Ozbek et al. 2016 — Trace metal determination in Turkish vinegars by MIP OES
This study validated a microwave-induced plasma optical emission spectrometry (MIP OES) method for simultaneous determination of 10 elements (Al, B, Co, Cr, Cu, Fe, Mg, Mn, Pb, Zn) in 32 Turkish vinegar samples, requiring only simple dilution into 2% acetic acid without acid digestion. All measured concentrations fell well below the Turkish Food Codex maximum allowable values (Pb ≤1 mg/L; Cu + Zn ≤10 mg/L; Fe ≤10 mg/L); Pb levels in particular were low, with the highest observed value approximately 0.15 mg/L in grape vinegars. The method is notable for its simplicity and suitability for routine quality-control analysis of acidic food matrices.
Key numbers
Method LODs (µg/L): Al = 0.62, B = 7.67, Co = 4.55, Cr = 0.52, Cu = 1.22, Fe = 5.72, Mg = 1.32, Mn = 0.35, Pb = 2.42, Zn = 26.0. LOQs are approximately 3.3× LOD.
Vinegar concentrations (mg/L, Table 4, n=32 samples):
- Al: 0.02 (homemade) to 5.19 (Apple 8); median grape vinegars approximately 1.2; balsamic 1 = 1.63, balsamic 3 = 2.29
- Pb: ranged from 0.01 to 0.15 mg/L (i.e., 10–150 µg/L or ppb). Highest in grape and apple vinegars. Turkish Codex limit is 1 mg/L. All samples far below limit.
- Cr: consistently 1.95–3.95 mg/L across all vinegar types (notably higher than other studies; authors attribute this to geographic origin)
- Cu: 0.001–0.05 mg/L across most samples
- Fe: 0.06–7.01 mg/L; highest in balsamic (6.59 and 7.01 mg/L); Turkish Codex limit 10 mg/L
- Mg: 15.86–169.03 mg/L; highest in fig vinegar (169.03)
- Zn: 0.16–2.42 mg/L; all below Codex 10 mg/L combined Cu+Zn limit
- Co: below LOD in most samples; detected only in grape 1 (0.34), grape 2 (0.62), balsamic 1 (0.26), balsamic 2 (0.09)
- B: not detected in many apple samples; highest in balsamic (8.76 and 7.80 mg/L)
- Mn: 0.003–1.51 mg/L
Recovery tests (3 vinegar types, n=3): all analytes 91–104%. Certified reference material (wastewater CWW-TM-E) confirmed accuracy.
Cr values were notably higher than prior literature; authors attribute this to the Turkish origin of samples rather than a methodological artifact.
Methods
Instrument: Agilent 4200 MIP OES with Inert One nebulizer and cyclonic spray chamber. Plasma sustained by nitrogen extracted from air. Samples diluted 1:1 with 2% acetic acid (total dissolved solids reduced to 2–4% to protect the torch). Aqueous standards calibration; no matrix-matched standards required. LOD = 3σ/slope (n=10 blank aspirations). Recoveries validated in balsamic, apple, and grape matrices. No acid digestion. Units reported as mg/L (= mg/kg wet weight for aqueous food matrices of density ≈1).
Limitation: MIP OES cannot speciate arsenic (total As only); Cd was not measured in this study. The paper focuses on 10 analytes and does not cover As, Cd, Hg, or Ni, which are critical for HMT&C.
Implications
Certification: This paper establishes Pb concentrations in Turkish vinegars are low (all <150 ppb, mostly <50 ppb), well below the Turkish Food Codex 1 mg/L limit. Balsamic vinegars contain meaningfully higher Al and Fe than wine or apple vinegars due to concentration effects. Cr values here (2–4 mg/L) are anomalously high compared to other literature — certifiers should not use this paper in isolation for Cr limits in vinegar.
Courses: Useful illustration of direct-aspiration MIP OES as a practical alternative to ICP-MS for routine vinegar monitoring. Demonstrates that matrix effects are manageable in diluted acetic acid matrices.
App: Pb in Turkish grape and apple vinegars: typical 10–80 ppb, max observed 150 ppb. These figures are from Turkey and likely underestimate balsamic risk. Al in balsamic vinegars substantially higher than in wine or apple vinegars.