Ep 17 — Basic Instrument Operating Procedure (General FTIR)

Series: Infrared Spectroscopy Encyclopedia: From Principles to Practice
Chapter: Part 2 · Beginner — Entering the Lab
Target Audience: High school/undergraduate/graduate students, lab technicians new to the field
Prerequisites: Ep 11 (Dispersive vs FTIR), Ep 12 (Michelson Interferometer), Ep 13–16 (Sampling and Sample Preparation)
Reading Time: ~38 minutes

Introduction: The Hand That Touches the Instrument for the First Time

Trainers love to tell a story: PhD student Zhang had been doing synthesis for three years, and for the first time he approached a Bruker Tensor, staring at the control panel full of buttons, palms sweating. Which button to start? Where is the background collection? Is that red button the laser?

This "stranger effect" is very common in IR labs. FTIR instruments look like mini refrigerators, the control panel is simplified to just a few buttons, and the software interface appears complex—this "simple + complex" combination often leaves people unsure where to start [1][2].

But the truth is: The FTIR operating procedure is actually very standardized. Whether it's Thermo Nicolet, Bruker Tensor, or Shimadzu IRTracer, the underlying logic is the same set:

Power on → Purge → Stabilize → Background collection → Sample collection → Data save → Shutdown

Once you understand the purpose of each step, you can operate any instrument. This episode will explain the principles, key points, and pitfalls of each step in detail, and provide specific operations using Thermo Nicolet iS50 and Bruker Tensor II as examples. After reading this episode, you will be able to independently operate a new FTIR and avoid 90% of novice mistakes.

💡 Episode Positioning: Ep 11–16 covered theory, sampling, and sample preparation. This episode is the "instrument operation chapter," stringing that knowledge together into "a complete measurement."

1. Startup Procedure: "Waking Up" the Instrument

1.1 Pre-startup Checks

Startup is not just pressing the power button. Before powering on, the following items must be checked [1][3]:

Environmental Check:

• Room temperature 18–25°C (recommended 22°C, stable ±2°C)
• Relative humidity < 60% (best < 40%)
• No strong air currents in the room (avoid fans blowing directly at the instrument)
• No vibration sources on the instrument bench

Instrument Check:

• Power cord securely connected
• Desiccant (e.g., silica gel) effective (color-changing silica gel not pink)
• Sample compartment door closed
• Detector interface correct (DTGS default; MCT detector requires liquid nitrogen precooling for 30 minutes)

Supporting Equipment:

• Pellet press, mortar, liquid cell etc. ready (see Ep 16)
• Data storage media (USB drive or network storage)
• Software started (Thermo OMNIC, Bruker OPUS)

⚠️ Common Novice Mistake: Not checking desiccant before startup. If the silica gel has turned pink (saturated with water), the instrument interior may be damp, causing severe water vapor interference after startup [1][3].

1.2 Startup Steps (Using Bruker Tensor II as Example)

1. Connect power (switch on back panel)
   ↓
2. Start computer, log into OPUS software
   ↓
3. Click "Connect" in OPUS to connect to instrument
   ↓
4. Instrument self-test (~30 s, automatic)
   ↓
5. Start laser stabilization (auto, ~5 min)
   ↓
6. Start source (Globar or NIR source)
   ↓
7. Wait for source stabilization (~15–30 min)
   ↓
8. Instrument enters "Ready" state

Figure 1: Bruker Tensor II startup flow diagram (Reference [2])

Thermo Nicolet iS50 Procedure Similar [1][4]:

1. Press power (front panel)
2. Start computer, open OMNIC software
3. Software auto-connects to instrument
4. Select source (Globar for mid-IR)
5. Wait for source stabilization (~20 min)
6. Status bar shows "Ready"

1.3 Purging: Making the Instrument "Fresh"

The internal optical path of an FTIR is extremely sensitive to water vapor and CO₂ [1][3][5]:

• Water vapor: Sharp peaks at 3400, 1640, 550–700 cm⁻¹ and elsewhere
• CO₂: Double peaks at 2349 and 2360 cm⁻¹

These "ghost peaks" interfere with sample signals and must be removed by purging [1][3][5].

