One product page says “pure”, another says “99.5%”, and a third says “for analysis”. Which piece of information helps you choose? Anyone ordering chemicals needs more than just the highest possible percentage: what matters is whether the documented properties match the intended use. This guide shows how to compare purity specifications and what information you should check before buying.

Table of contents

What does “pure” mean for chemicals?

“Pure” is first of all a grade designation. It does not mean that a chemical is completely free from water, secondary constituents, or other impurities.

Therefore, always read the designation together with the product specification: Which substance does it describe? What minimum content is specified? Are there limits for certain impurities?

A single percentage is not a substitute for this information. Depending on the application, different test parameters can be decisive: for example, the content of certain metals, the water content, or impurities that affect a laboratory procedure.

So the right question is: Which properties must the product demonstrably meet for my application?

Technical, pure, and for analysis: the differences

The following designations help you find your bearings. However, they cannot be reliably converted into a general table with fixed percentage limits.

Requirements also differ within analytical grades. Trace analysis, for example, may require particularly low limits for specific impurities.

For ordering, this means: Use the requirements of your method or process as the basis for your choice, rather than choosing solely by the highest percentage.

What a percentage tells you – and what it doesn't

Statements such as “≥ 99.5%” give a lower limit. However, their precise interpretation requires knowledge of the reference basis and, if applicable, the test method.

A simple hypothetical example: If a mass fraction of at least 99.5% in the delivered state is explicitly specified, 100 g of product corresponds to at least 99.5 g of the named substance. If, in contrast, the value refers to dried or anhydrous substance, this calculation cannot be applied unchanged to the package contents.

Therefore, look in the documentation for statements such as “based on the anhydrous substance.” The assay and water content may be listed separately. Also check whether limit values are specified for the impurities relevant to your application.

This illustrates two points:

• The main content does not automatically describe the type and amount of every individual impurity.
• Values can only be meaningfully compared if their reference basis and the relevant test parameters match.

If your process, for example, requires a specific maximum iron content, a statement of “99.9% pure” alone is not sufficient to confirm this requirement.

Two examples from the Biolaboratorium product range

Sodium bicarbonate: read the specific statement.

For the sodium bicarbonate 1 kg from Biolaboratorium, the product description states a purity of at least 99.5%.

This is specific information about the offered product. However, it does not automatically answer every further question, such as a limit value for a certain impurity required for your process. You should compare such requirements with the available specification before ordering.

L-ascorbic acid: consider the substance name and the product purpose together.

The L-ascorbic acid 1 kg from Biolaboratorium is described with a purity specification of 99.5% and as a product for professional use.

The substance name “Vitamin C,” which is also used, is not a substitute for confirmation that the product may be used as a food or food supplement. This suitability cannot be inferred from the name and percentage alone.

For your purchase decision, the documented specification of the specific product is what matters.

Which documents help with selection?

Start with the product description. If your application has special requirements, also check the technical documentation or ask targeted questions.

The safety data sheet provides information on hazards and the safe handling of the product. It does not replace a complete quality specification or a batch-specific analytical certificate.

A helpful inquiry to the supplier would be, for example:

“For our process, we need an iron content below X ppm. Is this limit specified for the article, and is there batch-specific evidence for it?”

This makes it possible to clarify an open question much more precisely than with “Is the product very pure?”

Checklist for purchasing chemicals

Before ordering, check these five points:

1. Substance and form: Do the chemical name and the required form match—e.g., anhydrous, as a hydrate, or as a solution?
2. Quality statement: What quality does the supplier explicitly state?
3. Content and reference basis: Is a minimum content stated, and what does it relate to?
4. Critical impurities: Are the limits relevant to your process documented?
5. Intended use: Has the required suitability been confirmed, or is information still missing?

If a requirement remains open, clarify exactly that point before purchasing. A higher percentage value for another product will not necessarily answer it.

Frequently asked questions about purity declarations

Does “pure” always mean 99.9%?

No. The term alone does not provide a universally valid percentage threshold. Read the specific purity statement and the associated specification.

Is 99.9% generally better than 99.5%?

For the same substance and the same reference basis, the stated main content is higher. Whether the product is better suited to your application also depends on the relevant impurities and additional requirements.

Is a pure chemical automatically harmless?

No. Purity says nothing about hazard. Pay attention to the labeling and the safety data sheet of the specific product.

Can I use a laboratory raw material because the same substance also occurs in food?

That cannot be inferred from this. What matters is whether the product offered meets the requirements for the intended use.