ppm, mcg and percentage (%) In Pharmaceutical Analysis: 5 Minutes Quick Learning

ppm, mcg and percentage are the units of measurement and play a crucial role in pharmaceutical development.

In both synthetic and analytical chemistry, precise measurements are key to accurate sample preparation and analysis. Among the most frequently used units in this process are ppm, mcg/µg, and % – terms that, while common, often lead to confusion for many chemists. Whether you’re an analytical chemist or working in quality control, a solid grasp of these units is essential for effective work.

The goal of this post is to clarify any uncertainties you may have about these terms and to provide you with the knowledge to confidently answer questions like:

• What is PPM?
• What does µg mean?
• How are PPM, µg, litres, and kilograms related?
• What do µg, µg/ml, and % represent?
• How do you convert PPM to % and vice versa?
• What is the difference between PPM and µg/ml?
• Where is PPM used vs. where is µg used?

By the end of this guide, you’ll be equipped with the knowledge to navigate these concepts with ease and apply them confidently in your day-to-day work.

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ppm, mcg and percentage

ppm, mcg and percentage play a crucial role in pharmaceutical development in both synthetic and analytical chemistry.

ppm

ppm stands for parts per million, or out of 1000000 or out of 10⁶. This is a mode of expressing the presence of a substance ( at a very low concentration) in the main substance, such as the presence of an impurity in a drug substance. It is a dimensionless quantity. Examples: 

• The limit of toluene in an API (active pharmaceutical ingredient) is 890 ppm,  which means the allowable limit of toluene per kg or per 10⁶mg or 1000000 mg of API is 890 mg.
• The limit of Ethanol in an API  is 5000 ppm,  which means the allowable limit of Ethanol per kg or per 10⁶ mg or 1000000 mg of API is 5000 mg.
• The limit of Lead in an API is 10 ppm,  which means the allowable limit of Lead per kg or per 10⁶ mg or 1000000 mg of API is 10 mg.
• The limit of Calcium in Soil is 540 ppm,  which means the allowable limit of Calcium per kg or per 10⁶ mg or 1000000 mg of soil is 540 mg.

ppm is generally used to keep the specification of an impurity in the main Analyte or API. It is expressed in terms of weight by weight (w/w) and volume by volume (v/v).

mcg or µg

It stands for microgram. It is the unit of weight. It is expressed as  weight by volume

mcg or µg= (1/1000)mg or 1mg=1000 mcg or µg

mcg/ml or /µg/ml

It stands for microgram out of 1 ml or microgram per ml. mcg/ml or µg/ml is used to specify the concentration in solution and not to specify the impurity limit.

Example:

• 5000mcg/ml or µg/ml of ethanol in water; which means 1ml water contains 5000 microgram of Ethanol
• 890 mcg/ml or µg/ml of toluene in Toluene, which means 1mlof Ethanol contains 890 micrograms of toluene

Relation between Percentage and ppm

%=(ppm/1000000)×100 or

Case study: What will be the percentage of 5000 ppm Ethanol?

%=(5000/1000000)×100=0.5%

Relation between ppm, mg and litre (L) and Kg

• 1 ppm = 1 mg/L or
• 1 ppm = 1 mg/Kg

What is the difference between mcg and ppm?

ppm is relative to the main compound, whereas mcg/ml is relative to the solvent used for dilution. Secondly, ppm is denoted in w/w or v/,v whereas mcg is denoted in w/volume.

mcg (microgram) and ppm (parts per million) are both units used to express concentrations, but they are used in different contexts and have different meanings.

mcg (microgram):

• A microgram is a unit of mass that is equal to one-millionth of a gram (1 mcg = 0.000001 g).
• It’s commonly used to measure small amounts of a substance, especially when dealing with things like nutrients, pollutants, or medications.
• When you see a concentration in mcg, it’s referring to the mass of the substance (for example, a drug or contaminant) per given amount of a sample.

ppm (parts per million):

• ppm is a unit of concentration that expresses the number of parts of a substance per one million parts of the total mixture.
• It is commonly used for concentrations in gases, liquids, or even in solid mixtures where the substance is present in extremely small quantities.
• 1 ppm is equivalent to 1 mg of a substance in 1 liter of water (if it’s a liquid) or 1 mg of a substance in 1 kg of the material (if it’s a solid).

mcg to ppm conversion or how to convert mcg to ppm?

