Saei-Dehkordi et al. 2012 — Pb, Cd, Cu, Zn in Iranian vinegars by stripping chronopotentiometry
This study measured lead, cadmium, copper, and zinc in 96 commercial Iranian vinegars (four types: date, apple, white grape, red grape) using stripping chronopotentiometry (SCP), validated against graphite furnace atomic absorption spectrometry (GFAAS). All metal concentrations were below the Iranian maximum allowable limits (Pb: 1,000 ng/mL; Cu + Zn: 10,000 ng/mL); no cadmium MAL exists under Iranian standards. Date vinegars had the highest Pb and Zn concentrations, while apple vinegars had the highest Cu and Cd. The SCP and GFAAS methods showed no significant differences (p > 0.5), validating the rapid electrochemical approach.
Key numbers
All concentrations in ng/mL (= µg/L = ppb). Method LODs: Cu 2.6, Pb 2.9, Cd 1.2, Zn 3.4 ng/g.
Lead (Pb), n=24 per type:
- Date vinegar: 4.4–253 ng/mL, mean 67.4 ± 13.5, median 47.6
- Apple vinegar: 15.8–156.3 ng/mL, mean 47.2 ± 7.3, median 32.7
- White grape vinegar: 3.3–85.6 ng/mL, mean 27.3 ± 4.5, median 23.3
- Red grape vinegar: 8.7–167 ng/mL, mean 58.0 ± 8.3, median 47.8
- Date and red grape Pb significantly higher than white grape (p < 0.05)
- Iranian MAL: 1,000 ng/mL — all samples far below
Cadmium (Cd):
- Date vinegar: nd–78 ng/mL, mean 12.8 ± 4.0, median 4.5
- Apple vinegar: 0–69.7 ng/mL, mean 13.9 ± 3.4
- White grape vinegar: 0–59.3 ng/mL, mean 8.7 ± 2.8
- Red grape vinegar: 0–51.1 ng/mL, mean 11.1 ± 2.9
- Cadmium not detected in 7 samples across all types (below LOD of 1.2 ng/g)
- No significant differences among types (p > 0.05)
Copper (Cu):
- Date vinegar: 36.6–611.3 ng/mL, mean 204 ± 30.7, median 148
- Apple vinegar: 32–1,129 ng/mL, mean 301 ± 58.0, median 186 (highest)
- White grape vinegar: 21.5–570.1 ng/mL, mean 117 ± 28.3, median 107.8
- Red grape vinegar: 12.8–584.3 ng/mL, mean 154 ± 29.7, median 48.2
- Apple and date Cu significantly higher than white grape (p < 0.05)
Zinc (Zn):
- Date vinegar: 398–3,725 ng/mL, mean 1,616 ± 177, median 1,528 (by far the highest)
- Apple vinegar: 48–1,389 ng/mL, mean 470 ± 74.3
- White grape vinegar: 26.1–657 ng/mL, mean 211 ± 38.9
- Red grape vinegar: 115.8–1,948.2 ng/mL, mean 619 ± 95.3
- Four of six pairwise Zn comparisons significant (p < 0.05)
Regulatory comparison: Pb well below Iranian MAL (1,000 ng/mL) and Turkish/Codex MAL (1 mg/L = 1,000 ng/mL). Cu + Zn combined well below 10,000 ng/mL MAL.
Methods
SCP (stripping chronopotentiometry) using PSA ION 3 analyzer with glassy carbon working electrode (mercury film coating), Ag/AgCl reference, platinum auxiliary. Simultaneous Cu, Pb, Cd at −900 mV electrolysis for 300 s; Zn at −1,200 mV for 180 s. Sample prep: 10 mL vinegar filtered (0.45 µm), added to 10 mL 2 M HCl plus 1 mL HgCl2 (for Cu/Pb/Cd); separate Zn analysis with acetate buffer pH 4.7. Validation by GFAAS (Perkin-Elmer 4100) on 16 randomly selected samples (n=4 per type); recoveries 99–101%. LODs: Cu 2.6, Pb 2.9, Cd 1.2, Zn 3.4 ng/g (SCP); GFAAS LODs: Cu 2.75, Pb 5.0, Cd 2.75, Zn 2.5 ng/g. Precision and repeatability: 3.40–9.69% RSD.
Limitation: Cd in some samples fell below LOD (1.2 ng/g); paper reports them as “nd.” Date vinegar Cd range 4.5–78 ng/mL with some nd’s, suggesting true heterogeneity. Only four metals measured; As, Hg, Ni, Al not included.
Implications
Certification: Provides a useful baseline for Iranian vinegar types. Date vinegars show the highest Pb (mean 67 ppb) and Zn among Iranian samples — this is one of the higher Pb readings in the vinegar literature globally, though still far below any regulatory limit. Apple vinegars have the highest Cu and Cd. These data inform condiment risk-ranking: date vinegar > red grape > apple > white grape for Pb.
Courses: Good illustration of SCP as a rapid, cost-effective alternative to GFAAS for simultaneous multi-metal determination in acidic food matrices. Demonstrates method comparability via paired t-test.
App: Pb typical range in Iranian commercial vinegars: 3–253 ppb (ng/mL) depending on type; date vinegar median 47.6, max 253. Cd: 0–78 ppb, most samples low or non-detect.