Chromatographic Identification and Toxicological Risk Assessment of Unidentified Non Intentionally Added Substances
Chromatographic identification couples GC-MS and LC-HRMS screening with Cramer classification to clear unidentified non intentionally added substances below 0.01 mg/kg.
Detector
Initial Screening Workflow
Analytical laboratories running food-contact conformance trials routinely confront dozens of chromatogram peaks bearing zero match in commercial mass spectral libraries. A printed folding carton, an adhesive-laminated pouch, or a high-barrier dispersion-coated board presents a chemical matrix where volatile degradation products, curing side-reactions, and cross-contaminants co-exist. The process begins with broad-spectrum untargeted screening.
Volatile and semi-volatile compounds yield to gas chromatography coupled with mass spectrometry (GC-MS), using electron ionization at 70 eV paired with capillary columns like 5 percent diphenyl and 95 percent dimethylpolysiloxane. Polar, non-volatile, and thermally labile migrants pass to liquid chromatography coupled to high-resolution accurate mass spectrometry (LC-HRMS), typically utilizing electrospray ionization in positive and negative modes over a quadrupole time-of-flight (Q-TOF) or Orbitrap analyzer. Resolving power exceeding 30,000 FWHM resolves isobaric mass interferences in complex extracts, separating real packaging migrants from spectral noise.
Quantification of unknown peaks proceeds by assigning surrogate internal standards across retention windows. For GC-MS, deuterated hydrocarbons and acenaphthene-d10 establish semi-quantitative response factors. For LC-MS, stable-isotope-labeled plastic additives supply semi-quantitative calibration curves.
Migration screening applies simulant protocols defined in EN 1186 and Regulation EU 10/2011, exposing converted packaging surfaces to modified polyphenylene oxide (Tenax) for dry goods, 3 percent acetic acid for acidic media, or 50 percent ethanol for aqueous-fatty matrices. When an unknown peak exceeds an area corresponding to an analytical screening limit of 0.01 milligrams per kilogram of food simulant, confirmation workflows trigger immediately.
An uncalibrated chromatographic peak running against an arbitrary surrogate standard carries an inherent three-fold response factor uncertainty.
Confidence in non-target structural assignment rests on standardized identification levels. Level 1 demands definitive confirmation via matching retention time, accurate mass, and fragmentation spectra against an authentic chemical standard injected under identical operational parameters. Level 2 represents probable structure based on diagnostic library fragmentation spectra and accurate mass matches within 5 parts per million error, supported by high-match isotopic abundance distributions.
Level 3 designates a tentative candidate family or functional class, where fragment ions reveal specific substructures (such as phthalate fragment m/z 149 or ethoxylated nonylphenol ion series) without resolving the specific positional isomer. Level 4 remains an unambiguous molecular formula derived from monoisotopic mass and isotopic patterns. Level 5 reflects an exact mass retention peak yielding no unambiguous formula.
Converting operations generating printed cartons experience peak emergence during oxidative drying, UV photopolymerization, or water-based barrier drying tunnels. Acrylic cross-linking leaves residual dimer and trimer species. Secondary breakdown products form through thermal degradation at hot nips during thermal lamination.
The analytical system documents each peak retention time, exact parent mass, isotopic distribution pattern, and characteristic MS/MS collision-induced fragments. When an unknown compound fails Level 1 identification due to the lack of reference material, toxicological evaluation takes over the assessment sequence.
Triage
Hazard Tier Assignment
Toxicological qualification of unidentified compounds relies on the Threshold of Toxicological Concern (TTC) approach, structured according to the classic Cramer decision tree as updated by food safety authorities. Chemical structure fragments extracted from Level 2 or Level 3 chromatographic evaluations feed into automated in silico profiling platforms. The workflow scans first for direct DNA reactivity alerts.
Compounds bearing aromatic amines, alkyl halides, epoxides, hydrazines, or nitroso groups face categorization under the genotoxicity threshold. When chemical structure assignment yields high probability of an active DNA-reactive structural alert, the applicable human exposure threshold caps at 0.0025 micrograms per kilogram body weight per day, which translates into a packaging migration limit of 0.00015 milligrams per kilogram food for a sixty-kilogram adult consuming one kilogram of packaged food daily.
