Cyclamate detection systems

Since cyclamate has poor UV absorbing characteristics, HPLC methods for the analysis of this sweetener require specific detection systems, such as indirect photometry or conductivity. Herrmann et al. (24) used indirect photometry for the detection of cyclamate at 267 nm against a UV-absorbing mobile-phase component, p-toluenesulphonate. Biemer (17) and Wu et al. (47) used a conductivity detector for the determination of cyclamate. According to Biemer (17) the use of this detector offers distinct advantages, since compounds coeluting with cyclamate may not exhibit an electrochemical response and, hence, not appear in the chromatogram. 

Nasraoui, R., D. Floner, C. Paul-Roth, and F. Geneste. Flow electroanalytical system based on cyclam-modified graphite felt electrodes for lead detection. J. Electroanal. Chem. 638, 2010 9-14. 

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). 

No methods could be found in the literature for the individual flow analysis determination of acesulfame-K. The first flow analysis method for acesulfame-K was proposed by Nikolelis et al. 2001 [72]. This method allowed the electrochemical flow injection monitoring and analysis of mixtures of acesulfame-K, cyclamate, and saccharin using stabilized systems of filter-supported bilayer lipid membranes (BLMs). Detection consisted of t time-dependent appearance of a transient ion current peak in which the time-dependence could be used to distinguish the presence of different artificial sweeteners, and the peak magnitude was related to the concentration of the artificial sweetener. The BLM-based system is able to monitor each artificial sweetener in mixtures. The apparatus for the formation of stabilized BLMs is shown in Figure 24.4. The method also offers response times of less than 1 min, which are the fastest times reported for any similar... 

Cyclamate salts are not readily detected by spectroscopic techniques. So, a chemical derivatization is often performed in order to improve the characteristics of cyclamate for detection. Two spectrophotometric FIA methods were proposed. Gouveia et al. [79] proposed a procedure based on the reaction of cyclamate with an excess of nitrite solution. The unconsumed excess of nitrite is monitored spectrophotometrically using the Griess reaction to eliminate interference caused by dye additives, an alumina column was incorporated into the flow system and used for both colorless and colored samples. 

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). 

Only two flow analysis methods have been published for multianalyte determination including cyclamate as analyte. Both methods determine cyclamate with other artificial sweeteners. One of them used stabilized systems of filter-supported BLMs in a FIA manifold [72], and the other is based on CE with contactless conductivity detection employing a sequential injection manifold based on a syringe pump [77]. 

Saccharin is also determined with FIA methodologies, which allow multianalyte determination. These methodologies include methods cited previously for acesulfame-K and/or cyclamate a method based on electrochemical detection of these three artificial sweeteners using stabilized systems of filter-supported BLMs [72] online dialysis for sample pretreatment prior to the simultaneous determination of saccharin and caffeine, benzoic acid, and sorbic acid by HPLC-FID [76] and molecular spectroscopic methods in the UV region based on the transient retention of analytes on solid phases, silica Cjg [74], and quaternary amine ion exchanger [75]. 

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