Bracketing Standards
Definition
Calibration standards or quality control samples injected before, during and after a batch of case samples. They track instrument drift through the run. The CFSL Chandigarh toxicology SOP requires a bracketing standard every ten case injections; if the bracket fails, the case samples between the last passing bracket and the failing one are re-run.
- Purpose
- Track instrument drift through an analytical run
- Placement
- Before, during and after a batch of case samples
- Example SOP
- CFSL Chandigarh toxicology, every ten case injections
- Failure response
- Re-run samples between last passing and failing bracket
Common questions
What problem do bracketing standards actually catch?+
They catch gradual instrument drift, such as a slipping calibration curve or declining detector sensitivity, that would not show up on a single calibration run at the start of a batch but can shift quantitation for samples analysed later in a long sequence.
Why does a failed bracket only invalidate some of the samples in a batch, not the whole run?+
Because drift is progressive, only the samples analysed between the last bracket that passed and the one that failed are at risk of inaccurate results; samples bracketed by two passing standards are considered reliable, which limits how much of a batch must be re-run.
Related terms
- Calibration Curve
- In RIA, a set of standards containing known concentrations of unlabelled analyte that are run alongside test samples. Bound radioactivity is measured...
- Certified Reference Material (CRM)
- A sample with one or more analyte concentrations established by an accredited body and traceable to a national metrology institute. NIST SRM...
- Extraction
- The first step in sample preparation. The analyte is pulled out of its original matrix (blood, urine, viscera, soil, paint chip) into...
- Internal Standard (IS)
- A compound chemically near-identical to the analyte, often a deuterated isotopologue (d3-morphine, d5-EDDP, d5-alprazolam, pyrene-d10), spiked into every sample at a known...
- Limit of Detection (LOD) and Limit of Quantitation (LOQ)
- LOD is the lowest concentration the instrument can reliably distinguish from blank, defined as three times the standard deviation of the blank...
- Recovery
- The fraction of analyte that survives the extraction and clean-up workflow, measured by spiking a known amount of analyte into a blank...