CEI-MS-04 — procedure

§4Procedure

The procedure below is written in the second person, which is the only place in the Institute's document set where that register is used. A procedure is an instruction and is written as one.

1. Condition the cell until the drift falls below 20 µg/min and remains stable for 5 minutes.
2. Verify the system with the water standard. Recovery must fall within 97.5–102.5 %.
3. Transfer 5 to 20 mg of sample into a tared septum vial inside the dry enclosure. Record the exact mass. Hygroscopic peptides gain water measurably within 60 seconds of exposure to ambient air, so the transfer time should be recorded.
4. Introduce the sample into the cell through the septum without opening the cell.
5. Titrate to the electrometric endpoint with the drift correction applied.
6. Perform three determinations. Where the relative standard deviation exceeds 5 %, investigate sample homogeneity and transfer technique before reporting.
7. Report water content as a percentage of sample mass, to one decimal place, together with the number of determinations.

References cited on this page

References are numbered in order of first citation in this document. Each superscript in the text links to its entry below.

1. United States Pharmacopeial Convention. General Chapter ⟨921⟩ Water Determination. United States Pharmacopeia — National Formulary (USP–NF) 2024;USP 2024 Issue 1. identifier not held by the Institute

Identifiers are reproduced only where the Institute holds them. Where a digital object identifier or PubMed identifier is not shown, the Institute has recorded the journal and year and has not constructed an identifier.