Determination of lead in vinegar by ICP-MS and GFAAS: evaluation of different sample preparation procedures

Overview

This study measured lead in 59 commercial vinegars purchased from California retail using both inductively coupled plasma mass spectrometry (ICP-MS) and graphite furnace atomic absorption spectrometry (GFAAS), with the primary objective of identifying the most reliable sample-preparation protocol. Direct analysis without digestion produced erroneously high and poorly reproducible results on both instruments because of organic-matrix interferences; nitric acid digestion brought the two instrumental methods into close agreement (R = 0.997, slope 0.94), and nitric acid digestion with UV photolysis was identified as the fastest and most complete preparation when hydrogen-peroxide reagent-blank Pb is acceptable. Balsamic vinegars — particularly traditionally barrel-aged varieties — carried substantially higher lead than other vinegar types, with the highest single sample at 307 µg/L and the lead source attributed to production and storage processes rather than the agricultural inputs.

Key numbers

All concentrations are reported as µg/L of as-sold vinegar (= ppb for the aqueous matrix). Means and ranges below come from Table 4 (p. 4) unless otherwise noted; the all-vinegar summary statistic is reported on the same table’s bottom row.

Balsamic vinegar (n = 52), Table 4 sub-groups:

• Younger balsamic (n = 36): range 15–68 µg/L, mean 44 µg/L, SD 15.
• Mid-tier balsamic (n = 12): range 73–110 µg/L, mean 85 µg/L, SD 12.
• High-tier balsamic (n = 2): range 174–179 µg/L, mean 173 µg/L, SD 4.
• Aged balsamic-1 (n = 1): 276 µg/L.
• Aged balsamic-2 (n = 1): 307 µg/L.

Aggregate balsamic statistic (text, p. 5): range 14.9–307 µg/L, mean 68 ± 56 µg/L. The two aged-balsamic single-sample values dominate the high end; the highest (307 ± 19.5 µg/L, n = 6 replicate digestions) was reportedly produced by traditional Aceto Balsamico di Modena methods involving 25-year storage in vintage wood barrels. The text additionally notes a balsamic at 257 µg/L “aged for 18 years” (p. 5); this 257 µg/L value is not the Table 4 aged-1 row (276 µg/L), and the paper does not reconcile the two figures — both are reported here as the source presents them.

Other vinegar types (Table 4 single-sample or small-n rows):

• Wine vinegar (n = 4): range 36–62 µg/L, mean 50 µg/L, SD 12.
• Garlic vinegar (n = 1): 15 µg/L.
• Apple cider vinegar (n = 1): 6.6 µg/L.
• Rice vinegar (n = 1): 19 µg/L.

All vinegars combined (n = 59): range 7–307 µg/L, mean 64 ± 54 µg/L.

Method performance:

• GFAAS method detection limit (after nitric acid + heating-block digestion): 0.12 µg/L (mean blank 0.03 µg/L, n = 4; SD 0.04).
• Spike recovery on 6 different vinegars: 96 ± 5 %.
• NIST 1640 SRM (trace metals in natural waters, certified 27.89 ± 0.14 µg/L Pb) recovery: 97.4 ± 1.3 %.
• Relative standard deviation for duplicate analyses: < 8 %.
• Cross-instrument agreement after nitric acid digestion: R = 0.997, slope m = 0.94 (simple linear regression of GFAAS vs. ICP-MS on the same digests).
• Reagent contamination: TMG (trace-metal-grade) hydrogen peroxide carried ~15 µg/L Pb, comparable to the lead concentration in the lower-end vinegars and limiting UV photolysis with H₂O₂ for samples below ~50 µg/L Pb.

Effect of digestion on apparent Pb (Table 3, p. 3): four balsamic vinegars analyzed both ways. Direct dilution gave significantly higher and less precise values than nitric acid digestion on both instruments (paired t-test, P ≤ 0.05). For example, Balsamic-1: GFAAS direct dilution 595 µg/L (RSD 18 %) vs. acid-digested 319 µg/L (RSD 9 %); ICP-MS direct dilution 447 µg/L (RSD 7 %) vs. acid-digested 306 µg/L (RSD 6 %).

Methods (brief)

ICP-MS: ThermoFinnigan Element magnetic-sector high-resolution ICP-MS, Glass Expansion Conikal nebulizer, Scott-type double-pass spray chamber (cooled to 10 °C), standard nickel cones. ²⁰⁸Pb measured at low resolution (r = 300) with ²⁰⁹Bi as internal standard; RF power 1250 W; 200 scans per acquisition (Table 1, p. 2).

