Validation of Delvotest® Fast BT for Detection of ß-Lactams and Tetracyclines in Raw Cow's Milk: Performance Tested MethodSM 102104.

BACKGROUND: Delvotest® Fast BT is a rapid test for qualitative detection of ß-lactams and tetracycline residues in raw, comingled cow's milk. OBJECTIVE: The test kit was validated under the AOAC Performance Tested MethodSM certification program. Detection capabilities of penicillin G and tetracycline residues were determined. Also, the test method ruggedness, cross-reactivities, interference and masking effects by other antibiotic residues, influence of bacterial and somatic cells, product consistency, and stability of the test kit were studied. METHOD: The test cassette is placed in the specially designated incubator (Delvotest® Fast Start III), the milk sample is added to the loading site, and the cassette is incubated for 7 min at 50°C. The test result is read instrumentally using a specially designated reader (Delvotest® Fast Go Max). RESULTS: Measurements in the method developer study and subsequent confirmation during independent laboratory study showed detection capabilities of 2.1 ppb penicillin G and 95 ppb tetracycline. Regarding robustness, no false positives nor false negatives were found in the method ruggedness, cross-reactivity, masking, and interference studies. In addition, the test performance is not affected by a high number of bacterial or somatic cells present in the milk sample. Stability studies demonstrated good performance of the kit during the shelf life of 12 months. CONCLUSIONS: The validation study demonstrates that Delvotest® Fast BT conforms to the product performance claims and confirms the robustness of the test toward small variations in the operation parameters and normally expected variations in milk samples. HIGHLIGHTS: Delvotest® Fast BT provides users in the entire milk flow logistics from grass to glass (e.g. farmers and dairies) with a rapid and easy to use method for qualitative detection of ß-lactams and tetracycline residues in raw cow's milk.

Successive Translocation of the Rings in a [3]Rotaxane.

A [2]rotaxane, a [3]rotaxane and the corresponding thread containing two succinamide (succ) binding stations and a central redox-active pyromellitimide (pmi) station were studied. Infrared spectroelectrochemical experiments revealed the translocation of the macrocycle between the succinamide station and the electrochemically reduced pmi station (radical anion and dianion). Remarkably, in the [3]rotaxane, the rings can be selectively translocated. One-electron reduction leads to the translocation of one of the two macrocycles from the succinamide to the pyromellitimide station, whereas activation of the shuttle through two-electron reduction results in the translocation of both macrocycles: the dianion, due to its higher electron density and hence greater hydrogen-bond accepting affinity, is hydrogen bonded to both macrocycles. Systems with such an on-command contraction are known as molecular muscles. The relative strengths of the binding between the macrocycle and the imide anions could be estimated from the hydrogen-bond-induced shifts in the C=O stretching frequencies of hydrogen-bond accepting amide groups of the macrocycle.

Infrared study of intercomponent interactions in a switchable hydrogen-bonded rotaxane.

The macrocycle in rotaxane 1 is preferentially hydrogen bonded to the succinamide station in the neutral form, but can be moved to the naphthalimide station by one-electron reduction of the latter. The hydrogen bonding between the amide NH groups of the macrocycle and the C double bond O groups in the binding stations in the thread was studied with IR spectroscopy in different solvents in both states. In addition, the solvent effect on the vibrational frequencies was analyzed; a correlation with the solvent acceptor number (AN) was observed. The conformational switching upon reduction could be detected by monitoring the hydrogen-bond-induced shifts of the nu(CO) frequencies of the C double bond O groups of the succinamide and the reduced naphthalimide stations. The macrocycle was found to shield the encapsulated station from the solvent: wavenumbers of nu(CO) bands of the C double bond O groups residing inside the macrocycle cavity remain unaffected by the solvent polarity.

Fluorescent perylene diimide rotaxanes: spectroscopic signatures of wheel-chromophore interactions.

[2]- and [3]-rotaxanes with a tetraphenoxy perylene diimide core were synthesized. Hydrogen bonding between the wheel and the imide changes the optical properties of the perylene chromophore: the absorption and fluorescence spectra are red-shifted. The decay times of the rotaxanes are shorter in comparison with that of the axle. Single molecule fluorescence measurements reveal relatively narrow distributions of emission maxima and decay times. The averages are in agreement with ensemble measurements. The observed red shifts make the perylene diimide a suitable chromophore for sensing the position of the wheel on the axle.

Reverse shuttling in a fullerene-stoppered rotaxane.

The preparation and characterization of a solvent-switchable rotaxane that shuttles in the opposite direction to that expected are reported. The reverse shuttling is confirmed by NMR spectroscopy and can be monitored by cyclic voltammetry. The electrochemically generated anions on the fullerene moiety are stabilized by the closer proximity of the macrocycle.