フッ化物は、歯の脱灰を防ぐ効果があり、歯のエナメル質の再石灰化をサポートすることが示されています[1,2]。飲料水、牛乳、または塩のフッ素化に加えて、フッ化物はフッ化物錠剤、歯磨き粉、マウスウォッシュ、ジェルとしても使用されます[2,3]。しかし、その効果は濃度や用量に大きく依存し、過剰摂取やフルオローシスを避けるためにも重要です[2]。
イオンクロマトグラフィ（IC）などの分析方法が、フッ化物錠剤が米国薬局方および国家規準（USP-NF）で定められた品質基準を満たしていることを保証するために使用されています。
抑制導電度検出を備えたICは、USPによってナトリウムフッ化物錠剤のフッ化物含有量を定量化するための検証された方法として承認されています[4]。Metrosep A Supp 16 - 250/4.0 カラムを使用し、水酸化物溶出剤を適用することで、フッ化物とアセテートの必要な分離が提供されます。資格はUSP一般章[5–7]に従って実施され、すべての受容基準がUSPモノグラフ「ナトリウムフッ化物錠剤」[4]から満たされました。
The system suitability solution and the standard solutions are prepared from a USP Sodium Fluoride RS certified standard by dilution with ultrapure water (UPW). The system suitability solution contains 2.0 µg/mL sodium fluoride (NaF) and 1.0 µg/mL of sodium acetate. The standard solutions contain 2.0 µg/mL NaF.
Samples were prepared from ground sodium fluoride tablets. A 0.215 g portion of the powder was accurately weighed and transferred into a 1000 mL volumetric flask. The flask was subsequently filled up to the mark with UPW.
To ensure complete dissolution, the mixture underwent ultrasonic agitation for 10 minutes. The resulting solution was then subjected to filtration using a 0.2 µm pore size membrane filter. The filtered solution was diluted 1:10 with UPW to achieve a final concentration of 2.0 µg/mL NaF.
Samples and standard solutions were injected directly into the IC using an 858 Professional Sample Processor (Figure 1).
Fluoride was separated from acetate by applying a binary potassium hydroxide gradient (Tables 1 and 2) and using the Metrosep A Supp 16 column (L91) followed by chemically suppressed conductivity detection.
Table 1. Requirements for the IC method as per USP Monograph «Sodium Fluoride Tablets» [4].
| Column with L91 packing | Metrosep A Supp 16 - 250/4.0 |
|---|---|
| Flow rate | 1.0 mL/min |
| Eluent | A: 100 mmol/L Potassium hydroxide B: Ultrapure water |
| Temperature | 40 °C |
| Injection volume | 20 μL |
| Detection | Suppressed conductivity |
Table 2. Binary gradient program for USP Monograph «Sodium Fluoride Tablets» [4].
| Time (minutes) | Eluent A (%) | Eluent B (%) |
|---|---|---|
| 0.0 | 15 | 85 |
| 7.0 | 15 | 85 |
| 8.0 | 80 | 20 |
| 15.0 | 80 | 20 |
| 15.1 | 15 | 85 |
| 25.0 | 15 | 85 |
The IC method presented for fluoride determination in sodium fluoride tablets was qualified according to the general requirements of USP and the USP Monograph «Sodium Fluoride Tablets» [4–7].
The appropriate separation of fluoride and acetate on the A Supp 16 column was achieved by applying a hydroxide gradient (Table 3). The chromatogram is shown in Figure 2.
The relative retention times (rG, unadjusted) for fluoride and acetate are 1.0 and 1.3, respectively. These unitless values are automatically calculated with the MagIC Net software by applying the following formula:
rG = relative retention time, unadjusted
tRi = retention time peak of interest
tRst = retention time peak of reference peak (peak corresponding to the substance to be examined, sodium fluoride)
Table 3 shows that the system suitability criteria are met, including resolution, tailing factor, and relative standard error (RSD) of multiple standard injections [4].
Table 3. System suitability test requirements and results from the study.
| Parameter | Actual | USP requirement | Status |
|---|---|---|---|
| Resolution fluoride/acetate | 3.7 | NLT 1.5 | Pass |
| Tailing factor for fluoride | 1.4 | NMT 2.0 | Pass |
| RSD fluoride (%, n=5) | 0.4 | NMT 2.0 | Pass |
The calibration for the sample analysis was performed using a single standard at 2.0 μg/mL NaF injected six times. The sample was analyzed in duplicate and fulfilled the respective USP validation criteria as shown in Table 4.
Table 4. Sample test showing the calculated percentage of the labeled amount of sodium fluoride (NaF) in the used tablets reached in the analysis.
| Parameter | Actual | USP requirement | Status |
|---|---|---|---|
| Fluoride sample [%] | 99.4 | 90–110 | Pass |
Ion chromatography (IC) has successfully passed the qualification tests for quantifying the fluoride content in pharmaceutical tablets, in full compliance with the USP Monograph «Sodium Fluoride Tablets». The qualification was conducted in accordance with the guidelines set by the USP.
Regarding system suitability and sample analysis, the IC method passed all predefined acceptance criteria including resolution, tailing factor, and the relative standard deviation for repeated standard injections as well as for the sample result. Consequently, ion chromatography has qualified as a reliable and highly automated method for fluoride quantification in pharmaceutical compounds, offering both user-friendliness and accurate results.
- Pollick, H. The Role of Fluoride in the Prevention of Tooth Decay. Pediatric Clinics of North America 2018, 65 (5), 923–940. https://doi.org/10.1016/j.pcl.2018.05.014.
- Yeung, C. A. A Systematic Review of the Efficacy and Safety of Fluoridation. Evid Based Dent 2008, 9 (2), 39–43. https://doi.org/10.1038/sj.ebd.6400578.
- ADA Science & Research Institute, LLC. Fluoride: Topical and Systemic Supplements. Department of Scientific Information, Evidence Synthesis & Translation Research, ADA Science & Research Institute, LLC. 2023.
- U. S. Pharmacopeia/National Formulary. USP Monographs, Sodium Fluoride Tablets; USP/NF, Rockville, MD, USA.
- U. S. Pharmacopeia/National Formulary. <621> Chromatography. In General Chapter; USP/NF, Rockville, MD, USA.
- U. S. Pharmacopeia/National Formulary. General Chapter, <1065> Ion Chromatography; USP-NF: Rockville, MD, USA, 2023. https://doi.usp.org/USPNF/USPNF_M897_01_01.html.
- U. S. Pharmacopeia/National Formulary. General Chapter, <1225> Validation of Compendial Procedures; USP-NF: Rockville, MD, USA, 2023. https://doi.org/10.31003/USPNF_M99945_04_01.
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