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| Water Standard Oil: |
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A New 15ppm Standard for |
| Coulometric Karl Fischer Analysis |
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of Oil Samples |
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Validation and control requirements for Karl Fischer (KF)
instrumentation is specified in standard methods and regulatory guidelines, such as
ASTM, GLP/GMP, ISO. Typically, certified water standards are used which are traceable
to a standard reference material (SRM) and specially formulated for this purpose.
The use of such standards applies to direct KF titration methods, as well as to
methods that involve using a KF Oven or an Oil Evaporator in conjunction with the
titrator.
The vast majority of water standards currently used in KF are based on organic
solvents, such as xylene or methoxybenzene. The dissolution characteristics of these
standards in KF solvents differ substantially from the dissolution characteristics
of most petroleum product samples. Additionally, current low-moisture KF standards
for coulometry have water content in the 50 ppm to 1000 ppm range, whereas the water
content of many oil samples can be considerably lower.
The AQUASTAR® Water Standard Oil (EMD No.
1.88055.0010) provides a number of distinct advantages over conventional standards:
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Lowest available water content for increased accuracy in the low ppm range |
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Transformer oil-based formulation for increased
confidence in results by eliminating sample vs. standard dissolution profile dissimilarities |
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NIST-traceability to facilitate
compliance with GMP/GLP, ISO, ASTM requirements |
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Universal suitability for titrators
and Oil Evaporators to allow the use of the same standard for both direct
and evaporator-based KF methods |
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This innovative standard is directly traceable to SRM
2890 from the National Institute of Standards and Technology (NIST).
Each package of 10 sealed, single-use 8mL ampoules is shipped with a
Certificate of Analysis listing the exact water content, accuracy,
minimum shelf life and method traceability to the NIST batch.
The new AQUASTAR® Water Standard Oil
is specially formulated for both direct coulometric KF methods (where
the oil sample is injected directly into the titration cell) and for
indirect coulometric KF methods (which employs an Oil Evaporator in
conjunction with a KF titrator). |
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This standard was developed through collaboration with the extensive
research efforts of our parent company, Merck KGaA (Darmstadt, Germany)
and Mettler-Toledo, Inc. (Columbus, OH). This novel NIST-traceable KF
water standard was formulated specifically for the petrochemical industry.
It is based on a transformer oil matrix and has the lowest certified water
content of any KF standard commercially available |
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Aquastar Water Standard Oil
EMD No. 1.88055.0010 |
Aquastar Water Standard Oil 0.01%
EMD No. 1.88050.0010 |
| Certified Water Content (PPM) |
15±3 |
94±10 |
| Trial 1 - Direct
Injection Into Titration Cell of Coulometer |
Anolyte
Catholyte |
Aquastar Coulomat A (AZ1697A)
Aquastar Coulomat C (AX1697C) |
Aquastar Coulomat A (AZ1697A)
Aquastar Coulomat C (AZ1697C) |
| Mean Water Content (PPM) |
17.638 |
96.442 |
| Standard Deviation (PPM) |
0.527 |
0.976 |
| Rel. Standard Deviation (%) |
2.99 |
1.01 |
| Trial 2 -
Injection Into Evaporatoin Chamber of Oil Evaporator |
Anolyte
Catholyte |
Aquastar Coulomat A (AX1697A)
Aquastar Coulomat C (AX1697C) |
Aquastar Coulomat A (AX1697A)
Aquastar Coulomat C (AX1697C) |
| Mean Water Content (PPM) |
16.570 |
100.719 |
| Standard Deviation (PPM) |
1.343 |
2.774 |
| Rel. Standard Deviation (%) |
8.10 |
2.75 |
| Instrument: Mettler Toledo DL39 |
Method: l(pol) = 2µA, U(stop) = 100mV, Gen. rate=normal, Rel. drift stop=3µg/min |
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The table above illustrates the performance of the
new Aquastar Water Standard Oil in the Mettler DL39 coulometer equipped with
a fritted cell, as compared to a conventional xylene-based 100ppm water standard.
In the first trial, the standards were injected directly into the titration
cell; while in the second trial, the standards wree injected into the
evaporation chamber of the Aquastar EV2000L Oil evaporator used in
conjunction with the coulometer. |
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