Measuring Transmittance & Optical Properties of Liquids Using the VISTA Spectrophotometer

Overview

This procedure uses the VISTA Spectrophotometer and provides a structured approach to measuring and characterizing liquid specimens' Transmittance and optical properties. It ensures accurate, repeatable results for a variety of liquids, including hydrocarbons, alcohols, glycols, edible oils, solvents, fuels, water, and food liquids. This procedure is a practical example and is intended to be used as a guideline to ensure proper operation, accuracy, and reliability in the results.

Key Objectives

• Ensure proper instrument operation and calibration.
• Follow best practices for sample handling and measurement. 
• Minimize errors and improve repeatability,
• Adhere to industry standards and Quality Assurance protocols.

     ⚠ Note: This procedure is a guideline and does not replace manufacturer specifications, regulatory compliance, or company-specific SOPs.

For formal instructions and compliance with industry standards, refer to your organization's Quality Assurance protocols and the HunterLab User’s Manual—Vista with EasyMatch Essentials 2.0.

1. Instrument Setup & Calibration

1.1 Verify Spectrophotometer Readiness
       Before starting, confirm:

• The VISTA spectrophotometer is functioning correctly.
• All required accessories are available.
• The instruments and standards have stabilized in their environment.
  • Recommendation:
    • 4 hours at Standard Temperature and Pressure (STP).
    • 8 hours re-standardization interval (varies by environment)

1.2 Select the Absorption Cell

Choosing the appropriate absorption cell is essential for obtaining precise Transmittance measurements in the VISTA spectrophotometer. While any absorption cell can be used, the optical material and path length must be considered, as these factors influence measurement accuracy.
The table below provides guidance on selecting the optimal absorption cell based on the sample type:

Category Examples Best Cell Type High-Purity Liquids Ultra-pure water, RI standards Quartz or borosilicate glass Volatile Solvents Alcohols, ketones, ethers Sealed quartz/glass cuvettes Corrosive Chemicals Acids, bases, oxidizers Borosilicate or fluoropolymer-coated glass Oils & Hydrophobic Liquids Edible oils, essential oils Glass or quartz UV-Vis Absorbing Solutions Dyes, biological stains UV-transparent quartz Highly Viscous Liquids Syrups, resins, gels Thick-walled glass

When selecting an absorption cell, consider:

• Path Length: Longer path lengths enhance sensitivity but may lead to higher absorbance values.
• Material Compatibility: Ensure chemical compatibility to prevent degradation or contamination.
• Spectral Range: Quartz is preferred for UV-Vis applications due to its broad optical transparency.

2. Measurement Procedure

2.1 Spectrophotometer Configuration

• Turn on the instrument and allow it to warm up.

2.2  Select Measurement Mode:

• Total Transmittance (TTRAN) – Measures all transmitted light (regular plus scattered - For hazy, translucent, or semi-transparent liquids. 
• Regular Transmittance (RTRAN) – Measures only direct Transmittance - For highly transparent liquids.

2.3 Select the Illuminant & Observer:

• D65 & 10° Observer Function (Recommended).
• Consult SOP for other Illuminant–Observer Conditions

2.4 Choose the Right Scale & Indices:

• CIEXYZ, CIELAB, Haze %, YI, WI (as required)

3. Standardization & Blanking

3.1 Importance of Blanking

Blanking ensures accurate reading by correcting for:
✔ Cuvette absorption
✔ Solvent interference
✔ Instrument drift

3.2 Blanking Methods
In spectrophotometry, blanking (also called baseline correction or reference measurement) is crucial for liquid measurements to ensure accurate Transmittance, absorption, and colorimetric data. Different liquid measurement methods require specific blanking approaches depending on the solvent, cuvette type, and measurement mode.

Measurement Type	Why Blanking is Needed	Blanking Method	Examples
Transmittance & Absorbance (UV-Vis/NIR)	Removes cuvette & solvent background	Blank with matching solvent	Hydrocarbons, alcohols, oils
Haze & Clarity           (ASTM D1003)	Corrects stray light & scattering	Blank with an empty glass cell or clear oil	Lubricants, beverages, and biological fluids
Colorimetric             (APHA, Saybolt, Gardner)	Ensures accurate color	Blank with ultra-pure water or clear oil	Fuels, vegetable oils, cosmetics
pH & Chemical Reactions	Removes buffer interference	Blank with buffer-only solution	Protein assays, enzyme kinetics
Refractive Index & Turbidity	Corrects light refraction/scattering	Blank with the reference liquid	Water quality, industrial process fluids

 

 

   Note:  See Appendix A for a thorough discussion on Blanking.

4. Data Collection & Analysis
4.1 Measuring the Sample

• Open the VISTA Sample Compartment
• Insert the specimen into the holder
• Close the compartment door
• Initiate the measurement sequence

4.2 Analyzing & Interpreting Data
✔ Transmittance (%T)
✔ Absorbance (A)
✔ Optical Density  (OD)
✔ Colorimetric Data (CIELAB, CIEXYZ values)
✔ Indices (Haze, Yellowness Index, Whiteness Index, etc.)

4.3 Quality Control & Repeatability
✔ Perform multiple readings and average the values
✔ Follow SOP guidelines for sample handling
✔ Verify that the VISTA spectrophotometer remains calibrated after use

5. Applications & Industry Use
This procedure is widely used across multiple industries for quality control:
✔ Hydrocarbons & Fuels (Gasoline, Jet Fuels, Lubricants)
✔ Pharmaceuticals & Cosmetics (IV Solutions, Perfumes, Skincare)
✔ Food & Beverage (Edible Oils, Juices, Dairy, Alcohol)
✔ Industrial Liquids (Coolants, Paints, Resins)
✔ Water & Aqueous Solutions (Ultra-pure water, Buffers, Acids)

Final Notes
For further details, refer to 📖 HunterLab User’s Manual – Vista with EasyMatch Essentials 2.0.
🔗 HunterLab User Manual