The method looks set to prove especially useful for firms concerned with ensuring products conform to consumer preferences for all-natural foods.
Writing in the journal Food Chemistry, the researchers describe the process as "rapid shaking-based ionic liquid dispersive liquid phase microextraction".
It identifies the presence of six synthetic colours: Tartrazine, Amaranth, Sunset Yellow, Allura Red, Ponceau 4R, and Erythrosine, the study claims.
Four of these are members of the so-called Southampton Six group of synthetic colours, which were linked in a 2007 Southampton University study to hyperactivity in children. Subsequently, the UK Food Standards Agency recommended EU food manufacturers should phase them out by 2009.
The test improves on previous approaches in that extraction does not require heat or ultrasonication, the paper's authors claim. This makes it extremely cost-effective and means it requires little energy use.
In addition, it dispenses with the need for a dispersive solvent or chemical reagents, which might pollute the environment, the scientists state.
"1-Octyl-3-methylimidazolium tetrafluoroborate ([C8MIM][BF4]) was dispersed in an aqueous sample solution as fine droplets by manual shaking, enabling the easier migration of analytes into the ionic liquid phase," they state.
"Factors such as the [C8MIM][BF4] volume, sample pH, extraction time, and centrifugation time were investigated.
"Under the optimum experimental conditions, the proposed method showed excellent detection sensitivity with limits of detection (signal-to-noise ratio = 3) within 0.015–0.32 ng/millilitre (mL). The method was also successfully used in analyzing real food samples."
The process was combined with high pressure liquid chromotography- (HPLC)-ultraviolet spectrophotometry as a means of identifying the colours.
A homogeneous sample solution (10.0 mL) containing the analytes was placed in a 15 mL screw-cap conical-bottom graduated plastic centrifugal tube.
Using a 500 microlitre (μL) syringe, 350 μL of RTIL was injected into the sample solution. Manual shaking (30 times in 20 seconds) resulted in the formation of a turbid solution, which was centrifuged for eight min at a rate of 3,500 revolutions a minute.
The upper aqueous solution was removed using a pipette, and the volume of residual IL was almost 180 μL. Methanol was added to the IL residue enriched with analytes to obtain a volume of 300 μL.
Using a 25 μL HPLC microsyringe, 10 μL of the enriched solution was injected directly into the HPLC system. All experiments were performed in triplicate. The syringe was rinsed with methanol and acetonitrile multiple times to remove residual analytes and IL.
"These results indicated that the present approach was a simple and sensitive procedure to determine synthetic food colorants at trace level," the researchers conclude. "It can also be extended to be applied in many other food samples."
Source: Food Chemistry; http://www.sciencedirect.com/science/article/pii/S0308814613003166; 'A rapid shaking-based ionic liquid dispersive liquid phase microextraction for the simultaneous determination of six synthetic food colorants in soft drinks, sugar- and gelatin-based confectionery by high-performance liquid chromatography'
Authors: Hao Wu1; Jing-bo Guo2; Li-ming Du1; Hong Tian1; Cheng-xuan Hao1; Zhi-feng Wang2; Jie-yan Wang1
1: Analytical and Testing Center, Shanxi Normal University, Shanxi Linfen, China
2: Department of Engineering, Shanxi Normal University, Shanxi Linfen, China