Quantitative analysis of Cu in pig feed by microwave-assisted laser-induced breakdown spectroscopy

Given the severe risks heavy metals introduce to pig diets, rapid detection is essential to monitor and control heavy metal content in pig feeds, ensuring they do not reach consumers. This work introduces microwave-assisted laser-induced breakdown spectroscopy (MA-LIBS), a variant of the popular LIBS, using it to detect Cu content in pig feed. The MA-LIBS technology couples microwave radiation into the plasma through the microwave probes, extending the plasma lifetime and enhancing the plasma signal. In this study, the effects of three kinds of microwave probes (ring needle, single needle, and double needle) on the sample signal, noise, and signal noise ratio (SNR) at different microwave powers were compared and analyzed, and then the microwave probe placement height was also optimized. Results showed that the best enhancement effect was obtained at 120 W microwave power and the double needles were placed at a height of 2 mm. The detection limit of (LOD) Cu by MA-LIBS was 5.15 mg/kg (the recommended content of Cu in pig diet in the Specification for the Safe Use of Feed Additives is 3–6 mg/kg), which is 9.6 times higher than that of traditional LIBS. Thus, MA-LIBS can effectively enhance Cu spectra in pig feed the emission intensity, SNR and reduce the LOD, enabling the rapid and pig feed samples accurate detection with low Cu content.