ANALYSIS OF FREE INOSITOL STEREOISOMERS IN DIETARY SUPPLEMENTS AND FOODS BY HYDROPHILIC LIQUID CHROMATOGRAPHY

Importance of the topic

Free inositol stereoisomers (nine known cyclic hexahydroxy stereoisomers, notably myo- and D-chiro-inositol) are biologically active compounds implicated in glucose metabolism, insulin sensitivity, and conditions such as metabolic syndrome, PCOS and gestational diabetes. Rising use of inositol in dietary supplements and fortified foods creates a practical need for analytical methods that can separate and quantify multiple stereoisomers rapidly, sensitively and without complex derivatization, enabling quality control, label verification and nutritional surveillance.

Objectives and study overview

• Develop fit-for-purpose hydrophilic interaction liquid chromatography (HILIC) coupled to mass detection (QDa II / MS(/MS)) methods to separate and quantify free inositol stereoisomers simultaneously in dietary supplements and diverse food matrices (milk, plant-based milks, infant formula, grains).
• Demonstrate method performance: linearity, sensitivity (LOQ), selectivity versus common monosaccharides, accuracy/recovery, precision and ruggedness across columns and runs, and apply methods to commercial products.

Methodology and experimental approach

• Chromatography: HILIC gradient separations optimized (injection volume, column temperature, gradient conditions) to resolve closely eluting stereoisomer pairs (allo/muco, chiro/neo, myo/scyllo).
• Detection: QDa II mass detector (single-ion recording and MS/MS approaches used for sensitivity and selectivity); myo-inositol-d6 employed as an internal standard for quantitation.
• Calibration: Multi-point calibration using quadratic fits for each stereoisomer; correlation coefficients (R2) typically ≥0.997 (most ≥0.999), demonstrating excellent linearity across the working ranges.
• LOQ and sensitivity: Limits of quantitation in solvent were low (approx. 0.09–0.9 µg/mL depending on isomer); LOQs in complex matrices (e.g., whole milk) increased modestly but remained fit for purpose (matrix LOQs reported around 0.2–0.3 µg/mL for some analytes).
• Sample preparation: Simple extraction/sample cleanup tailored to matrix (dilution and aqueous/organic handling appropriate for HILIC); spiking experiments performed for accuracy and precision assessment.
• Selectivity testing: Evaluated potential interferences from common monosaccharides (glucose, fructose, galactose, mannose); no significant interference observed under the developed conditions.

Instrumentation used

• ACQUITY Arc Premier UPLC (method platform referenced).
• ACQUITY QDa II mass detector (single quadrupole MS detector) used for targeted inositol monitoring.
• Waters BEH-type HILIC stationary phases and associated column formats (multiple column batches/formats tested for ruggedness).

Main results and discussion

• Chromatographic separation: Adequate resolution achieved for critical pairs (allo/muco ~1.6, chiro/neo ~2.3, myo/scyllo ~2.0), enabling baseline or near-baseline quantitation of individual stereoisomers.
• Linearity and calibration: Quadratic calibration models produced R2 values from ~0.997 to 0.9995 across stereoisomers, supporting accurate quantitation across the tested concentration ranges.
• LOQ and sensitivity: LOQs in solvent were low (≈0.09–0.9 µg/mL); matrix LOQs modestly higher but compatible with typical product levels.
• Accuracy and precision: Spiking experiments in supplements and foods returned recoveries generally within ~97–106% for supplements and ~96–118% across food matrices; repeatability RSDs were commonly <3% and rarely exceeded 7% in more challenging matrices.
• Ruggedness and selectivity: No statistically significant differences observed when comparing results across three different column batches/formats (tested by one-way ANOVA, α=0.05). No interference from common monosaccharides was detected, supporting method selectivity.
• Application to real samples: Method successfully quantified inositols in commercial dietary supplements (example mean concentrations reported ~2.35–3.72 µg/mL in analyzed preparations) and a range of foods (plant milks, whole milk, infant formula, grains), demonstrating broad applicability. Measured myo- and D-chiro-inositol in food samples were in the low single-digit mg per 100 g/mL range for many products, with higher values observed in fortified or specific formulations.

Benefits and practical application of the method

• Simultaneous separation and quantitation of multiple inositol stereoisomers without chemical derivatization, offering faster turnaround than typical GC-based approaches.
• Fit-for-purpose sensitivity and selectivity for routine QC of dietary supplements and food products, including matrix-prone samples such as milks and infant formula.
• Simplified workflow compatible with standard LC-MS capabilities in quality-control and research laboratories, aided by an isotopically labeled internal standard for robust quantitation.
• Demonstrated ruggedness across column batches and reasonable resistance to common interfering saccharides supports routine implementation.

Future trends and applications

• Tighter method standardization and inter-laboratory validation to enable regulatory adoption and harmonized reporting of inositol stereoisomers in foods and supplements.
• Integration of isotopically labeled standards for all major stereoisomers to improve accuracy in complex matrices.
• Use of higher-resolution or tandem MS workflows where needed to further increase selectivity for trace-level isomers in very complex matrices.
• Extension to profiling of bound/derivatized inositol forms, metabolic studies, and nutritional epidemiology where stereoisomer distribution is of biological interest.
• Automation of sample preparation and data analysis to support higher throughput testing in commercial QC environments.

Conclusion

The presented HILIC–MS(/MS) solutions provide robust, sensitive and selective approaches for simultaneous analysis of free inositol stereoisomers in dietary supplements and a variety of food matrices. Validation data indicate excellent linearity, low LOQs, high recoveries and good precision, and the methods proved applicable to real commercial products. These workflows are suitable for routine quantitation and quality control, offering a practical alternative to derivatization-based GC methods.

References

• Yang J., Harden S., Rainville P. HILIC-MS/MS Analysis of Free Inositol Stereoisomers in Foods. Application Note 720009200. Waters Corporation; 2026.
• Yang J., Harden S., Rainville P. Analysis of Free Inositol Stereoisomers in Dietary Supplements by Hydrophilic Liquid Chromatography using the Arc Premier System and ACQUITY QDa II Mass Detector. Application Note 720009186. Waters Corporation; 2025.