How to read a certificate of analysis

A certificate of analysis (COA) is a document issued for one batch of a material that lists each test performed on that batch, the acceptance limits for each test and the numerical results obtained. ICH Q7 defines a batch, or lot, as a specific quantity of material produced in a process or series of processes so that it is expected to be homogeneous within specified limits (ICH Q7, FDA docket FDA-1995-D-0288). A certificate reports results for samples drawn from that quantity.

Identity and purity are separate results

ICH Q6B lists identity and purity as separate specification items. It states that identity tests should be highly specific, based on unique aspects of the molecular structure or other specific properties, and that more than one test may be necessary (ICH Q6B, FDA docket FDA-1998-D-0003). A review by Lian and colleagues describes liquid chromatography-mass spectrometry as increasingly used to characterize synthetic peptides and their impurities (Lian et al. 2021, PMID 34110145). A purity result does not establish identity.

ICH Q6B also notes that identity tests can be qualitative in nature (ICH Q6B, FDA docket FDA-1998-D-0003), so an identity result may be reported as a match rather than as a number.

Purity is method-dependent

Mant and colleagues describe the major HPLC modes for peptides as separating by differences in size (size-exclusion), net charge (ion-exchange) or hydrophobicity (reversed-phase); they state that peptide bonds absorb strongly in the far ultraviolet, below 220 nm, so detection is generally at 210-220 nm, and that peptide resolution in reversed-phase HPLC can be adjusted by varying the steepness of the acetonitrile gradient (Mant et al. 2007, PMID 18604941).

ICH Q6B states that the determination of absolute, as well as relative, purity presents considerable analytical challenges and that the results are highly method dependent (ICH Q6B, FDA docket FDA-1998-D-0003). A purity figure is therefore read together with the method that produced it.

Batch number and dates

Section 11.4 of ICH Q7 lists the name of the material, its grade where appropriate, the batch number and the date of release, and states that where the material has an expiry date or a retest date, that date should be given on the label and the certificate (ICH Q7, FDA docket FDA-1995-D-0288). A certificate from another batch is a record of different material.

What a COA cannot establish

ICH Q6B lists endotoxins, sterility and microbial limits as separate pharmacopoeial tests (ICH Q6B, FDA docket FDA-1998-D-0003). A certificate reports on sterility or endotoxin only where it lists such a test, and each result applies only to the samples tested by the method used.