Stir Bar Sorptive Extraction (SBSE) and Headspace Sorptive Extraction (HSSE): An Overview -

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Stir Bar Sorptive Extraction (SBSE) and Headspace Sorptive Extraction (HSSE): An Overview

May 1, 2009
By: Carlo Bicchi, Erica Liberto, Chiara Cordero, Barbara Sgorbini, Patrizia Rubiolo
LCGC North America

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Ronald E. Majors

The increase in the number of controls an analytical laboratory must make that has occurred over the last 15–20 years has induced a radical change in the approach to chemical analysis. The present trend for routine laboratories, in particular those where large numbers of homogeneous samples must be analyzed, is to develop, wherever possible, the so-called "Total Analysis Systems" (TAS) — that is, automatic systems in which sample preparation and analysis are merged into a single step, with the aim of reducing the workload to a minimum. This need has influenced greatly the development of both the main steps of an analytical procedure, that is, sample preparation and analysis, and within sample preparation it has increased greatly the importance of solvent-free sample preparation techniques (that is, techniques whereby an analyte or analytes are isolated from a matrix without using a liquid solvent).

Stir-bar sorptive extraction (SBSE) belongs to a group of techniques that have been developed in view of the previously mentioned analytical approach. This article is an overview on both SBSE and headspace sorptive extraction (HSSE) about 10 years after their introduction mainly focusing on their evolution after David and colleagues' review (1) published by LCGC in 2003 and on their perspectives of development.

The Technique

Figure 1

SBSE was introduced in 1999 by Pat Sandra's group to overcome some of the limits of the existing techniques, in particular in the recovery of medium-to-high volatility analytes when sampled in liquid phase with polydimethylsiloxane-open tubular traps (PDMS-OTT); a further aim was to improve the limited recovery achievable in ultratrace analysis with solid-phase microextraction (SPME), especially under unfavorable phase ratios when working with small volumes of sorptive material (in general PDMS) coating the fused-silica fiber (2). SBSE was first developed for sampling in liquid phase and is based upon sorption of the investigated analytes or fraction onto a very thick film of PDMS coated onto a glass-coated magnetic stir bar (commercially known as Twister, Gerstel GmbH, Muelheim, Germany). Figure 1a gives a scheme of a conventional PDMS SBSE device. Sampling is done by directly introducing the SBSE device into the aqueous sample; in the original experiments, the analytes sampled for a given time were recovered by thermal desorption and then on-line transferred to a gas chromatography (GC) or GC–mass spectrometry (MS) system for analysis. Later, liquid desorption in combination with high performance liquid chromatography (HPLC) also was applied, mainly for analytes not analyzable by GC (3,4).

Basic Concepts of SBSE

SBSE is based upon sorption, which is a form of partition based upon the analyte's dissolution in a liquid-retaining polymer from a liquid or vapor sample, thus, originating a bulk retention (5–9). The main advantages of sorption are related to high inertness of PDMS, which gives better performance for labile, polar, or reactive compounds; absence of catalytic degradation reactions; analyte recovery mechanism based upon a well-known chromatographic process; and linearity of sorption isotherms, which is fundamental for quantitative analysis.

Sandra's group also advanced a theory for SBSE that was rather similar to that of SPME. It was based upon the approximation that the partitioning coefficient of an analyte between PDMS and water is proportional to its octanol–water partition coefficient (K_O/W); thus, its theoretical recovery can be calculated through the following equation:

R_th = m_PDMS/m₀ = α/1 + α

where α = K_O/W/β and + m_PDMS is the mass of the analyte present in the PDMS, m₀ is the total amount of analyte originally present in the water sample, and β is the volume of water/volume of PDMS phase ratio.

The use of SBSE was extended almost immediately to sampling in vapor phase (headspace) by Bicchi and colleagues (5) and Tienpont and colleagues (6); the technique is known as HSSE. In HSSE, sampling is operated in static mode by suspending the PDMS SBSE device in the vapor phase in equilibrium (or not) with the solid or liquid matrix. Again, analyte recovery is by thermal desorption combined on-line with GC or GC–MS analysis of the desorbed analyte.

SBSE and HSSE have been the object of many reviews, singly or jointly or within surveys on sample preparation of specific classes of compounds or matrices (8–21).

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