Structures lacking genotoxicity alerts route through the three standard Cramer classes based on metabolic handling and known subchronic toxicity profiles. Cramer Class I contains substances of simple chemical structure with efficient metabolic degradation pathways and low oral toxicity, carrying an intake threshold of 30 micrograms per kilogram body weight per day (1.8 milligrams per person per day). Cramer Class II covers substances containing functional groups less benign than Class I but lacking characteristics of high systemic toxicity, capped at 9 micrograms per kilogram body weight per day (0.54 milligrams per person per day).
Cramer Class III comprises complex organic molecules, heteroaromatic systems, or functional groups indicating significant toxicity or bioaccumulation potential, limited to an intake threshold of 1.5 micrograms per kilogram body weight per day (0.09 milligrams per person per day, translating to 0.015 milligrams per kilogram of food).
| TTC Classification | Structural Characteristics | Human Intake Threshold (ug/kg bw/day) | Food Migration Equivalent (mg/kg food) | Screening Action Required |
|---|---|---|---|---|
| Genotoxicity Alert | Alkylating agents, aromatic amines, nitroso, epoxides | 0.0025 | 0.00015 | Mandatory compound isolation, NMR verification, or process purge |
| Cramer Class III | Heteroaromatics, branched structures, multi-functional esters | 1.5 | 0.015 | Targeted structural elucidation, barrier optimization |
| Cramer Class II | Unconjugated cyclic structures, complex aliphatic esters | 9.0 | 0.090 | Semi-quantitative monitoring, migration kinetic checks |
| Cramer Class I | Linear hydrocarbons, simple fatty acids, benign carbohydrates | 30.0 | 1.800 | Documentation within compliance dossier without intervention |
| Threshold calculations assume 60 kg adult body weight and daily consumption of 1 kg packaged food matrix per EU exposure guidelines. | ||||
Organophosphate flame retardants, plasticizers, and carbamates fall into distinct neurotoxicity categories outside standard Cramer Class III thresholds. The neurotoxicity branch imposes an intake threshold of 0.3 micrograms per kilogram body weight per day. When chromatographic screening detects characteristic fragments of alkyl phosphates or alkylthiophosphates in migration simulants from coated board, the safety dossier defaults immediately to 0.0018 milligrams per kilogram in food.
Converting managers must recognize that failure to identify an unknown migrant forces the testing authority to apply the conservative default assumption. If chromatographic fragmentation leaves structural alerts ambiguous, toxicological assessors assign the substance to the genotoxic class by default, immediately halting commercial distribution of the packaging batch.
Claiming compliance based solely on total volatile organic compound measurements avoids the regulatory question entirely.
Fragment
Structural Elucidation Protocols
Resolving an unknown non-intentionally added substance (NIAS) down to a verifiable chemical structure requires a coordinated analytical campaign between accurate mass spectrometry and thermal desorption techniques. Quadrupole time-of-flight instruments capture high-resolution isotopic clusters. Comparing experimental isotopic distribution against theoretical isotopic models provides the first filter for elemental composition.
Mass defect filtering separates hydrocarbon-rich polyolefin breakdown products from oxygenated acrylic fragments and halogenated processing aids. Alkyl chains linked to standard photoinitiators exhibit negative mass defects, whereas fluorinated surface treatments exhibit strongly negative defects, allowing software to segregate complex total ion chromatograms into distinct chemical series.
MS/MS fragmentation using collision-induced dissociation (CID) provides positional data. Ramping collision energy across 10 to 50 eV cracks parent adducts into diagnostic daughter ions. In UV-cured flexographic varnishes, common unlisted peaks stem from the cleavage and recombination of standard free-radical photoinitiators like 1-hydroxycyclohexyl phenyl ketone or 2,4,6-trimethylbenzoyl-diphenylphosphine oxide.
Photolytic cleavage yields benzoyl and phosphonyl radicals that abstract hydrogen atoms or bond to low-molecular-weight acrylic monomers present in the uncured film, generating novel chemical species not cataloged in REACH inventories or polymer clearance lists.
- Accurate mass confirmation establishes monoisotopic mass to within three decimal places, generating empirical formulas filtered by nitrogen rule compliance and double-bond equivalents.
- Isotope ratio validation compares observed relative intensities of carbon-13 and sulfur-34 isotopic peaks with theoretical abundance to eliminate incompatible formulas.
