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The routine analysis of transformer oil requires no sample preparation other than to collect a
clean sample without introducing any extraneous sources of chloride into the sample, such as
perspiration or road salt. This is important because, for transformer oil, there is no sample
cleanup procedure to remove inorganic chloride contamination. Once collected, the sample is
reacted and the resulting chloride is extracted and quantified.
The chlorine quantified in this case is the total chlorine contained in the sample. Transformer oil
is typically free of inorganic chlorine, eliminating the need for any sample cleanup procedure. In
special cases where transformers have failed due to water contamination or have been removed
for service and stored in areas near seawater or road salt, inorganic chloride may cause an
elevated reading.
Before a soil sample can be analyzed, the organic contaminants must be extracted using an
organic solvent. Because soil samples invariably contain inorganic chlorine, the soil extract is
cleaned up to remove all traces of the inorganic chloride. The cleaned extract is then reacted and
the resulting chloride is quantified. For soil analyses, only the organic chlorine content is ever
quantified. Extraneous sources of chloride contamination such as road salt or sea salt are
not
detected.
As with soil samples, a water sample must also be extracted prior to final analysis. The ratio of
the solvent volume to the sample volume determines the sensitivity of the test. The extract is
reacted and the chloride is quantified as above. In water samples, only the organic chlorine is
quantified.
Wipe tests require that a specific area be wiped using a hexane-soaked gauze. The gauze is
extracted with an organic solvent, reacted, and the chlorine content determined. For wipe
samples, the standard procedure eliminates most all inorganic chlorine contamination. Areas
with very high surface concentration of salts may need to be prepared differently.
Chloride Conversion Reaction
Once the sample has been prepared, the remaining chloride conversion steps are the same for all
sample types. The conversion step is a reaction of the sample with an excess of metallic sodium
in the presence of a catalyst to convert the covalently bound organic chlorine into free chloride
ions. This reaction of metallic sodium with organo-chlorine compounds is vigorous and goes to
completion, converting all of the organic chlorine to chloride.
Quantification
Upon the completion of the conversion reaction, the resulting chloride ions are extracted into an
aqueous buffer. The chloride content in the final extract/buffer is then quantified using a
chloride specific electrode and converted to an equivalent analyte concentration using the
conversion factors programmed into the chosen analysis method of the instrument. The
conversion factor is made up of the percent chlorine, the sample size multiplier, and the
extraction efficiency multiplier. The analyte concentration is determined by first subtracting the
blank from the raw chloride reading (except when the Blank Subtraction has been turned off),