Solution Concentration Reference for Research Materials
For research use only. Not for human or veterinary use. PureLab Performance supplies analytical research materials to qualified laboratory researchers. Nothing on this page is guidance for preparing, administering, or using any material in a person or animal.
What this page covers
This reference explains how concentration is expressed and recorded in laboratory documentation. It is a units-and-records reference. It does not describe how to prepare any PureLab material, and it does not provide preparation steps, volumes, or administration information for any product.
How concentration is expressed in laboratory settings
- Mass concentration (mg/mL, µg/mL, ng/mL). The mass of a substance per unit volume of solution. 1 mg/mL equals 1,000 µg/mL; 1 µg/mL equals 1,000 ng/mL.
- Molar concentration (mol/L, mM, µM). The amount of substance per litre. Converting between mass and molar concentration requires the compound’s molecular weight, which should come from a verified source such as the certificate of analysis or a primary chemical reference.
- Percent (w/v, w/w, v/v). Common for buffers and reagents; the basis (weight or volume) must always be stated.
- Parts per million / billion. Typically used for trace impurities such as residual solvents or heavy metals in analytical reports, not for working solutions.
Purity versus content: why the label number is not the whole story
A certificate of analysis can report two different numbers:
- Purity (HPLC area %) describes how much of the detected signal belongs to the target compound relative to detected impurities.
- Content versus label (assay) describes how much target compound was measured compared with the amount stated on the label.
A material can be high purity yet contain less (or more) compound than labeled, because counterions, water, and other non-peptide mass are present. Any concentration recorded in a laboratory notebook should note which figure it relied on. PureLab publishes content-versus-label results as returned by the testing laboratory where they were measured.
Documentation standards for research solutions
Good laboratory records for any solution typically include:
- Material name and exact lot number, linked to its certificate of analysis
- Certificate ID, testing laboratory, and report date
- Which assay figure (purity or content) was used for calculations
- Solvent or buffer identity, grade, and lot
- Stated concentration with units and basis
- Preparer, date, and storage conditions recorded per the laboratory’s own SOP
- Expiry or re-test date as defined by the laboratory’s quality system
Verifying the inputs
Before relying on any concentration figure, confirm the lot on hand matches the certificate you are reading. See:
- Certificates of Analysis library
- How to read a peptide certificate of analysis
- How to verify a certificate of analysis
- What research use only means
Why older guides were retired
PureLab previously published compound-specific preparation articles. Those pages have been retired and redirected here so our educational content stays focused on analytical documentation and lot verification.
For research use only. Not for human or veterinary use. Products are not drugs, foods, cosmetics, or dietary supplements and are not intended to diagnose, treat, cure, or prevent any disease. Purchasers are responsible for handling materials under their institution’s safety and regulatory requirements.