Page 15 - 5_TOC in daily practice

Sum parameter – Total Organic Carbon

Blank value consideration in TOC analysis

SCA-130-508

Water plays a dual role in TOC trace With careful sample preparation and analysis,
analysis. On one hand, it is applied as a this blank value can be minimized and
measuring medium and consumable in the reliably determined. The blank value
TOC analyzer. It is used to prepare standards consideration and the analysis of a system
and to rinse the instrument. The automatic blank value is only useful in very low
dilution function of the TOC-L uses ultrapure concentration ranges of < 1 mg/L.
water for dilution of the samples or the
standard solutions for multi-point calibration. Purified waters that have been produced
using highly complex water treatment
On the other hand, ultrapure water is a systems, have different water grades. The
sample type in TOC analysis. In ultrapure DIN ISO 3696 standard specifies the
water applications, including the analysis of requirements and test methods for water for
water for injection and cleaning validation, analytical use and classifies these waters
ultrapure water samples are analyzed to according to 3 grades.
determine their organic impurities.
Ultra
Pure Pure
Parameter water water pure
water
Typ III Typ II
Typ I

Ions,
resistance >0,05 >1,0 >18,0
(M.cm)

Ions,
resistance < 20 <1,0 <0,055
(µS/cm)

Organix, <200 <50 <10
TOC (ppb)
Pyrogene
(EU/ml) NA NA <0,03
For the determination of low concentrations at Particle
the trace-level, knowledge on the blank value >0,2µm NA NA <1
is essential. The blank value is usually (U/ml)
composed of several components. First, there Bacteria
is the instrument blank, secondly residual (KBE/ml) <1000 <100 <1
concentrations can occur in the solvent and in Tab 1: specification according to DIN ISO 3696
the reagents used. The influence of the blank
value is particularly significant in TOC
analysis, as carbon compounds are present
everywhere and a widespread carbon input
can, therefore, not be prevented.