PAL SPME Arrow--evaluation of a novel solid-phase microextraction device for freely dissolved PAHs in water

Abstract

After more than 25 years, solid-phase microextraction (SPME) has gained widespread acceptance as a well-automatable and flexible microextraction technique, while its instrumental basis remained mostly unchanged. The novel PAL (Prep And Load solution) SPME Arrow combines the advantages of SPME with the benefits of extraction techniques providing larger sorption phase volumes such as stir bar sorptive extraction (SBSE). It thereby avoids the inherent drawbacks of both techniques such as limitations in method automation in the case of SBSE, as well as the small sorption phase volumes and the lacking fiber robustness of classical SPME fibers. This new design is based on a robust stainless steel backbone, carrying, the screw connection to the PAL sampler, the enlarged sorption phase, and an arrow-shaped tip for conservative penetration of septa (hence the name). An outer capillary encloses this phase apart from enrichment and desorption processes and rests against the tip during transfer and penetrations, resulting in a homogeneously closed device. Here, we present an evaluation and a comparison of the novel PAL SPME Arrow with classical SPME fibers, extracting polycyclic aromatic hydrocarbons (PAHs) as model analytes, from the freely dissolved fraction in lab water and groundwater via direct immersion using polydimethylsiloxane (PDMS) as common sorption phase material. Limits of detection, repeatabilities, and extraction yields were determined for the PAL SPME Arrow and compared to data of classical SPME fibers and SBSE bars. Results indicate a significant benefit in extraction efficiency due to the larger sorption phase volume. It is accompanied by faultless mechanical robustness and thus better reliability, especially in case of prolonged, unattended, and automated operation. As an exemplary application, the water-soluble fraction of PAHs and derivatives in a roofing felt sample was quantified.

Keywords: Microextraction; PAH; PAL SPME Arrow; PDMS; SPME.

Graphical Abstract

Picture of a PAL SPME Arrow during extraction of a stirred water sample

Fig. 1

Sketch of a classical SPME fiber and a novel PAL SPME Arrow. The SPME fiber possesses a 100-μm × 10-mm, 0.6-μL sorption phase. The PAL SPME Arrow is equipped with a 250-μm × 30-mm, 15.3-μL sorption phase, respectively, has a stainless steel inner core with a diameter of 0.4 mm, and an overall external diameter of 1.5 mm

Fig. 2

Extraction optimization measurements for PAL SPME Arrow extractions of PAH from aqueous solutions: a extraction time (stirring rate kept at 1500 rpm), b stirring rate (extraction time kept at 70 min). All samples contained 500 ng L⁻¹ of PAHs and were extracted by a PAL SPME Arrow with a PDMS sorption phase (250 μm × 20 mm, 10.2 μL). Exponential trend lines were added via Origin Pro 2015

Fig. 3

Theoretically extracted percentages for three extraction techniques and exemplary PAHs under equilibrium conditions calculated for an aqueous sample volume of 19 mL with indicated PDMS volumes and log K _fs values from literature [23]

Fig. 4

Depletion curves for three exemplary PAHs, extracted by a classical SPME fiber (100 μm × 10 mm, 0.6 μL) (a) and a PAL SPME Arrow (250 μm × 20 mm, 10.2 μL) (b)