**3. Recent trends for sample treatment**

As mentioned before, environmental samples comprise complex matrices where target analytes are not generally amenable to direct determination by instrumental analysis, requiring sample treatments. Regarding this aspect, solid phase extraction is undoubtedly the most common treatment applied in MSFIA systems as shown in Tables 1 and 2. Besides the examples presented before in the text, MSFIA capabilities have been recently exploited to perform solid phase extraction using bead injection (BI) prior to chromatographic analysis.

The bead injection concept consists of handling solid suspensions in a fully automatic fashion, where the solid-phase sorbent, presented as micrometric beads, is renewed in each individual analytical cycle, rendering a fresh portion of sorbent for each analysis. Moreover, bead injection allows the simultaneous monitoring of both effluent and solid phase itself (optosensing) in real time, which brings complementary and enhanced insight into the solid phase extraction procedure in a single assay (Gutzman et al., 2006).

The bead injection concept is often associated to the lab-on-valve (LOV) platform. The LOV module comprises a monolithic structure with microconduits machined in a polymethylmethacrylate or polyetherimide unit, which is mounted atop a multiposition valve (Fig. 2), representing a step forward towards automation and miniaturization of flow injection systems. The LOV-BI approach offers two main advantages, not matched by any other automatic, flow-based solid phase extraction scheme: (i) the automatic renewal of sorbent, without any intervention of operator or replacement of devices or physical parts of the system, so as to circumvent the progressive deactivation and tighter packing of permanent in-line solid phase extraction cartridges; and (ii) the accurate metering of sorbent and eluate quantities by resorting to bi-directional programmable flow, as precisely controlled by the multisyringe burette (Miró et al., 2011).

Multisyringe Flow Injection

problems.

Chlorotriazine

Pharmaceutical

Polychlorinated

separation

pharmaceutical residue analysis, for instance.

Analysis for Environmental Monitoring: Applications and Recent Trends 291

However, reliable manipulation of bead suspensions within the flow manifold is the major challenge in mechanized BI protocols for repeatable trapping of beads in microcolumns with subsequent minimization of the uncertainty measurement of the overall analytical method. Initially, spherical shape, uniform size distribution and waterwettability (for reversed-phase materials) were identified as imperative requisites for sorbent selection. Recently, novel strategies for microfluidic handling the sorbent suspensions have been proposed (Oliveira et al., 2011), extending the application of LOV-BI to a larger scope of sorbents, not fitting the previous requirements and opening up new opportunities for preconcentration using molecular imprinted polymers for

The hyphenation of LOV-BI-MSFIA to chromatography provided a step further on automation for environmental analysis as sample preparation and analyte separation by chromatography were integrated. Previous automation of sample treatment prior to chromatographic analysis involved robotic analyzers, meaning high equipment costs and expensive operation. By using LOV-BI-MSFIA, while one sample is injected in the chromatographic equipment, the following sample is processed in the MSFIA equipment for matrix removal and analyte enrichment. This is an important, advantageous aspect when

As depicted in Fig. 2, connecting the liquid chromatograph equipment to LOV-BI-MSFIA is rather simple requiring that one of the lateral ports of the LOV platform is directly connected to the injection valve present in the chromatograph, allowing the introduction into the injection loop of all eluate or merely a fraction of it via heart-cut injection protocols. The transfer of the entire volume of eluate into the separation system is essential to reach low limits of detection required by analysis of pollutants in environmental samples, especially when using low-sensitivity detectors, for instance UV spectrophotometers. This approach, along with the handling of a well-defined volume of sample (about 10 ml), fostered the determination of non-steroidal anti-inflammatory drugs (NSAIDs) (Quintana et al., 2006) and chlorotriazine herbicides and some of its metabolites (Boonjob et al., 2010) in environmental samples at the low-µg l-1 level (Table 3). The screening of UV filters in swimming pool and seawaters also profited from the combination LOV-BI-MSFIA (Oliveira et al., 2010). In-line dilution was necessary after analyte elution in order to match the eluate composition to the aqueous content of the mobile phase, avoiding band broadening

herbicides 0.1 - 10 µg l-1 0.02 – 0.04 µg l-1 <5.5 (Boonjob et al., 2010)

residues (NSAIDs) 0.4 - 40 µg l-1 0.02 – 0.67 µg l-1 <11 (Quintana et al., 2006)

biphenyls 2 - 100 ng l-1 0.5 – 6.1 ng l-1 <9 (Quintana et al., 2009) UV filters 5 - 160 µg l-1 0.45 – 3.2 µg l-1 <13 (Oliveira et al., 2010)

Table 3. Analytical figures of LOV-BI-MSFIA system coupled to chromatographic

(RSD%) Reference

dealing with labile analytes that cannot sit on automatic injectors for a long time.

Analyzed species Working range Limit of detection Precision

Fig. 2. Schematic representation of multisyringe flow injection system coupled to lab-on-valve for sample treatment, hyphenated to liquid chromatography. LOV: lab-on-valve, MS: multisyringe, HPLC: liquid chromatograph, Si: syringe, Vi: three way commutation valve, A: air, CS: conditioning solvent, C: carrier solution, Dil: diluent, W: waste, CC: central channel, EL: eluent, B: channel for bead discarding, Sa: sample/standard solution, HC: holding coil, P: chromatographic pump, IV: injection valve, MC: chromatographic column, λ: diode array detector. Reproduced with kind permission from Springer Science+Business Media.

