Teledyne 6750 User Manual download pdf (Page 23)

Total Organic Carbon Analyzer Theory of Operation

Teledyne Analytical Instruments 11

2.4 Subsystems Principles of Operation

The Model 6750 TOC Analyzer is comprised of five subsystems:

1. Sample Handling

2. Inorganic Carbon Removal

– OR –

Inorganic Carbon Analysis/TOC-True Method

3. Oxidation

4. NDIR CO

Gas Detection

5. Electronic Signal Processing, Display and Control

The sample system is designed to accept the liquid sample and any

required reagents, transporting them through the analyzer to the

appropriate components. For TOC (actually, NPOC) analysis, the

sample is pumped initially to the sparger, where it is mixed with acid to

lower the pH between 2.0 and 3.0. At that pH, all inorganic

carbon/carbonates are converted to dissolved CO

gas, which is sparged

out of the liquid solution by the air/O

carrier gas. At this point, any

volatile organic carbon is also sparged out and lost for inclusion in the

“TOC” analysis, unless a TOC-True analysis is performed, as described

below.

2.4.1 Sample Handling

The sample is processed through the analyzer in two phases: liquid

and gaseous

2.4.1.1 LIQUID PHASE SAMPLE HANDLING

Referencing Figures 2-6 and 2-7, the sample is introduced to the

analyzer with a self-priming peristaltic pump (P-4). It is then initially

directed to the Inorganic Carbon (IC) Sparger, where it is mixed with

acid delivered by pump (P-2). The pH of the solution is lowered to

approximately 2, converting the inorganic carbon to CO

, which is

sparged out by the carrier gas and measured as Total Inorganic Carbon

(TIC) by an infrared analyzer (NDIR-2) in the “TOC-True” mode.

The “TOC-True” mode is the preferred method of use if volatile

hydrocarbons are present, which would otherwise be lost in the sparging

process. Thus, through subsequent analysis of Total Carbon (TC) and

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Teledyne 6750 User Manual Page 23