A: Generally TAI recommends the OZONE PROMOTED/HYDROXYL RADICAL oxidation method. The problem with salts is that the chlorine released during the oxidation phase of TOC analysis interferes with the oxidation of the carbon.
UV/PERSULFATE method will not adequately function in this application. Depending on the concentration and species of the salts, decreased oxidation between 30% and 65% for carbon is generally experienced. Seawater is approximately 3% salt. We have conducted some successful TOC recovery tests with the UV/PERSULFATE method at the 0.1% salt levels but the required dilution in most applications to that concentration makes this method undesirable for salt applications.
TAI has successfully applied the OZONE PROMOTED/HYDROXYL RADICAL method with undiluted seawater and industrial salts up to 26%. On occasion this method had low oxidation efficiency on a few complex samples and had to recommend the HIGH TEMPERATURE COMBUSTION method for them.
HIGH TEMPERATURE COMBUSTION is the best and most efficient method for oxidation. However, the relatively severe increased maintenance problems associated with this method involve catalyst poisoning (TAI has both catalytic and non-catalytic combustion methods) and clogging the reactor with molten salts in the condensation phase of the reaction.
Sea salt melts at approximately 801 degrees C, so even with higher combustion temperatures of 1000 degrees C, there remains a problem. TAI has techniques to minimize these problems but the user should be aware of the limitations of this method when used with seawater and industrial salts.
Consider sending TAI approximately a liter of your worst sample. We will then test it on all applicable methods and give a confidential report of the analysis, along with a recommended application method.
