Sorbent Extraction in programmable Flow Injection Format
Combination of Sorbent Extraction (SE) with programmable Flow Injection in lab-on-valve format (LOV) is a novel method, described for the first time in this Tutorial. It offers following advantages;
Repetitive accumulation of target analyte from large volumes of sample
Flexibility in choosing processed sample volume
Wide choice of flow rates for adsorption, elution and cleanup achieved by flow programming
Stop flow for incubation of sample with reagents in solution or on column
Choice of the length of light path for spectrophotometric measurement
Choice between elution of analyte or its optosensing on sorbent layer
Elution of analyte from SE micro column enhances spectrophotometric assay of Fe by ferrozine up to 1000 times. (A). The enhancement of sensitivity is defined as the slope of calibration line obtained by elution method from the analyzed sample, divided by slope of calibration line computed from molar extinction coefficient Thus for Fe(II) ferrozine complex with molar extinction coefficient e = 2.86.10 exp4 AU the slope is 0.0286 AU/μM of Fe or 0.00053 AU/ppB Fe.
Repetitive accumulation of Fe(II) ferrozine complex (A) obtained by processing sample volumes from 1 to 4 mL, resulted in up to 1084x enhancement of sensitivity of spectrophotometry as computed from molar extinction coefficient, while the eluate was monitored using 10 cm long flow cell (For details of this experiment see next page). The flexibility of choosing processed sample volume automatically and with high precision, is a key feature of this approach.
Equally important is the configuration
of micro column in close proximity to the inlet of the long light path flow cell (B). Due to minimized volume of flow path between the microcolumn and the flow cell, the enriched eluate is not diluted on the way into the optical path.
The sorbent is held in column by the (green) cladding of the optical fiber, in a way previously designed and tested for Bead Injection technique (Chapter 3). The advantage of this column configuration is low flow resistance and possibility to renew the sorbent by microfluidic manipulations. (3.1.3.B.)