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Objective <p>This study aimed to determine the minimum toenail mass needed for reliable fluoride analysis, and to compare fluoride extraction efficiency (%FE) using two protocols.</p> Methods <p>Toenail samples (n = 98 from 11 participants) were grouped into masses ranging from 1.0 to 5.0&#xa0;mg (± 0.5&#xa0;mg). Fluoride content was analyzed using a hexamethyldisiloxane(HMDS)-facilitated diffusion method and a fluoride-ion selective electrode. Pooled toenail samples (3.0 ± 0.5&#xa0;mg) from four participants were analyzed using two protocols: protocol-A used 1&#xa0;mL of HMDS-saturated 3N sulfuric acid/2&#xa0;mL DI water; and protocol-B used 3&#xa0;mL/3&#xa0;mL. Samples were re-analyzed twice to calculate %FE. Minimum mass-threshold was determined by intraclass correlation coefficients (ICC) with 95%-confidence intervals (CI) from linear mixed-effects models and change-point analysis, accounting for intra-participant variability. F-tests compared the variance in %FE between protocols.</p> Results <p>Fluoride content ranged from 0.82 to 9.22&#xa0;µg/g. Excellent reliability (ICC = 0.90, 95%CI:[0.71, 0.95]) was observed in samples ≥ 2.5&#xa0;mg. A change-point was identified at 2.20&#xa0;mg(95%CI:[1.70, 2.70&#xa0;mg]). A less variable %FE was observed with protocol-A (43–58%) compared to protocol-B (38–80%) (F-ratio = 0.23, p = 0.02).</p> Conclusion <p>Toenail sample mass affects the reliability of fluoride analysis. The use of a minimum toenail mass of about 2.2–2.5&#xa0;mg increases the reliability of fluoride analysis at the participant level. Variability in %FE should be considered in future efforts to standardize analytical protocols.</p>

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Impact of sample mass on the reliability of toenail fluoride for exposure assessment

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2026年4月27日

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  • Guillermo Tamayo-Cabeza,
  • Michael Zenni,
  • Gina A. Castiblanco-Rubio,
  • Frank Lippert,
  • David B. Flora,
  • Janet L. Peacock,
  • Christine Till,
  • Carly V. Goodman,
  • Bruce P. Lanphear,
  • Susan A. Korrick,
  • Margaret R. Karagas,
  • E. Angeles Martinez-Mier

摘要

Objective

This study aimed to determine the minimum toenail mass needed for reliable fluoride analysis, and to compare fluoride extraction efficiency (%FE) using two protocols.

Methods

Toenail samples (n = 98 from 11 participants) were grouped into masses ranging from 1.0 to 5.0 mg (± 0.5 mg). Fluoride content was analyzed using a hexamethyldisiloxane(HMDS)-facilitated diffusion method and a fluoride-ion selective electrode. Pooled toenail samples (3.0 ± 0.5 mg) from four participants were analyzed using two protocols: protocol-A used 1 mL of HMDS-saturated 3N sulfuric acid/2 mL DI water; and protocol-B used 3 mL/3 mL. Samples were re-analyzed twice to calculate %FE. Minimum mass-threshold was determined by intraclass correlation coefficients (ICC) with 95%-confidence intervals (CI) from linear mixed-effects models and change-point analysis, accounting for intra-participant variability. F-tests compared the variance in %FE between protocols.

Results

Fluoride content ranged from 0.82 to 9.22 µg/g. Excellent reliability (ICC = 0.90, 95%CI:[0.71, 0.95]) was observed in samples ≥ 2.5 mg. A change-point was identified at 2.20 mg(95%CI:[1.70, 2.70 mg]). A less variable %FE was observed with protocol-A (43–58%) compared to protocol-B (38–80%) (F-ratio = 0.23, p = 0.02).

Conclusion

Toenail sample mass affects the reliability of fluoride analysis. The use of a minimum toenail mass of about 2.2–2.5 mg increases the reliability of fluoride analysis at the participant level. Variability in %FE should be considered in future efforts to standardize analytical protocols.