Is There a Right Time to Use PPM Instead of μg/mL in Technical Communication?

Is There a Right Time to Use ppm over μg/mL?

The choice between ppm (parts per million) and μg/mL (micrograms per milliliter) depends on context, clarity needs, audience, and formal correctness. While ppm is widely used informally and in some technical fields, μg/mL provides clearer, less ambiguous communication—especially in formal, biochemical, or regulatory settings.

Understanding ppm and μg/mL

ppm essentially means one part substance per million parts total. It can represent weight/weight (w/w), volume/volume (v/v), or, less formally, weight/volume (w/v). However, ppm’s formal definition restricts it primarily to w/w or v/v ratios. When used as a w/v measure, ppm is common but technically incorrect.

μg/mL

Clarity and Communication

Clear communication is key in scientific contexts. Using ppm without specifying the basis (w/w, w/v, or v/v) can cause confusion.

• ppm without a unit basis is ambiguous.
• μg/mL is specific and less prone to misinterpretation.
• For formal documents, standards, and reports, μg/mL or mg/L should be preferred.

Overall, the trend is moving away from ppm to eliminate ambiguity and improve clarity.

Audience and Professional Context

Which unit to use often depends on the professional audience:

• Engineers tend to use ppm more frequently, as their work often involves large-scale systems where ppm is convenient.
• Biochemists and medical professionals favor μg/mL for its precision and relevance to biological concentrations.
• Within technical teams familiar with specific tests and reports, ppm can be a quick shorthand.

Adjusting the units to the audience’s expectations improves understanding.

Informal versus Formal Usage

ppm works well in informal discussions due to its brevity and familiarity.

However, ppm is less suitable for formal contexts, such as:

• Scientific publications
• Technical reports
• Specification sheets
• Regulatory documents

These settings require unambiguous, standardized units like μg/mL, mg/L, or % w/w, ensuring compliance with IUPAC nomenclature.

Technical Teams and Internal Communication

In teams where everyone understands the testing and reporting units, ppm (or ppb, ppt) serves as an efficient shorthand.

Yet, even in such settings, all solutions and standards are ideally labeled in μg/mL, μg/L, or ng/L to maintain consistency and reduce errors.

Formal Correctness and Ambiguity

Aspect	ppm	μg/mL
Definition	Formally w/w or v/v; w/v tolerated but incorrect	Weight per volume; precise and correct
Ambiguity	Requires specifying w/w, w/v, or v/v to avoid confusion	Clear and unambiguous
Context of Use	Informal conversation or specific technical fields	Formal publications, biochemical, clinical analyses

Reliable communication demands specifying the unit basis when using ppm. Without it, ppm causes confusion.

Other Contextual Uses of ppm

ppm does not always imply mass or volume concentration. For example, in proton nuclear magnetic resonance (NMR), ppm denotes a ratio of frequencies (Hz/MHz) used for chemical shifts.

This highlights the importance of context when interpreting ppm values.

Recommendations for Choosing Between ppm and μg/mL

• Use μg/mL in formal writing, biochemical, clinical, and regulatory documents to ensure clarity and accuracy.
• Reserve ppm for informal communication among colleagues or engineering contexts where its meaning is well understood.
• Always specify the basis (w/w, w/v, or v/v) when using ppm to avoid ambiguity.
• Be aware of contextual meanings of ppm outside mass/volume (e.g., NMR) and clarify as needed.
• Adopt standardized SI units like mg/L, % w/w for publications to maintain international consistency.

Key Takeaways

• ppm is convenient but often ambiguous if used without clear unit basis.
• μg/mL provides unambiguous weight/volume concentration and suits formal communication.
• Choice depends on audience: engineers prefer ppm; biochemists opt for μg/mL.
• Formal documents should avoid ppm unless clearly defined; informal talk allows more flexibility.
• Context matters; ppm may mean something else (e.g., frequency ratio) in some fields.

When is it acceptable to use ppm instead of μg/mL?

Use ppm informally in quick conversations within experienced teams. It’s faster but only clear if everyone understands the units involved. For formal documents, μg/mL or other clear units are better.

Why can ppm cause confusion compared to μg/mL?

ppm can mean weight/weight, volume/volume, or sometimes weight/volume. Without specifying this, it’s ambiguous. μg/mL clearly shows mass per volume, avoiding this confusion.

Does the choice between ppm and μg/mL depend on the audience?

Yes. Engineers often use ppm, while biochemists prefer μg/mL. Adjust units based on who you’re communicating with for clarity.

Is using ppm as weight/volume always correct?

No. ppm is formally weight/weight or volume/volume. Using ppm as weight/volume, like μg/mL, is common but technically incorrect and may cause misunderstanding.

Are there cases when ppm means something other than mass concentration?

Yes. In proton NMR, ppm refers to frequency ratio (Hz/MHz), not mass concentration. So, ppm’s meaning depends on the field and context.