Aspartame detection systems

As in the case of aspartame, in determination of sorbitol chromatographic methodologies have been preferred, taking into account that in normal-phase partition methods the elution of alditols overlaps that of monosaccharides. In this context, flow methodologies, mainly FIA, emerged as alternative tools for automation of the determination of sorbitol while creating online strategies for the elimination of interferents in different kinds of detection systems. 

RPLC with MS detection was used for the analysis of seven artificial sweeteners (aspartame, saccharin, acesulfame-K, neotame, sucralose, cyclamate, and alitame) and one natural sweetener (stevioside). Samples were extracted using methanokwater and injected without any cleanup into the LC—MS system. Separation is carried out using a Cis column and gradient elution. Sweeteners were quantified using selective-ionization recording (SIR) at m/z 178, 397, 377, 293, 641, 312, 162, and 182 for cyclamate, sucralose, neotame, aspartame, stevioside, alitame, acesulfame-K, and saccharin, respectively, with a warfarin sodium m/z = 307) used as an internal standard [24]. For a detailed discussion of other analytical methods to determine artificial sweeteners, refer to [25]. 

Some sweeteners (aspartame, cyclamate, saccharin, and acesulfame K) were determined by CE-SIA with contactless conductivity detection (Stojkovic et al., 2013). The analyses were carried out in an aqueous running buffer consisting of 150 mM 2-(cyclo-hexylamino)ethanesulfonic acid and 400 mM tris(hydroxymethyl)aminomethane at pH 9.1 in order to render all analytes in the fully deprotonated anionic form. The four compounds were determined successfully in food samples the experimental set-up and typical analysis results are illustrated in Figure 2.9. Another SIA system combined with solenoid valves was used to automate an enzymatic method for the determination of aspartame in commercial sweetener tablets. The method involves the enzymatic conversion of aspartame to hydrogen peroxide by the chymotrypsin-alcohol oxidase system, followed by the use of 2,2-azinobis(3-ethylbenzthiazoline-6-sulfonic acid) (ARTS) as electron donor for peroxidase. Chymotrypsin and alcohol oxidase enzymes were immobilized on activated porous silica beads (Pena et al., 2004). 

A monolithic minicolumn was incorporated in a FIA manifold for the simultaneous analysis of eight analytes, including sweeteners (aspartame, acesulfame-K, saccharin) and a few preservatives and antioxidants (Garcia-Jimenez et al., 2007). The singlechannel FIA system with a short monolithic C18 column, which allowed the separation of analytes according to their retention time, was used for quantification by measuring the intrinsic UV absorption of the analytes. The system was applied to the detection in different foodstuffs and the results obtained were in agreement with a reference FiPLC method. 

A flow injection system coupled to a monolithic column has been described for the simultaneous determination of antioxidants (PG and BHA), sweeteners (potassium acesulfame, sodium saccharin, and aspartame), and preservatives (methylparaben, eth-ylparaben, propylparaben, and butylparaben), using photometric detection [56]. The monolithic column used as separation system was a 5 mm commercial precolumn of silica Cjg. The mixture was separated in only 400 s with resolution factors greater than 1.1 in all cases. Detection was accomplished by means of a DAD at the respective wavelength of each compound. The detection limit obtained for PG was 0.02 pg/mL. The method was applied to the analysis of food and cosmetic samples and the results were compared with those obtained using a conventional LC method. 

Solid-phase chemistry associated with spectrophotometric detection in flow systems is also a good alternative for the determination of aspartame in food items. In this topic, one must consider not only the utilization of solid phase exchangers or adsorbents to build flow-through optosensors [36,37,40] but also the immobilization of reagents on a solid matrix in packed reactor format [41,42], This approach has been successfully explored mainly for the analysis of analyte mixtures through the use of microcolumns... 

Cabero et al. [80] developed a method based on the conversion of cyclamate to cyclo-hexylamine and the subsequent reaction with l,2-naphthoquinone-4-sulfonate, yielding a spectrophotometrically active derivative, which is detected at 480 nm thus, other sweeteners, such as saccharin or aspartame, do not interfere in these determinations. The hydrolysis step is performed batchwise by treatment of cyclamate with hydrogen peroxide and hydrochloric acid, while the cyclohexylamine derivatization is carried out in the flow injection system (Figure 24.9). Rocha et al. [81] reported a flow system based on multicommutation for fast and clean determination of cyclamate. The procedure exploits the reaction of cyclamate with nitrite in an acidic medium and the spectrophotometric determination of the excess of nitrite by iodometry. The flow system was designed with a set of solenoid micropumps to minimize reagent consumption and waste generation (Figure 24.10). 

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