Determination of Galacto-Oligosaccharides in Samples by Ion Chromatography with Amperometric Detection
2026-11-17
Background
Galacto-oligosaccharides (GOS) are natural functional oligosaccharides, typically built from a galactose or glucose core carrying 1–7 galactosyl units, with degrees of polymerisation ranging from 2 to 8. In the human gut they are used by probiotics such as bifidobacteria and lactobacilli, promoting their growth and proliferation. GOS is abundant in human milk, effectively supports bifidobacteria proliferation in infants, and offers further nutritional benefits including improved mineral absorption, constipation prevention and immune support. As a result, GOS is added to many infant formula products.
Several methods exist for GOS determination: thin-layer chromatography, gas chromatography, and high-performance liquid chromatography (HPLC-ELSD, HPLC-RID and HPLC-MS). Ion chromatography is also used, and high-performance ion chromatography is the main approach for GOS in milk powder. Thin-layer chromatography requires home-made plates together with prepared developing and colouring reagents, which makes it laborious and poorly quantitative. HPLC sample preparation is also complex, usually needs several standards, and the mass spectrometric detectors involved raise the cost of analysis.
This case applies ion chromatography to the determination of GOS in samples, using a Wayeal ion chromatograph with an amperometric detector and sodium hydroxide/water eluent. Sample preparation is simple, recovery is good and sensitivity is high.
Instrument Configuration and Test Conditions
| Item | Description |
|---|---|
| Ion chromatograph | IC6300 intelligent ion chromatograph |
| Analytical column | PA20, 3 × 250 mm |
| Detector | Amperometric, gold electrode (AAA amino acids, sugars, water-soluble vitamins waveform) |
| Consumables | 0.22 µm aqueous syringe filter, 2 mL disposable syringe, 0.1 mg balance |
| Reagents | Galactose, glucose and lactose standards (1000 mg/L each); KH2PO4/K2HPO4; HPLC-grade acetonitrile; 50% NaOH; anhydrous sodium acetate; galactosidase (~150,000 U/g) |
| Parameter | Setting |
|---|---|
| Eluent | 200 mmol/L NaOH + sodium acetate, gradient |
| Flow rate | 0.4 mL/min |
| Run time | 70 min |
| Injection volume | Full-loop injection, 20 µL |
| Column temperature | 30 °C |
| Detection cell temperature | 30 °C |
Sample Preparation
An appropriate amount of sample is prepared according to GB 1903.27-2022, the national food safety standard for the food nutritional fortifier galacto-oligosaccharide. The extract is diluted to a suitable factor, filtered through a 0.22 µm aqueous filter and injected. A blank solution is run in parallel to confirm a clean baseline before quantification.
Results
Linearity: five-level calibration series were prepared for galactose, glucose and lactose. All three sugars showed correlation coefficients above 0.999, confirming good linearity over the working range.
| Sugar | Linear equation | R |
|---|---|---|
| Galactose | y = 4107.57500x + 438.01030 | 0.99938 |
| Glucose | y = 4956.41900x + 762.55520 | 0.99903 |
| Lactose | y = 2942.84300x − 506.00990 | 0.99994 |
Repeatability: a standard mixture was injected six times. Retention times were highly stable (galactose 7.144 min, glucose 7.994 min, lactose 17.322 min) with retention-time RSD of 0.435%, 0.503% and 0.758%, and peak-area RSD of 0.790%, 0.708% and 0.729% respectively. Calculated concentrations averaged 1.050, 1.001 and 1.082 mg/L against a nominal 1 mg/L, with RSD of 0.861%, 0.801% and 0.606%.
| Parameter | Galactose | Glucose | Lactose |
|---|---|---|---|
| Mean retention time (min) | 7.144 | 7.994 | 17.322 |
| Retention time RSD (%) | 0.435 | 0.503 | 0.758 |
| Peak area RSD (%) | 0.790 | 0.708 | 0.729 |
| Mean concentration (mg/L) | 1.050 | 1.001 | 1.082 |
Sample testing: three GOS samples (A0, A1 and A2) were prepared as described and quantified by external standard calibration, with consistent chromatographic profiles across the series.
Conclusion
Using a Wayeal IC6300 intelligent ion chromatograph with amperometric detection, GOS in samples can be determined qualitatively and quantitatively after simple sample preparation, chromatographic separation and external standard calibration. The method is easy to operate, repeatable and sufficiently sensitive and accurate — a practical alternative to thin-layer, gas and HPLC approaches for GOS content control in milk powder and related products.
