A rapid colorimetric method for the detection of carminic acid in samples based on visible color change

[Display omitted] •A cost-effective method based on the detection of carminic acid using lead nitrate.•A rapid color change is observed which can be easily differentiated from the human eye.•Carminic acid can be detected with a LOD of 0.0025 mg mL−1.•Applicable to the wide use of samples including food and the non-food items.•The structural study of Carminic acid-Pb2+ complexes was also studied. Carminic Acid (CA), an insect-derived red color, is widely used as a colorant and additive in food and non-food items. The detection of CA is of great concern since it is unacceptable for vegetarians and vegans consumers. Therefore, it is important for food authorities to have a rapid detection method for CA. We describe here a simple and rapid method for the qualitative detection of CA, using Pb2+ for complex formation. As a result, the sample solution shows a visible change from pink to purple (bathochromic shift) which could also be analyzed through a spectrophotometer at λmax = 605 nm. The structure of the CA-Pb2+ complex was also studied through advanced spectroscopic techniques. Moreover, the presence of iron results in the formation of a stable CA-Fe2+ complex without any significant color change, as Fe2+ has a stronger binding affinity with CA. Thus, sodium fluoride (NaF) was used to prevent CA-Fe2+ complex formation. Therefore, two methods were developed based on the absence (method I) and presence (method II) of NaF. The LOD and LOQ for the method I was 0.0025 and 0.0076 mg mL−1, and for method II, values were 0.0136 and 0.0415 mg mL−1, respectively. The methods were also validated by intra and inter-day analyses. A total of 45 commercials, including food and non-food samples, were screened for the detection of CA. The developed methods are applicable for the effective and rapid surveillance of CA in various samples without the use of high-tech instruments.