Researches On Agarose Gel Properties Based On Low-Field Nuclear Magnetic Resonance Technology

Agarose as a purifying part of agar,due to the low content of sulfuric acid base in structure,with more excellent gel properties than agar.Agar is widely used in food additives,chemical,textile,etc for its stability and hysteresis.While agarose is used in the medical examination and analysis for its high purity.Good gel characteristic is the basis that they can be widely used.At present,detection of gel products is generally use macroscopic method,namely the texture instrument to stretch,squeezing,cutting the gels to determine such as hardness,viscosity,cohesiveness of gel properties.But the production would be broken,polluted and cannot be reuse again.Structural changes in the material microstructure and macroscopic properties change always linked.Organism contains a large number of protons,and because of different physical and chemical environment in which protons will lead to different proton relaxation state,which provides the basis for microscopic testing.As a non-destructive testing technology,Low-field nuclear magnetic resonance(LF-NMR),which have simple sample preparation,fast measurement,high accuracy and more important use in water distribution to the study have obvious advantages.In this paper,we do different agarose gel for transverse relaxation time(T2)detection using the LF-NMR technology,through multi exponential inversion curve fitting of T2 data processing,to find the micro proton T2 change rule caused by external factors,so provide a non-destructive,accurate detection of new ideas of test for polymer gel.The main content of this paper includes the following three parts:Firstly,the basic principles of nuclear magnetic resonance and the theory of low field nuclear magnetic resonance are described,and the application of low field nuclear magnetic resonance technology in chemical and food testing is reviewed.Secondly,three groups of agarose gel by the same volume but different concentrations/pH/ionic strength were prepared to test their transverse relaxation times(T2)on low field nuclear magnetic resonance spectrometer.Obtained transversal relaxation times and signal amplitude data in MATLAB software using CONTIN method for multi exponential inversion and get different relaxation group relaxation time and group content distribution.Though analysis of data inversion,It's found that:(1)agarose gel with high purity and due to the relationship between the relative content,the transverse relaxation data inversion reflect only water molecules in the 1H components;(2)with the agarose concentration increases,gel show trend of shorter T2;(3)with pH ascending,T2 of agarose gel tend longer first,then become shorter,at pH=7,T2 has the maximum;(4)with ionic strength increasing,T2 of agarose gel get longer first,then become shorter,in the I=0.8 T2 has the has maximum value.(5)the influence of concentration to T2 is much bigger than pH and ionic strength.Finally,we test the T2 of agarose aqueous solution system and agarose gel system in different heating procedure(10?/20min?10?/30min).Test the two kinds of systems from room temperature 298 K began after gradient heating to the 368k and then gradient cooling to room temperature 298 K to gel formation process in different temperature condition of T2.Of variable temperature T2 data analysis,it is found that for agarose aqueous solution system,the T2 of heating process in the 103--104 ms range increased gradually and with the temperature rising,the rate of increase T2 turns bigger,at 348 K there is a turning point for the phase transition of system;the T2 of cooling process in the 103--104 ms range decrease gradually with the temperature decreased,but it suddenly dropped to 102 ms when the temperature achieve room temperature,that indicates the formation point of the gel.For agarose gel system,T2 does not change significantly before 348 K in heating process,but there is increasing trend,after 348 K with temperature rise,T2 increases much,that indicates the gel melting point;T2 decreases with temperature decrease in Cooling process,and T2 suddenly dropped to 102 ms when the temperature drops to room temperature,shows the system response to gel state.