GFAAS: Perkin-Elmer SIMAA 6000 with Zeeman background correction and AS72 auto-sampler. End-capped, transversely heated pyrocoated graphite tubes with integrated L’vov platform. Lead electrodeless discharge lamp at 283.3 nm, lamp current 450 mA. Chemical modifier: 0.05 mg NH₄H₂PO₄ + 0.003 mg Mg(NO₃)₂ per 5 µL. The Perkin-Elmer manufacturer maximum ashing/atomization is 400/1400 °C (§4.3, p. 4); with the chemical modifier, the authors initially optimized at 800/1400 °C against NIST 1640 (digested natural-water SRM), but that program produced low recoveries on spiked vinegar digests because of a sharp absorbance drop between 700 and 800 °C in vinegar digests that was not seen in the SRM (Fig. 1, p. 5). The authors attribute this to relatively labile, volatile organolead compound(s) in vinegar digests and recommend a lowered program of 600 °C ashing / 1300 °C atomization specifically for vinegar (Conclusions, p. 6). Table 2 (p. 3) tabulates the working GFAAS program as 700 / 1400 °C; this is an intermediate working setting rather than the paper’s final published recommendation, and the paper does not reconcile the two.

Three sample-preparation paths compared:

1. Simple aqueous dilution (no digestion): produced poor precision and erroneously high values on both instruments; not recommended.
2. Nitric acid heating-block digestion: 0.5–1.0 g vinegar weighed into Teflon vessels, 10 mL TMG nitric acid, initial 50 °C for 2–3 h, then 90 °C to dryness, reconstituted in 1 M TMG nitric acid. Effective, clean, but slow.
3. Nitric acid + 30 % H₂O₂ UV photolysis: 0.5 g vinegar, 1 mL TMG nitric acid, 0.5 mL 30 % H₂O₂, custom PTFE digestion cups with quartz caps under a 1200 W medium-pressure Hg vapor lamp (9.2 ± 0.4 mW cm⁻² monitored throughout). Fastest and most complete; UV photolysis works for vinegar but the H₂O₂ reagent blank (~15 µg/L Pb) limits applicability to vinegars > 50 µg/L Pb. Cleaner H₂O₂ would be needed for low-concentration samples.

Recommended protocol: nitric acid digestion with UV photolysis where matrix-Pb permits; nitric acid heating-block digestion otherwise. ICP-MS or GFAAS detection; for GFAAS, use 600 °C ash / 1300 °C atomization rather than manufacturer defaults.

Contamination control: HEPA-filtered Class 100 laboratory; Teflon vessels cleaned in 8 M TMG HCl overnight then ≥ 8 h hot TMG HNO₃; all plastic ware double-bagged in trace-metal-clean Zip-loc bags. Sample batches included three method blanks, three spiked analytical samples, and three reference materials.

Implications

Certification: Establishes that balsamic vinegar — and particularly traditional barrel-aged balsamic — sits at the high end of the vinegar-category Pb distribution, with single-sample values reaching 307 µg/L. The Pb source is attributed to vinification contact materials (wood-barrel metal fittings, alloy welds in production equipment) by analogy to wine-vinification studies, not to the grape or the soil. This supports treating balsamic vinegar as a distinct sub-row from other vinegar types in any HMTc certification scheme. The non-balsamic vinegars in this dataset (wine, apple cider, garlic, rice) sit well below 100 µg/L Pb, with the apple cider, garlic, and rice single-sample values all under 20 µg/L.

Courses: Useful teaching case for analytical method validation in acidic food matrices. The organolead volatility finding (sharp absorbance drop 700–800 °C in vinegar digests but not in the NIST 1640 water SRM) is a self-contained illustration of why matrix-matched method optimization matters even when an SRM appears to validate the method. Also illustrates the trade-off between UV photolysis speed and reagent-blank contamination limits.

App: For US-retail vinegar in this sample set — balsamic Pb mean 68 ± 56 µg/L with extreme aged samples to 307 µg/L; wine vinegar Pb mean 50 µg/L; apple cider, garlic, rice single-sample Pb all under 20 µg/L. Vinegar serving sizes are small (typically 5–15 mL for dressing use), so even the 307 µg/L extreme corresponds to ≤ 4.6 µg Pb per serving; daily-intake context for app users should account for typical low-volume use rather than treating vinegar concentrations as drink-equivalent.

Microbiome: Not applicable; the paper does not address gut-microbial endpoints.

