Trace Detection in Consumer Product Safety — The Analytical Chemistry Behind the Diaper Formamide Controversy

A Technical Question Raised by a Panic

On June 18, media reported that the toxic substance formamide had been detected in infant diapers from brands including Huggies, Babycare, and Biba Baobei (碧芭宝贝). The news shot to the top of the trending charts within hours, and the Shandong Public Health Clinical Center promptly issued a statement: the specially-appointed expert cited had never said that the formamide detected by the center's mass-spectrometry laboratory had anything to do with infant diapers, and the center had never carried out any related research. The brands named in the report each issued statements in turn, declaring that the addition of formamide is strictly prohibited and that they had commissioned authoritative third-party testing institutions to conduct independent spot checks.

Outside the swirl of public opinion, a deeper question surfaced: is the testing itself reliable?

Limit of Detection and Limit of Quantitation — Two Easily Overlooked but Decisive Numbers

For any test report, the first question worth asking is not "what was detected" but "how much can it detect."

Two foundational concepts in analytical chemistry are decisive here:

Limit of Detection (LOD): the lowest concentration that can be reliably distinguished from background noise. Below this concentration, the signal an instrument registers may simply be part of the noise.

Limit of Quantitation (LOQ): the lowest concentration that can be reliably quantified (with acceptable precision and accuracy). Even if you "see" a faint formamide signal, if its intensity sits below the LOQ, you cannot answer the question "how much is there."

Consider a scenario: suppose an instrument's sensitivity (the lowest concentration it can reliably detect) is 30,000 ng/mL, yet the expected concentration of formamide in the target sample is only 2,000 ng/mL. In that case, if you watch the instrument readout fluctuating between 2,000 and 4,000, the first things you should suspect are baseline noise, solvent contamination, matrix interference, or carryover contamination — not "we measured it."

Why Choosing the Right Instrument Matters So Much

Detecting small, polar molecules such as formamide makes instrument selection the first critical decision. Different instruments each have domains where they excel — and domains where they do not.

Gas chromatography–mass spectrometry (GC-MS) is a mature method for detecting formamide in EVA/PE/XPE foam materials — backed by published literature, with standard operating procedures and reliable quantitation. Liquid chromatography–tandem mass spectrometry (LC-MS/MS) can equally analyze extract solutions: with a suitable column (a HILIC column, for instance, suits polar small molecules) and optimized sample pretreatment, it delivers stable quantitation.

Single-photon-ionization time-of-flight mass spectrometry (SPI-TOFMS) is an entirely different story. This instrument excels at the qualitative analysis of gas samples — not the absolute quantitation of liquid samples. Using it to measure formamide concentration directly in blood — quite apart from the fact that blood is a complex matrix of high salt, high protein, and high lipid — has almost no precedent in the public literature supporting a feasible routine or validated method. In plain terms: "Using SPI-TOFMS to perform absolute quantitation of formamide in blood is, at present, essentially science fiction."

Performing absolute quantitation of formamide in blood directly with SPI-TOFMS (single-photon-ionization time-of-flight mass spectrometry) is, at present, essentially science fiction. The practical operation faces enormous technical obstacles, and there is almost no public literature supporting a feasible routine or validated method. — Baorong Wanwu Henghe Shui (包容万物恒河水)

The Difficulty of Blood Testing — Why "Testing Blood" Is Itself Extraordinary

In this incident, the reporting mentioned that blood testing for formamide had been performed. But from the standpoint of analytical chemistry, that in itself is worth questioning:

Blood is one of the most complex matrices among liquid samples — high salt, high protein, high lipid. To extract formamide from such a complex matrix and quantify it accurately requires:

1. Suitable sample pretreatment (protein precipitation, solid-phase extraction, etc.) to remove matrix interference
2. Suitable internal standards (such as ¹³C- or ¹⁵N-labeled formamide) to compensate for matrix effects
3. Establishment of MRM ion pairs for highly selective quantitation
4. Full validation of specificity, linear range, LOD/LOQ, precision, accuracy, recovery, matrix effects, and stability

Developing a targeted LC-MS/MS method for blood formamide is technically feasible, but it demands: a legitimate research institution or testing center, a professional analytical-chemistry team, high-quality chromatography and mass-spectrometry instruments, reference standards and isotope-labeled internal standards, and a large volume of method-validation experiments. Development costs run from tens of thousands to several hundred thousand RMB, on top of ongoing maintenance and quality control. The cost of a single test would also be far higher than that of a routine physical-examination item.

