OECD Tests, Section 1:
Physical - Chemical Properties

OECD Guidelines for the Testing of Chemicals series of tests are used by various regulatory authorities around the world in the registration of industrial chemicals and polymers. ISI is experienced at carrying out these tests by Canadian standards (Spirit of GLP) and by international standards (OECD GLP). All tests require the strictest quality control and comprehensive reporting. The Guidelines are divided into 4 Sections:

Section 1: Physical-Chemical Properties
Section 2: Effects on Biotic Systems (often referred to as Ecotoxicity)
Section 3: Degradation and Accumulation (often referred to as Biodegradation)
Section 4: Health Effects (often referred to as Mammalian Toxicity)

Below is a fairly detailed description of each of the OECD Section 1 (Physical-Chemical Properties) tests currently offered by ISI. For a more succinct listing click here.

The following Section 1 (Physical - Chemical Properties) tests are currently offered by ISI:

101: UV-VIS Absorption Spectra
The absorption spectrum and molar absorption coefficient are determined in water at various pH values, or in special cases in other solvents. The spectrum of a substance refers to a characteristic behaviour, usually the absorption of radiation, displayed by the substance when placed in the appropriate device. The UV spectrum is a characteristic absorption of ultraviolet light caused by specific chemical groups in the molecule. The printout from the UV spectrophotometer is called a spectrum.

Note: the CEPA regulation allows other spectral techniques (IR, MS, NMR) to be used as well. The IR spectrum is similar to UV, but uses infrared (IR) light. Both types of spectra provide general information about the chemical groups present in the new substance. Both mass spectrometry (MS) and nuclear magnetic resonance (NMR) spectra are more complex than UV or IR and yield specific and useful structural information about the molecule. For regulatory purposes the key point is that all four of these techniques give a spectrum that is characteristic of the substance in question. They may therefore be used to verify the identity of the material and, in some circumstances, may verify the purity or show the presence of impurities, starting materials, and other reactants.

102: Melting Point
The melting point or range of thermal decomposition of solid test substance. This is a relatively straightforward test. The melting point is determined using a melting point apparatus. Crystals of the substance are heated in a controlled fashion until they melt. In a standard automatic melting point apparatus, the melting point is determined when a light beam is able to pass through the sample.

103: Boiling Point
The boiling point or range of thermal decomposition of a liquid test substance. This is a relatively straightforward test. Traditionally, the substance is placed in a glass vessel alongside a thermometer and heated in a hot oil bath until it boils.

104: Vapour Pressure
Vapour pressure is an indicator, along with melting point, of the volatility of a substance. ISI generally employs the Gas Saturation method, but other methods can be used. The test measures the amount of substance that is released into a stream of inert gas, which passes over the material at a defined flow rate and temperature. Alternatively, the vapour pressure can be calculated from other physical parameters by our chemists.

105: Water Solubility
This test is meant for pure chemical compounds (see OECD 120 for polymers). ISI employs the Flask Method to determine the ideal solubility or maximum concentration of a stable suspension. The test substance is stirred or shaken in a flask with water at a carefully controlled temperature until the concentration of the substance in the water has stabilized. This may take several days to a month. All of the solubility methods require a specific method of detecting the chemical of interest in water (or solvent, see Note). This method usually requires a specific UV or IR absorbance, a specific chemical reaction, or a chromatographic separation, or in some cases all three. Non-specific tests such as weight (gravimetric) or Total Organic Carbon (TOC) are frowned upon in the method descriptions. They are typically used only when there is no other workable option.

Note: this method can also be adapted for determination of the solubility of a chemical in solvents other than water, such as n-octanol. Please inquire for details.

106: Adsorption-Desorption Using a Batch Equilibrium Method
This soil adsorption/desorption test is environmentally significant. The soil adsorption-desorption test determines how readily the test substance sticks to soil, and is released by the soil. The test employs 5 well characterized local soils having a range of pH values, clay, silt and organic content. The test substance is dissolved in salt water and incubated with the soils. The amount and rate of disappearance of the substance from the soil is measured. Once the substance has adsorbed to the soil, the rate of release into fresh water is measured. The result of the test is K_d, which is the ratio of the mass of the substance adsorbed to the soil at equilibrium to the mass of the substance in the water at equilibrium.

