Chemical testing laboratory selection: scope, method and the report

Commissioning the work

1. Name the analyte, the matrix and the method. The same compound in water, in soil and in a formulated product is three different tests with three different preparations and three different detection limits. A request naming only the analyte will be quoted against whatever the laboratory assumes.
2. Check the accreditation scope, not just the certificate. Accreditation is granted for specific methods on specific matrices over specific ranges. The scope document is public and it is where you confirm the laboratory is accredited for your test, rather than for a test that sounds like it.
3. State the detection limit you need. A limit of quantitation below your decision threshold is the point of the exercise. A result reported as less than a limit that sits above your specification answers nothing, and this is discovered after the invoice more often than before.
4. Agree sampling, or accept that the result is about the sample only. A result describes what was tested. Where the sample was taken, by whom and how it was preserved decides what it represents, and a laboratory that did not sample cannot answer for that half of the measurement.
5. Fix turnaround and the rush policy in writing. Standard turnaround, the rush premium and what happens if a result fails quality control and needs a repeat. The repeat clause is the one nobody reads and the one that decides the real timeline.

Sampling, preservation and holding times

Many methods have a holding time that starts at collection, and a sample analysed outside it produces a qualified result at best. Ask for the container, preservative and holding time per analyte before sampling rather than after.

Record the collection time on the container and on the chain of custody. A sample with no collection time cannot be shown to be within its holding time, whatever the laboratory does afterwards.

Reading the report from an analytical services laboratory, and what analytical laboratory services cover

The report should carry the method, the preparation, the limits of detection and quantitation, the quality control results for the batch, any qualifiers and the measurement uncertainty. A bare table of numbers is not reviewable.

Read the qualifiers. A result flagged for a failed spike recovery or an exceeded holding time is telling you something specific, and those flags are routinely ignored by people reading only the number column.

When a subcontracted test appears

Laboratories subcontract analyses outside their scope, which is legitimate and must be stated on the report. Ask in advance which tests would be subcontracted and to whom, because it adds transit, a second schedule and a second set of records.

Where the subcontracted test is the one that matters, consider going to that laboratory directly. The margin is real and so is the extra week.

Read chemical testing laboratories' schedules, and the method with them

Accreditation is granted method by method and matrix by matrix. A laboratory accredited for a metal in drinking water is not thereby accredited for the same metal in soil, and a result outside the schedule is not an accredited result even when the same instrument produced it.

Ask which published method will be used, at what reporting limit, and whether your matrix is on the schedule for it. Where a method is prescribed by a regulator, the prescribed method is the one that counts, and a technically better alternative is not a substitute.

Pharmaceutical raw material testing is specification-driven

Testing a raw material means testing it against a monograph or an agreed specification: identity, assay, impurities and any material-specific test, each by the stated method. The work is defined by the specification rather than by the analyte, which is why a quotation needs the specification attached.

Extractables and leachables studies are a different shape: a designed study on the container closure or device, at exaggerated conditions and then at real ones, with a toxicological assessment of what is found. They take months and are scoped by a protocol, not by a price per sample.

Evidential work has requirements beyond the analysis

Where a result may be used in a legal process, chain of custody, sample integrity, the analyst's competence record and the defensibility of the method all become part of the deliverable. The analysis is often the straightforward part.

That is why forensic laboratories are accredited under schemes with additional requirements and why their reports are written differently. Commissioning evidential work from a laboratory used to routine testing is a common and expensive mistake.

Environmental and building testing is regulated by sector

Asbestos, mould, radon, water quality and indoor air each have their own accreditation schemes, their own prescribed methods and, frequently, their own licensing for the people who take the samples. The sampling is where the result is decided, and a laboratory analysing a badly taken sample reports the sample faithfully.

For a building or a workplace, ask who takes the samples, under what scheme, and what the report will conclude. A laboratory result and an assessment of a building are different products, and the second is what a decision usually needs.

Emerging analytes and where the difficulty sits

Some analytes are difficult less because of the instrument than because of everything around it: ubiquitous contamination from laboratory materials, reporting limits at the edge of what is achievable, and an evolving list of compounds. Fluorinated compounds are the current example.

Ask which compounds are on the list, at what reporting limit, and what blank controls the laboratory runs. A method that reports a long list at a high limit and one that reports a short list at a low limit are answering different questions.

Corrosion testing laboratories, and the tests they run

Corrosion work is a set of standard exposures rather than one test. Salt spray and cyclic corrosion chambers rank coatings and finishes; immersion and electrochemical methods, polarisation and impedance, measure rate and mechanism on a material; and specific tests exist for pitting, crevice, intergranular attack and stress corrosion cracking. Each names a standard that fixes the specimen, the solution and the duration, so a quote is only comparable when the standard is named. Ask what the report states beyond a pass, since a rate in millimetres per year is what a design decision needs.

An analytical testing laboratory, and what to ask before sending

A general analytical laboratory is chosen on scope and on the paperwork rather than on instruments. Ask which methods it holds accreditation for, since accreditation is per method and per matrix and a laboratory can run a technique it is not accredited in; ask what the reporting limit is for your analyte in your matrix, which is a different number from the instrument's detection limit; ask how samples are received and stored, because holding time decides whether the result is defensible; and ask to see a specimen report, which is the deliverable you are actually buying.

A mineral testing laboratory, and what it runs

Mineral and ore work is a defined sequence: sample preparation by crushing, splitting and pulverising, which is where most error enters; assay by fire assay for precious metals, by four acid or aqua regia digestion with plasma spectrometry for base metals, and by X-ray fluorescence for rapid screening; plus moisture, density and sometimes mineralogical work by microscopy or diffraction. Ask about the preparation protocol and the quality control samples inserted per batch, since those decide whether a grade can be relied on.

A coal testing laboratory, and the standard suite

Coal is tested against a defined suite: proximate analysis for moisture, ash, volatile matter and fixed carbon, ultimate analysis for carbon, hydrogen, nitrogen and sulfur, calorific value by bomb calorimeter, ash fusion behaviour, and trace elements where emissions matter. Every one names a standard, and sample preparation, crushing, dividing and air drying, is where most of the variance enters. Ask which standards the laboratory is accredited for and how it controls the preparation, since a grade dispute is usually about the sample rather than the instrument.

Common questions

How do I check a chemical testing laboratory can do my test?

Read its scope of accreditation, which names the methods, matrices and ranges it is accredited for. A laboratory holding accreditation is not thereby accredited for everything it can physically run.

What has to be in a testing request?

The analyte, the matrix, the method or the specification you are testing against, the detection limit you need, the number of samples and the turnaround. Without those, two quotations are not comparable.

What does the measurement uncertainty on a report mean?

The range within which the true value is expected to lie. It matters most when a result sits near a specification limit, because a result inside the limit with an uncertainty that straddles it is not a clear pass.

Can a laboratory advise on what to test?

Many will, and it is worth asking early. A conversation before the samples are taken frequently changes the method, the preservation and the number of samples, and it is much cheaper than repeating the exercise.

Is an accredited result guaranteed for my sample?

Only if your method and matrix are on the laboratory's schedule. Accreditation is granted method by method and matrix by matrix, so ask which published method will be used and at what reporting limit.

Why is evidential testing different?

Because chain of custody, sample integrity, analyst competence records and method defensibility are part of the deliverable. Forensic laboratories are accredited under schemes with additional requirements and write their reports differently.

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