1. High Performance Liquid Chromatography (HPLC)
High performance liquid chromatography is commonly used to analyze pigments. Most HPLCs are equipped with UV-Vis, diode array, or photodiode array detectors. There are various mobile phases and stationary phases. The commonly used separation columns are octadecyl column and monomer octyl column. The detection limit and quantification limit of Acid Red 27 in carbonated beverages, cocktails, candies, jelly and ice cream determined by HPLC-spectrophotometry were 6.4 and 19 ng/mL, respectively. The ultra-high performance liquid chromatography derived on the basis of high performance liquid chromatography not only has higher analysis accuracy, but also greatly shortens the analysis time. The content of amaranth in meat products was determined by ultra-high performance liquid chromatography, and the detection limit was 0.02mg/kg, and the quantification limit was 0.05mg/kg.
2. Liquid chromatography-mass spectrometry
Liquid chromatography-mass spectrometry is one of the chromatographic techniques used to determine pigments in food. Its principle is the same as that of ordinary high performance liquid chromatography, and it is necessary to select a suitable mobile phase and stationary phase. But mass spectrometers can overcome spectral interference and make measurements more accurate. The chromatographic analysis method based on liquid chromatography-mass spectrometry was used to determine Acid Red 27 in ice cream, chocolate and candy, and the detection limit and quantification limit were 5 and 10 mg/kg, respectively.
Thin-layer chromatography is another basic chromatographic method that screens for unknown compounds in food by comparing the ratio shift and color of a sample to a standard. Thin-layer chromatography has a relatively small sample load, and generally uses silica gel as the stationary phase, and the mobile phase is selected according to the difference in sample properties. The determination of Acid Red 27 in beverages by thin-layer chromatography has a lower detection limit than high-performance liquid chromatography, and its sensitivity is not outstanding enough.
4. Electrochemical sensor
Electrochemical sensors have been widely used in the fields of proteomics, biochemistry, drug and food analysis due to their advantages of high sensitivity, easy operation, good selectivity, and easy miniaturization. In electrochemical systems, the key point is to design and modify highly sensitive and selective working electrodes. An electrochemical sensor platform based on graphene nanosheets to detect the content of amaranth in beverages. Ultrasonic exfoliation of graphite powder in N-methylpyrrolidone broadens the linear range from 2.5nm to 125nm. In the electrochemical system, the oxidation reaction between different RF polymers and Acid Red 27 showed different electrochemical activities, and this new sensing system has a good application prospect in monitoring synthetic pigments.
5. Molecularly imprinted polymers
Molecularly imprinted polymers
It is a biomimetic synthetic receptor with a specific cavity designed for the target molecule. Molecular polymers can not only specifically bind target molecules, but also participate in the composition of optical fiber sensors, which are widely used in environmental analytical chemistry, clinical analysis, and food. A newly developed molecularly imprinted electrochemical sensor uses a composite material induced by a magnetic field to self-assemble redox graphene and ferroferric oxide. In the molecular imprinting technique, the complex includes the functional monomer of aniline, Acid Red 27 sample and ferric oxide, which are pre-placed on the template through p-p stacking and hydrogen bond self-assembly, and then polymerized under magnetic field induction.
6. Capillary Electrophoresis
Electrophoresis is the general name for a family of separation techniques involving the application of an electric field in a capillary. According to different separation modes, capillary electrophoresis can be divided into capillary zone electrophoresis, capillary micellar electrokinetic chromatography, and capillary isotachophoresis. Due to the narrow inner diameter of the capillary, the capillary electrophoresis technique has a very low sample capacity, resulting in a low detection limit for the analyte. However, this method has achieved good results in the detection of amaranth in beverages and ice cream. Capillary zone electrophoresis combined with PDA detector was used to determine the content of Acid Red 27 in the beverage. At the wavelength of 280nm, the detection limit and quantification limit of Acid Red 27 were 1.1 and 3.61 mg/mL, respectively.