Verification notes

Page was originally drafted under the legacy manual-fetch-kimi raw_handle and last updated 2026-05-14. Merge-enhanced on 2026-05-26 against the source PDF to:

• Replace legacy raw_handle: manual-fetch-kimi with the canonical MFK_determination-of-lead-in-vinegar-by-icp-ms-and-gfa handle, matching the convention used on sibling vinegar source Copper Complexing Capacity and Trace Metal Content in Common and Balsamic Vinegars: Impact of Organic Matter.
• Correct truncated raw_path (prior value cut off at “evaluation.pdf”; corrected to the full filename “…evaluation of different sample preparation pro.pdf”).
• Correct three transposed single-sample Pb values in Key numbers. Prior version reported Garlic vinegar (n=1): 276 µg/L, Apple cider vinegar (n=1): 15 µg/L, and Rice vinegar (n=1): 6.6 µg/L. Source Table 4 (p. 4) actually shows Garlic = 15 µg/L, Apple = 6.6 µg/L, Rice = 19 µg/L. The prior page had pulled the wrong column or scrambled rows; 276 is the Table 4 Balsamic (aged)-1 row, which was separately missing from the page. All four values corrected.
• Correct misread n in Key numbers. Prior version reported Balsamic group 3 (n=4, older/traditional): range 174–179 µg/L, mean 173 µg/L. The “4” was the standard-deviation column in Table 4, not the sample count. Correct n is 2.
• Add the two aged-balsamic single-sample rows (276 and 307 µg/L) that the prior version omitted, and note the paper-internal discrepancy between Table 4’s aged-1 = 276 µg/L and the text’s “another balsamic … 257 µg/L … aged for 18 years” without inventing a reconciliation.
• Expand Table 3 cross-method comparison (direct dilution vs. nitric acid digested, for four balsamics on both instruments) in Key numbers; prior version omitted the magnitude of the dilution-vs.-digestion bias and only mentioned it qualitatively.
• Expand the Methods section to capture the instrumental detail (RF power, isotopes monitored, internal standard, modifier composition, contamination control) that supports the A-tier classification.
• Add garlic-vinegar to matrices: (the source measured one); prior version omitted it.
• Remove the legacy ## Wiki pages updated on ingest heading per the current Part 6 template; downstream-page list lives in the routing audit, not on the source page.
• Restate the µg/L = ppb equivalence explicitly in Key numbers for the aqueous matrix.
• License kept as “All rights reserved” — Talanta (Elsevier) 2004 paywall paper, no open-access notice on the PDF.

Auto-audit subagent (2026-05-26) verdict REVISE; Checks 1, 3, 4, 5 clean. Check 2 ⚠️ flagged the matrices: / ingredients: asymmetry — matrices contains rice-vinegar and garlic-vinegar (which the paper measures as n = 1 each) while ingredients: does not list them. Verified against the source: 1 rice and 1 garlic vinegar are reported in §3.3 and Table 4. Verified against the corpus: no wiki/ingredients/rice-vinegar.md or wiki/ingredients/garlic-vinegar.md page exists, and Part 10’s ingredient-promotion threshold is 5 papers treating the sub-variant as a distinct commodity. With n = 1 each in this paper alone, neither slug crosses the threshold for an ingredient page. Resolution applied:

• Keep rice-vinegar and garlic-vinegar in matrices: (descriptive of what was measured).
• Keep them out of ingredients: (no extant page to route to; both are folded under the generic Vinegar coverage).
• Routing audit confirms 0 unresolved / 0 malformed for this source after the change, so the asymmetry does not produce broken fan-out.

This is the same broad-scope-matrices, narrow-ingredients pattern documented on the sibling vinegar source Copper Complexing Capacity and Trace Metal Content in Common and Balsamic Vinegars: Impact of Organic Matter for its fruit-vinegar matrix.

Self-caught during audit-application (not flagged by the subagent): the Methods section initially misattributed the GFAAS recommended program. Corrected to attribute 600 / 1300 °C to the paper’s Conclusions section (p. 6) rather than Table 2 (Table 2 shows 700 / 1400, an intermediate working program). Also corrected the manufacturer’s recommended maximum from “800 / 1400” to “400 / 1400” per §4.3 (p. 4); the 800 / 1400 figure was the authors’ first-pass optimization against the NIST 1640 SRM, not the manufacturer default.

Update history

The five most recent substantive edits to this page, classified major (evidence or structure moved), correction (a published value or statement was wrong and has been fixed), or minor (narrative rewritten without changing the underlying evidence). Each description is derived from what the edit did to this page; the linked commit is the authoritative record, routine regeneration passes are excluded, and the full version history lives in git. When DOI minting comes online (see schema docs), each entry below will also link to a version-pinned DataCite DOI.