An Overview about Recent Advances of Micro-Solid Phase Extraction in Flow Based Techniques

Review Article

Austin J Anal Pharm Chem. 2014;1(2): 1006.

An Overview about Recent Advances of Micro-Solid Phase Extraction in Flow Based Techniques

Warunya Boonjob*

Department of Analytical Chemistry, Charles University, Czech Republic

*Corresponding author: :Warunya Boonjob, Department of Analytical Chemistry, Charles University in Prague, Heyrovského 1203, 500 05, Hradec Králové, Czech Republic

Received: June 02, 2014; Accepted: July 13, 2014; Published: July 16, 2014


Sample preparation makes appearance on faster and more reliable sample preparation method with suitable and selectivity up to limit of legislation. The article presents an overview of the miniaturized and automated sample preparation method development in micro-SPE using flow based techniques.

Most of samples such as environmental or biological samples are usually not ready for direct introduction into the analytical instruments [1]. Sample preparation is an important and essential step which aimed to transform target compounds to a form and concentration suitable for analysis. In the analytical procedures, sample preparation is the slowest and the most costly part of the analytical process. Particularly multi-step procedures are utilized which takes about 50-75% of the total time of the analysis [2]. For this reason, the faster sample preparation can be done, the more quickly the analysis will be completed. Thus, sample preparation is required highly reproducibility and without considerable loss of the analyses.

Solid Phase Extraction (SPE)

Solid phase extraction (SPE) is a widely sample preparation method prior to chromatographic technique [3] which based on transfers of analyses from the liquid sample matrix to the solid sorbent. Knowledge of the hydrophobic, polar and/or ionogenic properties of both analyses and sorbent due to the selection of appropriate conditions of the liquid matrix and the sorbent according to the physico-chemical properties of the analyses, namely van der Waals forces (non-polar interactions), hydrogen bonding, dipole-dipole forces (polar interactions) and action-anion interactions (ionic interactions) are required.

A typical SPE procedure involves the following steps:

Conditioning - the sorbent is activated by wetted with a suitable solvent to activate the functional groups on its surface, afterward followed by water.

Loading - the sample is percolated through the sorbent.

Washing - interfering or non specific components of the matrix are removed while taking care not to elude the analytes as well.

Elution - analytes of interest are eluted with an appropriate solvent and further pre-concentration takes place by evaporation with N2 gas and reconstitution in desired medium prior to analysis.

Retention and capacity are more relevance parameters influencing the efficiency of the SPE process. In this context, retention of analyses on the sorbent should be maximum during the loading and washing steps but minimal during the elution step. Method development in SPE is accomplished by investigating different stationary phase and their masses, volumes of conditioning, sample loading, wash, and elution solvents, and amount of sample used in the experiment.


Each of mixed-mode and multidimensional SPE, analysts retain through a primary mechanism such as by Van der Waals interactions, polar dipole-dipole forces, hydrogen bonding, or electrostatic forces. However, sorbents often exhibit retention by a secondary mechanism as well. Bonded silica ion-exchange sorbents primarily exhibit electrostatic interactions, but the analysis also experiences non polar interaction with the bonded legend. Non polar bonded silica primarily retain analyses by hydrophobic interactions but exhibit a dual-retention mechanism, due to the silica backbone and the presence of un reacted surface silanol (-SOH) groups [4].

A mixed-mode sorbent is designed chemically to have multiple retentive sites on an individual solid sorbent particle. These sites exploit different retention mechanisms by chemically incorporating different ligands on the same sorbent. For example, sorbents have been manufactured that contain hydrophobic alkyl chains and cation-exchange site on the same sorbent particle useful for the exchange of the extraction of polar organic analyses from bio fluids [5]. Alternatively, there are several approaches to achieving mixed-mode or multi-dimensional mode (Figure 1). Sorbent particles of different types (i.e., a hydrophobic sorbent and an ion-exchange sorbent) that exhibit separate mechanisms of retention can be homogeneously admixed, or blended in the same column, or they can be layered into the same column by packing one phase over another. Additionally, multi-dimensional phases can be stacked by arranging in tandem series sorbents of different retention mechanisms contained in separate columns [6]. The technique of stacking or sequencing sorbents in tandem columns, termed chromatographic mode sequencing (CMS), can afford very selective isolation of analyses [7]. Multi-dimensional SPE mode approaches.