N-[3-(dimethylamino)propyl]stearamide monoacetate

Water solubility

Link to relevant study record(s)

Reference

Endpoint:

water solubility

Type of information:

experimental study

Adequacy of study:

key study

Study period:

2014-09-14 to 2014-10-29

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

test procedure in accordance with generally accepted scientific standards and described in sufficient detail

Remarks:

The substance is a surfactant whose physical-chemical properties make it impossible to measure its water solubility using traditional methodology described in the OECD 105 test guideline.

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 105 (Water Solubility)

Principles of method if other than guideline:

This study was conducted under EPA TSCA Good Laboratory Practice Standards (40 CFR 792)

GLP compliance:

no

Type of method:

other: Determination of the critical micelle concentration (CMC) for the test substance employing surface tension measurements at multiple test substance concentrations in water.

Key result

Water solubility:

>= 129 - <= 134 mg/L

Conc. based on:

test mat.

Temp.:

23 °C

Remarks on result:

other: pH not relevant

Estimation of Water Solubility by Determination of Critical Micelle Concentration:

Results for the measurement of surface tension as a function of concentration for the substance are presented in in Table 1 and presented graphically in Figure 1.

The CMC was calculated as the point of intersection of the linear least squares regression lines for the two linear regions of the graph (data points 1 – 7 and data points 8 – 12).

 

Data Points 1 – 7

Slope (m₁) = -11.03

Intercept (b₁) = 17.37

r₂ = 0.86

 

Data Points 8 – 12

Slope (m₂) = 0.19

Intercept (b₂) = 38.60

r₂ = 0.10

 

For intersection of the two lines 

y₁ =m₁x+b₁ =y₂ =m₂x+b₂

m₁x - m₂x = b₂ - b₁

(m₁ -m₂)x=b₂-b₁

x = (b₂ - b₁) / (m₁ - m₂)

x = log [C_{wt% total active substance}] = (38.60 - 17.37) / (-11.03 - 0.19)

log [C_{wt% total active substance}] = log (21.23 /-11.22) = -1.89

C = 10^-1.89 = 0.0129 wt% total active substance = 129 mg total active substance/L = 134 mg test substance/L

 

The limit of water solubility of the substance was determined to be 129 mg total active substance/L employing surface tension measurements at multiple test concentrations to determine the CMC. Based on a test substance purity of 96 wt% total active substance, this corresponds to a solubility limit of 134 mg test substance/L.

Above 129 mg total active substance/L any added surfactant will not increase the concentration of the solvated material but instead increases the number of colloidal particles of aggregated molecules called micelles. These structures are not generally visible as discrete particles to the human eye, but rather appear as a haze or, may be optically clear. As the concentration of the surfactant continues to increase the micelles begin to coalesce into lamellar structures which likely will separate as free-phase. These are non-watery structures large enough to be visible to the human eye. These lamellar structures are the surfactant molecules and water very neatly packed into layers. This is not a normal solute. The intermolecular interactions between surfactant molecules are much more important than the interactions with the solvent.

Conclusions:

The limit of water solubility of the substance was determined to be 129 mg total active substance/L employing surface tension measurements at multiple test concentrations to determine the CMC. Based on a test substance purity of 96 wt% total active substance, this corresponds to a solubility limit of 134 mg test substance/L.

Executive summary:

The values for water solubility for the test substance were determined experimentally employing measurements of surface tension at multiple concentrations of the test substance in water. The experimental data were employed to determine the critical micelle concentration which is considered equivalent to water solubility for surfactant test substances.

The values for water solubility are 129 mg total active substance per liter, and 134 mg test substance per liter.

Description of key information

Values for water solubility were determined based on measurement of surface tension at multiple test substance concentrations in water to determine the Critical Micelle Concentration for the test substance. The values for water solubility are 129 mg total active substance per liter, and 134 mg test substance per liter.

Key value for chemical safety assessment

Water solubility:

134 mg/L

at the temperature of:

23 °C