The Bogeyman is Real - Chromium(VI) Determination in Toys

You may deem the chance slim that mythical monsters are hiding underneath your offspring’s beds. However, danger might be lurking there in the form of toy blocks, action figures, or crayons. Hazardous substances found in everyday items, including toys, pose a particular threat to children. Even low concentrations have the potential to cause significant harm to their small bodies, and since children don’t just discover the world through their eyes and hands, but by putting things in their mouths too, they are at high risk of ingesting these substances.

New Directive Imposes Tighter Restrictions

National and EU-wide standards stipulate strict limit values for hazardous substances in toys. EU directive 2009/48/EC, also known as the ‘toy safety directive’, came into force on 20 July 2013, and has imposed tighter restrictions on the migration limits for some hazardous substances in toys, including the carcinogenic substance chromium(VI). The migration limit refers to the maximum quantity of a hazardous substance that a product is permitted to release. In the new directive, it is this type of value that now replaces the limit values expressed in terms of bioavailability that were defined in the previous version. The directive draws a distinction between three types of materials used in toys: (1) dry, brittle, powder-like, or pliable materials, (2) liquid or sticky materials, and (3) scraped-off materials. Each of these groups is subject to different migration limits according to the accessibility of the hazardous substances through sucking, licking, swallowing, or prolonged skin contact. The limit values that apply to hexavalent chromium according to the new EU directive are listed in Table 1.
Free Choice of Test Method
European standard EN 71 Part 3 outlines the test methods associated with the toy safety directive, including sample preparation and results evaluation. Sample preparation involves producing a migration solution by releasing hazardous substances from the toy material under realistic conditions; that is, mimicking what happens when the material comes into contact with skin, is swallowed, or is put in the mouth, for instance. The user is free to choose whichever analysis method he or she prefers, as long as it is validated. Ion chromatography with UV/VIS detection following post-column derivatisation is suitable for chromium(VI) determination in scraped-off toy materials, as well as dry, brittle, powder-like, or pliable materials, in accordance with the migration limits specified in Table 1. This method can be almost entirely automated. This, in combination with matrix elimination and preconcentration of chromium(VI), ensures highly reliable and precise analyses. To illustrate the method, the information that follows outlines the process of analysing samples of finger paint, opaque white paint, coloured pencils, inks, watercolours, and varnishes.
Table 1. The three types of toy materials and their migration limits for chromium(VI) according to EU directive 2009/48/EC, plus some examples.

Sample Digestion using Synthetic Gastric Juice

Chromium(VI) is extracted from the toy material at body temperature using hydrochloric acid. This type of sample digestion simulates how gastric juice dissolves out the harmful substance from swallowed toy material. The sample that is obtained using this method is then manually neutralised and diluted. Dilution is required because the high ion concentration present in the sample – which is caused by hydrochloric acid extraction and subsequent neutralisation – does not permit preconcentration of chromium(VI).
Automation Improves Convenience and Safety
All the remaining steps are automated (Figure 1). To start with, the entire sample flow path is equilibrated using sample. A dosino then feeds a defined sample volume onto the preconcentration column. The dosino allows to control with accuracy the injection volume, and this is what forms the basis of reliable determination, especially when dealing with low analyte concentrations.

Matrix Elimination and Preconcentration for Reliable Trace Analysis

The preconcentration column contains an anion exchanger that binds chromium(VI). The cations in the sample and the organic matrix are eliminated by rinsing with 50% acetone, along with anions that bind weakly to the exchanger, such as chloride. Matrix elimination prevents interfering peaks, which compromise the evaluation of the chromium(VI) peak, and extends the service life of the analytical column. The acetone-containing rinsing solution eliminates not only ions and organic sample components, but also pigments: as pigments can interfere with VIS detection, it is crucial that they are thoroughly removed. During the process, the hexavalent chromium remains in the preconcentration column: thanks to its lengthy retention time, up to 10 ml of rinsing solution can be used without eluting chromium(VI); this means that the majority of the matrix can be rinsed out.
Separation and Detection
Chromium(VI) is released from the preconcentration column by the eluent and then proceeds via the separation column to the post-column reactor. Here, it is reacted with the post-column reagent 1,5-diphenylcarbazide (Figure 2). When combined with chromium(VI), 1,5-diphenylcarbazide forms optically active complexes that can be quantitatively determined using the uv/vis detector because of their absorption in the vis range.MagIC Net software is used to control the system and evaluate the measured data.
Inline matrix elimination is an indispensable tool, in particular when color is involved, as pigments will interfere with detection in the VIS range.
Figure 3 illustrates two determinations of a known concentration (0.04 μg/L) of chromium(VI) as well as one determination of ultrapure water. The method delivers results that are highly reproducible, thanks not least to the full automation of the ion chromatographic determination process – which not only saves time and money, but also prevents errors and contamination.
Ion chromatography is an accurate, reliable method of determining hexavalent chromium in toys. Thanks to the analyte preconcentration and matrix elimination, it is the ideal choice, in particular when it comes to analysing low concentrations, and as a result is compatible with the new European standard EN 71 Part 3. The fact that the method is almost entirely automated makes it a winning choice too – allowing it to not only cut down on time and effort, but also ensuring maximum safety during analysis.