Purge Gas:

• Dry air (most common, RH < 10%)
• Dry N₂ (purer, higher cost)
• Liquid nitrogen boil-off (self-drying)

Purge Flow Rate:

• Sample compartment: 5–10 L/min (fast exchange)
• Optics compartment: 1–2 L/min (continuous purge)

Purge Time [1][3][5]:

• Routine measurements: 10–15 min
• High-precision measurements: >30 min
• After long shutdown: >1 hour

💡 Pro Tip: During purging, you can collect a "real-time monitoring spectrum" (open beam). If water/CO₂ peaks at 3400 and 2350 disappear or are below 0.05, purging is sufficient [5].

1.4 Source Stabilization

The FTIR source (Globar) requires time to reach thermal equilibrium [1][3]:

• Just after power-on, the source intensity drifts significantly, causing unstable baseline
• Typically 15–30 min stabilization needed
• High-end models (e.g., Bruker Vertex) have intensity monitoring; software indicates when stable

Methods to Judge Source Stability [3]:

• Collect a 100% line (background-background); flatness < 1% indicates stability
• Instrument software usually automatically shows "Ready" or "Stable"

1.5 Detector Preparation

DTGS Detector (most common) [1][3]:

• Room temperature operation, no liquid nitrogen needed
• Moderate sensitivity, suitable for routine analysis
• Ready immediately after power-on

MCT Detector (high sensitivity) [1][3]:

• Requires liquid nitrogen cooling (77 K)
• After filling with liquid nitrogen, wait 30 min for thermal equilibrium
• Liquid nitrogen needs replenishment every 8–12 hours
• Sensitivity 10–100 times higher than DTGS, suitable for trace analysis, imaging

⚠️ MCT Detector Usage Note: Insufficient liquid nitrogen will cause the MCT to warm up, dramatically increasing output noise. Always check liquid nitrogen level before each startup [1].

2. Background Spectrum: "Zeroing" Before Measurement

2.1 What Is a Background Spectrum?

Infrared spectroscopy measures the "absorption" of the sample, but the instrument itself and the air in the optical path also absorb IR light. To obtain pure sample absorption, these "non-sample" factors must be subtracted [1][3][6].

The background spectrum is the "zero reference" collected before measuring the sample—it includes:

• Spectral distribution of the source
• Absorption of optical components (beamsplitter, windows)
• Absorption of air in the optical path (water vapor, CO₂)
• Detector response curve

2.2 Background Collection for Transmission Mode

Transmission background: The optical path contains nothing (empty beam path); collect background [1][3].

Background:    Source ─→ [Air] ─→ Detector
                          ↑
                     Empty beam, no sample

Sample:        Source ─→ [Sample] ─→ Detector
                          ↑
                     Sample inserted

Important Principles [1][3][6]:

• Environmental conditions (temperature, humidity, purge) must be identical for background and sample collection
• Interval between background and sample collection should be as short as possible (< 5 min preferable)
• If any component in the optical path is changed (e.g., beamsplitter replaced, liquid cell added), background must be recollected

2.3 Background Collection for ATR Mode

ATR background: Collect background with the crystal surface clean and no sample [3][6].

Background:    Source ─→ [ATR crystal] ─→ Detector
                          ↑
                     Clean crystal (no sample)

Sample:        Source ─→ [ATR crystal + sample] ─→ Detector
                          ↑
                     Sample on crystal

Important Principles [3][6]:

• Crystal must be thoroughly cleaned before background collection (wipe 2–3 times with ethanol)
• Do not disturb the crystal after background collection (e.g., re-pressurize)
• If crystal temperature changes significantly during measurement (e.g., heating), recollect background

2.4 "Semi-permanent" Nature of Background

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2.4 "Semi-permanent" Nature of Background

Background spectra are not permanently valid. When to re-collect [1][3][6]:

• Must re-collect: Change detector, change beamsplitter, change light source, change optical path accessory
• Recommended re-collect: Interval > 1 hour, significant temperature or humidity change
• Can continue to use: Continuous measurement of similar samples within 30 minutes

2.5 Practical Operation

Bruker OPUS [2][6]:

1. Click "Advanced Measurement" → "Background" on the main interface
2. Set parameters (resolution, number of scans, range)
3. Confirm the optical path is empty (transmission) or crystal is clean (ATR)
4. Click "Start" to collect, about 30 seconds
5. The software automatically saves the background and subtracts it for the next measurement

Thermo OMNIC [1][4]:

1. Click "Collect Background" on the main interface
2. Set parameters
3. Confirm the optical path status
4. Click "OK" to start collection
5. The background is automatically saved as a .bkg file

3. Parameter Settings: Three Knobs That Determine Spectral Quality

FTIR measurement has three core parameters: resolution, number of scans, and spectral range. They directly determine spectral quality, measurement time, and data size [1][3][7].

