Reference
115
Frequently asked questions
Solvents
Measurement
Question
Answer
What are the main
differences between
analysis using S-316 and
analysis using the normal
hexane method (JIS
K0102)?
In addition to a different extraction solvent, the principle of measurement used for the
extracted oil content is different.
The OCMA detects oil content by infrared absorption, whereas the normal hexane
method measures the weight of the oil content. For this reason, the extraction efficiency
and types of oil detected are different.
In particular, the normal hexane method cannot be used to measure oil types that have a
low boiling point, and thus the measured values are occasionally less well regarded.
Question
Answer
Can seawater be
measured?
Yes. However, zero and span calibration must be performed using seawater that does
not contain oil.
A salting-out effect occurs, and thus there is no problem regarding the seawater and
solvent separation conditions.
As long as the oil extraction ability of the solvent is the same, a seawater sample is
considered to be equivalent to a fresh water sample.
Can I measure a sample
water if it contains chelate
compounds?
Yes. However, zero and span calibration must be performed using a chelate aqueous
solution that does not contain oil.
Chelates are water-soluble and thus unlikely to be extracted by the solvent. As long as
the concentration is low, accurate measurement is thought to be possible.
What if the sample water
contains suspended matter?
Remove the suspended matter prior to measurement.
Care must be taken to not clog the joints.
If the suspended matter is visible, there is a risk that the joints will become clogged.
Before dispensing the sample water into the extraction tank, separate the suspended
matter with a separating funnel.
If suspended matter remains in the solvent layer, treat as needed by centrifugation or
other method, and then carefully collect the supernatant liquid to eliminate the
suspended matter.
Suspended matter, which cannot be removed by the above method, must be filtered
through filter paper; however, pay attention to adherence of the oil content to the filter
paper.
What if the sample water
contains emulsifying
substances?
If the concentration of the emulsifying substances is 1 mg/L or less, measurement may
be possible without further treatment. However, measurement is very difficult when the
concentration is higher.
Ideally the sample should be pretreated by diluting the sample water, adjusting the pH,
adding table salt or Ca salt, or otherwise, to eliminate the effects of the emulsifying
substances.
An emulsifying substance is amphipathic, and thus not only does the emulsifying
substance remain in the water tank and impede oil content extraction, but it may also be
extracted into the solvent layer.
The effects of the emulsifying substances on measurement results may appear in 3 ways
as follows:
The effect of the emulsifying substances impedes dissolution of the sample water oil
content into the solvent, resulting in an indicated value that is lower than the actual oil
content concentration.
The emulsifying substance is itself dissolved into the solvent, resulting in an indicated
value that is higher than the actual oil content concentration.
The effect of the emulsifying substances increases the amount of water content
dissolution, resulting in a higher indicated value.
