Sweetener Analysis (Part 1 of 3)
Determination of residues of sweeteners in fresh water
In water analysis the investigation of residues of sweeteners has gained more importance in the last few years. With the increased consumption of reduced calorie products, many sweeteners are widely distributed in the environment unchanged (without degradation). This is also true for many cosmetic products. Sweeteners are a good indicator for anthropogenic pollution of water, as well as an indicator to the degree of entry of surface water into drinking water. In the environmental analysis the investigation of sweeteners is common.
Determination of residues of sweeteners in drinking water is made either when the water quality is a crucial factor or pristine water quality is a requirement. The need for residue analysis applies to mineral water and in particular for organic mineral water. The content (orientation value) of 50 µg/L of each sweetener indicates an anthropogenic pollution in mineral water which is comparable to pollution by pesticides and pharmaceuticals. In 2015, the investigation of residues of sweeteners in mineral waters is part of the national monitoring program in Germany and the results are incorporated into health risk assessment.
This shows that efficient analytical methods are necessary for determination of sweetener residues – even in very low concentrations – which demands separation and quantification of the compounds of interest. The method development was considered on the following compounds:
Figure 1: Molecule formulas
Sample Preparation with SPE (Solid Phase Extraction)
Sweeteners are a heterogeneous group of analytes. They show clearly different polarities which is important to consider when designing a method for enrichment.
Hydrophobic polystyrene-divinylbenzene copolymer, CHROMABOND® HR-X, is often recommended for trace analysis in water. The efficiency of the enrichment of sweeteners is described in the following.
The enrichment of sweeteners in water samples is influenced by many factors such as:
- sample volume
- concentrations of analytes
- pH value of water sample
- particle size and capacity
- filling amount of polystyrene-divinylbenzene resin
With small sample volume and higher concentrations of analytes very good recovery rates are achieved for all sweeteners, see Figure 2. The enrichment of the neohesperidin dihydrochalcone (NHDC) is a little lower with 62 %. The recovery rate of NHDC could probably be improved with a larger filling amount of polystyrene-divinylbenzene resin. The influence of pH is less clear under these (analytically favorable) conditions.
Figure 2: Influence of pH value at small sample volume
Analytical Conditions: Sweeteners
SPE Column type: CHROMABOND® HR-X polypropylene columns 45 µm, 3 mL, 60 mg; Sample pretreatment: addition of 0.25 mL 1 mol/L KH2PO4 buffer pH 2.5, 3.0 or 3.5 to 10 mL 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: 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, 3.0 or 3.5); Elution: 3 mL methanol
A smaller particle size and a surface enlargement of the solid phase material are increasing the recovery rate of the most of the respective sweeteners (see Figure 3). This effect should be more distinctive with bigger test volume and smaller concentration of the sweeteners.