3.1 Resolution

Physical meaning of resolution: The minimum wavenumber difference at which the instrument can distinguish two adjacent peaks [1][7].

Common options [1][3][7]:

• 1 cm⁻¹ (high resolution)
• 2 cm⁻¹
• 4 cm⁻¹ (standard, most commonly used)
• 8 cm⁻¹ (low resolution, fast)
• 16 cm⁻¹ (very low, only for screening)

Selection basis [1][3][7]:

Table 1: Resolution selection guide (compiled from [1][3][7])

Key insights [1][7]:

• Doubling resolution increases scan time by 4 times (signal also decreases by 4 times)
• 4 cm⁻¹ is the "best value for money", covering 90% of applications
• Do not "blindly pursue high resolution" — most liquid/solid samples have peak widths > 10 cm⁻¹, and 2 cm⁻¹ shows no difference from 4 cm⁻¹

3.2 Number of Scans

Physical meaning of number of scans: The number of times the instrument repeatedly scans and accumulates signal-to-noise [1][3].

SNR improvement follows statistical law [1][7]:

$$\text{SNR} \propto \sqrt{N}$$

where $N$ is the number of scans. That is, doubling the number of scans only improves SNR by $\sqrt{2} \approx 1.41$ times [1][7].

Common options [1][3][7]:

• 16 scans (routine recommendation)
• 32 scans (higher SNR)
• 64 scans (trace analysis, weakly absorbing samples)
• 128+ scans (very low SNR scenarios, such as monolayers)

Scan time estimation [3]:

• DTGS detector, 4 cm⁻¹ resolution, scan speed 0.6 cm/s
• Single scan about 0.5 seconds
• 16 scans about 8 seconds; 64 scans about 32 seconds

Selection basis [1][3][7]:

Table 2: Number of scans selection guide (compiled from [1][3][7])

💡 Professional advice: Better to scan more than less. The time difference between 16 and 64 scans is only 20 seconds, but the SNR difference is 2 times [1][7].

3.3 Spectral Range

Spectral range: The wavenumber interval measured by the instrument [1][3].

Common options [1][3]:

• 4000–400 cm⁻¹ (mid-infrared standard): Covers all functional groups
• 4000–650 cm⁻¹ (KBr windows, commonly used)
• 7800–350 cm⁻¹ (wide range)
• 4000–200 cm⁻¹ (far-infrared extension)

Selection basis [1][3]:

• Most organic compounds: 4000–400 cm⁻¹ is sufficient
• Organometallic compounds, coordination compounds: extend to 200 cm⁻¹
• Only functional groups: 4000–1400 cm⁻¹ (functional group region)

Relationship with detector/beamsplitter [3][7]:

• Mid-IR: KBr beamsplitter + DTGS detector
• Near-IR: Quartz beamsplitter + InGaAs detector
• Far-IR: Polyethylene beamsplitter + DTGS (polyethylene windows)

3.4 Other Parameters

Aperture [3][7]:

• Automatic (recommended): Instrument automatically adjusts based on source intensity
• Manual: 8 mm (default), 6 mm, 4 mm, etc.

Scan Velocity [3][7]:

• 0.6 cm/s (DTGS standard)
• 1.6 cm/s (MCT fast scan)
• 2.5–5 cm/s (high time-resolution kinetic measurements)

Zero Filling [7]:

• 2x zero filling (recommended): Data points doubled, smoother spectrum
• 4x zero filling: extra smooth, only for special needs

Phase Correction [3][7]:

• Mertz (default): Automatic phase correction
• Suitable for most samples

4. Sample Measurement Procedure

4.1 Transmission Method Sample Measurement

Steps (using KBr pellet as example) [1][3]:

1. Confirm background has been collected (< 5 minutes ago)
   ↓
2. Open sample compartment door
   ↓
3. Place KBr pellet into sample holder
   ↓
4. Close sample compartment door
   ↓
5. Click "Collect Sample" in software
   ↓
6. Wait for scan completion (16 scans ~8 seconds)
   ↓
7. Software automatically subtracts background, displays absorbance spectrum
   ↓
8. Check spectrum quality (main peak 0.3–1.5, good SNR, no water ghost peaks)
   ↓
9. Save data

