QC Consistency · Guide
Quality Control · FTIR.fun
Guide

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

1Build the reference libraryUpload qualified historical FTIR files for one material. Use only batches that are already accepted by your normal qualification process.
2Screen an incoming sampleSelect the correct material library, upload the new FTIR file, and run the comparison.
3Review the evidenceRead the result together with the overlay, difference peaks, similarity score, and multivariate diagnostics when applicable.

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.

FAQ

Can I use this for complex mixtures?
It works best when the qualified product itself is compositionally stable. If components vary intentionally across samples, Research Batch is usually a better comparison workflow.
How often should I update the reference library?
Add newly qualified batches when they represent normal production variation. Keep the reference set aligned with your current material specification and SOP.
What if an apparently good material is flagged?
Check acquisition conditions, sample preparation, the spectral overlay, difference peaks, and whether the reference set represents current normal variation. Investigate before changing thresholds or adding the sample as a reference.
Is the QC history a formal compliance record?
It is a dated traceability record. Whether it satisfies a formal quality or regulatory requirement depends on your validated procedure, SOP, electronic-record controls, and applicable regulations.
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