**8**

**B EL**

**V1**

**S1**

**MS**

**Sa**

**LOV**

**A**

**<sup>6</sup> <sup>3</sup> 4**

**5**

**CS**

**<sup>2</sup> <sup>7</sup>**

**1**

**HC**

**L1**

**L2**

**W**

**HPLC**

**MC**

**IV**

**P**

Fig. 2. Schematic representation of multisyringe flow injection system coupled to lab-on-valve

**S2 S3**

**V2 V3**

**CC**

for sample treatment, hyphenated to liquid chromatography. LOV: lab-on-valve, MS: multisyringe, HPLC: liquid chromatograph, Si: syringe, Vi: three way commutation valve, A: air, CS: conditioning solvent, C: carrier solution, Dil: diluent, W: waste, CC: central channel, EL: eluent, B: channel for bead discarding, Sa: sample/standard solution, HC: holding coil, P: chromatographic pump, IV: injection valve, MC: chromatographic column, λ: diode array

**W C Dil**

detector. Reproduced with kind permission from Springer Science+Business Media.

However, reliable manipulation of bead suspensions within the flow manifold is the major challenge in mechanized BI protocols for repeatable trapping of beads in microcolumns with subsequent minimization of the uncertainty measurement of the overall analytical method. Initially, spherical shape, uniform size distribution and waterwettability (for reversed-phase materials) were identified as imperative requisites for sorbent selection. Recently, novel strategies for microfluidic handling the sorbent suspensions have been proposed (Oliveira et al., 2011), extending the application of LOV-BI to a larger scope of sorbents, not fitting the previous requirements and opening up new opportunities for preconcentration using molecular imprinted polymers for pharmaceutical residue analysis, for instance.

The hyphenation of LOV-BI-MSFIA to chromatography provided a step further on automation for environmental analysis as sample preparation and analyte separation by chromatography were integrated. Previous automation of sample treatment prior to chromatographic analysis involved robotic analyzers, meaning high equipment costs and expensive operation. By using LOV-BI-MSFIA, while one sample is injected in the chromatographic equipment, the following sample is processed in the MSFIA equipment for matrix removal and analyte enrichment. This is an important, advantageous aspect when dealing with labile analytes that cannot sit on automatic injectors for a long time.

As depicted in Fig. 2, connecting the liquid chromatograph equipment to LOV-BI-MSFIA is rather simple requiring that one of the lateral ports of the LOV platform is directly connected to the injection valve present in the chromatograph, allowing the introduction into the injection loop of all eluate or merely a fraction of it via heart-cut injection protocols. The transfer of the entire volume of eluate into the separation system is essential to reach low limits of detection required by analysis of pollutants in environmental samples, especially when using low-sensitivity detectors, for instance UV spectrophotometers. This approach, along with the handling of a well-defined volume of sample (about 10 ml), fostered the determination of non-steroidal anti-inflammatory drugs (NSAIDs) (Quintana et al., 2006) and chlorotriazine herbicides and some of its metabolites (Boonjob et al., 2010) in environmental samples at the low-µg l-1 level (Table 3). The screening of UV filters in swimming pool and seawaters also profited from the combination LOV-BI-MSFIA (Oliveira et al., 2010). In-line dilution was necessary after analyte elution in order to match the eluate composition to the aqueous content of the mobile phase, avoiding band broadening problems.


Table 3. Analytical figures of LOV-BI-MSFIA system coupled to chromatographic separation

Multisyringe Flow Injection

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Boonjob, W.; Miró, M. & Cerdà, V. (2008). Multiple Stirred-Flow Chamber Assembly for

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Introduction of Slurry Samples in Multi-Syringe Flow Injection Analysis: Determination of Potassium in Plant Samples. *Analytical Sciences*, Vol.24, No.5,

Simultaneous Automatic Fractionation of Trace Elements in Fly Ash Samples Using a Multisyringe-Based Flow System. *Analytical Chemistry*, Vol.80, No.19, (Oct 2008),

Carbon Nanofiber-Based Microsolid-Phase Extraction Coupled to Liquid Chromatography for Automatic Determination of Trace Levels of Priority Environmental Pollutants. *Analytical Chemistry*, Vol.83, No.13, (Jul 2011), pp.

Hyphenation of Multimodal Microsolid Phase Extraction Involving Renewable Molecularly Imprinted and Reversed-Phase Sorbents to Liquid Chromatography for Automatic Multiresidue Assays. *Analytical Chemistry*, Vol.82, No.7, (Apr 2010),

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Chromatography (MSC) Using a Monolithic Column for the Determination of

The hyphenation of LOV-BI-MSFIA to gas chromatography is not as simple as it is for liquid chromatography. First, lower injection volumes are required and the analytes should be eluted in a solvent prone to fast vaporization. In fact, only one application has been described so far, where low values for limit of detection were attained through the automatic, on-line transfer of all eluate to a gas chromatograph equipped with an electron capture detector and a programmable temperature vaporization injector for determination of polychlorinated biphenyls in solid-waste leachates at the 2–100 ng L-1 range (Quintana et al, 2009).
