Page 23 - 5_TOC in daily practice

Sum parameter – Total Organic Carbon

Silanisation of the syringe –

TOC-determination of surfactants

SCA-130-512

The TOC determination of a surfactant ■Preparation and security notes
solution was not reproducible, nor did they First the syringe has to be clean and dry.
correspond with the theoretically calculated Please refer to the warning remarks of the
values. Subsequently, TOC direct used chemicals, wear protective clothing and
determination of the surfactant was executed work under the extractor hood.
using the solid sampler SSM. The
measurement values obtained this way ■ Procedure
corresponded well with the theoretical values.  Take the silanization reagent (1ml) and
This led to the conclusion that conversion of put it into the syringe
carbon to CO 2 was not the problem, rather  Turn the syringe 5 – 10 minutes to coat
that the surfactant exhibits interactions with the complete surface
the glass surface. Consequently, carbon is
being removed from the surfactant solution,
which explains the lower TOC measurement
values.

The main module of the TOC-L CPH is the
ISP module (integrated sample preparation
system). It consists of an 8-port valve and a
syringe with sparging connection. The syringe
is made of glass. In order to prevent
interaction of the surfactant with the glass
surface, the syringe is first silanized.  Drain the silanisation reagent
 Remove the excess MSTFA by washing
■ Required material for silanisation two times with 10ml methanol.
 1ml N-Methyl-N-(trimethylsilyl)trifluoro-  Following this procedure, the syringe is
acetamide (for GC derivatization, ≥98.5%) rinsed with water and dried (at 40°C -
– e. g.: von Fluka, No. 69479) 50°C in the dying cabernet)
 approx. 20ml methanol  After 24 hours, the syringe is ready for
 1ml syringe with needle use

■ Note
It is difficult to assume about the long-term
stability of this silanization. It depends of
different influences.