This test comprises three tiers: preliminary study, screening test, and determination of kinetics or Freundlich adsorption or desorption isotherms. Typically, the regulatory agencies are only interested in the adsorption phase and are satisfied with the screening portion of the test.

Note: in some cases, OECD 121 may be used instead. Please inquire for details.

107: Partition Coefficient (n-octanol/water)
The octanol/water partition coefficient (P_ow) is simply the extent to which a substance partitions between octanol and water. The test was developed many years ago to estimate the extent to which a chemical dissolved in water would partition into a cell membrane, such as the skin of a mammal. n-Octanol was used because its polarity was thought to be closely similar to that of the inside of a cell membrane. The test presents a fairly simplistic view of a chemical transport, but the n-octanol/water partition coefficient, or its logarithm (log P_ow), has gained worldwide acceptance in the environment regulatory world. It provides a useable estimate of the tendency of a material to bioaccumulate in animals. According to the theory, any substance with a log P_ow of 3 or greater will bioaccumulate by building up in animal fat, assuming that the chemical is not readily broken down. A value of 3 means essentially that the substance is 1000 times more soluble in n-octanol (and theoretically, fat) than in water. It has been shown experimentally that there is a good correlation between log P_ow and bioaccumulation in fish.

The Shake Flask method used by ISI empirically determines the P_ow of a test substance, using a flask containing n-octanol, water, and the test substance. n-Octanol floats on water and if the substance is fat soluble, it will partition preferentially into the upper, or n-octanol, phase. The partition coefficient (P_ow) is the ratio of the concentration of the substance in the n-octanol phase to the concentration in the water phase.

Note: depending on the nature of the test substance, the P_ow can also be determined by an HPLC model (see OECD 117), a titration method (see OECD 122), or the Slow-Stirring method (see OECD 123). Please inquire for more information.

109: Density of Liquids and Solids
The liquid density or the bulk density of solids is determined. Density is the mass of the substance that can be held in a container of a known volume. The bulk density is most commonly used for regulatory purposes. Bulk density does not account for the air spaces between the particles of the sample. As such, it gives an estimate of the volume occupied by a known amount of the sample. As an illustration, a kilogram of Styrofoam chips used for packing may fill a small room. A kilogram of gold is only slightly bigger than a pile of business cards one centimetre high. ISI generally employs USP 24, 616 (Bulk Density and Tapped Density) for solid powders, ASTM D792 (Test Method A) for solids not affected by water, and CIPAC MT 3 (Pyknometer Method) for non-viscous liquids. Other methods can also be used. Please inquire for details.

110: Particle Size Distribution / Fibre Lengths and Diameter Distribution
ISI subcontracts this work to a GLP-compliant laboratory for testing by either microscopy or coulter counter.

111: Hydrolysis as a function of pH
This test measures the rate of breakdown of a substance in water at various pH values and temperatures normally found in the environment. The test requires a detection method capable of distinguishing the starting material from the breakdown products. This typically requires some type of chromatography such as HPLC or gas chromatography. This test is a tiered approach, generating many samples for analysis, and can take up to two months to complete.

The test gives a hydrolysis rate constant (K_obs) at each pH and temperature, from which the half-life (t_0.5) of the reaction can be calculated. The half-life is the time required for the initial amount of the test substance to decrease by half.

When rate constants (K_obs) are known at two or more temperatures, the Arrhenius Activation Energy (E) can be determined. A plot of ln(K_obs) versus 1/temperature gives a straight line with a slope of -E/R. Based on the calculated rate constants, activation energy and pH dependence of the hydrolysis, an educated guess can be made as to the mechanism of the hydrolysis.

112: Dissociation Constants in Water
ISI employs the potentiometric titration method for the determination of the pKa of a test substance. This test can provide very useful information as to the structure of the test substance.

113: Screening Test for Thermal Stability and Stability in Air
ISI carries out the accelerated storage test for determining storage stability of a substance with respect to heat and air. This test is very similar to pharmaceutical storage trials.

