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Survey of chemical substances in kohl and henna products
3 Chemical analyses
3.1 Inorganic substances
3.1.1 Analyses
In co-operation with the Danish Environmental Protection Agency, 18 kohl and 17 henna products were selected for quantitative analysis of lead and screening for elements and among others heavy metals.
The screening analyses covered all elements from atomic mass 6 (lithium) to mass 238 (uranium). The analyses were performed by Inductively Coupled Plasma Mass Spectrometry (ICP-MS) after
microwave induced preparation of the products with nitric acid in autoclaves. Selected elements including heavy metals were quantified subsequently by ICP-MS and/or Inductively Coupled Plasma Atom
Emission Spectrometry (ICP-AES).
Lead (Pb) was quantified in all products and the same were elements that were measured at a concentration above 10 mg/kg by the screening analysis.
The detection limits in the screening analyses were in the range from 0.05 to 10 mg/kg.
In relation to the quantification of selected elements, duplicate determinations were performed and the %RSD calculated.
The found content of elements is compared to the regulation in the Statutory Order on cosmetics if the substance is regulated.
3.1.2 Methods
3.1.2.1 Test preparation
Approximately 500 mg sample – precisely weighed – was prepared by micro wave induced heating in a PFA autoclave with 20 ml 7 M HNO3 (subboiling quality). The resulting solution was filtered and
then diluted to 50 ml using demineralised water (Milli-Q Plus).
Duplicate preparations were performed.
Blanks were prepared in the same way.
3.1.2.2 Standards
Standards and control samples were prepared from a Perkin-Elmer and a Merck multi-element standard solution, respectively, by dilution with 2.8 M HNO3. The internal standard solution was prepared
from Perkin-Elmer single element standards of Ge, Rh and Re by dilution with 0.14 M HNO3.
3.1.2.3 Apparatus
A Perkin-Elmer Sciex Elan 6100 DRC Plus ICP Mass Spectrometer with a FIAS 400 flow injection system and autosampler AS 93 Plus and a Perkin-Elmer Optima 3300 DV inductively-coupled-plasma
atomic emission spectrometer with autosampler AS-90 plus were used.
3.1.2.4 Screening analysis
Adding germanium, rhodium and rhenium as internal standards ”on-line”, the prepared solutions were screened for content of trace elements by inductively-coupled-plasma mass spectrometry (ICP-MS)
using the expert programme TotalQuantIII that from an instrument response curve for the elements from mass 6 (Li) to mass 238 (U) quantifies the content. The instrument response curve was updated by a
multi-element standard containing 30 elements that covers the total mass range. The elements Br, C, Cl, F, I, N, O, P and S are not quantified due to interferences.
3.1.2.5 Quantitative analysis
All prepared solutions were analysed quantitatively for lead by ICP-MS and the same were elements which by the screening were measured at a concentration higher than 10 mg/kg (Zn 50 mg/kg). Cobalt,
copper, nickel and vanadium were analysed by ICP-MS and boron, barium, bismuth, manganese, strontium and zinc by ICP-AES.
3.2 Organic substances
3.2.1 Analyses
Selected henna products were analysed quantitatively for the content of p-phenylenediamine and lawsone.
The analysis for p-phenylenediamine was performed by capillary gas chromatography using mass spectrometric detection (GC-MS) after extraction of the substance with dichloromethane (DCM). The detection limit for p-phenylenediamine was in the range from 4 to 20 mg/kg.
The analysis for lawsone was performed by liquid chromatography using mass spectrometric detection (LC-MS) after extraction of the substances with ethanol/water. For lawsone the detection limit was 20 mg/kg.
Duplicate determinations were performed and the %RSD is calculated.
3.2.2 Methods
3.2.2.1 Test preparation of p-phenylenediamine
Approximately 1 g sample – precisely weighed – in a 50 ml vial was added 20 ml extraction solution containing naphthalene-d8, aniline-d5 and phenol-d5 as internal standards in dichloromethane. The sample was first ultrasonically extracted for 1 hour and then mechanically extracted for 1 hour further and finally centrifuged.
Duplicate determinations were performed.
Blanks were prepared in the same way.
3.2.2.2 Test preparation of lawsone
Extraction and sample preparation performed according to Bakkali et al. (1997). Approximately 50 mg sample – precisely weighed – in a 50 ml vial was added 50 ml extraction solution. The sample was
extracted for 16 hours under constant agitation, then centrifuged, added 50 µl acetic acid and extracted with 3 x 10 ml chloroform. The extracts were dried over sodium sulphate, evaporated to dryness and
re-dissolved in methanol and added water corresponding to the eluent composition. Blanks and recovery controls were made according to the same procedure. The recovery was 83 %.
3.2.2.3 Quantitative analysis for p-phenylenediamine
External standards were made from p-phenylenediamine (Sigma P6001/ 033K3482, CAS no. 106-50-3) in the extraction solution.
The analysis was performed using GC-MS.
3.2.2.4 Quantitative analysis for lawsone
External standards were made from lawsone (2-hydroxy-1,4-naphthoquinone, Sigma H-0508 lot no. 072K3652, CAS no. 83-72-7) in the extraction solution.
The analysis was performed using LC-MS with methanol/water as eluent.
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Version 1.0 September 2005, © Danish Environmental Protection Agency
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