ANNEXDETERMINATION OF DICHLOROMETHANE AND 1,1,1-TRICHLOROETHANE

IDENTIFICATION AND DETERMINATION OF NITROMETHANE

1.SCOPE AND FIELD OF APPLICATION

This method is suitable for the identification and determination of nitromethane at up to about 0,3 % in cosmetic products packed in aerosol dispensers.

2.DEFINITION

The nitromethane content of the sample determined according to this method is expressed in percentage by mass of nitromethane, in the total aerosol dispenser content.

3.PRINCIPLE

The nitromethane is identified by colour reaction. Nitromethane is determined gas chromatographically after addition of an internal standard.

4.IDENTIFICATION

4.1.Reagents

All reagents should be of analytical purity.

4.1.1.

Sodium hydroxide, 0,5 M solution.

4.1.2.Folin's reagent

Dissolve 0,1 g of sodium 3,4-dihydro-3,4-dioxonaphthalene-l-sulphonate in water and dilute to 100 ml.

4.2.Procedure

To 1 ml of sample add 10 ml of 4.1.1 and 1 ml of 4.1.2. A violet coloration indicates the presence of nitromethane.

5.DETERMINATION

5.1.Reagents

All reagents must be of analytical quality.

5.1.1.

Chloroform (internal standard 1).

5.1.2.

2,4-dimethylheptane (internal standard 2).

5.1.3.

Ethanol, 95 %.

5.1.4.

Nitromethane.

5.1.5.Chloroform reference solution

Into a tared 25 ml volumetric flask, introduce about 650 mg of chloroform (5.1.1). Accurately reweigh the flask and contents. Make up to 25 ml with 95 % ethanol (5.1.3). Weigh and calculate the percentage by mass of chloroform in this solution.

5.1.6.2,4-dimethylheptane reference solution

Make up in a similar manner to the chloroform reference solution but weigh 270 mg of 2,4-dimethylheptane (5.1.2) into the 25 ml volumetric flask.

5.2.Apparatus

5.2.1.

Gas chromatograph with flame ionization detector.

5.2.2.

Apparatus for sampling of aerosols (transfer bottle, microsyringe connectors, etc.) as described in Chapter II of the Annex to Commission Directive 80/1335/EEC of 22 December 198010.

5.2.3.

Usual laboratory apparatus.

5.3.Procedure

5.3.1.Preparation of the sample

Into a 100 ml tared transfer bottle, purged or evacuated according to the procedure described in 5.4 of Chapter II of the abovementioned Directive, introduce about 5 ml of either of the internal standard solutions (5.1.5 or 5.1.6). Use a 10 or 20 ml glass syringe, without needle, adapted to the transfer piece following the technique described in paragraph 5 of Chapter II of the above-mentioned Commission Directive. Reweigh to determine the quantity introduced. Using the same technique, transfer into this bottle about 50 g of the contents of the aerosol dispenser sample. Again reweigh to determine the quantity of sample transferred. Mix well.

Inject about 10 μl using the specified microsyringe (5.2.2). Make five injections.

5.3.2.Preparation of the standard

Into a 50 ml volumetric flask, accurately weigh about 500 mg of nitromethane (5.1.4) and either 500 mg of chloroform (5.1.1) or 210 mg of 2,4-dimethylheptane (5.1.2). Make up to volume with 95 % ethanol (5.1.3). Mix well. Place 5 ml of this solution into a 20 mg volumetric flask. Make up to volume with 95 % ethanol (5.1.3).

Inject about 10 μl using the specified microsyringe (5.2.2). Make five injections.

5.3.3.Gas chromatographic conditions

5.3.3.1.Column

This is in two parts, the first containing didecyl phthalate on Gas Chrom Q as packing, the second having Ucon 50 HB 280X on Gas Chrom Q as packing. The prepared combined column must yield a resolution ‘R’ equal to, or better than, 1,5, where:

R= 2 d' r2 - r1W1 + W2math

let:

r1 and r2

retention times (in minutes),

W1 and W2

peak widths at half height (in millimetres),

d'

the chart speed (in millimetres per minute).

As examples the following two parts yield the required resolution:

Column A:

Material: stainless steel.

Length: 1,5 m.

Diameter: 3 mm.

Packing: 20 % didecyl phthalate on Gas Chrom Q (100 to 120 mesh).

Column B:

Materia: stainless steel.

Length: 1,5 m.

Diameter: 3 mm.

Packing: 20 % Ucon 50 HB 280X on Gas Chrom Q (100 to 120 mesh).

5.3.3.2.Detector

A suitable sensitivity setting for the electrometer of the flame ionization detector is 8 × l0-10A.

5.3.3.3.Temperature conditions

The following have been found suitable:

Injection port: 150 oC,

Detector: 150 oC,

Column: between 50 and 80 oC depending upon individual columns and apparatus.

5.3.3.4.Suitable gas supplies

Carrier gas: nitrogen.

Pressure: 2,1 bar.

Flow: 40 ml/min

Detector supplies: as specified by the makers of the detector.

6.CALCULATIONS

6.1.Response factor of nitromethane, calculated with reference to the internal standard used

If ‘n’ represents nitromethane:

let:

kn

its response factor,

m'n

its mass (in grams) in the mixture,

S'n

its peak area.

If ‘c’ represents the internal standard, chloroform or 2,4-dimathylheptane:

let:

m'c

its mass (in grams) in the mixture,

S'c

its peak area,

then:

Kn = m'nm'c × S'cS'nmath

(kn is a function o2 the apparatus).

6.2.Concentration of nkromethane in the sample

If ‘n’ represents nitromethane:

let:

kn

its response factor,

Sn

its peak area.

If ‘c’ represents the internal standard, chloroform or 2,4-dimethylheptane:

let:

mc

its mass (in grans) in the mixture,

Sc

its peak area,

M

the mass (in grams) of the aerosol transferred,

then the % (m/m) nitromethane in the sample is:

mcM × Kn × SnSc × 100math

7.REPEATABILITY11

For a nitromethane content of about 0,3 % (m/m), the difference between the results of two determinations carried out in parallel on the same sample should not exceed an absolute value of 0,03 % (m/m).