Glossary

HPLC separates compounds based on how strongly each one interacts with the column packing relative to the liquid solvent (the mobile phase). Different compounds leave the column at different times, called retention times, and are recorded as peaks on a chromatogram. The area under each peak is proportional to the relative amount of that compound in the sample.

For peptide certificates of analysis, HPLC is the usual method for reporting purity. A typical specification reads something like purity by HPLC at 220 nm greater than or equal to 98 percent, where 220 nm is the detection wavelength used to register the peptide bond.

A mass spectrometer converts molecules into charged ions, sorts those ions by their mass-to-charge ratio, and counts how many arrive at each ratio. The result is a spectrum of intensity versus mass-to-charge that acts as a fingerprint of the sample.

In peptide work the central use is identity confirmation. The observed mass is compared against the theoretical mass calculated from the amino acid sequence, and a small mass error between the two supports that the correct compound is present. Mass spectrometry is frequently paired with a separation step, as in LC-MS, so that each separated peak can also be weighed.

Retention time is measured from the moment a sample is injected to the moment its peak reaches the detector. A compound that interacts strongly with the column packing moves slowly and has a longer retention time, while a weakly interacting compound moves quickly and elutes sooner.

Because retention time depends on the column, the mobile phase, the temperature, and the flow rate, it is only meaningful when those conditions are held constant. Reported alongside a reference standard run under the same conditions, a matching retention time is one piece of evidence that a peak is the expected compound.

Section 503A describes the conditions under which a compounded preparation is exempt from certain federal requirements that apply to manufactured drugs, such as new drug approval and the full set of current good manufacturing practice rules. A 503A pharmacy generally compounds on a patient-specific basis pursuant to a prescription.

The substances a 503A pharmacy may compound with are constrained by frameworks such as the relevant bulk drug substances lists. This entry describes the regulatory category and does not assert the status of any specific substance, which can depend on its listing, its form, and current agency action.

A beyond-use date is set by the compounder based on factors such as the preparation type, the sterility risk level, the storage conditions, and any available stability data. It reflects how long the preparation is expected to retain its quality and sterility after it is prepared or after a container is first entered.

Beyond-use dates differ from expiration dates, which are established by a manufacturer through formal stability studies on a packaged product. Standards such as USP <797> provide default beyond-use date limits for sterile preparations, which can be extended only when supported by appropriate testing.

USP General Chapter <797> defines the standards for compounding sterile preparations in the United States, including air quality classifications, facility and equipment controls, personnel garbing and hand hygiene, and the assignment of beyond-use dates.

One frequently cited provision is the handling of multi-dose containers, which the chapter directs be discarded within a set window after first entry unless the manufacturer specifies otherwise. The chapter is enforceable where adopted by state boards of pharmacy and similar authorities. It describes a framework for sterile practice and does not by itself address the legal status of any particular substance.

In lyophilization the sample is frozen and then placed under vacuum so that the ice converts directly from solid to vapor without passing through a liquid phase. The result is a dry, porous cake or powder.

Peptides are commonly supplied lyophilized because a dry powder is far more stable than a solution and can be stored longer. Residual moisture in the powder is often measured by Karl Fischer titration, since leftover water can shorten stability and affect the accuracy of the stated content. The powder is returned to solution by reconstitution before use.

Half-life describes the rate at which a substance leaves the system, defined as the time for its concentration to drop to one half of a starting value. A short half-life means rapid clearance, while a long half-life means the substance persists.

Half-life governs how concentrations build toward steady state during repeated exposure and how long they take to decline afterward. As a rough guide, a compound approaches steady state after roughly four to five half-lives, and clears by a similar number. The parameter is descriptive and is presented here to explain how pharmacokinetic data are reported, not as guidance for any use.

A certificate of analysis (COA) summarizes the testing performed on a particular batch or lot, reporting each measured attribute next to its specification and a pass or fail result. Common entries include identity confirmation by mass spectrometry, purity by HPLC, water content, and endotoxin level.

The value of a COA depends on what is behind it. A certificate tied to a specific lot, naming the methods used, identifying the laboratory, and ideally backed by the underlying raw data such as chromatograms and peak tables, is more verifiable than a generic certificate with results alone. Comparing the stated batch and lot against the physical product is part of confirming that a certificate actually applies to the material in hand.

Semaglutide is a peptide engineered from the GLP-1 sequence with modifications that resist enzymatic breakdown and bind albumin, extending its half-life to allow once-weekly injection (or a daily oral form). As a GLP-1 receptor agonist it enhances glucose-dependent insulin secretion, slows gastric emptying, and reduces appetite.

It is approved by the FDA and other regulators: as Ozempic (injectable) and Rybelsus (oral) for type 2 diabetes, and as Wegovy for chronic weight management. Because it is an approved drug, legitimate supply is through prescription. This entry describes the compound and its regulatory status and is not guidance for use.

Tirzepatide is a single peptide that activates both the GIP and the GLP-1 receptors, a combination intended to improve glycemic control and weight outcomes relative to GLP-1 action alone. Like semaglutide it is modified for a long half-life and once-weekly injection.

It is approved by the FDA and other regulators as Mounjaro for type 2 diabetes and as Zepbound for chronic weight management. As an approved drug, legitimate supply is by prescription. This entry is descriptive and not guidance for use.

BPC-157 is a stable synthetic peptide of 15 amino acids based on a partial sequence of a protein isolated from gastric juice. Most published work is preclinical, in cell and animal models, examining effects on tendon, ligament, muscle, and gut tissue repair and on blood vessel formation. Human clinical evidence is limited.

BPC-157 is not approved for human use in the United States or other major jurisdictions. The FDA reviewed it as a bulk drug substance for 503A compounding and identified significant safety and characterization concerns, placing it in the category that the agency does not intend to allow during review. This entry describes the compound and its status neutrally and is not guidance for use.