• You can convert between mcg and ppm, but the conversion depends on the density and the total mass or volume of the solution or sample. In some cases, when dealing with water or liquids with similar density, you can consider:1 ppm ≈ 1 mcg/mL (for water).So, 1 ppm in water is roughly equal to 1 mcg per milliliter of the solution.

Example:

If you have 1 ppm of a substance in water, it means you have 1 mcg of that substance in 1 liter (1000 mL) of water.

mcg to mg or how to convert mcg to mg?

To convert micrograms (mcg) to milligrams (mg), you can use the following relationship:

1 milligram (mg) = 1,000 micrograms (mcg)

So, to convert mcg to mg, divide the number of micrograms by 1,000.

Example: If you have 500 mcg, to convert it to mg, it will be 500/1000 = 0.5mg

How to convert ppm to mg or kg

ppm to mg (for liquids):

• 1 ppm = 1 milligram per liter (mg/L) in water (for dilute solutions).
• To find the mass in mg, use this formula:

Case Study: if you have a concentration of 10 ppm in 2 litres of water:

Mass in mg = 10 ppm×2 L=20 mg

ppm to kg (for liquids):

• Since 1 mg = 10⁻⁶ kg, you can convert mg to kg by dividing by 1,000,000.
• To find the mass in kilograms, use the formula:

Case study: if the concentration is 10 ppm in 2 liters: (10 × 2) ÷ 1000000 = 0.00002kg

Percentage (%)

% stands for parts per 100 or out of 100 or out of 10²

Conclusion

This is a crucial topic, as a clear understanding of units like ppm, mcg, and % is essential across all types of analytical techniques – including chemical analysis, HPLC (High-Performance Liquid Chromatography), GC-MS (Gas Chromatography-Mass Spectrometry), and more. Mastery of these units ensures precision and reliability in every step of the analysis.

I hope this post has helped clarify your doubts and deepened your understanding of This is a crucial topic, as a clear understanding of units like PPM and µg is essential across all types of analytical techniques—including chemical analysis, HPLC (High-Performance Liquid Chromatography), GC-MS (Gas Chromatography-Mass Spectrometry), and more. Mastery of these units ensures precision and reliability in every step of the analysis.

I hope this post has helped clarify your doubts and deepened your understanding of PPM, µg, and related units. If you found this helpful, I encourage you to share your learnings or any remaining questions in the comments. Your feedback motivates me to continue creating more skill-focused content for the chemistry community, and related units. If you found this helpful, I encourage you to share your learnings or any remaining questions in the comments. Your feedback motivates me to continue creating more skill-focused content for the chemistry community.

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FAQs

How do you convert mcg to ppm?

pm and mcg both are same. ppm is used to specify impurity or a substance (at low concentration) in the main substance whereas mcg/ml is used to specify the dilution

What is relationship between ppm and mcg?

ppm and mcg both are same. ppm is used to specify impurity or a substance (at low concentration) in the main substance whereas mcg/ml is used to specify the dilution

What is 1 ppm equal to?

Following is the relationship between % and ppm

%=(ppm/1000000)×100.

Therefore 1 ppm is equal to 0.0001%. It means a drug substance contains 1 ppm of Benzene (as a impurity) and a drug substance contains of Benzene (as a impurity) 0.0001% are same.

What is 100 ppm equal to?

The following is the relationship between % and ppm

%=(ppm/1000000)×100. Therefore 100 ppm is equal to 0.01%.

Is 1 ppm equal to 1 microgram /ml?

Yes

How many ppm in a mg?

1 mg is equal to 1000000 ppm

Can you convert ppm to mg and Kg?

Yes. ppm is a relative value and it is used to specify impurity or a substance (at low concentration) in the main Drug substance/ main Analyte whereas mg and Kg are absolute terms.

1 ppm is equal to 1/1000000 mg or 10^-6 mg or 10^-18 Kg. For example Paracetamol drug substance having toluene as an impurity and its value is 1 ppm. We can say paracetamol have 1 ppm of toluene or 10^-6 mg of toluene or 10^-18 Kg of toluene.

Abbreviations:

• ppm: Parts per million
• mcg or µg: microgram
• mcg/ml or µg/ml: microgram per ml
• w: weight
• v: volume
• mg: milligram
• L: litre
• Kg: kilogram