Orange II is commonly used in organic light-emitting diodes (OLEDs), wood stains and the textiles industry. However, the dye is sometimes illegally used to restore the red colour in food commodities – including chilli sauces from China and Indian sweets – despite its adverse health effects if eaten. Orange II is thought to cause liver damage as well as reduce red blood cell levels. Checking for Orange II in foodstuffs is therefore essential to maintain food safety.
‘Currently, the determination of Orange II uses techniques such as chromatography-mass spectrometry and polarography,’ says Tian Gan at Xinyang Normal University who led the work. ‘Although these techniques are either sensitive or selective for Orange II, they usually require complicated instrumentation, are very time consuming and are unsuitable for in situ analysis.’
Gan’s team have taken a step towards a quicker and more practical method by making a titanium dioxide-modified graphene electrode that can help detect the electrochemical signals of Orange II. They were able to spot the dye at nanomolar concentrations in ketchup and chilli product samples.
Gino Bontempelli, an expert in electrochemical sensors for environmental and food analysis at the University of Udine, Italy, questions the selectivity of the sensor. ‘Almost all azo dyes are characterised by the presence of at least one phenol moiety, which acts as the electrochemically active group, and consequently all azo dyes are expected to be oxidised at quite similar potential values. For this reason, the behaviour of possible interfering species needs to be carefully considered,’ says Bontempelli. The team are currently following up this line of investigation to test the sensitivity of their electrode to other synthetic dyes.
T Gan et al, Anal. Methods, 2013, DOI: 10.1039/c3ay40250a