Figure 2: Transmission method sample measurement flow diagram (reference [1])

Liquid cell measurement [1][3]:

1. Fill liquid cell (see Ep 16)
2. Place liquid cell into sample holder
3. Follow steps 4–9 as above

4.2 ATR Method Sample Measurement

Steps (using diamond ATR as example) [3][6]:

1. Confirm crystal is clean (wiped with ethanol)
   ↓
2. Collect background (when crystal is clean)
   ↓
3. Place sample (1–5 mg or 1–2 drops liquid)
   ↓
4. Tighten pressure screw (manual ATR) or press pressure button (pneumatic ATR)
   ↓
5. Click "Collect Sample" in software
   ↓
6. Wait for scan completion
   ↓
7. Software displays raw ATR spectrum
   ↓
8. Apply ATR correction (if needed)
   ↓
9. Check spectrum quality
   ↓
10. Save data
   ↓
11. Clean crystal (wipe with ethanol 2–3 times)

Figure 3: ATR method sample measurement flow diagram (reference [3])

4.3 Common Problems During Measurement

Problem 1: Signal too weak [1][3]

• Transmission: Too little sample / pellet not transparent
• ATR: Poor contact
• Solution: Increase sample amount / re-grind / increase pressure

Problem 2: Signal too strong (flat-top) [1][3]

• Transmission: Too much sample
• ATR: Possibly strong absorbing sample (e.g., pure water)
• Solution: Reduce sample / dilute

Problem 3: Baseline drift [1][3]

• Cause: Temperature or humidity change after background collection
• Solution: Re-collect background

Problem 4: Spurious peaks [1][3]

• Cause: Sample contamination, crystal contamination, KBr moisture absorption

• Resolution: Clean crystal, re-prepare sample

V. Data File Formats

FTIR software from different manufacturers uses various proprietary formats, but also supports universal formats [1][3][8].

5.1 Major Manufacturer Proprietary Formats

Table 3: Proprietary formats of major FTIR manufacturers (compiled from [1][3][8])

Advantages of proprietary formats [1][3]:

• Preserve all metadata (background, parameters, operator, time)
• Natively supported by manufacturer software for convenient subsequent processing
• Can be converted among manufacturer software

Disadvantages of proprietary formats [8]:

• Poor cross-manufacturer compatibility (Thermo's SPA cannot be directly opened in Bruker OPUS)
• Long-term archiving risk (manufacturer discontinuation or software upgrades may render old formats incompatible)
• Binary format, not editable or viewable as text

5.2 Universal Formats

① JCAMP-DX [3][8][9]

JCAMP-DX (Joint Committee on Atomic and Molecular Physical Data eXchange) is an international standard format developed by IUPAC [9]:

• Extension: .dx, .jdx
• Text format, readable
• All manufacturer software can import and export
• Suitable for long-term archiving and cross-manufacturer exchange

JCAMP-DX file structure [9]:

##TITLE=Polystyrene film
##JCAMP-DX=5.01
##DATA TYPE=INFRARED SPECTRUM
##ORIGIN=Your Lab
##OWNER=Your Name
##XUNITS=1/CM
##YUNITS=ABSORBANCE
##XFACTOR=1.0
##YFACTOR=1.0
##FIRSTX=4000.0
##LASTX=400.0
##NPOINTS=1801
##FIRSTY=0.001
##XYDATA=(X++(Y..Y))
4000 0.001 0.002 0.001 0.001 ...
3998 0.002 0.001 0.002 0.001 ...
...
##END=

② CSV / TXT [3][8]

• Simple two columns (wavenumber, intensity)
• Can be opened directly by all data processing software (Excel, Origin, Python, MATLAB)
• Suitable for data processing and secondary development

③ SPC [3]

• Universal format proposed by Galactic Industries
• Binary, compact and efficient
• Supported by multiple software including Thermo, Bruker

5.3 Format Selection Recommendations

Long-term archiving [3][8][9]:

• Save both proprietary format + JCAMP-DX
• Proprietary format retains all information
• JCAMP-DX ensures future readability

Data exchange [3][8][9]:

• Prefer JCAMP-DX (standard)
• Next CSV/TXT (simple and universal)

