Theoretical principles and applications of high performance capillary electrophoresis

Abstract

This book chapter is aimed at addressing the theoretical principles and applications of capillary electrophoresis (CE) for the separation of high intensity artificial sweeteners. Electrophoresis is a technique in which solutes are separated by their movement with different rates of migration in the presence of an electric field. Capillary electrophoresis emerged as a combination of the separation mechanism of electrophoresis and instrumental automation concepts in chromatography. Its separation mainly depends on the difference in the solutes migration in an electric field caused by the application of relatively high voltages, thus generating an electro-osmotic flow (EOF) within the narrow-bore capillaries filled with the background electrolyte. Currently capillary electrophoresis is a very powerful analytical technique with a major and outstanding importance in separations of compounds such as amino acids, chiral drugs, vitamins, pesticides etc., because of simpler method development, minimal sample volume requirements and lack of organic waste. The main advantage of capillary electrophoresis over conventional techniques is the availability of the number of modes with different operating and separation characteristics include free zone electrophoresis and molecular weight based separations (capillary zone electrophoresis), micellar based separations (micellar electrokinetic chromatography), chiral separations (electrokinetic chromatography), isotachophoresis and isoelectrofocusing makes it a more versatile technique being able to analyse a wide range of analytes. The ultimate goal of the analytical separations is to achieve low detection limits and CE is compatible with different external and internal detectors such as UV or photodiode array detector (DAD) similar to HPLC. CE also provides an indirect UV detection for analytes that do not absorb in the UV region. Besides the UV detection, CE provides five types of detection modes with special instrumental fittings such as Fluorescence, Laserinduced Fluorescence, Amperometry, Conductivity and Mass spectrometry. Infact, the lowest detection limits attained in the whole field of separations are for CE with laser induced fluorescence detection. Regarding the applications of CE, the separation and determination of high intensity sweeteners were discussed in this chapter. The materials which show sweetness are divided into two types (i) nutritive sweeteners and (ii) non-nutritive sweeteners. The main nutritive sweeteners include glucose, crystalline fructose, dextrose, corn sweeteners, honey, lactose, maltose, invert sugars, concentrated fruit juice, refined sugars, high fructose corn syrup and various syrups. Non-nutritive sweeteners are sub-divided into two groups of artificial sweeteners and reduced polyols. On the other hand, based on their generation; artificial sweeteners can further be divided into three types as (a) first generation artificial sweeteners which includes saccharin, cyclamate and glycyrrhizin (b) second generation artificial sweeteners are aspartame, acesulfame K, thaumatin and neohesperidinedihydrochalcone (c) neotame, sucralose, alitame and steviol glycosides falls under third generation artificial sweeteners. Artificial sweeteners are also classified into three types based on their synthesis and extraction: (i) synthetic (saccharin, cyclamate, aspartame, acesulfame K, neotame, sucralose, alitame) (ii) semi-synthetic (neohesperidinedihydrochalcone) and (iii) natural sweeteners (steviol glycosides, mogrosides and brazzein protein). Polyols are other groups of reduced-calorie sweeteners which provide bulk of the sweetness, but with fewer calories than sugars. The commonly used polyols are: erythritol, mannitol, isomalt, lactitol, maltitol, xylitol, sorbitol and hydrogenated starch hydrolysates (HSH). The studies revealed that capillary electrophoresis was successfully used for the separation of high intensity artificial sweeteners such as neotame, sucralose and steviol glycosides. Additionally, the available methods for the other artificial sweeteners using capillary electrophoresis were reviewed besides the above indicated sweeteners.