what about related substance test in HPLC?

[mfahe]

hi
i want know what does related substance mean? and why we use it? and how we calculated it"it's equations"?
many thanks

[tom jupille]

A "related substance" is a pharmaceutical industry term for contaminants which are structurally similar to the active drug (the are chemically "related"). In practice, the term is often applied to impurities and contaminants in a drug whether or not they are chemically related.

The importance should be self-evident. If I take an aspirin tablet, I want some assurance that the active is not highly contaminated with methyl salicylate.

The "equations" are extremely simple. The percentage by mass of each contaminant. If the "related substance" is present at a very low level, such that it cannot be identified, then you assume that the response is similar to that of the active drug and proceed accordingly.

[Yorkie31]

Just to expand on Tom's comments.

Related substances can be broken down into essentially 3 catagories.

Process Impurities - These will have come from the actual reactions used to create the final substance. These could be organic substances that may have been used as part of the reactions, or impurities created during the reactions. These can be Organic or Inorganic in nature.

Residual Solvents - All organic reactions will have been performed using organic solvents as a reaction media. Residual amounts of these may be left over from the reactions.

Degradation Products - Once the final product has been made, it may start to break down, creating smaller sub-molecules. These are degradation products and would be monitored as part of a stability study.

All of these come under the realm of "Related Substances". They are all related in some way to the main compound.

[Bruce Hamilton]

I suspect that residual solvents are classified separately in most countries, and are not considered as related substances.

Other terms may have different definitions, such as foreign substances, and the USP "Impurities" ( which then is defined into subclasses like ordinary impurities, toxic impurities, signal impurities, concomitant components etc etc.).

The EP defines related substances and residual solvents separately. It sets related substances limits for reporting, identification, and qualification based on the use ( human or animal ), substance concentration, and/or daily dose of the drug.

Bruce Hamilton