Data processing [3]:

• Prefer CSV/TXT (friendly to Excel, Origin, Python)
• Unscrambler, Pirouette, etc. support SPC

5.4 File Naming Convention

Recommended naming rule [3]:

• <Date>_<SampleID>_<Method>_<Operator>.spa
• Example: 20260724_API-001_KBr-press_zhang.spa

Metadata should include [3][8]:

• Sample name, ID, batch number
• Measurement method (Transmission/ATR/Liquid cell)
• Sample preparation conditions (KBr ratio, pathlength, crystal)
• Measurement parameters (resolution, number of scans, range)
• Operator, measurement date
• Instrument model, serial number

💡 Professional tip: All measurement parameters and sample information should be written into file metadata or notes for future traceability. File name alone is insufficient [3][8].

VI. Thermo Nicolet iS50 Operation Example

Below is a complete operation workflow using the Thermo Nicolet iS50 as an example [1][4].

6.1 Startup Procedure

1. Connect power
2. Start computer, open OMNIC software
3. Software automatically detects instrument, shows "Connected"
4. Select light source (mid-IR Globar)
5. Select detector (DTGS or MCT)
6. Wait for light source to stabilize (approx. 20 minutes)
7. Set purge if required

6.2 Parameter Settings

Set in OMNIC main interface:

• Number of scans: 16 or 32
• Resolution: 4 cm⁻¹
• Spectral range: 4000–400 cm⁻¹
• Background mode: Collect before each measurement (recommended)
• Detector: DTGS (automatic)

6.3 Collect Background

1. Click "Collect Background" on main interface
2. Software prompts "Please ensure the sample compartment is empty"
3. Confirm optical path is empty, click "OK"
4. Software starts scanning, completes in approx. 8 seconds
5. Software displays 100% line, background saved as .bkg

6.4 Collect Sample (KBr pellet)

1. Click "Collect Sample" on main interface
2. Software prompts "Please place the sample"
3. Open sample compartment, insert KBr pellet, close door
4. Click "OK", software starts scanning
5. Software automatically subtracts background, displays absorbance spectrum
6. Inspect spectrum quality
7. Click "File" → "Save As" to save as .spa

6.5 Data Processing

Built-in OMNIC functions [1][4]:

• ATR correction
• Baseline correction
• Smoothing
• Normalization
• Library search (library purchase required)

6.6 Shutdown

1. Close sample compartment
2. Stop purge
3. Click "Disconnect" in software
4. Close software
5. Turn off instrument power
6. Turn off computer

VII. Bruker Tensor II Operation Example

Below is an example using the Bruker Tensor II [2][6].

7.1 Startup Procedure

1. Connect power (rear panel)
2. Start computer, open OPUS software
3. Software automatically detects instrument
4. Wait for laser to stabilize (approx. 5 minutes)
5. Start light source
6. Wait for light source to stabilize (approx. 30 minutes)
7. Start purge if required

7.2 Parameter Settings

In OPUS "Advanced Measurement" window:

• Number of scans: 16 or 32
• Resolution: 4 cm⁻¹
• Spectral range: 4000–400 cm⁻¹ (mid-IR)
• Detector: RT-DLaTGS (default)
• Beamsplitter: KBr (default)
• Sample mode: Absorbance
• Background mode: Single background (recommended per measurement)

7.3 Collect Background

1. In "Advanced Measurement", click "Background Single Channel"
2. Confirm optical path empty (transmission) or crystal clean (ATR)
3. Click "Start"
4. Wait for scan to complete (approx. 8 seconds)
5. Software saves background to current session

7.4 Collect Sample

1. In "Advanced Measurement", click "Sample Single Channel"
2. Place sample, close compartment door
3. Click "Start"

4. Software automatically subtracts background, displays absorbance

5. Click "Save" to save as .0 or .opus file

7.5 Data Processing

Built-in functions in OPUS [2][6]:

• Baseline correction (Rubber band, polynomial)
• Smoothing (Savitzky-Golay)
• Normalization
• ATR correction
• Derivation (first order, second order)
• Library search (requires spectral library)

7.6 Shutdown

1. Close the sample compartment
2. Click "Disconnect" in OPUS
3. Close OPUS
4. Turn off the instrument power
5. Turn off the computer

8. Shutdown and Daily Maintenance

8.1 Shutdown Procedure

Standard Shutdown Sequence [1][3]:

