How to Measure Peroxide Value in Edible Oil with a UV-Vis Spectrophotometer
Key Points for Food Quality Control Laboratories
Peroxide value is a key indicator of primary oxidation in edible oils and fats.
UV-Vis analysis can convert a peroxide-related chemical reaction into a measurable absorbance signal.
For laboratories evaluating Food Safety Testing Instruments, key considerations include wavelength performance, photometric stability, measurement functions, and long-term usability.
The UV-1800 provides 190–1100 nm wavelength coverage and quantitative measurement functions for laboratory analysis.
Why Is Peroxide Value Important in Edible Oil Testing?
Edible oils gradually undergo oxidation when they are exposed to oxygen, heat, light, or other unfavorable storage conditions. During the early stage of this process, hydroperoxides and related peroxide compounds are formed. As oxidation continues, these compounds can break down into secondary oxidation products that contribute to undesirable odors and flavors.
Peroxide value (PV) is a quantitative indicator of the amount of hydroperoxides present in an oil. The Food and Agriculture Organization of the United Nations describes PV as an indicator of hydroperoxides formed through lipid oxidation and expresses the result in milliequivalents of active oxygen per kilogram of oil.
This makes PV useful for monitoring raw materials, production batches, storage conditions, and finished edible oils. However, PV should not be interpreted as a complete measurement of all oxidation products. It mainly reflects primary oxidation, while tests such as the p-anisidine value can provide information about secondary oxidation products.
For laboratories, this distinction is important because an oil can change continuously during oxidation.
What Is the Principle of Peroxide Value Measurement by UV-Vis Spectrophotometry?
The basic principle is to transform peroxide-related chemical activity into a colored reaction that can be quantified by absorbance.
In the experimental method, peroxides in edible oil react with potassium iodide (KI) in a chloroform–glacial acetic acid medium. The reaction releases iodine. After starch is added, the iodine produces a blue-colored complex. The intensity of this color is then measured with a spectrophotometer.
The measurement can be summarized as:
Peroxides in oil → iodine formation → starch color reaction → absorbance measurement → calibration curve → peroxide value calculation
A calibration curve is also important. Known iodine concentrations are measured first, and their corresponding absorbance values are used to establish the relationship between concentration and absorbance. The sample absorbance can then be compared with this curve to determine the corresponding iodine concentration.
This approach illustrates one of the main strengths of UV-Vis analysis: a chemical reaction that produces a measurable color change can be converted into quantitative laboratory data.
How to Measure Peroxide Value in Edible Oil Step by Step
Step 1: Prepare the Reagents and Iodine Standards
The source method uses chloroform–glacial acetic acid as the reaction medium, potassium iodide as the reagent, and starch as the color-forming reagent. Iodine standard solutions are prepared at known concentrations for calibration.
The original method includes iodine standards ranging from 0.0002 to 0.008 mol/L. These values belong to the described experimental procedure and should not automatically be treated as universal requirements for every PV method.
Step 2: Build the Calibration Curve
Measure the absorbance of the iodine standards at 535 nm. Plot iodine concentration against absorbance and establish the calibration relationship.
| Measurement element | Role in the analysis |
| Iodine standard | Provides known concentration values |
| 535 nm | Measurement wavelength in the described method |
| Absorbance | Measurable response from the color reaction |
| Calibration curve | Relates absorbance to iodine concentration |
| Sample result | Used to determine the peroxide-related concentration |
A good calibration curve helps reduce uncertainty when converting the measured absorbance of an unknown sample into a concentration value.
Step 3: Prepare the Edible Oil Sample
In the source procedure, 0.20 g of edible oil is mixed with 5 mL of chloroform–glacial acetic acid solvent, followed by 10 mL of 10% KI and three drops of 1% saturated starch. The reaction mixture is allowed to stand for five minutes before measurement.
Sample handling should remain consistent between measurements. It also recommends sealing samples properly and performing three measurements before calculating the average.
Step 4: Measure Absorbance and Calculate the Peroxide Value
After the reaction has developed, measure the sample at 535 nm. The measured absorbance is compared with the calibration curve to obtain the corresponding iodine concentration.
The final peroxide value is then calculated according to the equation and conversion factors specified by the analytical method being followed.
This distinction matters in routine laboratory work: the uv vis spectrophotometer provides the absorbance measurement, but the complete PV result also depends on sample mass, reagent volumes, reaction conditions, calibration, and the calculation method.
What Affects the Accuracy of Peroxide Value Measurement?
A reliable result requires more than simply selecting the correct wavelength. Several steps before and during measurement can influence the final value.
Sample Preparation and Reaction Consistency
Oil samples should be representative of the material being tested. Differences in sample mass, reagent volume, mixing, reaction time, or exposure to air can affect the color reaction. Consistent handling is especially important when comparing multiple batches.
