QC Consistency — How to Use
Compare an incoming FTIR spectrum with qualified historical batches of the same material. The workbench supports consistency screening and investigation; it does not by itself replace your laboratory SOP or release decision.
What this workbench does
- Builds a reference library from qualified historical batches you already trust.
- Compares each incoming sample with that material-specific reference library.
- Shows a graded result together with spectral and numerical evidence.
- Highlights important spectral differences and monitoring regions.
- Keeps a dated QC history for traceability and later review.
When to use QC Consistency
- Incoming raw-material screening.
- Batch-to-batch consistency checks.
- Supplier or process-change investigation.
- Stability or retained-sample comparison.
- Routine checks where the question is: does this spectrum look like my qualified material?
The workflow in three steps
Step 1 — Build a good reference library
Create a separate library for each material or grade that you want to monitor. The reference set should represent normal, qualified variation rather than a mixture of unrelated materials.
- Material name — Use a clear name such as 'Aspirin API' or 'Polyethylene Grade A'.
- Reference batches — Upload historical batches that have already passed your normal qualification process.
- Context — Keep composition and batch notes where they help explain expected variation.
Good practice: Add representative qualified batches over time, but do not add a new batch simply because it failed the current comparison.
Analysis modes
The default mode changes with reference-library size:
- Similarity: 1–19 references — Direct spectral similarity and peak-difference evidence.
- PCA: 20–49 references — Adds multivariate modeling of the variation in the qualified reference set.
- SIMCA-style class model: 50+ references — Adds class-model diagnostics for larger qualified reference sets.
Note: These are the default thresholds. A deployment can configure different thresholds, and the workbench shows the active mode.
Step 2 — Screen the incoming sample
- Choose the correct reference library — Do not compare a sample with a different material or grade just because the spectra look similar.
- Upload only the incoming sample — Qualified historical batches belong in the reference library, not in the incoming-sample field.
- Run the comparison — The workbench preprocesses the spectrum and applies the active analysis mode and monitoring windows.
Step 3 — Read the result
Do not rely on the headline label alone. Review the evidence that produced it:
- Result label — The wording is mode-dependent; similarity mode can report Highly Consistent, Moderately Consistent, or Inconsistent.
- Spectral overlay — Shows the incoming spectrum against the qualified reference pattern.
- Difference peaks — Shows where the incoming sample differs most from the reference.
- Similarity or multivariate diagnostics — The exact numerical evidence depends on whether Similarity, PCA, or the class model is active.
How to interpret a flag
Strongly consistent result — The spectrum falls within the configured reference criteria. Apply your normal QC and SOP review before disposition.
Borderline or moderate result — Review the overlay, difference peaks, acquisition conditions, and batch context before deciding what to do next.
Inconsistent result — The spectrum falls outside the configured reference criteria. This tells you that the sample differs; it does not by itself identify the cause.
Monitoring windows
Monitoring windows focus attention on spectral regions that matter for your material. Use them when a known band or region is especially important, but keep the whole-spectrum evidence in view.
- Add or review recommended monitoring regions for the material.
- Compare the incoming sample with the reference behavior in each monitored region.
- Treat a window-level difference as evidence to investigate, not as a standalone chemical identification.
QC history
Each screening can be revisited from the QC history with its sample, date, reference library, result, and detailed evidence. This provides a dated traceability record for internal review.
