Page 228 - Photodetection and Measurement - Maximizing Performance in Optical Systems

Measurand Modulation

Measurand Modulation 221

Sample
injection Optical
Buffer source
Delay Delay
To
Reagent waste
Detection system
Standards Bypass (photometer)

Absorbance
Multichannel Multiple repeats,
peristaltic pump multiple concentrations

Injection
loop
Standard Time
solutions
Figure 10.7 Flow-injection analysis (FIA) modulates the sample concentration,
making detection, even with short path-length optical detectors, more effective.

Pumped Sample Air Sample Air Sample
flow

Source
Sample Ref. Air Sample Reference

Detector
Figure 10.8 Samples can be separated from each other and from ref-
erence liquids using bubbles (“segmented flows”), although these are
not needed if the pipe diameters and flow rates are chosen correctly.

TABLE 10.1 Referencing Choices for Water
Absorption Measurement

Primary Measurement Reference Measurement
1. Sample water Air/Gas bubble
2. Sample water Pure water
3. Sample water Purified sample water
4. Sample water plus indicator chemical Sample water
5. Sample water buffered at acid pH Sample water buffered at
alkaline pH

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