A strip provides a figure in minutes. Conclusive evidence requires criteria, controls and sometimes a secondary technique.
The question is not which method is better, but which method suits the decision. An receiving pit requires an answer within five minutes. An enforcement officer requires a result that withstands second-opinion testing. Between those two realities lies a vast difference in requirements.
A quantitative lateral flow test such as a ROSA strip is a screening method with a quantitative readout. It is designed to estimate a concentration within the relevant range and to declare a lot rapidly compliant or suspect. It is not designed to identify a substance by structural analysis or to settle a legal dispute.
Confirmation is carried out using a chromatographic method, typically LC-MS/MS, in which the substance is separated and identified on the basis of mass and fragmentation. That method is slower and more expensive, but provides the evidence that a screening strip cannot deliver.
| Method | Time | Strength | Limitation |
|---|---|---|---|
| Lateral flow (ROSA) | 2 – 10 min | rapid, simple, quantitative within range | no identification; matrix- and dilution-dependent |
| ELISA | 1 – 2 hours | sensitive, high sample throughput per plate | cross-reactions, less robust with complex matrices |
| HPLC | hours to days | established reference method | less sensitive than MS/MS for some toxins |
| LC-MS/MS | hours to days | identification and confirmation, multi-toxin | cost, expertise, not suitable for field use |
Regulation (EU) 2023/2782 sets requirements for methods in Annex II: a recovery of 70 to 120%, a relative standard deviation under repeatability of at most 20%, a reproducibility of at most 25%, and a limit of quantification of at most half the maximum level, preferably one fifth. For aflatoxin B1 in baby food, an LOQ of 0.1 µg/kg applies.
Those criteria formally apply to official controls. They also serve as a useful benchmark for in-house methods: anyone using a strip without knowing the recovery and the LOQ for their own matrix does not know whether the figure is reliable. The supplier provides the data per matrix; the laboratory should verify this using its own samples.
Every result has an associated margin. With a maximum level of 1,000 µg/kg DON and a measurement uncertainty of 15%, a result of 1,050 µg/kg does not automatically mean the consignment is rejected. The decision rule requires comparing the result, corrected for recovery, minus the expanded measurement uncertainty, with the maximum level. This argues in favour of not disputing the strip in case of doubt, but taking a second sample or performing confirmation.
Charm's instructions prescribe daily temperature monitoring, daily calibration strips, and weekly positive and negative control samples. That discipline is no mere formality: without a control sample, a divergent result cannot be distinguished from a faulty strip, an expired kit, or an incorrect dilution.
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