- Collision-induced dissociation maps fragment spectra across variable energy bands to identify diagnostic functional groups, cleavage points, and persistent parent cores.
- Chromatographic retention index matching cross-checks retention indices on non-polar stationary phases against quantitative structure-retention relationship algorithms.
Gas chromatography coupled with electron ionization provides access to reproducible 70 eV spectra, but thermal breakdown inside the injection port often creates artifacts. A hot splitless injector held at 280 degrees Celsius degrades delicate wax coatings, fatty acid amides, and secondary antioxidants, creating false non-intentionally added substances. Programmed temperature vaporization injectors and cold on-column injection systems preserve fragile migrants, delivering unaltered molecules to the analytical column.
When GC-MS and LC-HRMS spectra disagree on molecular mass, thermal lability tests distinguish actual substrate migrants from injector-generated artifacts.
Under standard electron ionization conditions, injection liner temperatures exceeding 260 degrees Celsius cause primary degradation of secondary phosphite antioxidants into unmapped dialkyl phosphites.
Coupling mass spectrometry with nuclear magnetic resonance (NMR) spectroscopy remains necessary when stereoisomers or closely related positional isomers dictate the toxicological classification. Isolating sufficient quantities of an unknown packaging migrant from migration simulants requires large-scale extraction. Continuous liquid-liquid extraction of several liters of food simulant or solvent desorptions of square meters of finished board concentrates the migrant into milligram fractions suitable for proton and carbon-13 NMR.
Isolation operations represent significant capital and time expenditure, yet they provide the only pathway to lift a non-target peak out of the conservative Cramer Class III or genotoxic default categories.
Chemical verification concludes when an authentic standard, procured via custom organic synthesis if commercially unavailable, reproduces the retention time, mass spectra, and fragmentation pattern within established tolerance limits.
Press
Converting Pass Chemistry
Every pass through a printing or converting line introduces mechanical and chemical stresses that foster the formation of non-intentionally added substances. The base paperboard matrix contributes native extractives: resin acids, terpene derivatives, and lignosulfonates. Recycled fiber grades bring a complex legacy burden of residual printing inks, mineral oil aromatic hydrocarbons (MOAH), mineral oil saturated hydrocarbons (MOSH), bisphenols, and diisopropylnaphthalenes.
When recycled board moves through an infrared or hot-air drying hood, elevated web temperatures drive volatile short-chain hydrocarbons out of the fiber web, while simultaneously inducing oxidative scission of residual starches and sizing agents.
Lamination units running polyurethane or solvent-free adhesives create a distinct chemical profile. Polyurethane adhesives rely on diisocyanates (such as methylene diphenyl diisocyanate, MDI, or toluene diisocyanate, TDI) reacting with hydroxyl-terminated polyols. Incomplete curing leaves unreacted monomeric diisocyanates.
In the presence of moisture from paperboard fibers or ambient humidity, these monomers hydrolyze into primary aromatic amines (PAAs). Primary aromatic amines fall under toxicological classification as group 1 or 2 carcinogens, carrying zero-tolerance thresholds. European regulations dictate that migration of sum total primary aromatic amines must remain non-detectable, using a detection limit of 0.002 milligrams per kilogram of food simulant.
Secondary reactions between excess isocyanates and trace ambient moisture yield cyclic urea oligomers, creating persistent unknown peaks on LC-HRMS screens.
Embossing and hot foil stamping apply localized heat and intense compression. Heated metal dies operating between 110 and 160 degrees Celsius compress coated paperboard calipers by 20 to 40 percent under tons of hydraulic force. This localized thermal surge initiates pyrolytic breakdown of the sizing agents and synthetic latex binders (such as styrene-butadiene rubber or acrylic dispersions) applied during mill coating.
Hot stamping foil layers include release waxes, aluminum vapor coats, and heat-activated sizing coats. If release temperatures drift past formulation limits, volatile acrylic degradation fragments migrate into adjacent fiber channels, showing up in subsequent solvent extraction assays.
