UV-1200 ultraviolet spectrophotometer phenol reagent colorimetric method for measuring formaldehyde in air - Database & Sql Blog Articles

Determination of Formaldehyde Content in Air Using the Colorimetric Method with Ultraviolet Spectrophotometer

American Instrument Co., Ltd.

Keywords: ultraviolet spectrophotometer; formaldehyde; aesthetic instrument; V-1100; V-1200

The method for determining formaldehyde in air involves the absorption of formaldehyde by a phenol reagent solution, which then reacts to form an azine compound. This compound is oxidized by high-iron ions in an acidic environment to produce a blue-green substance that can be measured colorimetrically.

The instruments required include a bubble absorption tube, an air sampler with a flow range of 0.1–1 L/min, a 10 mL colorimetric tube, and a UV spectrophotometer (V-1100 or V-1200) used at a wavelength of 630 nm with a 10 mm cuvette.

Reagents include a phenol reagent stock solution, an absorption liquid, hydrochloric acid, ammonium ferric sulfate, iodine solution, potassium iodate standard solution, starch solution, and sodium thiosulfate standard solution. Each reagent has specific preparation steps and storage conditions.

A formaldehyde standard solution is prepared by diluting a concentrated formaldehyde solution. Its exact concentration is determined using an iodometric method. Two working solutions are also prepared for calibration purposes.

During sampling, 10 L of air is drawn through a bubble absorption tube containing 10 mL of the absorption liquid at a flow rate of 0.5 L/min. The temperature and atmospheric pressure are recorded. The sample must be analyzed within 24 hours.

For analysis, a standard curve is created by preparing several standard color tubes with known amounts of formaldehyde. Absorbance is measured at 630 nm, and the slope of the curve is used to calculate the sample concentration.

The formula for calculating the formaldehyde concentration in air is based on the absorbance difference between the sample and the blank, along with the volume of the sample collected under standard conditions.

The method has a sensitivity of 0.079±0.012 absorbance for 0.2 µg of formaldehyde in 5 mL of absorption liquid, with a detection limit of 0.05 µg/5 mL. When sampling 10 L, the minimum detectable concentration is 0.01 mg/m³.

The method shows good reproducibility and accuracy, with relative standard deviations ranging from 3% to 5%, and recovery rates between 93% and 101%. The measurement range varies depending on the volume of the sample solution used.

Keywords: ultraviolet spectrophotometer; formaldehyde; aesthetic instrument; V-1100; V-1200