Talanta 79 (2009) 205–210 Contents lists available at ScienceDirect Talanta journal homepage: www.elsevier.com/locate/talanta A single standard calibration module for flow analysis systems based on solenoid microdevices Lukasz Tymecki ∗ , Kamil Strzelak, Robert Koncki University of Warsaw, Department of Chemistry, Pasteura 1, 02-093 Warsaw, Poland article info Article history: Received 8 December 2008 Received in revised form 6 March 2009 Accepted 12 March 2009 Available online 24 March 2009 Keywords: Flow analysis Calibration Solenoid device PEDD abstract Only two computer-controlled microsolenoid devices, namely two micropumps or one micropump and one microvalve, are sufficient for the construction of on-line dilution modules useful in several flow analytical systems for the calibration using single standard. Three simple constructions of such modules were tested and compared. The most promising is the one based on the concept of a microvalve controlling dilution ratio of the standard and a solenoid micropump playing a double role: solution pumping device and mixing segments homogenizer. All investigated modules were tested with paired emitter detector diode (PEDD) as photometric flow-through detector and bromothymol blue as a model analyte. The best module was implemented into more advanced flow-injection system dedicated for optical detection of alkaline phosphatase activity using UV-PEDD-based flow-through detector for the enzyme reaction product. © 2009 Elsevier B.V. All rights reserved. 1. Introduction The final goal of flow analysis (FA) is the automation or at least mechanization of whole analytical procedure from sampling to ana- lytical results acquisition. Indispensable step of each FA method is calibration. The set of standards method is the most popular method of calibration. According to the FA idea this step should also be auto- mated. For the analyst convenience off-line preparation of standard solutions should be simplified and therefore several FA systems requiring only one standard have been developed [1–8]. The mentioned approach can be realized by special units of FA manifolds dedicated for controlled dilution of single standard like the mixing chamber [1], system of dilution loops of different dimen- sions [2], fully rotating valve with set of dilution loops [3,4] etc. SIA approach exploits an additional loop to generate concentration gra- dient of standard [5]. Several calibration procedures in FA are based on either merging zones approach [6] in which segments of stan- dard can be superimposed and merged in a controlled way in the FA system, or zone sampling approach [7] where a small portion of dis- persed standard zone can be injected into another carrier stream. Similar possibilities are offered by modern, more or less sophis- ticated multi-pumping [9–11] and multi-commutation [12–14] FA systems, reviewed recently. In this study, simple FA modules (composed of only two computer-controlled solenoid devices) dedicated for a single stan- ∗ Corresponding author. E-mail address: luktym@chem.uw.edu.pl (L. Tymecki). dard calibration procedures, are investigated. The main goal of this study is the development of module useful for further applications in more sophisticated FA systems. The utility of investigated mod- ules will be tested with newly developed PEDD-based photometric detectors [15–17] designed for FA needs. 2. Experimental Alkaline phosphatase isolated from bovine intestinal mucosa (ALP, EC 3.1.3.1, powder 15 U mg -1 ) and p-nitrophenyl phosphate (NPP) were obtained from Sigma–Aldrich (USA). Bromothymol blue (BTB), p-nitrophenol (NP) and other reagents of analytical grade were obtained from POCh (Poland). Microsolenoid devices were purchased from Bio-ChemValve Inc. (Boonton, USA). The solenoid pumps (product no.120SP1210- 4TE) operated with 2 Hz frequency as recommended (http://www.biochemfluidics.com/) and indicated stroke vol- ume of 16 L. Moreover, three-way solenoid valves (product no.100T3MP12-62-5) were applied. Both devices were PC- controlled by the KSP Measuring System (Poland) [18]. Flow manifolds were arranged with PTFE Microbore tubings (ID 0,8 mm) from Cole-Palmer (USA). Architecture of investigated manifolds is shown in next section of this paper. Fabrication and analytical performance of flow-through PEDD detectors was reported elsewhere [15–17]. Red, blue an UV light emitting diodes (LEDs, diameter: 5 mm; lens: transparent, flat front; view angle: 140 ◦ ) were obtained from Optosupply (Hong Kong). Flow-PEDD for BTB detection was constructed using home-made polycarbonate cell (10mm optical pathlength, 90 L dead volume) 0039-9140/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.talanta.2009.03.028