What Detection Limits Mean on a COA

Three related limits

The LOQ is higher than the LOD. Between them, a substance may be detected but not measured precisely.

How laboratories set them

Laboratories establish limits during method validation by repeatedly analysing blanks and low-level samples, then calculating the level at which a signal can be reliably distinguished from background noise. Accredited laboratories document this process as part of their quality system.^[1]

Why limits vary

• MethodICP-MS reaches lower limits than older methods for metals; see ICP-MS.
• Sample matrixComplex materials like shilajit can raise limits.
• Sample amountMore sample can lower limits.
• DilutionDiluting a sample raises the effective limit.

Is a limit low enough?

A useful rule of thumb is that a detection limit should be a small fraction of the legal limit, so that results can show clear compliance. Against the GB mercury limit of 0.1 mg/kg,^[2] a limit of 0.01 mg/kg is useful; one of 0.1 mg/kg isn’t, because it can’t show a result below the maximum.

Results between LOD and LOQ

Some reports flag results that are detected but below the quantification limit, sometimes with notes such as “detected, < LOQ” or a value in brackets. These mean the substance is present at a low level, but the exact figure is uncertain.

Reading “<” values

A result such as “< 0.05 mg/kg” usually means below the reporting limit. The true value lies somewhere between zero and that figure. For exposure estimates, treating it as equal to the limit gives a cautious worst case; see what “not detected” means.

Limits and measurement uncertainty

Results close to the limits carry more relative uncertainty. That is normal and one reason laboratories report measurement uncertainty. A large stated uncertainty, such as 55% on the AGROLAB arsenic result for Nature Elixirs batch SJ2509, reflects the method and sample rather than a problem with the report.^[3] Nature Elixirs is a brand evaluated by Best Shilajit UK. Read our evaluation to see the evidence and documentation we reviewed.

What to ask

1. What are the LOD or LOQ for each metal?
2. Are they well below the GB limits?
3. Is any result detected but not quantified?

The full guide

For examples and how detection limits apply in microbiology and pesticide screens, see detection limits and “not detected” results explained.

Why no method reaches zero

Every instrument has background noise, tiny signals present even when a sample contains none of the target substance. The detection limit is the point where a real signal can be told apart from that noise. That is why no laboratory can report “zero”, only “below” a stated limit.

Comparing results from different laboratories

If two laboratories report the same metal with different detection limits, their ND results aren’t equivalent. An ND with a lower limit tells you more. When comparing products, compare the limits as well as the results.

Putting it into practice

When you read a report, write the detection limit next to each metal and compare it with the GB limit. A limit that is a small fraction of the maximum gives a meaningful result; a limit close to or above it doesn’t. If limits aren’t stated, ask the brand or laboratory for them.

Why shilajit can be challenging

Shilajit combines organic humic material with minerals, which can interfere with some measurements. Laboratories manage this with careful digestion, dilution and correction methods, but these can raise detection limits compared with simpler materials. That is one reason accredited methods validated for complex samples matter.

In short

A detection limit tells you how low a method can see. Without it, you can’t judge a “not detected” result. With it, and with the GB limits beside it, you can.

Asking the right way

If a report lacks detection limits, a short, specific request works best: “Could you tell me the detection limits for lead, cadmium, mercury and arsenic on the report for batch [number]?” A careful brand or laboratory can answer that quickly. Keep the reply with your report.

The bottom line

Detection and quantification limits tell you how low a method can see and measure. They vary by method and sample, and they need to be well below legal limits for results to be meaningful. Always check they are stated.

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