As one analytical-chemistry practitioner summed it up: "Normally it is urine that is tested, and even that is mainly confined to the occupational-hygiene field. Testing blood, as in the report, is itself very strange."

Where Formamide Comes From — The Industrial Source in Consumer Products

The presence of formamide, like ink on paper or patterns on a carpet, is a byproduct of industrialization — not some toxin deliberately introduced by anyone.

Low doses of formamide are widely present in all manner of plastic products and plastic-foaming processes. Beyond diapers, children's crawling mats and yoga mats may also contain formamide. In the European Union, there are mandatory rules for formamide in foam toys — but what the EU emphasizes is the release value, not the content.

Disposable hygiene products must not have formamide deliberately added during production. It is not a core raw material of a diaper but a residue from processing aids. The problem, however, is this: many diaper brands outsource production to other firms, which may in turn outsource to small factories. Along this chain, control over the production stage attenuates layer by layer, and formamide enters the final product as a process residue.

Waiting for the Authoritative Announcement — The Final Step of Science

In the contested middle ground of public debate, one analytical-chemistry blogger offered a seven-character verdict: "Waiting for the authoritative departments' announcement is the most scientific approach."

The logic behind that sentence is this: when a test result is mired in methodological dispute, a scan-style presentation alone is far from enough to settle anything. What is needed is: independent third-party replication; the establishment of an appropriate testing method together with method confirmation; and cross-validation from multiple independent laboratories. Until then, any party claiming to have "confirmed" or "refuted" the matter has gone beyond what the existing evidence can support.

The Paper Association's Official Response — An Industry-Level Clarification

On the afternoon of June 19, the Sanitary Products Committee of the China Paper Association issued a statement, adding an industry-level official response to the dispute. The Association's core argument centered on three key links:

First, the testing information is missing. The report claimed that formamide was detected in several diaper models, yet it disclosed none of the core information: the specific detected values, the testing institution, the testing standard, the testing equipment, or the testing method. The Association pointed out that a product-safety risk assessment must rest on scientific testing methods, standardized testing procedures, and complete testing data — and the level of disclosure in this reporting fell far short of that standard.

This reporting merely states in general terms that the relevant substance was "detected"; the key testing elements — testing method, testing data, and so on — are absent, and the conclusions reached lack credibility and any basis for acceptance. — Sanitary Products Committee of the China Paper Association

Second, the causal link is inadequately argued. The report directly attributed the detection of formamide in infant biological samples to the diapers, yet it neither verified whether the infants tested had actually used the brands named in the report over the long term, nor ruled out other external routes of formamide intake — diet, environment, and contact materials. The Association pointed out that drawing a direct association while "both the usage scenario and the traceability pathway remain unclear" amounts to an "incomplete chain of evidence."

Third, the compliance status of the companies involved. Upon verification, the brand companies named in the report had each commissioned authoritative third-party testing institutions holding CMA (China Metrology Accreditation) qualifications to conduct testing, and all published results came back as "not detected," in compliance with the relevant national standards.

Reporter Wang Wenzhi's Self-Defense of His Testing Methodology

On the evening of June 21, Wang Wenzhi, an investigative reporter with the Economic Information Daily (经济参考报), published An Open Letter to the Relevant Regulatory Departments, offering the most complete self-defense to date of the testing methodology questioned throughout the dispute. This was no simple rebuttal of rumors — it was an investigative reporter laying his entire methodology open in the sunlight, an institutional response.

