Antibiotics such as oxytetracycline (OTC) and streptomycin have been successfully used to control many plant diseases. Recently, OTC and streptomycin were approved for the control of Huanglongbing in citrus. Previous reports showed that most tetracyclines form a stable complex with europium and the fluorescence intensity of this complex was enhanced by the addition of a coligand. Although the europium method has been used to measure tetracyclines in different matrixes including milk and meat, it has not been applied to plant tissues. The objective of this study is to develop a sensitive method for the detection of OTC in citrus tissues using the europium method. Our results showed that plant metabolites such as phenols could interfere with the europium method. Consequently, the OTC was cleaned using a 60 mg hydrophilic-lipophilic balanced (HLB) cartridge. We also tried two coligands (cetyltrimethylammonium chloride (CTAC), and citrate (Cit)). The recovery of OTC from spiked leaves as measured using the Eu-OTC-CTAC complex was 75±7.6%. The Eu-CTAC method was also used to measure the level of OTC in trunk-injected trees, and it gave similar results to those obtained using the ELISA method. Our results also showed that Cit can be successfully used to replace CTAC. The Eu-OTC-Cit method showed high OTC recovery (&gt;80%) and gave similar results to Eu-OTC-CTAC complex. Finally, we were able to visualize the OTC in citrus leaf extract, under ultraviolet light, after it was cleaned with the HLB cartridge.

Development of europium-based methods for the detection of oxytetracycline in citrus tissues

ACS Fall 2021

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