In the present study, an analytical method using capillary electrophoresis with on-line preconcentration technique was developed for rapid determination of melamine in infant formula. Both stacking and sweeping preconcentration techniques had been investigated for the comparison of their effectiveness in melamine analysis. The limit of detection of melamine standard was 0.5 ng/mL for the field amplified sample stacking (FASS) technique and 9.2 ng/mL for the sweeping technique. Although the FASS technique provided better concentration efficacy than the sweeping technique, the matrix effect was more profound with the former. Matrix effect was evaluated by comparing the enhancement factor (EF) of melamine standard and post-extraction spiked infant formula solution. The EF was changed from 429.86 +/- 9.81 to the level less than 133.31 with significant peak distortion in the FASS system, and it was remained unchanged in the sweeping system. Sweeping-micellar electrokinetic chromatography (sweeping-MEKC) was demonstrated to be most suitable for real sample analysis. Under optimum sweeping-MEKC conditions, melamine content in infant formulas could be determined within 6 min. The developed solid phase extraction (SPE) procedures coupled with the sweeping-MEKC method was subjected to method validation. Run-to-run repeatability (n = 3) and day-to-day reproducibility (n = 3) of peak area were within 3.6% and 4.8% RSD, respectively. The accuracy was tested by spiking 0.5 and 2 microg/mL of melamine standard in the melamine contaminated milk powder provided by the European Commission, and the recoveries were 93.4 +/- 0.5% and 98.7 +/- 0.4%, respectively. Results of this study show a great potential for the sweeping-MEKC method as a tool for the fast screening of melamine in infant formulas.
"Sweeping, a mode of on-line sample concentration in MEKC, uses a pseudostationary phase (in this case, micelles) to accumulate the analytes into sharp zones  . Concentration factors (CF) of one to more than three orders of magnitude can be achieved  . However, sample preparation is often required in order to convert the sample into a form which is amenable to sweeping-MEKC, in particular by the use of a diluent devoid of the micelles. "
"The effect of the acetonitrile concentration in sample on stacking was studied and optimized as organic reagent acted as accelerator for speeding up the velocities of analytes . It could be seen (Figure 3), as the percent of the acetonitrile was lower than 50%, that the baseline around MEL became unsatisfied (arrow pointed in Figure 3) for separation and quantification, although the Rs value was higher enough between the interferent and MEL (Rs > 3.5). "
[Show abstract][Hide abstract] ABSTRACT: Melamine was measured in real milk products with capillary electrophoresis (CE) based on acetonitrile-salt stacking (ASS) method. Real milk samples were deproteinized with acetonitrile at a final concentration of 60% (v/v) and then injected hydrodynamically at 50 mBar for 40.0 s. The optimized buffer contains 80.0 mmol/L pH 2.8 phosphates. Melamine could be detected within 20.0 min at +10 kV with a low limit of detection (LOD) of 0.03 μmol/L. Satisfactory reproducibility (inter- and intraday RSD% both for migration time and peak area was lower than 5.0%) and a wide linearity range of 0.05 μmol/L ~ 10.0 μmol/L were achieved. The proposed method was suitable for routine assay of MEL in real milk samples that was subjected to a simple treatment step.
Journal of Analytical Methods in Chemistry 08/2014; 2014:212697. DOI:10.1155/2014/212697 · 0.79 Impact Factor
"Most reported methods are based on liquid chromatography coupled with mass spectrometry (Wang et al., 2007; Ge et al., 2011b) and gas chromatography/tandem mass spectrometry (Miao et al., 2009; Wu et al., 2009). Other techniques include sweeping-micellar electrokinetic chromatography (Tsai et al., 2009), high performance cation-exchange chromatography (Ono et al., 1998), capillary zone electrophoresis with diode array detection (Xia et al., 2010), spectrophotometric absorption measurement at 214 nm using Mannich reaction (Rima et al., 2009), Raman spectrometry (Cheng et al., 2010) and enzyme linked immunosorbent assay (Liu et al., 2010a; Liu et al., 2010b). Another amine reported in this study, 4-aminobiphenyl (4-ABP) has received less recent attention but is nevertheless, a potent human carcinogen according to International Agency for Research on Carcinogenicity (IARC, 1987). "
[Show abstract][Hide abstract] ABSTRACT: Colloidal nanoparticles of gold and silver were used in Surface-Enhanced Raman Scattering (SERS) analysis of melamine and 4-aminobiphenyl. Gold colloids allowed the SERS detection of melamine at levels below 0.1 μg/L using a previously unreported SERS peak at 275 cm<sup align="right"> −1 </sup> and yielded better detection limits compared to silver colloids. For 4-aminobiphenyl, the detection limits were found to be similar for both colloids at 0.05-0.1 mg/L. Analysis by transmission electron microscopy showed that the morphology of both Ag and Au nanoparticles were uniformly spherical with average diameters that were 69.3 ± 23.1 nm and 41.6 ± 19.1 nm, respectively. The SERS spectral intensities of both compounds were found to increase as the sample pH increased. The optimal signals were obtained at pH = 8.5 for 4-aminobiphenyl and pH = 11.5 for melamine. The enhancement factors for the determination of melamine are in range of 3.5 × 10<sup align="right"> 4 </sup>-6.3 × 10<sup align="right"> 4 </sup> for the silver colloid and 5.2 × 10<sup align="right"> 7 </sup>-2.1 × 10<sup align="right"> 9 </sup> for the gold colloid.
International Journal of Environmental Technology and Management 01/2013; 16(1/2):3 - 20. DOI:10.1504/IJETM.2013.050681
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