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Learn FTIR spectrophotometer calibration with step-by-step procedure, wavenumber verification, resolution checks, frequency, acceptance criteria, and FAQs.
FTIR Spectrophotometer Calibration: Procedure, Wavenumber Verification, Resolution, Frequency, And FAQs
FTIR Spectrophotometer Calibration is essential to ensure accurate wavenumber measurement, proper resolution, and reliable analytical results. This article provides a step-by-step SOP-based approach for FTIR calibration, including wavenumber verification, resolution performance checks, calibration frequency, and acceptance criteria.
Objective
The objective of this Standard Operating Procedure (SOP) is to describe the method for calibration and performance verification of the FTIR spectrophotometer, ensuring accuracy, reliability, and compliance with laboratory quality requirements.
Scope
This procedure applies to:
All FTIR spectrophotometers installed at XXXX (Company Name)
FTIR instruments used in the QC / Analytical Laboratory of XXXX
Responsibility
Research Scientists / Chemists / Analysts Responsible for performing FTIR calibration as per this SOP and documenting results.
Head of Department (HOD) Responsible for ensuring effective implementation of this SOP within the department (QC / Analytical / applicable area).
Operate the FTIR instrument as per the approved Operational SOP.
Ensure the instrument and sample compartment are clean and free from dust.
Use a certified Polystyrene film reference standard with a valid Certificate of Analysis (COA).
The thickness of the Polystyrene film should be:
38 µm (micron) or 0.038 mm
Instrument Parameter Settings
Place the Polystyrene film in the sample chamber and set the instrument parameters as follows:
Resolution: 2 cm⁻¹
Measurement Mode: % Transmittance
Number of Scans: 1 to 20
Scan Range: 4000 to 400 cm⁻¹
Note: The scan range may vary depending on the FTIR model. Always set the scan range according to the instrument manufacturer’s recommendation.
Related:
Procedure for Wavenumber Verification
Wavenumber accuracy is verified using the calibrated Polystyrene film, which exhibits characteristic absorption peaks (transmittance minima) at known wavenumbers.
Table 1: Wavenumber Verification Using Polystyrene Film
Standard Wavenumber (cm⁻¹)
Tolerance (cm⁻¹)
Acceptance Criteria (cm⁻¹)
3060.0
±1
3059 – 3061
2849.5
±1
2848.5 – 2850.5
1942.9
±1
1941.9 – 1943.9
1601.2
±1
1600.2 – 1602.2
1583.0
±1
1582.0 – 1584.0
1154.5
±1
1153.5 – 1155.5
1028.3
±1
1027.3 – 1029.3
Acceptance Criteria
All observed peak positions must fall within the specified tolerance range.
Procedure for Resolution Performance Verification
Record the FTIR spectrum of the Polystyrene reference standard.
Measure the % absorbance values at the following positions:
Resolution Check – Region 1
Absorption minimum at 2870 cm⁻¹
Absorption maximum at 2849.5 cm⁻¹
Acceptance Criterion: Difference in % absorbance (X) must be greater than 0.33
Resolution Check – Region 2
Absorption minimum at 1589 cm⁻¹
Absorption maximum at 1583 cm⁻¹
Acceptance Criterion: Difference in % absorbance (Y) must be greater than 0.08
Documentation
Record all calibration results in the FTIR Calibration Logbook or Electronic Record
Attach the spectrum printouts and the COA of the Polystyrene reference standard
Any deviation must be investigated and documented as per quality procedures
Why is polystyrene film used for FTIR calibration?
Polystyrene exhibits well-defined, sharp absorption peaks across the IR region, making it an ideal reference standard for wavenumber accuracy and resolution verification. Its coating also prevents the decay of the KBr window from the moisture effect
What is the thickness of polystyrene film for IR calibration?
About 38 micrometres (µm) thick
What happens if FTIR calibration fails?
If acceptance criteria are not met:
Stop using the instrument
Inform the HOD
Perform troubleshooting, maintenance, or service calibration before reuse
Is FTIR calibration mandatory for GMP labs?
Yes. FTIR calibration is required under GMP, GLP, and ISO guidelines to ensure data integrity and analytical accuracy.
