Beef, selective detection

Selective Detection of E. coli 0157 H7 in Gronnd Beef wash... 

Method development for the LC-MS analysis of HAA in meat was performed by the gronp of Galceran [83-90]. Initially, complex mnlti-step extraction and sample pretreatment methods were applied, e.g, hqnid extraction from meat, clean-up by solid-supported LLE, and ion-exchange SPE. Later on, different SPE procednres for sample clean-np were evalnated [85]. A combination of solid-supported-LLE and SPE on C18 material was most efficient in selective elution of the polar and less polar HAA. LC was first performed on a lOOxl-mm-lD Cig column (5 pm) with 50% acetonitrile in 5 nunol/1 aqueous ammonium acetate (pH 6.7) at a flow-rate of 50 pEmin. ESl-MS was applied in SIM mode, enabling detection of HAA at 1-6 pg/kg in beef extracts [83]. 

The very commonly used sorbic acid has been detected with low recoveries in raw beef (52-84%) by photometry, after distillation and extraction. Better recoveries ( 100%) and less manipulation have been achieved by the fluorescence technique in determination of 4-hydroxybenzoic methyl ester in nonalcoholic beverages. Additives can be present in combinations, and chromatographic methods are often used for selective individual or joint determination. Sorbic and benzoic acids have also been determined by thin-layer chromatography in beverages. This method involves minimal sample manipulation. HPLC is often the preferred method for determining additives present in mixtures, which are usually only just volatile. Simultaneous determination of additives, such as sweeteners, preservatives, and colorings in soft drinks is usually done by HPLC with UV... 

Trinuclear clusters have been detected in over 20 proteins as well as a number of enzymes, among them aconitase, beef heart succinate-ubiquinone oxidoreductase (120), Escherichia coli nitrate reductase (121), E. coli fumarate reductase (122), and succinate dehydrogenase (123). Selected instances of the occurrence of [3Fe-4S] clusters are listed in Table II. Because of the paramagnetic ground states of both oxidation levels, these clusters can be uniquely identified by a number of spectroscopic techniques. Among these, Mossbauer spectroscopy in applied magnetic fields (124, 128, 132, 141-143) and low temperature MCD spectroscopy (127, 138, 144-146) are decisive. While there are small spectroscopic differences among certain [3Fe-4S] centers, the similarities dominate and support the essential structure 3 for all. In a number of the earlier papers on protein... 

An example of the employment of NPs in the detection step within microfluidic systems to improve sensitivity and selectivity was the amperometric detection of five sulfonamide drugs after electrokinetic separation in beef, pork, chicken, and fish samples (Won et al., 2013). An Al203-AuNP-modified carbon paste electrode was used, placed at the end of the separation microchannel. AI2O3 was used to preconcentrate the sulfonamides through an adsorption process while, as aluminum oxide is nonconductive, AuNPs were used to enhance the performance of the modified electrode. The LODs obtained were in the 0.91-2.21 fmol range, 10 times lower than the values given by LC with fluorescence detection, and the modified electrode had a lifetime of 2 months. 

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