In-situ Dispersive Liquid–liquid Microextraction And Its Application In Water Analysis

The great progress in instrumental analysis is realized, but the sample preparation is still an important step prior to analysis by instrument. The aim of sample preparation is to clean-up sample, enrich analyte and converse sample matrix for the next instrument analysis. However, conventional methods for sample preparation(soxhlet extraction, distillation, centrifugation, precipitation) are highly time-consuming and labor intense which in consequence results in long exposure of laboratory personnel to harmful vapors from chemical reagents, particularly organic solvents. Dispersive liquid-liquid micro-extraction(DLLME) was introduced in 2006. It attracts considerable attention due to its rapidness, simplicity. Up to now the number of published articles concerning DLLME and its application has been more than 1000, and at least 700 articles were published in the latest three years.A new type of dispersive liquid-liquid microextraction is developed, of which chloroform as extraction solvent is formed by the reaction of chloral hydrate and sodium hydroxide. The formed chloroform is well dispersed in water sample without addition of any disperser solvent as in conventional DLLME. Extraction efficiency is higher in new DLLME than that in conventional DLLME. The new DLLME is so simple that it can be completed in a syringe, as both the addition of disperser solvent and the use of centrifuge are not required. The two methods, in-bulk and in- syringe, are applied to extract six amines in environmental water samples and analyze them by GC-FID. This paper will be divided into three chapters as follows.Chapter 1: Introduction. A brief introduction of the development of solvent-based microextraction and the progress of DLLME is presented. The principle of DLLME and its limitation are also discussed. The purpose of the work is pointed out at the end of the review part.Chapter 2: A new DLLME without direct addition of chloroform and disperser solvent into sample is developed for extraction of aniline, o-toluidine, N,N-dimethylaniline and 4-chloroaniline prior to analysis by GC-FID. In this paper, the principle of the proposed new DLLME is presented. The main factors influencing separation and extraction are examined in terms of GC separation conditions, the feeding ratio of chloral hydrate and sodium hydroxide, the choice of sedimentation methods and extraction temperature. The proposed DLLME is compared with conventional DLLMEs published in literature.Chapter 3: In view of the same principle of the new DLLME, an in-syringe DLLME is developed when the water sample, sodium hydroxide, chloral hydrate and water as separating phase are introduced into syringe as a proper order described in the text. The new in-syringe DLLME does not require the direct addition of chloroform and disperser solvent and the use of centrifuge. Some factors influencing in-syringe DLLME are studied in terms of the feeding ratio of chloral hydrate and sodium hydroxide, sedimentation methods, volume of separating phase solvent used, time for being transparent. A comparison of the new in-syringe DLLME and conventional DLLMEs is made when four selected aromatic amines are selected as model compounds.