Separation and determination of metal cations in milk and dairy products by CE

Abstract

To prevent casein adsorption and improve between-run repeatability, a CE procedure is developed for cation analysis in milk using a modified imidazole/alpha-hydroxyisobutyric acid (HIBA) BGE system to operate at pH 6 to match the pH of milk and elevate imidazole concentration to enhance its buffer action. The procedure is shown to produce a fast, economic and efficient method for cation separation in milk with only simple dilution. Upon direct hydrodynamic injection of diluted milk sample at 8 cm for 30 s in an uncoated column with a BGE consisting of 10 mM imidazole, 10 mM HIBA and 10% methanol at pH 6.0 under +18 kV, baseline separation was achieved for K(+), Na(+), Ca(2+), Mg(2+), Mn(2+), Cd(2+), Co(2+), Ni(2+)and Zn(2+). Agreeable results at 95% confidence level were obtained using CE and inductively coupled plasma-atomic emission spectrometry (ICP-AES) for milk samples after protein removal. Baseline-resolved peaks for essential minerals were obtained for fresh and non-refrigerated reconstituted milks. Long-term stability was demonstrated by repeated determinations without rinsing and improvement in repeatability was shown by rinsing with 60 mM SDS in BGE. Information on metal speciation useful for nutritional assessment was obtained from CE to complement the ICP methods.

Recent advances in the application of capillary electromigration methods for food analysis and Foodomics

“…Different ionic low molecular compounds containing iodine 136, bromine 137 or phosphorus 138–140 were analyzed in different food matrices including tomato leaves, table salts, meat and soya samples. Also, inorganic cations were analyzed by CE with indirect detection in milk and dairy products 141 and beverages 142. In‐capillary derivatization and FASI coupled to CE was evaluated for the analysis of metals (Co(II), Cu(II), Ni(II), and Fe(II)) in wine samples using 2‐(5‐nitro‐2‐pyridylazo)‐5‐( N ‐propyl‐ N ‐sulfopropylamino)phenol as the derivatizing agent 143.…”

Rapid determination of sodium in milk and milk products by capillary zone electrophoresis

“…These results agree with those of , who reported that imidazole was capable of creating a good resolution of milk cations, in the range from 5 to 15 mM at pH 4.5. Other authors (Sze et al, 2007) reported that 10 mM imidazole allows a satisfactory sensitivity for alkali and alkaline-earth metals.…”

Food analysis: A continuous challenge for miniaturized separation techniques

“…In the field of food quality, in recent years, CE has been a fundamental technique broadly applied for the analysis of protein profiles, proteins, amino acids, immunoglobulins and peptides 55–74 and antioxidant compounds 75–89. To a lesser extent, it has also been useful for the determination of organic acids 90–96, inorganic ions 97–99, carbohydrates 100–103 and other compounds such as salicylaldehyde 104, sorbate and benzoate 105, folic acid 106, saccharine and aspartame 107, glucosinolates 108 and water‐soluble vitamins 109 in different kinds of food matrices. Analysis of amino acids is also essential in food analysis, due to the information it can provide concerning food quality, adulteration, protein composition, etc .…”