise and drift of the signal are the proposed parameters to be tested during the periodic and motivated check of the LC electrochemical detector.

Method 1 (dummy cell)


DRIFT AND NOISE

Settings:
Cell potential of a dummy cell: 800 mV
Rise time filter: 0.1 s
Range: 0.1 nA
Temperature: 30 °C

Procedure:
Drift: Measure the electric current and subtract 2.67 nA (theoretical value)
Noise: Measure the noise over a period of 5 minutes

Limits:
Drift (cell current):  0.05 nA
Noise of the signal: max. 2 pA or 20 mV

Method 2 (without dummy cell and amperometric detector)


LINEARITY

Solutions:
1, 2, 4, 8, and 10 µM of Threonine in water for chromatography R

Settings:
Pressure: ≥1500 psi
Flow: 0.25 mL/min
Restriction capillary: L= 150 cm, ID = 0.13 mm, PEEK
Column: CarboPac PA1 Guard
Eluent: 50 mM NaOH, filtered through 0.2 µm Nylon, degassed
Detector settings: Waveform “Amino Acids” (pH, Ag, AgCl Reference)
Duration/run time: 3 min
Injection volume 25µL

Limits:
r² ≥ 0.999

DRIFT AND NOISE

Noise: Read the signal every minute.

Settings:
Pressure: ≥1000 psi
Flow: 1.0 mL/min
Restriction capillary: L = 150 cm, ID = 0.13 mm, PEEK
Column: CarboPac PA1 Guard
Eluent: 50 mM NaOH, filtered through 0.2 µm Nylon, degassed
Detector settings: Waveform “Amino Acids” (pH, Ag, AgCl Reference)
Run time: 20 min

Limits:
Drift: 1250 pC/20 min
Noise: MW20read outs < 160 pC
The dummy cell test gives you information on the physical behaviour of the detector. This is independent from amperometric or coulometric mode.
The amperometric and coulometric modes are measuring modes on typically one detector.
Method 2 is the test of the electrochemical condition of the cell and detector. Select the morking mode (amperometric or coulometric) which you are going to apply in your application.
Dr. Markus Laeubli
Manager Marketing Support IC
Metrohm AG
9101 Herisau
Switzerland
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