What are the factors that affect the fluorescence intensity of fluorescent whitening agents?

发布时间：2024-04-14 16:13:21 浏览次数：23次

　　The use of fluorescence intensity for quality control of fluorescent whitening agent products has the advantages of convenience, speed, and accuracy. However, there are also many factors that affect fluorescence intensity, among which the most important are the solvent, pH value of the solution, concentration of the solution, and the influence of light.

　　1. The influence of solvents

　　The absorption spectrum characteristics of fluorescent whitening agents are closely related to the solvent used. The position and intensity of the fluorescence spectrum of the same fluorescent whitening agent may vary significantly in different solvents. Therefore, measuring the fluorescence intensity of fluorescent whitening agents requires a suitable solvent to transform the sample into a solution. Improper solvent selection can lead to the solution not complying with the Lambert Beer law and inaccurate measurement results. The general selection of solvents should follow the following principles:

　　(1) The selected solvent does not undergo any chemical reaction with the test sample

　　(2) The test sample has a certain solubility in this solvent

　　(3) Within the measured wavelength range, the solvent itself does not absorb

　　(4) Solvents with low performance, non flammability, low toxicity, and low price should be selected

　　2. The influence of solution pH value

　　The pH value of the solution has a significant impact on the absorbance of anionic and cationic fluorescent whitening agents. The absorbance of cationic fluorescent whitening agents significantly decreases at pH ≥ 9; Anionic fluorescent whitening agents exhibit a sharp decrease in absorbance under acidic conditions, and the degree of reduction varies for different products. The influence of pH value of the solution on the absorbance of fluorescent whitening agents is bound to have a certain effect on the fluorescence intensity.

　　3. The influence of light

　　Some solutions of fluorescent whitening agents do not undergo significant changes under prolonged exposure to sunlight, but some fluorescent whitening agents, such as dilute solutions of styrene based fluorescent whitening agents, are prone to undergo cis trans isomerization changes under direct sunlight. This cis trans isomerization change causes changes in the extinction value, thereby affecting the stability of fluorescence intensity. Therefore, when dissolving and measuring the extinction value of fluorescent whitening agents, attention should be paid to speed and avoiding light.

　　4. The influence of solution concentration

　　The application of the law of light absorption has certain conditions, that is, the concentration of the solution should be controlled within an appropriate range, and within this concentration range, the absorbance A and concentration can have a linear relationship. For fluorescent whitening agents, the linear relationship between absorbance and solution concentration is limited to relatively dilute solutions. For more concentrated solutions, absorbance not only does not increase with the increase of solution concentration, but often decreases with the increase of concentration, deviating from the law of light absorption. At this point, the measured fluorescence intensity is no longer reliable, mainly due to fluorescence quenching and internal filtration.

　　In addition to the above influencing factors, temperature, coating effect, surfactants, etc. also have an impact on the fluorescence intensity of whitening agents, and attention should be paid during the measurement process.