Overprint varnishes and functional dispersion coatings introduce photoinitiator cleavage products, amine synergists, and cyclic siloxanes. Electron-beam curing avoids photoinitiators but induces radiolytic backbone scission in cellulose fibers and polymer backbones, generating low-molecular-weight aldehydes, ketones, and carboxylic acids that generate off-odors and elevated non-target peaks on Headspace GC-MS screening.
| Finishing Operation | Process Parameters | Chemical Transformation Mechanism | Dominant NIAS Compounds |
|---|---|---|---|
| Recycled Board Drying | Web temp 90 to 120 C, IR/Hot Air | Thermal desorption and oxidative scission | MOSH, MOAH, oxidized terpenes, aldehydes |
| Solvent-Free Lamination | Nip temp 60 C, 24 to 72 hr cure | Isocyanate hydrolysis and partial polymerization | Primary aromatic amines, cyclic polyol oligomers |
| UV Flexo Varnishing | Mercury lamps, 120 W/cm, line speed 150 m/min | Photolytic cleavage, incomplete free-radical cure | Photoinitiator fragments, unreacted acrylate oligomers |
| Hot Foil Stamping | Die temp 130 to 160 C, dwell 0.2 to 0.5 s | Pyrolysis of release lacquers and binder resins | Benzene derivatives, acrylic monomers, wax esters |
| Water Dispersion Barrier | Tunnel temp 140 C, high air velocity | Surfactant degradation, crosslinker condensation | Polysiloxanes, formaldehydes, ethoxylated adducts |
The sequence of application dictates the migration trajectory. When printing ink passes run prior to the functional water-based barrier pass, wet ink components interact with wet barrier emulsions. Surfactants and coalescing aids in the aqueous barrier extract soluble components from uncured inks, redistributing them through the cross-linked network.
Solvent retention measurements via static headspace GC-FID establish whether drying tunnels successfully drove off formulation solvents like ethyl acetate, ethanol, or 1-methoxy-2-propanol. If residual solvent concentrations surpass 15 milligrams per square meter, they act as carriers, accelerating the diffusion of non-volatile unidentified substances through the board calipers.
Set-off during stacking compounds these migration pathways. Finished sheets emerging from the delivery unit accumulate on pallets under substantial hydrostatic pressure. The unprinted food-contact reverse side presses directly against the heavily varnished, printed, or foiled obverse side.
Volatile and semi-volatile substances migrate across the boundary layer within hours of stacking, contaminating the food-contact surface long before the packaging reaches filling lines.
When an ink formulation drifts during long runs, the converter adjusts photoinitiator levels on the fly, creating unmapped chemical peaks in midnight production runs that hand the testing facility a compliance failure.
Barrier
Functional Layer Mass Transport
Deploying a functional barrier remains the principal engineering strategy to prevent non-intentionally added substances from entering dry or moist foodstuffs. European plastics regulation EU 10/2011 and FDA food-contact guidelines recognize the functional barrier principle: a layer within food packaging that blocks the migration of non-authorized substances into food, ensuring migration levels remain below 0.01 milligrams per kilogram. The barrier must retain its integrity across the stated shelf life under commercial storage conditions.
Achieving this standard requires rigorous mathematical and physical validation of mass transport phenomena, governed by Fickian diffusion kinetics.
Diffusion within a polymer coating or laminate obeys Fickian transport equations, where migrant flux depends on the diffusion coefficient of the substance in the barrier layer and its thermodynamic partition coefficient between the packaging substrate, the barrier polymer, and the foodstuff. The diffusion coefficient decreases exponentially with increasing molecular weight and molecular volume of the migrant, following established Piringer polymer diffusion models. Low-density polyethylene (LDPE) exhibits high diffusion coefficients, allowing rapid migration of substances with molecular weights below 300 Daltons within days at ambient temperatures.
Polyethylene terephthalate (PET) and ethylene vinyl alcohol (EVOH) offer orders-of-magnitude lower diffusion rates, functioning as true functional barriers against non-polar and semi-volatile organic contaminants.
Substrate choices face immediate operational trade-offs between chemical barrier performance, recyclability credentials, and processing costs. Modern paperboard sourcing increasingly demands the elimination of extruded plastic films, driving adoption of aqueous dispersion coatings based on styrene-butadiene, acrylic, or bio-based polymers. Dispersion coatings present microstructural porosity and variable film consolidation across the uneven surface of paperboard fibers.
Micro-cracks develop along score lines when the sheet undergoes bending and creasing during box forming, immediately breaching the functional barrier layer and exposing underlying fibers.
Applying a five-gram-per-square-meter water-based dispersion coating to virgin kraft board reduces volatile mineral oil migration by eighty percent, but fails completely to halt migration along reverse score creases.
