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Formaldehyde has highly active chemical properties, so there are many quantitative analysis methods suitable for formaldehyde, which can be mainly classified into five categories: titration method, gravimetric method, colorimetric method, gas chromatography, and liquid chromatography. Among them, the titration and gravimetric methods are suitable for the quantitative analysis of high-concentration formaldehyde, while the colorimetric method, gas chromatography, and liquid chromatography are suitable for the quantitative analysis of trace amounts of formaldehyde.
Quantitative analysis of formaldehyde in textiles belongs to ultramicroanalysis and is often done using colorimetric methods. The colorimetric method uses a UV-VIS spectrophotometer to analyze, and has great advantages in terms of analysis limit, accuracy, and reproducibility, but it is more cumbersome to operate. The quantification of formaldehyde in textiles can also be done using high-performance liquid chromatography (HPLC), but this method has some problems in sample pretreatment, technical conditions setting, and their adaptability, and has not been widely used yet.
Colorimetric methods can be divided into the following categories according to the different chromogenic agents used:
Acetyl method
The acetyl method uses an equimolar reaction between formaldehyde and acetal in the presence of excess ammonium acetate to generate a light yellow 2,6-dimethyl-3,5-diethylpyridine. The maximum absorption wavelength for colorimetric measurement is 412-415nm. This method has high precision (up to 0.1 × 10-16), good reproducibility, stable color development, and low interference.
Schiff's reagent method
The Schiff's reagent method involves the reaction of rose bengal (rosy pink aniline) salt with acidic sodium hydrosulfite and concentrated salt to generate rose bengal-acidic hyposulfite. Then, under strong acidic (or) conditions, it reacts with acetaldehyde to generate a rose-red (purple) salt, which is measured at the maximum absorption wavelength of 552-554nm. This method is simple to operate, but has low sensitivity (1×10-6), unstable color development, and poor reproducibility. It is suitable for quantitative analysis of higher formaldehyde content. For fabrics with lower formaldehyde content, the results of this method differ greatly from those of the acetyl method.
Resorcinol method
The resorcinol method uses alkaline (2.5mol/L sodium hydroxide) conditions for formaldehyde and resorcinol to generate an orange-red compound, which is analyzed at the maximum absorption wavelength of 460nm. The advantages and disadvantages of this method are similar to those of the Schiff's reagent method.
Chromic acid method
The chromic acid method involves the reaction of formaldehyde with chromic acid (1,8-dihydroxy-naphthalene-3,6-disulfonic acid) in the medium to generate a purple compound, which is analyzed at the maximum absorption wavelength of 568-570nm. This method has high sensitivity and good color stability, and is suitable for measuring low formaldehyde content in fabrics. However, this method is easily interfered with and is suitable for sample processing methods using gas phase extraction.
The determination of formaldehyde content can be divided into two categories according to the different sample preparations: liquid-liquid extraction method and gas-phase extraction method. The liquid-liquid extraction method measures the total amount of free formaldehyde in the sample and the free formaldehyde produced after hydrolysis to examine the possible harm to the human body caused by the release of formaldehyde due to sweating or wetting during.
