Liu 2010 — Mercury in white vinegar by photochemical vapor generation AFS
This paper presents a method development and validation study for the direct determination of total mercury in white vinegar by atomic fluorescence spectrometry (AFS) using matrix-assisted photochemical vapor generation, exploiting the acetic acid matrix to photochemically reduce Hg(II) to Hg0 under UV irradiation without any sample pretreatment. The method achieved a detection limit of 0.08 µg/L and was validated against certified reference materials and ICP-MS results, showing no significant difference between methods at 95% confidence. Of three commercial white vinegars tested, two were below the detection limit and one contained 1.8–2.0 µg/L mercury (mean of AFS and ICP-MS), indicating that mercury contamination in white vinegar is generally very low.
Key numbers
LOD: 0.08 µg/L (AFS, photochemical vapor generation). ICP-MS LOD after acid digestion: 0.06 µg/L. RSD: 4.6% (intra-day, n=9), 7.8% (inter-day, n=9) at 5 µg/L. Spike recovery: 92–98%.
Sample results (Table 2):
- White vinegar 1 (acidity 3.5%): n.d. (<0.08 µg/L by AFS, <0.06 µg/L by ICP-MS)
- White vinegar 2 (acidity 3.95%): n.d.
- White vinegar 3 (acidity 4.0%): 1.8 ± 0.2 µg/L (AFS), 2.0 ± 0.3 µg/L (ICP-MS)
Reference material validation:
- GBW(E) 080392 (certified 10 ± 0.1 µg/L): measured 9.6 ± 0.5 (AFS), 9.2 ± 0.3 (ICP-MS)
- GBW(E) 080393 (certified 100 ± 1 µg/L): measured 93 ± 2.3 (AFS), 91 ± 4.0 (ICP-MS)
No organomercury compounds (MeHg, EtHg) detected in real samples by C18 HPLC speciation method.
Methods (brief)
Photochemical vapor generation AFS (AFS-9800, Beijing Haiguang Instrument): PTFE reactor coil (3 m × 0.5 mm i.d.) under 20W UV lamp; argon carrier gas at 300 mL/min; 3% v/v acetic acid as photoreductant (optimized); 30 s irradiation time. White vinegar introduced directly without pretreatment. Sugar in non-white vinegars causes >10% interference at 1% v/v; method restricted to white vinegar (no added sugar). ICP-MS (Agilent 7500ca): acid digestion with HNO3/H2O2 at 180°C for 1h in closed Teflon bomb. Mercury speciation by HPLC-AFS (C18 column, direct injection); no organomercury found. Matrix effects from Fe (up to 20 mg/L), Co and Cu (up to 10 mg/L), Ni (up to 1 mg/L): no significant interference.
Note: This is a methods paper with a small (n=3) real-sample application. The mercury concentrations are used to demonstrate method performance rather than as a systematic occurrence survey. The one positive sample (2 µg/L) represents total mercury; speciation confirms no MeHg.
Implications
Certification: Mercury appears to be at very low levels in white vinegar (n.d. in 2 of 3 samples; 2 µg/L in 1). This is consistent with vinegar not being a seafood-derived or high-atmospheric-deposition product. White vinegar should be classified as a low tHg/MeHg risk matrix.
Testing: The photochemical vapor generation AFS method offers a practical alternative to acid digestion-ICP-MS for routine mercury screening in white vinegar, with comparable accuracy and no pretreatment. Applicable only to white vinegar due to sugar interference in other vinegar types.
App: tHg in white vinegar is likely a data gap to low-confidence; available data suggests <2 µg/L.