Hovanec 2004 — Arsenic speciation in peanut butter by IC-ICP-MS
This 2004 paper from West Coast Analytical Service (Santa Fe Springs, CA) is the first published arsenic speciation study on commercially available peanut butter. Six retail peanut butter samples (smooth, crunchy, organic, low-fat spread, and whole peanuts) were measured for total arsenic by ICP-MS, and three of those plus NIST SRM 2387 were subjected to full four-species IC-ICP-MS speciation (As(III), DMA, MMA, As(V)). The paper developed an extraction protocol using acetone pre-extraction followed by 50% 2-butoxyethanol, solving the problem of incomplete arsenic recovery from high-fat matrices that had caused prior methanol-water methods to fail. Critically, the dominant arsenic species in peanut butter were organic (DMA and MMA), not inorganic, suggesting lower toxicological concern than matrices dominated by iAs.
Key numbers
Total arsenic (ng/g, wet weight):
- JCPB1 (creamy): 19.0 ng/g
- GCPB1 (creamy): 7.5 ng/g
- SCPB1 (super chunk): 21.4 ng/g
- BPB1 (low fat spread): 6.5 ng/g
- SPPB1 (creamy 1 oz cups): 6.9 ng/g
- TJPB1 (crunchy salted): 14.4 ng/g
- WPPB1 (whole peanuts in shell): 9.9 ng/g
- SRM 2387 (NIST peanut butter): 12.0 ng/g
- Detection limit: 0.4 ng/g
Speciation of JCPB1 (creamy, total As = 19.0 ng/g):
- As(III): 1.6 ng/g
- DMA: 6.1 ng/g
- MMA: 4.9 ng/g
- As(V): 6.3 ng/g
- Sum of species: 18.9 ng/g (agrees with digestion total)
- Inorganic As (As(III) + As(V)): ~7.9 ng/g (~41% of total As)
Speciation of SCPB1 (super chunk, total As = 21.4 ng/g):
- As(III): ND
- DMA: 14.8–16.1 ng/g
- MMA: 7.9–9.1 ng/g
- As(V): ND
- Speciated total: 22.7–25.2 ng/g
SRM 2387 (NIST peanut butter, total As = 12.0 ng/g):
- As(III): ND
- DMA: 8.9 ng/g average
- MMA: 5.5 ng/g average
- As(V): ND
Methods (brief)
Analytical method: ICP-MS for total As (ELAN 6100, PerkinElmer) after heated HNO3/H2O2 digestion; IC-ICP-MS (ELAN 6000) for speciation after acetone de-fatting and 50% 2-butoxyethanol extraction. LOD for total As: 0.4 ng/g (includes 50x dilution factor). Four arsenic species separated using PRP X-100 anion exchange column, 30 mM NH4H2PO4 mobile phase at pH 6.5, 13 min isocratic run. Enriched Se-78 internal standard added post-extraction to monitor column efficiency and correct signal variation. Spike recoveries for JCPB1: As(III) 93%, DMA 90%, MMA 87%, As(V) 98%. Recoveries for TJPB1 were lower (40–122%) due to the spike concentration being near the solution detection limit. The 2-butoxyethanol method was novel at the time; prior methanol-water methods yielded <10% spike recoveries in high-fat peanut matrices.
Key limitation: small n=6 commercial samples, single analyst, 2004 vintage. Species present in SCPB1 were predominantly organic (DMA + MMA only, no inorganic As detected), which differs from JCPB1 where ~41% was inorganic. Product formulation differences (oil separation, salt, organic peanuts) may affect speciation; mechanism not fully explained.
Implications
Certification: Total As in peanut butter ranges 6.5–21.4 ng/g (ppb) on a wet-weight basis, which is low relative to rice-based ingredients. Inorganic arsenic appears to be a minority species in at least some products. However, the iAs fraction varies substantially between products (0% to ~41% of total As), so total-As measurement alone is insufficient for speciation-based risk assessment. HMT&C peanut-butter or nut-butter product pages should note both the low absolute concentrations and the variable iAs fraction.
Courses: Demonstrates why arsenic speciation matters for risk characterisation: a product with 20 ng/g total As but predominantly DMA/MMA has very different toxicological implications than the same total As dominated by iAs. Good teaching case for the speciation module.
App: tAs typical range for peanut butter: 6.5–21.4 ppb. iAs fraction: uncertain (0–41% of tAs). The app should avoid conflating total As with inorganic As for peanut-butter-containing products.