Overview
ISO 21458:2008 specifies a validated analytical method for the determination of glyphosate and its major metabolite AMPA (aminomethylphosphonic acid) in drinking water, ground water and surface water. The procedure uses derivatization with 9‑fluorenylmethyl chloroformate (FMOCCl) followed by high performance liquid chromatography (HPLC) and fluorometric detection. The method achieves a lowest limit of determination of about 0.05 µg/L and can be applied to other water types after appropriate validation.
Key topics and technical requirements
- Analytical principle: Derivatization of glyphosate and AMPA with FMOCCl in basic conditions, followed by HPLC separation and fluorescence detection.
- Detection: Fluorescence detector (example wavelengths: excitation 260 nm, emission 310 nm as indicated).
- Chromatography:
- Polar-phase column recommended (e.g., silica‑bonded NH; 3–5 µm particles; 2–4.6 mm i.d.; 250 mm length). Reverse‑phase C18 columns may also be used with adapted conditions.
- Mobile phase example: mix of acetonitrile and potassium dihydrogenphosphate buffer (document gives a 30:70 ratio by volume).
- Calibration and quantification: External calibration, internal standard or standard addition; method includes calibration, evaluation and expression of results.
- Sample handling and storage:
- Use polyolefin bottles; add sodium thiosulfate when free chlorine is present.
- Store samples at 4 °C (dark) up to 1 week or frozen (≥ −20 °C) for up to 1 month.
- Limitations and interferences:
- Potential overlapping peaks from co‑eluting fluorescent compounds; evaluation needed for surface waters.
- Divalent cations (Ca2+, Cu2+, Fe2+/3+, Zn2+) may complex analytes and cause underestimation - pretreatment recommended if hardness > 3 mmol/L.
- Sample pretreatment options (examples in the standard):
- Acidification to pH 1 then neutralization.
- Oxalic acid treatment (pH 2–3) then neutralization.
- Borate/EDTA treatment and refrigerated equilibration.
- Derivatization workflow: typical aliquot (3 mL), addition of internal standard, borate buffer, diethyl ether extraction, FMOCCl reaction (≈60 min), quench with phosphoric acid.
Applications and users
ISO 21458:2008 is used by:
- Environmental and public‑health laboratories testing water quality for regulatory compliance and monitoring glyphosate residues.
- Water utilities and consultants assessing contamination in drinking water, groundwater and surface water.
- Research laboratories studying pesticide fate and environmental monitoring programs.
Practical applications include routine monitoring, incident response, and method validation studies where sensitive quantification (≈0.05 µg/L) of glyphosate and AMPA is required.
Related standards
Normative references cited in ISO 21458:2008 include:
- ISO 3696 - Water for analytical laboratory use
- ISO 6058 / ISO 6059 - Water hardness (calcium, magnesium) titrimetric methods
- ISO 8466‑1 - Calibration and evaluation of analytical methods
Keywords: ISO 21458:2008, glyphosate, AMPA, HPLC, fluorometric detection, water quality, derivatization, FMOCCl, drinking water testing, limit of determination.