1. Stop purge
2. Exit software (save all data)
3. Turn off instrument power
4. Turn off computer
5. Turn off main power

Notes [1][3]:

• Long-term shutdown (> 1 week): Place desiccant inside the instrument
• Short-term shutdown (< 1 day): Keep purge at low flow (1 L/min) is sufficient
• Do not frequently power on/off: Each time the source needs 30 minutes to stabilize

8.2 Daily Maintenance

Daily [1][3][10]:

• Check desiccant (color-changing silica gel)
• Check liquid nitrogen level (MCT detector)
• Clean sample compartment
• Back up daily data

Weekly [1][3][10]:

• Measure a standard polystyrene film spectrum (system suitability)
• Check purge gas flow
• Clean ATR crystal

Monthly [3][10]:

• Clean interior of sample compartment
• Check optical alignment (if professional tools available)
• Replace desiccant

Quarterly [3][10]:

• Instrument performance verification (PV): Use polystyrene film to check peak position, peak width, and SNR
• Contact manufacturer for preventive maintenance (PM)

Annually [3][10]:

• Manufacturer annual maintenance
• Replace source (silicon carbide rod lifetime approx. 2–5 years)
• Detector inspection

8.3 System Suitability Test

Polystyrene Film Standard [3][10]:

• Thickness 0.04 mm (approx. 40 μm)
• Peak position standards (e.g., 3027.1, 2850.7, 1601.4, 1028.0, 906.7 cm⁻¹)
• Tolerance: ±0.3 cm⁻¹ (pharmacopoeia requirement)

Test Procedure [3][10]:

1. Measure transmission spectrum of polystyrene film
2. Check peak position accuracy: all standard peaks within ±0.3 cm⁻¹
3. Check resolution: doublet at 3027 and 3030 cm⁻¹ should be clearly resolved
4. Check SNR: 100% line noise < 0.05

Non-conformance Handling [3][10]:

• Peak shift: Recalibrate wavenumber axis (instrument self-test or manufacturer calibration)
• Insufficient resolution: Check beamsplitter, optical alignment
• Poor SNR: Check source, detector, purge

8.4 Common Troubleshooting

Table 4: Common Troubleshooting (compiled from [1][3][10])

9. Best Practices for Operation

9.1 Good Habits

① Pre-measurement check [1][3]

• Before the first sample each day, measure a polystyrene film to confirm instrument status
• Confirm background is valid (< 1 hour old)

② Data recording [3][8]

• Record sample information, sample preparation conditions, and operator in file metadata
• Use experiment notebook to record anomalies

③ Data backup [3]

• Backup data after each day
• Dual backup (computer hard drive + network storage/USB drive)
• Save both raw data and processed data

④ Instrument maintenance [3][10]

• Regularly check desiccant
• Perform system suitability tests regularly
• Manufacturer periodic maintenance

9.2 Common Novice Mistakes

Mistake 1: Not collecting background or using expired background [1][3]

• Consequence: Severe water/CO₂ interference
• Solution: Re-collect background every 30 minutes or when changing sample type

Mistake 2: Improper parameter settings [1][3]

• Consequence: Low resolution, poor SNR
• Solution: Use standard parameters (4 cm⁻¹, 16 scans, 4000–400 cm⁻¹)

Mistake 3: Not checking spectrum quality [1][3]

• Consequence: Obtain flat-top or very poor SNR spectrum
• Solution: Check main peak absorbance (0.3–1.5), SNR, baseline

Mistake 4: Frequent change of operator [3][10]

• Consequence: Inconsistent operation, poor reproducibility
• Solution: Assign fixed operator or write detailed SOP

Mistake 5: Saving data only in proprietary format [3][8]

• Consequence: Cannot open after many years
• Solution: Also save in JCAMP-DX universal format

9.3 Advanced Tips

① Automated Measurement [3][4]

• Use macros to automate repetitive measurements
• Thermo OMNIC and Bruker OPUS both support macro programming
• Suitable for high-throughput samples

② Online Monitoring [3][6]

• Use kinetics mode for continuous acquisition
• Collect one spectrum every 1–10 seconds
• Monitor reaction progress, sample stability

③ Multidimensional Measurement [3][6]

• Mapping (multi-point scanning)
• Imaging (FPA array detector)
• Suitable for heterogeneous samples

