As described in Section 6 of ASTM D1209, there are 2 criteria to validate a APHA/Pt-Co 500 standard: Continue reading
The reference document that defines the visual EP Opalescence scale is:
EP 2.2 Physical and Physico-Chemical Methods for color and opalescence
EP – European Pharmacopoeia, Section 2.2 Physical and Physico-Chemical Methods, Unit European Pharmacopeia, Strasbourg, France (1997: 15-16) http://www.pheur.org
This method describes the visual evaluation of scattering or opalescence in near clear liquids, typically pharmaceutical, relative to distilled water being a perfect clear.
There are two types of physical liquid standards for visual turbidity or opalescence – Formazin solution (with or without stabilizer) and polymer beads (polystyrene micro spheres). The Formazin solution is the historical liquid scattering standard but the polymer beads is considered more stable and homogenous.
Section 2.2.1 Clarity and Degree of Opalescence of Liquids in the EP 4th edition defines a Formazin Primary Opalescent Liquid Suspension (rated at 4000 NTU per EP 5th edition) as a solution of hydrazine sulphate solution and hesamethylenetetramine solution which is stable for 2 months stored in glass.
The EP 4th edition further defines a Formazin Standard of Opalescence (rated at 60 NTU per EP 5th edition) as a dilution of 15.0-ml of the Formazin Primary Opalescent Liquid Suspension (4000 NTU) to 1000.0–ml of water. This suspension must be freshly prepared and stored for no more than 24 hours.
To make the EP Reference suspensions or OP – Opalescence standards, the Formazin Standard of Opalescence (60 NTU) is mixed with distilled water in the following proportions to define 4 levels of liquid EPOP Opalescence Standards. Distilled water is nominally a fifth EPOP standard defining no opalescence or scattering.
|Table 2.2.1-1 EPOP Standards||0||I||II||III||IV|
|Formazin Standard of Opalescence (60 NTU)||0.0 ml||5.0 ml||10.0 ml||30.0 ml||50.0 ml|
|Distilled Water (fill to 100.0 ml mark)||100.0 ml||95.0 ml||90.0 ml||70.0 ml||50.0 ml|
Sources for EPOP Liquid Opalescence standards are:
Loveland, CO 80538 USA
Hach offers the STABLCAL Reference Suspension Set that consists of a range for EP Opalescence Standards per EP is 0 (distilled water >0.1), 3, 6, 18, 30 NTUs. Given the 2-year stability, stabilizers will have been added to these liquid EP standards.
Another source for the Formazin Primary Opalescent Liquid Suspension (rated at 4000 NTU) and EPOP Liquid Opalescence standards (rated at 0 – 30 NTU) is:
RICCA Chemical Company
Arlington, TX 76094 USA
Reporting of EP Opalescence using a HunterLab Sphere Instrument and EasyMatch QC Software
As of EasyMatch QC version 4.82 and higher HunterLab has implemented a correlation method to the EP Opalescence scale based on these standards and is able to report EPOP-10mm (D65/10) for liquid samples measured in a 10 mm path length transmission cell. EPOP values are reported to tenths of a unit, along with NTU values as well.
HunterLab diffuse sphere instruments are often used to measure liquid samples, especially clear liquids. The liquid fragrance shown above is one such example of a clear liquid. The fragrances is so clear that is resembles water.
Fragrances such as this are often added to cleaning supplies, air fresheners, or other consumer products. One of the problems that this type of sample can experience is that the chemistry of the liquid fragrance solution can deteriorate and the solution will start to visually yellow. This is often a concern for manufactures because if the liquid fragrance yellows it cannot be added to the end product.
HunterLab sphere instruments can measure the transmitted color of the liquid and report the yellowness index. The liquid fragrance should be measured in a 20mm path length cell. Since the sample is very clear, near water in color, this slightly larger path length allows for the light to pass through more of the sample. This measurement method ensures that smaller differences can be measured between samples.
With the proper instrument and the appropriate accessories from HunterLab, very clear liquid samples can be accurately and repeatedly measured for color consistency.
HunterLab sphere instruments with CIE d/8 geometries conform to the requirements of ASTM D1003 Section 8: Procedure B Spectrophotometer. The measurement of transmission haze using Procedure B instruments will be in close agreement with ASTM D1003 Procedure A Haze meter.
Here is a more detailed description of how the HunterLab UltraScan PRO, UltraScan VIS and ColorQuest XE meet the requirements of Section 8.
FAQ: “We have a scientist here who is looking at films containing small bubbles and attempting to do measure them by measuring Haze% on a HunterLab spectrophotometer. I suspect her problem in obtaining numbers that “make sense” from what you get from just eyeballing the samples (and trying to look through them at the outlines of a object behind the film to gage the amount of regular transmittance) is that her samples have Haze% > 30 %, which means that a spectrophotometer (or even a haze meter) isn’t the appropriate tool to use for the analysis.
How is transmission haze measured at levels > 30%?”
One application that often comes up is measuring the color of clean liquids such as the fragrance sample seen above. This liquid fragrances is clear and looks almost like water. Fragrances such as this are often added to cleaning supplies, air fresheners, or other consumer products. One of the problems that this type of sample can experience is that the chemistry of the liquid fragrance solution can go bad and it will start to visually yellow. This is a concern of the manufacture because if the liquid fragrance yellows it cannot be added to the end product. Continue reading
FAQ: “More customers are asking us about Chinese Pharmacopeia Numbers… is this similar to EP/USP Color?