Purpose: The purpose of this study was to demonstrate the robustness of the IPM array kit in the multiplex screening of Raw Farm Milk (RFM) and Raw Tanker Milk (RTM) samples followed by LC-MS/MS confirmation (at ILVO).
Methods: Simultaneous competitive chemiluminescent immunoassays defining discrete test sites on the biochip surface were employed and applied to the Evidence Investigator analyser. Up to 48 samples can be analysed within 2.5 hours. 23 RFM and 153 RTM samples were screened followed by LC-MS/MS confirmation. Neat milk samples (25µl) were added directly to the biochips.
The LC system consisted of an Aquity UPLC. Separation was achieved on a Kinetex C18 2.1 נ100mm, 1.7µm column, injection volume 5µl, flow rate, 0.4 ml/min of H2O/ACN (95/5%) + 0.3% AA. The MS equipment consisted of a Xevo TQ-MS (Waters). Analytes were determined with tandem electrospray positive or negative MS with two transitions. An Obelisc R (Sielc) 2.1 × 100mm, 5µm column was used for aminoglycosides separation. The column was held at 40°C, injection volume 10µl, eluent flow: 0.5 ml/min. The elution was performed gradually with changing amounts of H2O + 1% FA and ACN + 1%FA.
Results: 9 (34.6%) RFM and 2 (1.3%) RTM samples screened positive on IPM biochip array for at least one drug residue, including gentamicin, kanamycin, spectinomycin, cefquinome, cephalexin and florfenicol. Samples were confirmed by LC-MS/MS (except for florfenicol as it required confirmation by an ISO17025 accredited laboratory).
Significance: These findings indicate that the use of the IPM as a multi-analytical tool revolutionises the screening capacity for drug residues in test settings, which is beneficial for consumer protection.