Analysis Of Oligomeric Formaldehyde Based On Raman Spectroscopy And The Fluorescence Detection Of Formaldehyde

Formaldehyde(FA),as an important chemical,is widely used in the fields of furniture manufacturing,fur processing,biomedicine and food preservation.However,there is a dynamic equilibrium between FA oligomers and monomers in the solution of oligomeric FA,and the low monomer content will affect the reaction efficiency negatively and cause excessive use of FA.Therefore,to analyze the structure changes of FA in aqueous solution in real time and explore the favorable factors of hydrolysis of FA oligomers to monomers,which can not only strengthen the analysis of structure changes condition,but also provide guidance for FA rational use.In addition,once the use of FA is excessive,it will greatly threaten human health,thus it is necessary to take effective measures to detect and monitor the content of FA in samples,so that prevent unqualified products from entering the market.Therefore,it is particularly crucial to utilize a fast and reliable detection method to detect the trace FA with high sensitivity and selectivity to the finished products.Taking the ’use’ and ’detection’ of FA as the points,our research introduced the concept and method of optical sensing,with the help of Raman spectroscopy and organic small molecule fluorescent probes,which used as a single or combination.The research route was top-down,related to the high,low and trace levels of FA concentration:real-time analysis of FA oligomer hydrolysis in solution dynamically,optimization of oligomeric FA usage for collagen tissue fixation,and fast and accurate FA detection in fur products(collagen).At the same time,the reasonable and efficient use of FA and the accurate detection of FAcontaining products were gradually realized from the initial FA solution to the end product.The specific research context and results included as the following four aspects:(1)With the aid of Raman spectroscopy,the dynamic changes between FA oligomers and monomers in aqueous solution were studied.By using the Raman platform built by combined devices in dark room,FA in the aqueous solution was analyzed in real time,and the influences of different factors on the hydrolysis process of FA oligomers were determined,including comprehensive investigations of the buffered solution,time,concentration,pH and temperature.During the process,it was verified that two characteristic peaks(OCO)and vas(OCO)were related to oligomers and monomers of FA.By monitoring these two peaks,the different forms of FA oligomers to monomers were deeply discussed,and the hydrolysis points of FA oligomers under different conditions in aqueous solution were deduced.According to the results,the best conditions are generally obtained:In the buffered solution at room temperature,the FA solution with the maximum monomer content can be quickly obtained as diluted to a low concentration of ≤5%and adjusted to pH 8.5～9.5,which is the optimization of the FA solution.(2)The effects of changes of oligomeric FA on the fixation of collagen were studied by Raman spectroscopy.By adjusting the intensity of the near-infrared laser and adopting appropriate spectral processing methods,the Raman spectra of the collagen solution,solid and biological tissue(sheep skin)were obtained,and the relevant important characteristic peaks were assigned,including external FA peak,v(C-N)stretching vibration and δ(N-H)bending vibration of amide III band,v(C=O)stretching vibration of amide I band,and v(CH2)stretching vibration of amino acid carbon chain skeleton.On this basis,the hydrolysis conditions of FA oligomers(the previous conclusion)were applied,and by observing the changes of the mentioned characteristic peaks,it is confirmed that the optimization of FA oligomers is beneficial to strengthen the methylene bridge(-CH2-)formation in the collagen(fiber).A comparative study of the OPA method at the molecular level found that the amino group content of collagen was reduced by at least 15%under optimized conditions of the hydrolysis of FA oligomers,which verified the early literature that "the non-monomeric form of FA would be detrimental to the crosslinking effect".(3)Small-molecule fluorescent probe was used to monitor the volume of FA solution and detect the trace FA in fur.Based on the PET reaction mechanism,the naphthimide-based FA fluorescent probes FAPs were designed and synthesized.Among them,the probe FAP-1 has better water solubility and excellent sensitivity with a detection of limit 0.76 μM.By taking this advantage,it was initially used to monitor the changes of concentration of FA before and after the fixation on collagen.In addition,the probe FAP-1 has excellent selectivity in mild acidic and neutral conditions.After probe FAP-1 applying on a white fur with unknown FA content,it is found that its response time was 60 min,the lowest probe concentration was 8 μM,and the detection value was 29.6 mg/kg.Compared with two standard methods:high performance liquid chromatography(HPLC)and UVvis spectrophotometry(UV-vis),it is found that the detection accuracy of the fluorescence method was close to the accurate value of HPLC at 33.4 mg/kg and was better than the approximate value of UV-vis at 134.9 mg/kg.(4)In this part,to take the detection advantages of near-infrared fluorescent probes to FA in dyed fur and cells in vivo,we explored the synthesis of nearinfrared FA fluorescent probes of three by using the fluorophore DCM as the framework,according to the reported reactions mechanisms.First,the formimine type DCM-1:Found that it was affected by solvent,and the fluorescence intensity of the probe in isopropanol was the largest.Secondly,methylene hydrazine type DCM-2:mainly explored the separation and purification of the product in terms of synthesis.Finally,2-aza-Cope rearrangement type DCM-3:It was recrystallized in ether and methanol several times to obtain a relatively pure product.After incubating with FA,the product aggregated to quench the fluorescence.After improving the structure of the recognition group,the rapid response to FA was realized within 1 min.By exploring the synthesis of three small-molecule fluorescent probes,we found that the ability to adjust the amino activity of the probes and maintain the dissolving stability of the fluorophore are the key to realize the detection of FA.