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Vapour pressure

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Reference
Endpoint:
vapour pressure
Type of information:
experimental study
Adequacy of study:
key study
Study period:
2004-09-28 to 2004-10-07
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to
Guideline:
OECD Guideline 104 (Vapour Pressure Curve)
Version / remarks:
July 27 1995
Deviations:
no
Qualifier:
according to
Guideline:
EU Method A.4 (Vapour Pressure)
Deviations:
no
GLP compliance:
yes
Type of method:
gas saturation method
Key result
Test no.:
#1
Temp.:
25 °C
Vapour pressure:
0.068 Pa
Key result
Test no.:
#2
Temp.:
35 °C
Vapour pressure:
0.26 Pa
Key result
Test no.:
#3
Temp.:
45 °C
Vapour pressure:
0.64 Pa

The vapour pressure of the test item was measured at temperatures of 25°C, 35°C and 45°C. The experimental parameters of the vapour pressure determination are summarised in Table 1. The results and the amount of nitrogen used to calculate the vapour pressure of the individual experiments are summarised in Table 2. The tabulated values represent rounded results that were obtained by calculation using the exact raw data. To ensure saturation control, three different flow rates were used at each temperature. From Tables 1 and 2, it can be clearly seen that higher flow rates did not lead to lower vapour pressures which means that the nitrogen was saturated with the test item under the conditions of the test.

The trapping efficiency of the test item in the first cooling trap was very good. 100% of the test item was trapped in the first cooling trap. The trapping efficiency results are summarised in Tables 3, 4 and 5.

Figure 1 (attached) shows the vapour pressure curve of the test item. The extrapolation data are given in Table 6. A typical chromatogram of a standard calibration solution is given in Figure 2 (attached). An example of a sample solution chromatogram from the experiment at 25°C is shown in Figure 3 (attached). An example of the calibration data for the test item-standards is given in Figure 4 (attached) and Table 7. The r2 fit was 0.9997 (optimum 1.0000). This reflects the linearity of the HPLC system within the calibration range of 0.942 µg/mL to 112.98 µg/mL of the test item.

The good reproducibility and the high trapping efficiency led to the conclusion that the results of the vapour pressure determination of the test item are reliable.

In conclusion, the vapour pressure of the test item was determined to be 0.068 Pa at 25°C, 0.26 Pa at 35°C and 0.64 Pa at 45°C.

The calculation of the vapour pressure of the test item at 25°C by extrapolation based upon the simplified Clausius-Clapeyron equation resulted in a vapour pressure of 0.072 Pa at 25°C which is in very good agreement with the vapour pressure directly measured at 25°C.

Table 1: Experimental parameters used for the gas saturation method of the test item

Column No.

Temperature [°C]

Flow rate [mln/min]

Collecting time [min]

Volume [min]

1

45

30

328

9840

2

45

40

13120

3

45

50

16400

1

35

30

407

12210

2

35

40

16280

3

35

50

20350

1

25

30

1044

31320

2

25

40

41760

3

25

50

52200

 

Table 2: Results of the vapour pressure determination of the test item

Column No.

Temperature [°C]

Volume* [mL]

Amount of test item in trap 1 [µg]

Amount of test item in trap 2 [µg]

Total amount of test item [µg]

Vapour pressure [Pa]

Average vapour pressure [Pa]

1

45

11461

1009.281

0.00

1009.281

0.65

0.64

2

45

15281

1325.685

0.00

1325.685

0.64

3

45

19102

1681.623

0.00

1681.623

0.65

1

35

13775

481.484

0.00

481.484

0.25

0.26

2

35

18366

694.558

0.00

694.558

0.27

3

35

22958

875.127

0.00

875.127

0.27

1

25

34187

319.986

0.00

319.986

0.064

0.068

2

25

45582

449.390

0.00

449.390

0.068

3

25

56978

604.038

0.00

604.038

0.073

*corrected volume at test temperature

Table 3: Trapping efficiency of test item at 45°C

Saturator column No.

Amount of test item in 1st trap [µg]

Amount of test item in 2nd trap [µg]

Total amount of test item [µg]

Trapping efficiency of 1st trap [%]

1

1009.281

0.0

1009.281

100.0

2

1325.685

0.0

1325.685

100.0

3

1681.623

0.0

1681.623

100.0

 

Table 4: Trapping efficiency of test item at 35°C

Saturator column No.

Amount of test item in 1st trap [µg]

Amount of test item in 2nd trap [µg]

Total amount of test item [µg]

Trapping efficiency of 1st trap [%]

1

319.986

0.0

319.986

100.0

2

449.390

0.0

449.390

100.0

3

604.038

0.0

604.038

100.0

 

Table 5: Trapping efficiency of test item at 25°C

Saturator column No.

Amount of test item in 1st trap [µg]

Amount of test item in 2nd trap [µg]

Total amount of test item [µg]

Trapping efficiency of 1st trap [%]

1

319.986

0.0

319.986

100.0

2

449.390

0.0

449.390

100.0

3

604.038

0.0

604.038

100.0

 

Table 6: Data of the vapour pressure curve of the test item

Temperature [°C]

1/T [K]

ln Pvp

45

0.00314

-0.44

45

0.00314

-0.45

45

0.0314

-0.44

35

0.00325

-1.39

35

0.00325

-1.31

35

0.00325

-1.31

25

0.00335

-2.74

25

0.00335

-2.69

25

0.00335

-2.62

 

The tabulated results represent rounded values obtained by calculations based on the exact raw data.

Y = b*x + a

With

Y = ln (Pvpmean ln Pa)

x = 1/T [K]

b = -10656 (slope)

a = 33.115 (y-axis intercept)

r2= 0.989

calculated vapour pressure of the test item at 25°C is 0.072 Pa

Table 7: The calibration data of the test item

Concentration [µg/mL]

Peak area

Deviation [%]

0.9415

7.0112

-2.8

9.415

64.27

5.0

18.83

116.75

-3.8

37.66

245.14

1.5

75.32

486.74

1.0

112.98

715.55

-0.9

 

Conclusions:
Vapour pressure values of 0.068 Pa at 25°C, 0.26 Pa at 35°C and 0.64 Pa at 45°C were determined for the submission substance using a relevant test method and in compliance with GLP. The result is considered to be reliable.

Description of key information

Vapour pressure [whole substance]: 0.068 Pa at 25°C, 0.26 Pa at 35°C and 0.64 Pa at 45°C (OECD 104)

Vapour pressure [Constituent 1]: 3.6E-03 Pa at 25°C (QSAR)

Vapour pressure [Constituent 2]: 1.3E-07 Pa at 25°C (QSAR)

Key value for chemical safety assessment

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

Additional information

A measured vapour pressure of 0.068 Pa at 25°C, 0.26 Pa at 35°C and 0.64 Pa at 45°C were determined for the submission substance as a whole substance using the gas saturation method in accordance with OECD Test Guideline 104 and in compliance with GLP. The result is considered to be reliable.

The submission substance is a multi-constituent substance containing two main constituents, measured vapour pressure for the whole substance is preferred for the purpose of human health exposure assessment while for the purposes of environmental hazard and fate assessment; vapour pressures of the constituents have been predicted using a validated QSAR estimation method. Vapour pressure values of 3.6E-03 Pa at 25°C and 1.3E-07 Pa at 25°C for Constituent 1 and Constituent 2 respectively.