Page 4 - 5_TOC in daily practice
P. 4
SCA-130-501
The TOC is calculated from the difference ■ Addition method
between TC and TIC: TOC = TC - TIC For the addition method, the parameters POC
and NPOC are measured. The TOC is then
■ Limitations of the difference method calculated.
The inorganic carbon content may not be too
high in comparison to the TOC. POC: Degassing of the volatile compounds
Error propagation can result in a high level of with subsequent catalytic combustion at
uncertainty for the calculated TOC value. The 680°C and determination of the resulting
EN 1484 standard recommends that the TOC carbon dioxide using NDIR detection.
value, when using the differential method,
should be higher or equal to the TIC value NPOC: Measurement of the non-purgeable
(TOC ≥ TIC). organic compounds, after POC analysis
using catalytic combustion at 680°C and
Example: subsequent determination of the resulting
carbon dioxide using NDIR detection.
TC – Value = 100 mg/l (RSD = 2%) ± 2 mg/l
(98 – 102 mg/l) The TOC is calculated via addition:
IC – Value = 98 mg/l (RSD= 2%) ± 1,96 mg/l TOC = POC + NPOC
(96,04 – 99,96mg/l)
■ Direct method
TOC = 2 mg/l ± 3,96mg/l (- 1,96 - 5,96 mg/l) For the direct or NPOC method, it is assumed
that the sample does not contain any
Due to error propagation, the total error is ± significant amounts of volatile or purgeable
3.96 mg/L. organic compounds. According to this
assumption, the TOC is directly determined
According to the difference method, the error as NPOC.
of the total result is larger than the calculated
TOC content! In the worst case, this can NPOC: Acidification of the sample using a
result in a negative TOC value. mineral acid (for instance HCL) to a pH < 2,
whereby carbonates and hydrogen
carbonates are completely converted to
carbon dioxide. The carbon dioxide is
removed from the sample solution via a
sparge gas. Direct NPOC measurement
(similar to TC measurement) via oxidation to
CO 2. Subsequent NDIR detection.
The TOC corresponds to the NPOC:
TOC = NPOC