10. Safety Precautions

10.1 Instrument Safety

Laser Safety [1][3]:

• FTIR contains a HeNe laser (632.8 nm, 1 mW, Class 1)
• Class 1 is safe under normal use, but avoid direct eye exposure to beam path
• Do not open the instrument beam path cover

Power Safety [1][3]:

• Ensure proper grounding
• Use UPS uninterruptible power supply
• Avoid voltage fluctuations

Mechanical Safety [1][3]:

• Avoid shock when moving instrument
• Do not disassemble the beam path yourself

10.2 Sample Safety

Chemical Safety [3][10]:

• Prepare toxic samples in fume hood
• Avoid contact of corrosive samples with instrument
• Measure volatile samples under ventilated conditions

Biological Safety [3]:

• Handle biological samples according to biosafety regulations
• Wipe sample compartment with 70% ethanol before and after cleaning

10.3 Data Safety

Data Integrity [3][8]:

• Raw data must not be modified
• Save processed data as new files
• Operations traceable (electronic records)

Data Backup [3][8]:

• Dual backup
• Regularly check backup validity
• Backup important data to cloud

🔗 Further Reading: The operation procedures do not cover peak assignments; water/CO₂ interference in the background can be referenced to the water molecule page, and functional group quick reference is at ftir.fun.

Chapter Summary

Questions for Reflection

1. You are a new lab operator using a Bruker Tensor II for the first time. After powering on and waiting for the light source to stabilize, what preparations should you make? Why is purging for 15 minutes necessary?

2. During an experiment, you suddenly notice a distinct double peak at 2350 cm⁻¹ (CO₂), but this was not present before measurement. Analyze possible causes and provide solutions.

3. The main peak absorbance of a sample spectrum is 0.15 (less than 0.3), and the SNR is poor. Without changing the sample and preparation, how can you improve spectrum quality through instrument parameters?

4. You need to measure a dilute aqueous solution sample at 0.5% and want to avoid water interference but must use infrared spectroscopy. Design a complete measurement workflow (including method selection, parameter settings, data processing).

5. The lab is preparing to purchase an FTIR, and the saved spectra need to be interoperable with another Thermo instrument (both are Thermo). However, if a future switch to Bruker is possible, how should you choose a data format saving strategy?

References

[1] Griffiths P R, de Haseth J A. Fourier Transform Infrared Spectrometry. 2nd ed. Wiley, 2007. Chapter 4–6. ISBN: 978-0-471-19404-0.

[2] Bruker Optics. "Tensor II FTIR Spectrometer User Manual." Technical Documentation.
https://www.bruker.com/en/pro…

[3] Smith B C. Fundamentals of Fourier Transform Infrared Spectroscopy. 2nd ed. CRC Press, 2011. Chapter 5–7. ISBN: 978-1420069297.

[4] Thermo Fisher Scientific. "Nicolet iS50 FTIR Spectrometer User Guide." Technical Documentation.
https://www.thermofisher.com/…

[5] Perkins W D. "Purging Effects in FTIR." Spectroscopy, 1993, 8(8): 24–30.

[6] Bruker Optics. "OPUS Spectroscopy Software Tutorial." Version 8.5.
https://www.bruker.com/en/pro…

[7] Griffiths P R, Foskett C T. "Theoretical Background of FTIR." Analytical Chemistry, 1972, 44(13): 2219–2227. DOI:10.1021/ac60321a001.

[8] ASTM E131-10. "Standard Terminology Relating to Molecular Spectroscopy." ASTM International, 2010.

[9] McDonald R S, Wilks P A. "JCAMP-DX: A Standard Form for Exchange of Infrared Spectra in Computer Readable Form." Applied Spectroscopy, 1988, 42(1): 151–162. DOI:10.1366/0003702884428734.
https://www.jcamp-dx.org/

[10] USP General Chapter <851>. "Spectrophotometry and Light-Scattering." United States Pharmacopeia.
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Next Episode Preview: Ep 18 — Basics of Spectrum Processing: Baseline Correction, Smoothing, Normalization
We will systematically explain common processing methods for FTIR spectra, including baseline correction (polynomial fitting, rubber band), smoothing (Savitzky-Golay filter), normalization (maximum, area, ATR correction), and derivation (second derivative to resolve overlapping peaks). Also warn about the risk of "overprocessing creating artifact peaks."

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