Evaluating functional barrier efficiency requires challenge testing using standard surrogate substances representing diverse molecular sizes, polarities, and volatility ranges. A representative surrogate cocktail contains volatile substances like deuterated toluene, semi-volatile non-polar migrants like benzophenone and diisopropylnaphthalene, and polar compounds like phenylcyclohexane. The packaging sample separates the spiked donor substrate from the receiving collection medium (Tenax or food simulant) inside an inert migration cell.
Quantitative analysis after specific time and temperature intervals (such as 10 days at 40 degrees Celsius for long-term ambient storage, or 2 hours at 70 degrees Celsius for hot-fill applications) determines whether migration limits hold below 0.01 milligrams per kilogram.
Functional barrier failure surfaces rapidly during production scale-up. In an operational assessment of aqueous dispersion-coated boards intended for dry food containment, the uncreased flat sheets consistently restrict surrogate migration below analytical detection limits. Once passed through flatbed die-cutters, the mechanical shear crushed the dispersion layer along rule intersections.
High-resolution chromatography of extracts taken directly from carton corners showed breakthrough migration of paperboard sizing adducts and ink degradation compounds, exceeding Cramer Class III thresholds by an order of magnitude.
When the functional layer cracks under converting stress, testing laboratories must measure migration from folded samples rather than pristine flat swatches.
Ledger
Worked Risk Assessment
To ground the chromatographic and toxicological workflow in commercial operational realities, take a production lot of 500,000 printed folding cartons designed for dry direct-contact bakery products. The package construction uses a 350 grams per square meter virgin folding boxboard (FBB), offset-printed with four process colors, coated with an aqueous overprint dispersion varnish, and completed with an off-line spot UV screen varnish pass across branding elements. The run requires twelve pallets of board, yielding a converted surface area of 45,000 square meters.
Compliance verification mandates migration testing according to EN 1186 using Tenax simulant for 10 days at 40 degrees Celsius, representing a six-month ambient shelf life. The European packaging ratio assumption defines 6 square decimeters of packaging surface contact per 1 kilogram of food. GC-MS and LC-HRMS screening of the migration extract detects four prominent non-intentionally added substance peaks exceeding the analytical screening limit of 0.01 milligrams per kilogram food.
Peak A displays a retention time of 8.4 minutes; Peak B displays 14.2 minutes; Peak C elutes at 22.1 minutes; Peak D elutes at 29.8 minutes.
Peak A yields an exact parent ion m/z 108.0570 in GC-EI-MS, matching the molecular formula C7H8O. The fragmentation pattern identifies it definitively as benzyl alcohol at Level 1, a known solvent additive and oxidation product from printing inks, measured at a migration concentration of 0.12 milligrams per kilogram food. Benzyl alcohol belongs to Cramer Class I, carrying a migration threshold of 1.8 milligrams per kilogram food.
Peak A passes toxicological evaluation without further operational action.
Peak B elutes in LC-HRMS positive electrospray mode with an accurate mass of m/z 283.1332 (error 1.2 ppm), yielding an elemental composition of C15H22O5. High-resolution fragmentation spectra match an acrylic oligomer adduct: tripropylene glycol diacrylate hydrolysate (Level 2 identification). Chromatographic quantification against an internal diacrylate standard shows a migration level of 0.035 milligrams per kilogram food.
The structure carries no DNA-reactive alerts and classifies into Cramer Class III, which permits a migration threshold of 0.015 milligrams per kilogram food. The measured migration of 0.035 milligrams per kilogram breaches the allowable threshold by a factor of 2.3, failing compliance verification.
Peak C emerges on GC-MS at m/z 212.1775, matching a sesquiterpene hydrocarbon derivative from the mechanical wood pulp fraction (Level 3 identification), measured at 0.008 milligrams per kilogram food. Cramer Class I classification permits up to 1.8 milligrams per kilogram food, meaning Peak C passes comfortably.
Peak D produces a mass defect pattern indicative of an unlisted alkylated phosphate, showing an exact mass of m/z 381.1825 on LC-HRMS (Level 4 identification, empirical formula C18H38PO4). Quantification yields 0.004 milligrams per kilogram food. Because organophosphate fragments trigger the neurotoxicity evaluation tier, the applicable migration limit tightens to 0.0018 milligrams per kilogram food.
