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Metrohm has revealed that the Quick TOC loop can be used for the online determination of TOC in process water in the pharmaceutical industry.

Water used in the manufacturing process in the pharmaceutical industry should have very low TOC concentrations.

There are several main analytical requirements for this application.

The TOC determination itself should be based on reliable and strong oxidation techniques because the major concern in the pharmaceutical industry is ensuring that the products are free from germs, even when they are already dead.

The TOC of germs is fixed in macromolecules, which are difficult to oxidise.

The TOC concentration is rather low therefore the detection system should be quite sensitive and the sample volume as high as possible.

It is impossible to get TOC-free water for calibration dilutions – therefore the precise TOC concentration of the calibration sample is always unknown.

Before measuring, the TOC sample has to be acidified to remove the TIC.

Acidification agents such as dilute HCl do contain TOC and therefore increase the offset given by the internal blank of the instrument and the TOC of the dilution water.

The Quick TOC purity from LAR Process Analysers oxidises the TOC at temperatures of 1,200C.

This ensures the completeness of the oxidation.

All TOC is transferred into CO2.

Furthermore, a catalyst is not required, which is especially useful because a catalyst can always be the source of an internal blank.

The loop injection system allows injection volumes of up to 4ml.

This injection volume is realised by multiple injections from the loop, so the combustion system has not taken the whole volume at once.

In combination with a highly sensitive infrared (IR) detector, a detection limit of 3ppb can be realised.

The Quick TOC purity can be calibrated by gas injection.

This avoids the problem of finding low TOC water for preparing the standards.

The acidification can be done by acidifying the carrier gas.

For these reasons, the Quick TOC loop can be considered a highly sensitive, high-temperature TOC analyser.

In combination with its low internal blank, the system is said to be well suited for TOC analysis, even at low concentrations.

In this application described, the Quick TOC purity is used to analyse the TOC in a process water tank.

The pre-treatment of the water consists of ozonisation, electro de-ionisation, reverse osmosis, ion-exchange resins and the several filter steps.

This excessive pre-treatment leads to a stable TOC concentration of 40-70ug/l.

Due to the ion-exchange resins, the amount of carbonate (=TIC) can be estimated to 0, which allows the acidification and stripping procedure to be skipped.

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