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Vapour pressure

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Reference
Endpoint:
vapour pressure
Type of information:
experimental study
Adequacy of study:
key study
Reliability:
1 (reliable without restriction)
Qualifier:
according to
Guideline:
OECD Guideline 104 (Vapour Pressure Curve)
Principles of method if other than guideline:
The gas saturation procedure (nitrogen at 2, 4 and 8 cc/min) at 25ºC using a trapping resin (XAD-2) to adsorb gaseous test substance followed by liquid scintillation counting to analyze 14C-AHTN content was used to determine vapor pressure of AHTN.
GLP compliance:
yes (incl. certificate)
Type of method:
gas saturation method
Temp.:
25 °C
Vapour pressure:
0.068 Pa
Remarks on result:
other: Standard deviation: 0.0123 Pa. Relative standard deviation: 18.04%

Percent recovery (counting efficiency) of AHTN in XAD-2 resin was over 84%. Correlation coefficient: 0.9941 (average mass of AHTN volatilized vs. nitrogen flow rate) indicated that saturation conditions were achieved and vapor pressure values were consistent at all 3 gas flow rates.

Ideal gas law is used to calculate the vapour pressure. The figures are shown in Table 1 that has been attached.

Conclusions:
The overall averaged vapour pressure is 6.82 x 10(-2) Pa.
Executive summary:

The AHTN vapor pressure was determined by the gas saturation procedure at 25°C. Nitrogen was used to volatilise AHTN at flow rates of 2, 4 and 8 cc/min. AHTN in the gas phase was adsorbed by an XAD-2 trapping resin. Liquid scintillation counting was used to determine the 14C labelled AHTN. The recovery (counting efficiency of AHTN in XAD-2 resin) was over 84% for all the test concentrations. A linear regression plot of the average (triplicate samples) amount of AHTN against the nitrogen flow rate revealed a correlation coefficient of 0.9941, suggesting saturation for all test concentrations. The overall AHTN vapour pressure of 6.82 x 10-2Pa at a temperature of 25°C was calculated with the ideal gas law. The standard deviation was 1.23 x 10-2Pa.

Description of key information

The vapour pressure of the test item was determined to be 0.07 Pa using the gas saturation method, according ot the OECD 104 guideline under GLP compliance.

Key value for chemical safety assessment

Vapour pressure:
0.068 Pa
at the temperature of:
25 °C

Additional information

The melting point and boiling point of the test item are 54°C and 326°C respectively. The REACH technical guidance document on information requirements and chemical safety assessment (May 2008) states that ideally two vapour pressures at different temperatures in the range of 0 to 50°C should be reported. Hence, a measured value at 25°C and a calculated value at 50°C have been selected.

No phase transition (solid-liquid) occurs and the test item remains stable in the 25-50°C temperature range. The vapour pressure at 25°C has been experimentally determined by the gas saturation method and the vapour pressure at 50°C has been derived using EPI suite. EPI suite uses the formula described by MacKay, that was also put forward in the REACH technical guidance document. The vapour pressure is very low at room temperature and although the vapour pressure rises sharply with temperature within the temperature range of 25 to 50°C, the vapour pressure at 50°C is in absolute terms still very low.

The reliability of the model has been verified by comparing the calculated and measured vapour pressures at 25°C and both values are very close.

In the risk assessment, the experimental value has been put forward.