Peak D exceeds this limit by more than 100 percent, representing an immediate compliance failure.
| Peak Identifier | Analytical Mass / Formula | Identification Level | Measured Migration (mg/kg) | TTC Class Limit (mg/kg) | Compliance Status |
|---|---|---|---|---|---|
| Peak A (Solvent residue) | m/z 108.0570 / C7H8O | Level 1 (Confirmed) | 0.1200 | 1.8000 (Cramer I) | Passed |
| Peak B (Acrylic oligomer) | m/z 283.1332 / C15H22O5 | Level 2 (Probable) | 0.0350 | 0.0150 (Cramer III) | Failed |
| Peak C (Wood extract) | m/z 212.1775 / C15H24 | Level 3 (Tentative) | 0.0080 | 1.8000 (Cramer I) | Passed |
| Peak D (Alkyl phosphate) | m/z 381.1825 / C18H38PO4 | Level 4 (Formula only) | 0.0040 | 0.0018 (Neurotoxic) | Failed |
Commercial resolution of these failures demands process intervention rather than regulatory petitioning. Eliminating Peak B requires redesigning the spot UV varnishing pass. UV lamp output measurements reveal that aging mercury-arc lamps on the screen coater operated at only 78 watts per centimeter instead of the rated 120 watts per centimeter, causing incomplete monomer cross-linking.
Replacing the lamps and reducing line speed by 15 percent lowers Peak B migration to 0.003 milligrams per kilogram food, safely below the 0.015 milligram per kilogram threshold.
Investigating Peak D traces the alkyl phosphate contaminant to a synthetic antifoaming emulsion utilized in the aqueous overprint dispersion coater. Substituting the antifoam formulation with a certified food-grade polydimethylsiloxane dispersion removes the phosphate peak completely from subsequent LC-HRMS chromatograms.
The corrective measures shift the economics of the print run. Replacing UV curing lamps costs 1,200 dollars across the unit, while slowing the screen coater adds 18 machine hours, incurring an extra 2,700 dollars in press time. The food-grade certified aqueous dispersion coating carries a 22 percent material premium over standard formulations, adding 880 dollars across the ink and varnish bill.
Sourcing validation, re-sampling, and urgent turnaround for GC-MS and LC-HRMS re-testing billed at an analytical laboratory charges 6,500 dollars. Across the 500,000-carton order, resolving the non-intentionally added substance failures increases total job cost by 11,280 dollars, representing a unit cost increase of 0.0226 dollars per folding carton.
Scrapping the entire 500,000-carton run would have incurred a board loss of 38,000 dollars, alongside complete write-offs of prepress tooling, plates, and press setup charges. Early analytical screening at the make-ready stage isolates the chemical liability before volume converting begins.
Protocol
Procurement Audit Requirements
Managing chemical migration risks requires explicit technical terms embedded directly within raw material specifications and finishing purchase orders. Relying on generalized certificates of compliance guarantees zero commercial protection when an unknown chromatographic peak halts shipment at a brand customer audit. Packaging procurement teams must establish precise testing requirements across every tier of the supply chain.
- Non-intentionally added substance screening dossiers detailing full GC-MS and LC-HRMS untargeted chromatographic profiles, with analytical limits of detection reaching at least 0.002 milligrams per kilogram for food-contact substrates.
- Defined threshold of toxicological concern classifications for every unmapped peak exceeding 0.01 milligrams per kilogram food simulant, documented using validated in silico structural classification software.
- Raw material formulation declarations signed by chemical formulators, listing all catalysts, cross-linkers, photoinitiators, defoamers, and internal sizing agents alongside their respective molecular weights and CAS numbers.
- Curing energy compliance logs providing continuous radiometer or pyrometer verification records confirming minimum UV dosage or drying tunnel temperature targets were maintained across the production run.
Commercial contracts must define financial liability when analytical screening reveals non-compliant migrants. If testing detects primary aromatic amines, unlisted photoinitiator cleavage products, or neurotoxic plasticizers exceeding regulatory thresholds, the contract should assign all costs of re-testing, machine decontamination, board replacement, and downstream production delays directly to the finishing supplier or chemical formulator.
The technical annex of the purchase agreement stipulates that any unlisted peak emerging above the analytical screening limit must achieve at least Level 2 structural identification or satisfy Cramer Class I thresholds before goods acceptance.