Chromatography

Sweetener Analysis (Part 2 of 3)

Figure 3: Influence of the particle size

Sweetener Analysis 4

Conditions:

SPE Column type: CHROMABOND® HR-X polypropylene columns 45 µm or 85 µm, 3 mL, 60 mg; Sample pretreatment: addition of 0.25 mL 1 mol/L KH2PO4 buffer pH 2.5 to 10 mL water sample solution; Conditioning: 3 mL methanol, 3 mL KH2PO4 buffer (25 mmol/L pH 2.5) (with a flow of 1–2 mL/min); Sample application: 10 mL,  c = 5 ng/mL each of the respective standards (with a flow of 1–2 mL/min); Washing: 4 mL  KH2PO4 buffer (25 mmol/L pH 2.5); Elution: 3 mL methanol

In particular with small contents of sweetener pollutions the sample volume must be increased to correspond to regulation limits and detection limits. Figure 4 shows that sucralose, saccharin and NHDC have better recovery rates with a pH value at 2.5 on CHROMABOND® HR-X. For advantame, neotame and aspartame the enrichment works at all tested pH values, however, in contrast to the other sweeteners the pH 3.0 or pH 3.5 are better for SPE. To achieve the best results for the most part of the respective sweeteners, it is recommended pH 2.5

Figure 4: Influence of the pH value at 1 L sample volume

Sweetener Analysis 5

Conditions:

SPE Column type: CHROMABOND® HR-X polypropylene columns 45 µm, 3 mL, 60 mg; Sample pretreatment: addition of 25 mL 1 mol/L KH2PO4 buffer pH 2.5, 3.0 or 3.5 to 1 L water sample solution; Conditioning: 3 mL methanol, 3 mL KH2PO4 buffer (25 mmol/L pH 2.5, 3.0 or 3.5 ) (with a flow of 1–2 mL/min); Sample application: 1 L,  c = 50 µg/L each of the respective standards (with a flow of 5–10 mL/min); Washing: 4 mL  KH2PO4 buffer (25 mmol/L pH 2.5, 3.0 or 3.5); Elution: 3 mL methanol

Another important parameter for SPE is the filling amount of polystyrene-divinylbenzene resin in the cartridge. As expected, an improvement of the recovery rates could be confirmed with higher filling amounts for some critical sweeteners like saccharin, sucralose and aspartame. For acesulfame and cyclamate the enrichment doesn´t work under the tested conditions.

Figure 5: Influence of the filling amount of HR-X resin at 1 L sample volume

Sweetener Analyis 6

Conditions:

SPE Column type: CHROMABOND® HR-X polypropylene columns 45 µm, 3 mL, 60 mg, 100 mg or 200 mg; Sample pretreatment: addition of 25 mL 1 mol/L KH2PO4 buffer pH 2.5 to 1 L water sample solution; Conditioning: 3 mL methanol, 3 mL KH2PO4 buffer (25 mmol/L pH 2.5) (with a flow of 1–2 mL/min); Sample application: 1 L, c = 50 µg/L each of the respective standards (with a flow of 5–10 mL/min); Washing: 4 mL KH2PO4 buffer (25 mmol/L pH 2.5); Elution: 3 mL methanol; For 100 mg and 200 mg filling amount the volume of 3 mL is increased to 5 mL for conditioning, equilibration and elution.

Finally, it could be shown that an enrichment of sweeteners in fresh water with CHROMABOND® HR-X is well possible for 6 of the 8 respective analytes. Table 1 contains an overview of the recovery rates with 1 L of sample volume and with pH 2.5.

Table 1: Optimal recovery rates
(pH 2.5, filling amount 200 mg)
Substance Recovery rate [%]
Acesulfame 8
Aspartame 86
Cyclamate 15
NHDC 84
Saccharin 57
Sucralose 70
Advantame 95
Neotame 92
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Sweetener Analysis (Part 1 of 3)

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Sweetener Analysis (Part 3 of 3)

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