Ion-Selective Electrode Method: This is one of the commonly used methods. The principle is that when the fluoride ion-selective electrode contacts a fluoride-containing solution, the activity of fluoride ions in the solution changes, and the electromotive force of the cell also changes accordingly. During specific operation, a sample of disposable tableware needs to be processed first, such as being crushed and then soaked in hydrochloric acid to extract fluoride ions. Then, a total ionic strength buffer is added. After that, the fluoride electrode and the calomel electrode are inserted into the solution. By measuring the potential difference and comparing it with the standard curve, the content of fluoride ions can be obtained.
Ion Chromatography Method: Based on the principle of ion exchange, it rapidly separates various ions in the separation column. The strong electrolyte in the solution is removed by a suppressor, and the conductivity of each ion to be measured is determined by a detector. This method has the advantages of being fast, sensitive, and having good selectivity. The detection limit can reach 0.02mg/L, making it very suitable for the analysis of high-purity water. Similarly, the sample needs to be appropriately processed first to extract the fluoride ions into the solution before detection.
Spectrophotometry: Fluoride ions react with reagents and lanthanum nitrate in an acetate buffer medium to form a blue complex. The absorbance value of the complex at a wavelength of 620nm is proportional to the concentration of fluoride ions. This method is more accurate for the analysis of low-concentration samples, but the detection takes a long time. The sample of disposable tableware needs to be processed into a solution state first, and then the corresponding reagents are added for reaction. The absorbance is measured by a spectrophotometer to determine the fluorine content.
Checking Product Labeling and Instructions
Presence of Fluorine-Related Labeling: If the packaging or the product itself of disposable tableware has a clear indication of containing fluorine or not, relevant information can be directly obtained. For example, for some degradable disposable tableware that meets specific standards, if its fluorine content meets the standard requirements, the fluorine content range may be noted in the product description or it may indicate that it meets the fluorine-free requirement. Checking Raw Materials and Ingredient Descriptions: Carefully check the raw materials and ingredient list of the product. If it contains fluorine polymers such as polytetrafluoroethylene or clearly indicates the presence of fluoride additives, it can be determined that the tableware contains fluorine. If no fluorine-containing substances are mentioned in the ingredient list, the possibility of containing fluorine is relatively low, but the presence of fluorine impurities cannot be completely excluded.
Observing Appearance and Characteristics
Color and Transparency: Generally, disposable tableware containing fluorine may have specific color or transparency characteristics. For example, some tableware made of fluorine-containing plastics may have a relatively high transparency or a unique glossiness, but this is not absolute. The presence of fluorine cannot be accurately judged only by the appearance color and transparency.
Texture and Hardness: Disposable tableware made of fluorine-containing materials may differ from those without fluorine in texture and hardness. Fluorine-containing plastics usually have good flexibility, wear resistance, and corrosion resistance. The tableware made of them may be relatively tougher and less likely to deform or be damaged. However, tableware made of different materials and processes also have differences in texture and hardness. Therefore, this method can only be used as an auxiliary judgment means.
