Determination of Inositol Phosphates in Dried Distillers Grains with Solubles

Significance of the Topic

Inositol phosphates, particularly phytic acid (InsP₆), are the main storage form of phosphorus in plant-derived materials and play a critical role in animal nutrition when used in feedstocks such as dried distillers grains with solubles (DDGS). Understanding the degree of phytate hydrolysis and the profile of InsP₂–InsP₆ isomers in DDGS is essential for optimizing phosphorus bioavailability, improving feed formulation, and reducing environmental phosphorus excretion.

Objectives and Study Overview

This work aimed to develop a rapid, reliable sample preparation and ion‐chromatographic method for the determination of InsP₂–InsP₆ isomers in DDGS. Key objectives included simplifying extraction using OnGuard II cartridges, achieving baseline separation of up to 25 inositol phosphate isomers on a Dionex CarboPac PA100 column, and validating method performance in terms of linearity, detection limits, recovery, and precision.

Methodology and Instrumentation

Sample Preparation and Cleanup

• Extraction: DDGS samples were extracted with 0.5 M HCl, sonicated, and centrifuged.
• OnGuard II Cartridges: A series of RP and Ag/H cartridges removed hydrophobic interferences and chloride ions, eliminating resin capture/release steps.
• Filtration: Final filtrate passed through 0.2 µm PES filters and diluted 1:4 prior to analysis.

Chromatographic Separation and Detection

• Instrument: Thermo Scientific Dionex ICS-5000+ HPIC system with SP/DP pump, DC detector compartment, and AS-AP autosampler controlled by Chromeleon CDS v7.1.
• Column: Dionex CarboPac PA100 guard (4 × 50 mm) and analytical (4 × 250 mm) at 30 °C.
• Eluent: Gradient of DI water (A) and 0.5 M HCl (B), 1.0 mL/min flow.
• Postcolumn Reaction: 1% Fe(NO₃)₃·9H₂O in 0.33 M HClO₄ at 0.4 mL/min.
• Detection: UV absorbance at 290 nm.

Main Results and Discussion

The optimized HCl gradient achieved separation of 25 InsP isomers within 42 min, with isomers eluting in order of increasing phosphorylation. OnGuard II cartridge treatment removed early-eluting hydrophobic compounds and minimized column overload from chloride. Linearity (r² > 0.999) was demonstrated over 3.1–200 mg/L (InsP₄ and InsP₅) and 10–300 mg/L (InsP₆). LOD and LOQ were approximately 1.0 and 3.2 mg/L, respectively. Recovery of InsP₆ averaged 95.3% across cartridge steps; spike recoveries in DDGS ranged from 98% to 106%. Interday precision for InsP₆ was 2.8% RSD; retention time RSDs for all detected isomers were <0.15% and peak area RSDs <10%. Analysis of DDGS revealed InsP₂–InsP₆ distribution consistent with literature, with InsP₆ content around 2.0 mg/g on a dry matter basis.

Benefits and Practical Applications

The method provides a streamlined workflow for profiling inositol phosphates in complex matrices, reducing sample preparation steps and lowering chemical consumption. It enables feed producers and research laboratories to monitor phosphorus bioavailability accurately, optimize phytase supplementation, and support quality control in biofuel coproducts.

Future Trends and Applications

Further improvements may include alternative eluents such as methanesulfonic acid to reduce baseline drift, automation of cartridge conditioning, and extension to other plant-based feeds. High-resolution MS detection could augment isomer identification, and integration with real-time data analytics may support process monitoring in biofuel and feed production.

Conclusion

A robust ion‐chromatographic method with OnGuard II sample cleanup successfully separated and quantified 25 inositol phosphate isomers in DDGS. The approach delivers high sensitivity, accuracy, and precision, facilitating improved understanding of phosphorus availability in animal feeds.

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