Development Of Novel Single Drop Microextraction Technique

To improve the existing analytical methods and develop new ones especially in the field of sample preparation and clean up,the contemporary trends in analytical chemistry focused on the portmanteau word “QuEChERS” allusion of “Quick”,“Easy”,“Cheap”,“Effective”,“Robust”,and “Safe”.Toward the direction,scientists concentrate to develop novel methods that utilize minute chemicals by miniaturized techniques which are already deliberated as simple,economical and ecofriendly.Microscale sample preparation has drawn attention especially for complex sample matrix to concentrate target analytes in acceptable amount for detection and contamination free sample to produce satisfactory instrumental analysis.This thesis work devote to the key challenges in sample pretreatment through evolving miniaturized liquid phase microextraction techniques for enhancing sensitivity as well as speed.This study reports the development of three novel strategies for single drop microextraction technique,wherein organic solvent of a few micro-liters are utilized.Focusing on the overall objectives of the study,firstly a coupling microdevice has been designed to produce a compound drop termed as organic–aqueous pendant compound droplet as direct immersion three-phase single drop microextraction technique.Idea of generating organic–aqueous compound pendant droplet is to combine the benefit of both single drop microextraction and membrane microextraction by using a microsyringe that could not be realized before in three phase single drop microextraction mode.This new approach offers very lower limit of detection(0.02 ng/L)within 4 minutes with up to 1712 fold enrichment for five statins as model compounds.Three concepts play crucial role for high throughput,firstly the thin film phenomena in interfacial space in between two aqueous phases,secondly circulatory flowing liquid resultant from effective agitation,and finally iterative mode causes homogenization and renewal of deprotonation of targets at interfacial area of the droplet.Afterward,targeting in on-site extraction of volatile and semi-volatile compounds a new conception has been developed where an additional inner vial cap served as a mini cooling device for in-vial temperature gradient.Inner vial cap as a cooling tool for acceptor droplet in headspace coupled with simultaneous heating of sample matrix ensures a significant temperature gap between two phases that resulting in efficient extraction.This tactic leads to analytes extraction with higher enrichment factor from 302-388 folds within 2 minutes that is 3.5 to 4 times higher as compared to a typical HS-SDME.Higher enrichment due to the changing in surface tension of droplet owing to different temperature at liquid-air interface of droplet triggering heat and mass transfer because of Marangoni convection.Numerical simulation has been applied to justify the experimental results.Good agreement between experimental and numerical outcomes reveals that the method could be precisely designed and enlightened by multiphysics simulation.Good linearity(from the range of 0.03-0.5 ?g/ L to maximum 100 ?g/ L),repeatability(RSD < 5.9%)and the ng/L level limit of detection(7-10 ng /L)reflects the robustness,precision and usefulness for trace analysis of the method.Finally,a funnel-like cap assembled with a capillary tube and microsyringe has been applied to generate liquid–gas compound pendant drop to produce stable droplet proficient for faster and more efficient extraction.A simple manipulation enables to overcome the inadequacy of droplet instability typically encountered in direct immersion single drop microextraction.Additionally,output of liquid–gas compound pendant drop microextraction obtains 70 to 135 fold enrichment of pesticides in 3 minutes.Attributable to the increased contact area and adhesion force between capillary tip and drop improves the extraction efficiency and droplet stability.Likewise,the liquid flow pattern transition inside the droplet and Marangoni effect induced by the gradient in surface tension would effectively improve the mass transfer performance during the dynamic extraction.The concept of compound pendant drop is promising in sample pretreatment method for automated high-throughput analyses and also has profound potential in liquid-handling technologies such as digital microfluidics and on-chip liquid phase microextraction.In summary,three novel approaches have been presented to accelerate the sensitivity and fast extraction by producing two types of compound pendant drop and generating in-vial temperature gradient through microextraction device.The results presented in this thesis demonstrate that all three novel liquid phase microextraction could be outstanding alternative of current conventional sample pretreatment techniques for the trace analysis.