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

1. The influence of solvent

The absorption spectrum characteristics of optical brighteners are closely related to the solvent used. The position and intensity of the fluorescence spectrum of the same optical brightener in different solvents may be significantly different. Therefore, to determine the fluorescence intensity of the fluorescent whitening agent, it is necessary to select a suitable solvent when converting the sample to be tested into a solution. Improper selection of the solvent will cause the solution to not comply with the Lambert-Beer law, and accurate measurement results cannot be obtained.

Generally, the solvent selection should follow the following principles:

(1) The selected solvent does not chemically react with the sample to be tested.

(2) The sample to be tested has a certain solubility in the solvent.

(3) In the measured wavelength range, the solvent itself has no absorption.

(4) Choose a solvent with low volatility, low flammability, low toxicity, and low price.

Among these principles, keeping the sample to be tested has good solubility in the solvent is very important for the accurate determination of absorbance. This point can be well explained from the determination of the fluorescence intensity of the fluorescent whitening agent CXT.

2. The influence of solution pH

The pH value of the solution has a greater impact on the absorbance of anionic and cationic fluorescent whitening agents. The absorbance of cationic fluorescent whitening agents decreases significantly when pH ≥ 9; the absorbance of anionic fluorescent whitening agents drops sharply under acidic conditions, and the difference The degree of reduction of the product is also different. The influence of the pH value of the solution on the absorbance of the fluorescent whitening agent is bound to have a certain effect on the fluorescence intensity. The effect of solution pH on the extinction value and fluorescence intensity is a good example of the fluorescent whitening agent VBL.

3. The influence of light

Some fluorescent whitening agent solutions will not change significantly under sunlight (or excitation light containing enough ultraviolet light) for a long time, but there are some fluorescent whitening agents, such as dilute solutions of stilbene fluorescent whitening agents , Under direct sunlight, the change of cis-trans isomerism is prone to occur. This change of cis-trans isomerism causes a change in the extinction value, thereby affecting the stability of the fluorescence intensity. Pay attention to fastness and avoid light when extinction value.

Fourth, 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, within this concentration range, the absorbance A and the concentration have a linear relationship. For fluorescent whitening agents, the linear relationship between the absorbance and the concentration of the solution is limited to relatively dilute solutions. For thicker solutions, the absorbance not only does not increase with the increase of the concentration of the solution, but also often decreases with the increase of the concentration, which deviates. With the light absorption law, the measured fluorescence intensity is no longer reliable at this time, which is mainly due to the quenching of fluorescence and internal filtering.

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