The qualifications and equipment of the testing institution. The open letter made clear that the testing was completed by the mass-spectrometry laboratory of the Shandong Public Health Clinical Center. The core equipment used was high-resolution liquid-chromatography–mass-spectrometry and high-resolution gas-chromatography–mass-spectrometry instruments manufactured by U.S.-based Thermo Fisher — recognized first-line workhorses in the global toxicology field, fully compliant with the standards of a national-level public-health laboratory. Before this equipment list, the narratives of "hand-assembled equipment" and "fabricated data" that had circulated online collapsed on their own.

Stringently set detection limits. Rather than adopting a blood-formamide detection threshold on which no unified consensus yet exists, the laboratory set its detection limit at a standard far stricter than routine scientific research, and completed a double verification using reference-standard identification and isotope-internal-standard quantitation. Even under such stringent conditions, formamide concentrations posing a risk of health damage were still detected in a large number of infant samples — indicating that the signal was so strong and so widespread that it had moved beyond the range explainable by "instrument noise" or "matrix interference."

A causal loop closed by control experiments. The most powerful evidence came from the design of the control experiments:

• In the adult control group, only bedridden elderly people who used adult diapers long-term tested positive for formamide; the detection rate among ordinary healthy adults was essentially zero.
• Two formamide-positive infants, aged one and three, with their diet and living environment held completely constant, went from fully positive to fully negative in blood formamide after only three days of discontinuing diaper use.
• The reporter himself, under the guidance of professionals, strapped a diaper to the thin-skinned area of his arm to simulate an infant's close-contact scenario — after ten hours, his blood formamide concentration surged by nearly one-fold; ten hours after discontinuing, the value fell by two-thirds.

How Professional Judgment Was Dismantled by Institutional Pressure

In the early hours of June 19, the incident took an unexpected turn. One of the reporters behind the story, Wang Wenzhi, spoke publicly, revealing the obscured underside behind the reversal of public opinion.

According to audio recordings released by Wang Wenzhi, Yu Zhaoyan — the specially-appointed expert at the Shandong Public Health Clinical Center quoted in the report — was repeatedly pressured by the center's leadership after the reporting drew attention, and was forced to sign a statement of denial. Yu described the scene at the time: "A dozen leaders were sitting there, looking at me with stern faces. Our Party secretary said, 'It is you who caused this trouble.' Throughout the entire process, not a single person asked how these children would be treated, how they would be tested, or what would be done about the parents' concerns."

"They literally escorted me along; we had to sever all connection." — Reporter Wang Wenzhi

Within forty-eight hours, the focus of the incident leapt from "formamide detected in diapers" to "is the testing trustworthy," and then to "was the expert suppressed." At each step new information entered, and at each step the narrative foundation of the previous step was dismantled. The final step carried the greatest destructive force — because what it revealed was no longer a methodological disagreement but the intervention of institutional interests in professional judgment. Yu Zhaoyan expressed thorough disappointment with the hospital, saying that "after this matter ends, I may resign."

A dispute over testing methodology can be resolved through supplementary data and technical dialogue. But when an expert faces workplace pressure over a testing conclusion, the nature of the dispute changes. In the fragile chain of consumer-product safety, the weakest link is not insufficient testing precision — it is that when professional judgment collides with institutional interests, the former lacks institutional protection.

Extended Reflections

The lesson of this incident is less about whether a particular diaper brand bears responsibility than about the methodological standardization of the entire consumer-product-safety testing system. When what the public sees is a scan-style mass spectrum that has never been peer-validated, while the named companies produce standardized third-party testing reports, the gulf between the two is not a difference of position but the incommensurability of methodologies.

This also explains why the existence of the Norms for Online Testing and Evaluation Activities (网络测评活动规范) is not an administrative burden — it is a necessary bridge connecting scientific method and public understanding.

The passage from a methodological dispute to institutional silence is the most pressing question this incident leaves behind. When the next consumer-safety incident occurs, if institutional self-protection overrides professional truth, which link of the information chain should the public believe?