Blank Correction and Calibration
The blank accounts for absorbance contributed by the reaction medium and reagents rather than the sample itself. Calibration should also be checked regularly enough to support the laboratory’s quality-control procedure.
Absorbance Range and Repeatability
The source experiment recommends keeping absorbance within approximately 0.1–0.7 to help limit measurement error. The procedure also uses three replicates and calculates an average.
When the differences between batches of oil products are subtle, reproducibility becomes key to judging the reliability of the results. The optical system must be stable, and sample preparation must be standardized, so that changes in samples and measurement deviations can be separated and examined.
What Instrument Performance Matters?
When selecting a system for this type of analysis, laboratories should consider:
- Wavelength accuracy and repeatability
- Photometric accuracy and stability
- Appropriate wavelength range
- Measurement bandwidth
- Quantitative and calibration functions
These factors are also relevant when evaluating Food Safety Testing Instruments for broader laboratory workflows. The instrument should match the analytical method.
UV-1800 UV-Vis Spectrophotometer and Choosing the Right Manufacturer
For laboratories performing routine quantitative absorbance analysis, the UV-1800 UV-Vis Spectrophotometer is designed as a double-beam system with a 190–1100 nm wavelength range. This range includes the 535 nm measurement used in the peroxide-value method described above.
Why Is the UV-1800 Suitable for This Application?
The UV-1800 combines wavelength coverage with functions designed for quantitative laboratory analysis. Its wavelength accuracy is ±0.3 nm, wavelength repeatability is 0.1 nm, and photometric accuracy is ±0.2% τ. The listed stability is 0.0004 A/h at 500 nm.
| UV-1800 specification | Value |
| Optical system | Double beam |
| Wavelength range | 190–1100 nm |
| Bandwidth | 1.0 / 2.0 nm optional |
| Wavelength accuracy | ±0.3 nm |
| Wavelength repeatability | 0.1 nm |
| Photometric accuracy | ±0.2% τ |
| Stray light | ≤0.02% τ |
| Stability | 0.0004 A/h @ 500 nm |
| Photometric modes | T, A, C, E |
The instrument also supports wavelength scanning, kinetic tests, multi-wavelength testing, and quantitative measurement based on a standard curve. For the PV workflow, the quantitative function is particularly relevant because the analysis depends on establishing a relationship between standard concentration and absorbance.
Its 190–1100 nm coverage also allows the same instrument to support other UV-Vis applications beyond the specific 535 nm measurement described here.
What Should You Look for in a UV-Vis Spectrophotometer Manufacturer?
For B2B laboratory purchasing, the instrument itself is only part of the decision. A suitable manufacturer should also be able to support different analytical requirements and provide appropriate technical assistance.
Macylab focuses on laboratory analytical instruments including visible spectrophotometers, UV-Vis spectrophotometers, atomic absorption spectrophotometers, atomic fluorescence spectrometers, ICP-AES, ICP-MS, and micro-volume spectrophotometers. This product range allows laboratories to consider different analytical platforms as their testing requirements develop.
For overseas buyers, practical factors such as product configuration, application requirements, technical communication, warranty support, and after-sales service can also influence the long-term value of laboratory equipment.
FAQ
Can a UV-Vis spectrophotometer determine peroxide value in edible oil?
A: Yes. In the described method, peroxide-related reactions generate iodine, which produces a measurable blue color with starch. The absorbance is then measured to determine the corresponding concentration through a calibration curve.
What wavelength is used for peroxide value measurement?
A: The experimental method described in this article uses 535 nm for absorbance measurement. Other PV methods may use different analytical conditions, so the wavelength should follow the validated method being applied.
Why is a calibration curve necessary?
A: The calibration curve establishes the relationship between known iodine concentration and absorbance. This allows the absorbance of an unknown sample to be converted into a concentration value.
How can repeatability be improved?
A: Keep sample mass, reagent volumes, reaction time, wavelength, blank correction, and measurement conditions consistent. Multiple measurements can also help identify unexpected variation.
What should laboratories consider when choosing equipment for food testing?
A: Consider the analytical method first, then evaluate wavelength coverage, wavelength accuracy, photometric performance, stability, quantitative functions, and manufacturer support. The equipment should meet the actual testing workflow.
Conclusion
Peroxide value testing combines a chemical reaction with quantitative absorbance measurement. The key steps are consistent sample preparation, controlled reagent reaction, calibration, measurement at the appropriate wavelength, and reliable calculation.
For laboratories looking for a spectrophotometer for edible oil analysis and other quantitative applications, the UV-1800 offers 190–1100 nm coverage, double-beam optics, quantitative measurement through standard curves, and multiple measurement functions.
If you are evaluating a UV-Vis system for food quality control or other laboratory applications, contact us to discuss the UV-1800 and the configuration that best fits your testing workflow.
