Otto H. York Center for Environmental Engineering and Science

Tekmar-Dohrman Phoenix-8000 UV -Persulfate TOC Analyzer with Autosampler

• Concentration range: 2 ppb- 10,000 ppm
• Sample size: 500 µl to 20 ml

This is UV/Persulfate TOC analyzer used for measuring total carbon (TC), total organic carbon (TOC) and total inorganic carbon (IC) in aqueous samples.

Definitions / Abbreviations

• TC - Total Carbon
  Defined as all carbon in a sample, including inorganic, organic, and volatile carbon, as they may be present.  TC is reported in terms of total mass of carbon per unit of sample (mg C/L, etc.).

TC = TOC + IC

• IC - Inorganic Carbon
  Defined as that carbon in a sample, which is converted to carbon dioxide after acidification of the sample.  IC includes all dis­solved carbon dioxide, bicarbonate, and carbonate species and is reported in terms of total mass of carbon per unit of sample (mg C/L, etc.).

IC = TC - TOC

• TOC - Total Organic Carbon
  Generally defined as that carbon in organic compounds which is converted to carbon dioxide by oxidation, after inorganic carbon has been removed or subtracted.  Although TOC in water samples should ideally include carbon in volatile materials, most laboratories report TOC analyses of samples in which volatiles have been previously removed.  In fact, the methods involving persulfate oxidation, which are widely accepted and used, each call for acidification and purging to remove inorganic carbon before oxidation of organics.  This purging can also remove volatile organics before oxidation, though the results are still generally accepted as TOC.  Volatiles can be included in TOC by separately measuring TC and IC and calculating TOC by difference.

TOC = TC – IC (difference) / TOC = NPOC + POC (sum)

• POC - Purgeable Organic Carbon
  Defined as that organic carbon (volatile and semivolatile materials) which is purged from solution by a stream of gas under a specific set of purging conditions.  Specific conditions have not yet been standardized in the scientific literature. POC is generally less than 1% of TC in a sample.
• NPOC - Non-Purgeable Organic Carbon
  Defined as that organic carbon, which remains in solution after a sample has been purged by a stream of gas under a specific set of purging conditions.  NPOC is often reported as TOC due to popular methods, which require acidification and purging of TIC prior to oxidation of organics.  This substitution is valid for samples containing negligible volatile or purgeable organic compounds.
• POX - Purgeable Organic Halide
  Defined as organic species containing any halogen (e.g.  Cl, Br, I), which can be purged from solution by a stream of gas under a specific set of purging conditions.  Specific conditions have not yet been standardized in the scientific literature.
• DOC - Dissolved Organic Carbon
  Defined as that organic carbon which is determined by analysis of aqueous samples, which have been filtered through 0.45-micron filters.  DOC is reported in terms of total mass of carbon per unit of sample (mg C/L, etc.).
• SOC - Suspended Organic Carbon
  Defined as that organic carbon which is determined by analysis of particles captured by filtration of aqueous samples through 0.45 micron filters.  SOC is sometimes called Particulate Organic Carbon (POC) especially in the marine chemistry literature.  It is reported in terms of total mass of carbon and referred to as SOC.
• ppm C - parts per million Carbon
  Defined as mass units of carbon per million sample mass units (μg C/g).  In aqueous samples this is generally taken to be the same as mg C/L.
• ppb C – parts per billion Carbon
  Defined as mass units of carbon per billion sample mass units (ng/g).  In aqueous samples this is generally taken to be the same as μg C/L.
• Reagent Blank
  Defined here as the detector response generated from an analysis sequence (with reagents) without introduction of a sample or standard. The response is due to carbon contamination in the reagents, gas, reaction vessel, and/or tubing.
• Standard
  Defined as any sample to which a known amount of carbon has been added.

Summary of Method

Analyzing IC

The first step in analyzing IC in liquid samples is acidification with an inorganic acid to pH 3 or lower. The acidification converts carbonates and bicarbonates to carbon dioxide, which is then removed along with dissolved CO2 by the gas stream and measured to provide an IC value.

HCO₃^-, CO₃^2-, CO₂                  →                       CO₂ ↑ + H₂O
​                                     Carrier gas, acid

Analyzing TOC

TOC is determined by the measurement of carbon dioxide released by chemical oxidation of the organic carbon in the sample. Inorganic carbon is first removed by acidification and sparging. Then, the sample is simultaneously exposed to sodium persulfate (Na₂S₂O8), a strong oxidizer, along with UV radiation. When the oxidation reaction is completed, the carbon dioxide is purged from the solution and detected.

S₂O₈^2- + hν    →    SO₄^.-

H₂O + hν    →    H^. + OH^.

SO₄^.- + H₂O + hν    →    SO₄^2- + OH^. + H⁺

R + hν   →    R*

R* + OH^. + SO₄^.- + H₂O    →    nCO₂ …

What is a Sample Volume required for the TOC Analyses?

Sample size can vary between 500 μl and 20 ml (see the following Table).

Phoenix 8000 Sample Injection and Sample Usage Table.

*  In this method, enough sample for4 replicates is placed in the IC sparger.

**   Sample injected is automatically diluted 5:1. Total Dilution Volume will allow at least 4 analyses.

*** Sample injected is automatically diluted 50:1. Total Dilution Volume will allow at least 4 analyses.

Recipe for Reagents Preparation

• Oxidizer (Sodium Persulfate): 20 g of Sodium Persulfate (ACS reagent grade), 170 ml of Milli-Q water, 6 ml of 85% Phosphoric Acid.
• Acid (10% Phosphoric Acid): 30 ml of 85% Phosphoric Acid (ACS reagent grade), 150 ml of Milli-Q water.

Useful Hints

• For most accurate analyses, sampling containers should be free of organic contaminants.  Plastic bottles can bleed carbon into water samples, especially when they are new, or when they are used for low level samples (less than 200 ppb C).  Any new bottles (especially plastic) should ideally be filled with clean water for a period of several days or boiled in water for a few hours before use.
• Pyrex bottles should be washed and heated at 400oC before first use.
• Sample IC and POC can be affected by exposure to the atmosphere.
• Sample TOC below about 50 ppb C can also be affected by atmospheric exposure.  In these cases, sampling bottles should be kept closed when possible, and autosampler vials should be equipped with septa.