Section 4 Operation; Injection Valve Operation - Hach QC8500 Series 2 User Manual

Section 4

4.1 Injection valve operation

1 Stator
Port connection
Sample line
Sample loop
Carrier line
Manifold
Waste line
Operation
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The QuikChem System automates wet chemical determinations using the principle of
Flow Injection Analysis. The peristaltic reagent pump draws the sample from the sampler
into the injection valve. Simultaneously, reagents are continuously pumped through the
system. The sample is loaded into the sample loop of one or more injection valves. The
injection valve is then switched to connect the sample loop in line with the carrier stream.
This sweeps the sample out of the sample loop and on the manifold.
The sample and reagents then merge in the manifold (reaction module) where the
sample can be diluted, concentrated, dialyzed, extracted, incubated and derivatized.
Mixing occurs in the narrow bore tubing under laminar flow conditions. For each method,
the operating parameters are optimized to address high sample throughput, high
precision and high accuracy. The FIA peaks are transient, reflecting the non-steady state
conditions normally employed. In FIA, equilibrium is usually not attained.
The valve consists of a stator and a rotor
through which liquid passes. The direction in which the liquid flows through the valve
depends on the alignment of the grooves with the holes on the stator.
Figure 25 Stator and rotor
Table 5 describes the port connections for the six-point injection valve.
Table 5 Port connections
Description
The sample is pumped from the sampler or the sample probe to port 6 on the
injection valve.
Tubing that connects ports 1 and 4. The sample loop determines the volume of
sample to be injected on the manifold for analysis.
This is an artificial blank solution that will carry or sweep the sample on the
manifold. The carrier line input is always connected to port 2. The carrier
solution and the carrier line to be used for an analysis are specified in the
QuikChem method.
The carrier stream exits the valve at port 3 and flows to the manifold.
When running one channel only, the waste line is connected to port 5 on the
injection valve. When running two or more channels simultaneously, port 5 of
the first injection valve is connected to port 6 of the second injection valve. Port
5 of the second injection valve will then be connected to waste. The connection
between ports 5 and 6 consists of 15 cm Teflon
(Figure 25). The rotor has three tiny grooves
2 Rotor
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tubing 0.8 mm ID.
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