HPLC determination of oxalic acid using tris(1,10-phenanthroline)ruthenium(II) chemiluminescence—application to the analysis of spinach

The chemiluminescence (CL) of Ru(phen)₃²⁺ was applied to HPLC determination of oxalic acid. Oxalic acid was separated by a C₁₈ reverse-phase column with a mobile phase of 0.02 mol/l NH₄Ac. The eluted oxalic acid was mixed with 0.25 mol/l Ru(phen)₃²⁺ and 2.0 mmol/l Ce(SO₄)₂ in 0.08 mol/l H₂SO₄, and then pass through a modified luminometer used as a detector. The reaction of Ce(IV) oxidized Ru(phen)₃²⁺ and oxalic acid emitted light. The detection limit was 6.2×10⁻⁶ mol/l for oxalic acid at a S/N ratio of 3, the relative standard deviation for 5 replicate injections of 1×10⁻³ mol/l oxalic acid standard was calculated as 5.6%, and the linear calibration range was 1×10⁻⁵ to 4×10⁻³ mol/l. The method was successfully applied to determination of oxalic acid in spinach. ©     

Improving the application of SSR polymorphism analysis coupled with Lab-on-a-chip® capillary electrophoresis to assess food authenticity: Italian pigmented rice as case study

Genetic distances evaluated via SSR-based profiling can be usefully assessed by using capillary electrophoresis. In order to set up a method to distinguish pure Italian rice varieties from imported Asian blends, seven Italian rice genotypes and seven uncharacterized rice samples coming from outside Italy were studied using a classical SSR polymorphism analysis coupled with Lab-on-a-chip® microcapillary electrophoresis. A special algorithm for the elaboration of the raw outputs provided by the software was generated, thus overcoming the problems connected to the instrument intrinsic limits of resolution. The results showed that even considering just the smallest verifiable genetic distance between the employed samples, locally cultivated Italian rice varieties clustered separately from other foreign cultivars. Moreover, it was possible to clearly identify an artificial blend formed by Venere rice mixed with a black variety from Thailand, thus confirming the usefulness of this new post-analysis approach.     

Racemization of amino acids during classical and microwave oven hydrolysis — application to aspartame and a Maillard reaction system

The conventional acid hydrolysis routinely used in protein analysis induces partial racemization of the amino acids. An alternative method, using microwave heating, was evaluated with the aim of assessing its efficiency in preserving the amino acids in their original configuration. The method was employed on the dipeptide aspartame. The results showed that some advantages, implying less racemization, could be gained by using the microwave technique, but the method was applicable only at temperatures under 150°C. Mild, conventional hot oven-hydrolysis, involving a shorter hydrolysis time, could have the same mild effect. The different techniques were applied to aspartame treated at different pH, a soft drink and a Maillard reaction model system. The results showed that aspartame was insusceptible to racemization in acid and neutral environments, and not until very high pH did racemization start. The soft drink contained a small amount of d-amino acids, 0.27 mg d-asp and 0.14 mg d-phe/100 ml. The model system exhibited no racemization.