114: Viscosity of Liquids
ISI subcontracts this work out to a GLP-compliant laboratory.

116: Fat Solubility of Solid and Liquid Substances
ISI has carried out several of these tests over the years.

Note: Canadian chemical registration agencies no longer recognize this test.

117: Partition Coefficient (n-octanol / Water) High Performance Liquid Chromatography (HPLC) Method
This approach exploits the correlation between log Pow and HPLC retention time (how long it takes for the unknown compound to elute from the HPLC). Using Method 117, the HPLC is calibrated using a series of chemicals with known Pow . A plot of log Pow versus the log of the retention time gives a straight line. The unknown is run on the same system, and from the retention time, the Pow can be determined. For polymers, one usually sees a series of peaks, so the calculated Pow is the weighted average of the peaks that are detected. ISI has extensive experience in this test for both chemicals and polymers.

Note: depending on the nature of the test substance, the P_ow can also be determined by the Shake Flask method (see OECD 107), a titration method (see OECD 122), or the Slow-Stirring method (see OECD 123). Please inquire for more details.

118: Determination of the Number-Average Molecular Weight Distribution of Polymers using Gel Permeation Chromatography
GPC is a version of HPLC that separates molecules by their size, or molecular weight, rather than other physical characteristics. The test substance usually appears on a GPC chromatogram as one or more broad humps reflecting a distribution of molecular weights. This distribution is a feature of synthetic polymers and is unlike pure chemicals, which have a single discrete molecular weight. To determine the proportion of material at each molecular weight, the hump is sliced electronically at regular intervals, corresponding to known molecular weights. The amount of material in each slice is proportional to the area under the curve of the chromatogram. ISI's devoted gel permeation system is used to complete this test. ISI also has the in-house capability to determine the low molecular weight content (see OECD 119).

119: Determination of the Low Molecular Weight Content of a Polymer Using Gel Permeation Chromatography
This method looks carefully at the low molecular weight range (below 1000 Da). It is similar to OECD 118, but focuses the calibrations in the 500- 1000 molecular weight range and, depending on the polymer, may require a different GPC column set-up.

Note: the absence of low molecular weight material can, in some cases, be demonstrated by the GPC profile obtained by OECD 118, however if the hump extends into the low molecular weight region, OECD 119 is needed in order to obtain an accurate percentage.

120: Solution / Extraction Behaviour of Polymers
This test is similar to Water Solubility (OECD 105) but is used to determine the solution/extraction behavior of polymers in water. The water must be buffered to neutral, acidic or basic pH depending on the type of polymer. The required pH values are specified in the CEPA regulation. All of the solubility methods require a specific method of detecting the chemical of interest in the buffered water. This method usually requires a specific UV or IR absorbance, a specific chemical reaction, or a chromatographic separation or, in some cases, all three. Non-specific tests such as weight (gravimetric) or Total Organic Carbon (TOC) are frowned upon in the method descriptions. They are typically used only when there is no other workable option.

Note: this test is meant for solid polymers, but in some cases may be used with liquid polymers. Please inquire for more information.


Please inquire for the following Section 1 (Physical / Chemical Properties) methods:

121: Estimation of the Adsorption Coefficient (Koc) on soil and on sewage sludge using High Performance Liquid Chromatography (HPLC)
This method is similar to OECD 117, but uses a cyanopropyl column to determine the Koc.

Note: in some cases, this method may be used as a substitute for OECD 106. Please inquire for more information.

122: Partition Coefficient (n-octanol / water) pH-Metric Method for Ionisable Substances
This is a proposed guideline for evaluating the P_ow by phase separation and titration. Depending on the nature of the test substance, the P_ow can also be determined by the Shake Flask method (See OECD 107), an HPLC model (see OECD 117), or the Slow-Stirring method (see OECD 123). Please inquire for more information.

Note: this method has not yet been adopted by OECD and may not be acceptable for regulatory submissions.

123: Partition Coefficient (1-Octanol/Water): Slow-Stirring Method
This method is similar to OECD 107, but is used for higher P_ow values.