Principles of Flow Injection Analysis

Automated Sequential Injection-Capillary Electrophoresis for Dried Blood Spot Analysis: A Proof-of-Concept Study

A hyphenated analytical platform that enables fully automated analyses of dried blood spots (DBSs) is proposed by the at-line coupling of sequential injection (SI) to capillary electrophoresis (CE). The SI system, exploited herein for the first time for unattended DBS handling, serves as the "front end" mesofluidic platform for facilitating exhaustive elution of the entire DBS by flow programming. The DBS eluates are thus free from hematocrit and nonhomogeneity biases. The SI pump transfers the resulting DBS eluates into CE sample vials through an internal port of the CE instrument and homogenizes the eluates, whereupon the eluted blood compounds are automatically injected, separated, and quantified by the CE instrument. The SI and CE are commercially available off-the-shelf instruments and are interconnected through standard nuts, ferrules, and tubing without additional instrumental adjustments. They are controlled by dedicated software and are synchronized for a fully autonomous operation. The direct determination of endogenous (potassium and sodium) and exogenous (lithium as a model drug) inorganic cations in DBS samples has been used for the proof-of-concept demonstration. The hyphenated SI-CE platform provides excellent precision of the analytical method with relative standard deviation (RSD) values of peak areas below 1.5 and 3.5% for intraday and interday analyses, respectively, of the endogenous concentrations of the two inorganic cations. For the determination of lithium, calibration is linear in a typical clinical range of the drug (R² better than 0.9993 for 2-20 mg/L), RSD values of peak areas are below 4.5% (in the entire calibration range), the limit of detection (0.4 mg/L) and the limit of quantification (1.3 mg/L) are well below the drug's minimum therapeutic concentration (4 mg/L), and total analysis time is shorter than 5 min. The SI-CE platform reflects the actual trends in the automation of analytical methods, offers rapid and highly flexible DBS elution/analysis processes, and might thus provide a general solution to modern clinical analysis as it can be applied to a broad range of analytes and dried biological materials.

Computer-controlled fluid-flow chemical analysis (CC-FCA) and its application to environmental analytical chemistry

Computer-controlled fluid-flow chemical analysis (CC-FCA) was investigated for the determination of trace amounts of toxic pollutants in the environment. For CC-FCA, automated chemical analysis systems were developed by using computer-controllable pumping and valve modules, and polytetrafluorethylene (PTFE) tubing and connectors. The systems demonstrated in this work were a flow injection-type system, a sequential injection-type system, a mini-column pretreatment system (Auto-Pret system), and an Auto-Pret hyphenated with flow injection analysis (FIA) system. Such systems were fully controlled by a computer program; the lab-made programs were written in Visual Basic. The systems can be hyphenated with some detectors, such as a spectrophotometric detector, an electrochemical detector, electrothermal-atomic absorption spectrometry (ET-AAS), a liquid electrode plasma-atomic emission spectrometry (LEP-AES) and inductively coupled plasma (ICP)-AES. Such systems were successfully applied to the determination of trace amounts of toxic pollutants in environmental water samples: they were heavy metal ions (Pb, Cd, Cr, etc.). In this paper, the author aims mainly at investigating the CC-FCA method for the determination of trace amounts of Cr(VI) in environmental water samples by spectrophotometry. The techniques used in this work were FIA, sequential injection analysis (SIA), and Auto-Pret/FIA, which were all computer-controllable. Limits of detection of Cr(VI) by FIA, SIA, and Auto-Pret/FIA were 8 × 10–9 mol/L (0.4 μg/L), 1.1 × 10–8 mol/L (0.6 μg/L), and 1.4 × 10–9 (0.07 μg/L), respectively. The methods were applied to the determination of Cr(VI) in river and drinking waters.

Exploiting automatic on-line renewable molecularly imprinted solid-phase extraction in lab-on-valve format as front end to liquid chromatography: application to the determination of riboflavin in foodstuffs

In the present work, it is proposed, for the first time, an on-line automatic renewable molecularly imprinted solid-phase extraction (MISPE) protocol for sample preparation prior to liquid chromatographic analysis. The automatic microscale procedure was based on the bead injection (BI) concept under the lab-on-valve (LOV) format, using a multisyringe burette as propulsion unit for handling solutions and suspensions. A high precision on handling the suspensions containing irregularly shaped molecularly imprinted polymer (MIP) particles was attained, enabling the use of commercial MIP as renewable sorbent. The features of the proposed BI-LOV manifold also allowed a strict control of the different steps within the extraction protocol, which are essential for promoting selective interactions in the cavities of the MIP. By using this on-line method, it was possible to extract and quantify riboflavin from different foodstuff samples in the range between 0.450 and 5.00 mg L(-1) after processing 1,000 microL of sample (infant milk, pig liver extract, and energy drink) without any prior treatment. For milk samples, LOD and LOQ values were 0.05 and 0.17 mg L(-1), respectively. The method was successfully applied to the analysis of two certified reference materials (NIST 1846 and BCR 487) with high precision (RSD < 5.5%). Considering the downscale and simplification of the sample preparation protocol and the simultaneous performance of extraction and chromatographic assays, a cost-effective and enhanced throughput (six determinations per hour) methodology for determination of riboflavin in foodstuff samples is deployed here.