OptLab-SPX   Iodine Color Scale

The visual determination of the iodine color value is described in DIN 6162. The figure serves to describe “the color depth of clear liquids, e.g. solvents, softening agents, resins, oils and fatty acids, the color of which is similar to that of a potassium-iodine solution”.

The iodine color value is given as “the amount of iodine [mg] in 100 ml of an aqueous solution, which has the same color depth as the sample compared with the same thickness”. The norm describes a visual comparison.

       Iodine color calculation of a reference solution with Iodine Color value 2 with check
    for a test value and a check for color scale deviation

OptLab-SPX uses the spectrum of the sample measured in reference to pure water. The wavelength range is 380-780 nm and the cell path length is 1 cm. The spectrum is used to derive a specific color value, which is compared to the stored reference values. As a result iodine color values in the range of 0 - 50 units are output. Thus the procedure imitates the visual comparison by an objective measurement techniques and provides an comprehensible and documented determination of the iodine color value.

Working range
DIN 6162 designates iodine color values smaller than 1 as uncertain and recommends to use the Pt-Co color value instead. Experience shows that the OptLab-SPX procedure is able to determine iodine color values down to 0,2 units. Resulting negative values – either due to systematical and statistical errors of the spectrometric measurement or due to color deviations – are set to “0”.

DIN 6162 lists a reference solution of 50 mg/100 ml iodine as the strongest reference solution. Samples colored as strongly as this are typically rare. It is recommended, to critically observe samples with an iodine color value higher 30, because substantial errors can occur. Result larger than 50 are set to 99,9.

Color deviations
The norm expresses that “the method must not be used with larger deviations of the color of the sample compared to the color of the references. As with the other one-dimensional color scales, deviations of the color tone between sample and references will result in an uncertainty of estimation. Comparing colorless or red, green or blue colored samples can give erroneous or meaningless results, which will no longer correlate to visual judgments.

For each result, OptLab-SPX calculates the hue angle, which allows an estimation of the color deviation from the scale. Sample solutions should be within a typical range.

OptLab-SPX outputs the iodine color value as a figure and a check value for color deviations. It also allows comparing both values to a specified value. Header, messages and number format can be defined. Thus all necessary options for a routine usage are available.