Study On The Fluorimetric Determination Of Formaldehyde In Drink And Food Products By Flow Injection Analysis

With the development of the living standard of the people, increasinglyimportance has been attached to food quality security. Formaldehyde is anenvironmental pollution, which seriously threatens mankind's health; it is used to afood additive by a lot of mongers to improve food external appearance and used toantisepsis. So the examination of formaldehyde in food and drink products seems tobe very importance. There are a lot of methods reported for the determination offormaldehyde, but the articles of concerning the measurement of formaldehyde in thefood are not much, furthermore, they are not sensitive. Fluorescence analysis is atraditional analytical technology; its biggest characteristics are selective and sensitive,the flow injection technology and the fluorescence technology combine together, notonly simplified the operation, accurate and precision all get an exaltation, but also theanalytical efficiency greatly increased. In this research work, a technical ofmicrowave heating was introduced in the flow injection fluorescence analysis, thefluorescence derivatization was increased, so the analytical speed was raised and thesensitive was further improved. Because the sensitive and selective of the method isexcellence, the food sample aqua (or liquid sample aqua) needs a simple dilutionprocessing then, replaced the tedious and time-consuming steam distillationprocessing process in the reported articles, the analytical efficiency increased.There are two chapters in this thesis, review and study reports.Chapter one: review●Introduced the property of formaldehyde and the harm to human body.●Introduced the source of formaldehyde and in the last years the examinationpresent condition of formaldehyde.●Introduced the technology of flow injection analysis, fluorescence analysis andmicrowave heating and the developed present condition of them.Chapter two: study reportsFirst, the study of 5,5-dimethylcyclohexane-1,3-dione fluorimetric determinationof formaldehyde in drink by flow injection analysis. This method is based on the reaction between formaldehyde and 5,5-dimethylcyclohexane-1,3-dione in the present of ammonium acetate to form afluorescence compound. Formaldehyde can be quantitative determinate by detecting thefluorescence intensity of the fluorescence derivative which excited at 397 nm and emitslights at 465 nm. According to this, a method of flow injection fluorimetricdetermination of formaldehyde in drink was developed. The reaction system consists ofheating and cooling devices, the reaction coil was heated in a 95℃water bath. Thecalibration graphs were linear in the range of 0.005μg/ml-3μg/ml, the relative standarddeviation of 11 replicate determinations is 0.0061%, 18 samples can be analyzed perhour. The proposed method has advantages of simple, wide linear range, accuracy andselective. It was applied to the determination of formaldehyde in drink, samplesrequired only aqueous dilution prior to analysis, then we compared the proposedmethod with the steam distillation acetyl acetone spectrophotometry, the result isreliable.Second, the study of cyclohexane-1,3-dione fluorimetric determination offormaldehyde in drink and food by flow injection analysis.A sensitive flow-injection method using stop-flow technique for determination offormaldehyde in drink and food was developed. This method is based on the reactionbetween formaldehyde and cyclohexane-1,3-dione(CHD) to in the present ofammonium acetate to form a fluorescence compound, which has an excitationwavelength at 397nm and an emission wavelength at 465nm. Formaldehyde and thereagent was retained in a 95℃water bath instrument for 120s, then the fluorescenceintensity was examined after cooling in a water bath at 10℃. The sensitive degree ofthis system is very high. The linear range of formaldehyde is 0.2×10^-3～3μg/ml, thedetection limit is 0.04ng/ml.18 samples can be analyzed per hour; the relative standarddeviation of 11 replicate determinations is 1.89%. This method was applied to thedetermination of formaldehyde in drink and food, samples required only aqueousdilution prior to analysis, then we compared the proposed method with the steamdistillation acetyl acetone spectrophotometry, the results are basic to match, the recovery test havealso been carried out, and satisfactory results were obtained.Third, the study of microwave on-line heating fluorimetric determination offormaldehyde in drink and food by flow-injection analysis. Compared the two previous research works, we can found that thecyclohexane-1,3-dione system is more sensitive, on the basis of the second researchwork, replaced water bath to heat with the microwave heating, a method of microwaveon-line heating fluorimetric determination of formaldehyde in drink and food wasdeveloped. The same is in the ammonium acetate solution, formaldehyde reacted withcyclohexane-1,3-dione to form fluorescence compound, then examine the fluorescenceintensity for the excitation wavelength at 397nm and an emission wavelength at 465nm.Because microwave can greatly accelerate reaction, the fluorescence derivatization wasincreased, so the system doesn't need to stop-flow, the analytical speed gets anexaltation the sensitivity also gets a further improvement. According to this, a newmethod of determination of trace-formaldehyde was developed. The linear range offormaldehyde is 0.05ng/mL-2μg/mL, the detection limit is low to 0.014ng/ml, and 28samples can be examined per hour. This method also applied to determination offormaldehyde in drink and food, the sample per-treatment also required aqueousdilution. And the steam distillation acetyl acetone spectrophotometry method carried oncomparison, the recovery tests was carried out, the recoveries were in the range of 98%-103%, theresults is reliable.