Lab on valve

Schematic depiction of an MPFS controller system. A agitator, MP micropump. V solenoid valve. 

LOV [18,19] significantly facilitates integration of various analytical units in the valve and provides great potential for miniaturization of the entire instrumentation. 

First LOV system including a flow through cell. CC central conduit, HC holding coil. 

In addition to compactness, other advantages of these lab-on-valve systems is the permanent rigid position of the sample processing channels that ensures repeatability of microfluidic manipulations and a large volume to surface ratio, which minimizes the unwanted adsorption on channels walls that may result in carryover. This provides proven robusmess and reliability of operation, and makes the microfluidic system compatible with real-life samples and peripheral instruments. 

It is noteworthy that LOV-based techniques have not only been extensively employed in homogeneous solution-based assays, but have also shown promise in heterogeneous assays because flexible fluid manipulation is also suitable for delivering beads in flow-based manifolds, i.e. precise fluid manipulation by the LOV system and the channel configuration also make it a powerful platform for Bl [22,23]. In combination with the renewable surface concept, Bl has been widely exploited for separation and preconcentration of analytes in the presence of complex matrix components. Most importantly, the automated transport of solid materials in such a system allows their automatic renewal at will and thus provides measurement, packing and perfusion of beads with samples and 

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These two very recent papers deal with a novel method of MISPE, the lab-on valve format. Here renewable portions of MIP are dosed into the loop of an injection valve. The full MISPE and HPLC process evolves automatically. Besides a detailed description of the technique used, these papers are also important from other aspects. 

Oliveira HM et al (2010) 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. Anal Bioanal Chem 397(1 ) 77-86... 

Long, X., M. Miro, R. Jensen, and E.H. Hansen. 2006. Highly selective micro-sequential injection lab-on-valve (pSI-LOV) method for the determination of ultra-trace concentrations of nickel in saline matrices using detection by electrothermal atomic absorption spectrometry. Anal. Bioanal. Chem. 386 739-748. 

Development of the sequential injection analyser, as well as intensive studies exploiting beads (including magnetic beads) [80—82], led to the appearance of flow analysers incorporating bead injection [83] and lab-on-valve [84] devices. 

Sequential injection analysis with lab-on-valve was conceived by Ruzicka in 2000 [84] as a progression of the sequential injection system towards downscaling. All components are integrated in a single unit mounted on a multi-position valve. The detector compartment is reduced and placed very close to the sample inlet, thus minimising the required volumes of sample, reagent and wash solution. 

The multi-port selection valve of a sequential injection analyser can be regarded as an advanced commuting device, which selects one inlet port to be commuted to any one outlet port at a time. Also, the entire manifold can be accommodated in such a valve, leading to the lab-on-valve concept [84]. 

J. Ruzicka, Lab-on-valve universal microflow analyzer based on sequential and bead... 

C.-H. Wu, L. Scampavia, J. Ruzicka, B. Zamost, Micro sequential injection fermentation monitoring of ammonia, glycerol, glucose, and free iron using the novel lab-on-valve system, Analyst 126 (2001) 291. 

J.B. Quintana, M. Miro, J.M. Estela, V. Cerda, Automated on-line renewable solid-phase extraction-liquid chromatography exploiting multisyringe flow injection-bead injection lab-on-valve analysis, Anal. Chem. 78 (2006) 2832. 

X.-B. Long, M. Miro, E.H. Hansen, Universal approach for selective trace metal determinations via sequential injection-bead injection-Lab-on-Valve using renewable hydrophobic bead surfaces as reagent carriers, Anal. Chem. 77 (2005) 6032. 

J.-H. Wang, Lab-on-valve mesofluidic analytical system and its perspectives as a world-to-chip front end, Anal. Bioanal. Chem. 381 (2005) 809. 

M.D.L. Castro, J. Ruiz-Jimenez, J.A. Perez-Serradilla, Lab-on-valve a useful tool in biochemical analysis, Trends Anal. Chem. 27 (2008) 118. 

In summary, the versatility of a mixing chamber, the multiple tasks it can be used for and the distinct role it can have in the flow manifold are the driving forces for more advanced methodologies using mixing chambers, not only as a component of a flow system but also as a complete small-scale laboratory. Based on an active chamber module, flow batch [107] and lab-on-valve [108] systems can be included in this category, as they can perform diverse and relatively complex functions, as discussed in 2.6 and 5.3.3. 

The Lab-on-Valve flow system resembles the sequential injection analyser but the main components are assembled on a multi-position valve. Exploitation of optical fibres permits spectrophotometric measurements to be performed very close to the main reaction coil. The compact geometry of the system makes it attractive for, e.g., in situ assays. For more details of this system, see 2.4.2. 

Currently, pTAS [112] and sequential injection systems using the lab-on-valve approach [22] are more popular. The former exploits hydrodynamic injection and is now known as Lab-on-Chip due to the extreme reduction in dimensions. Reproducible analytical channels are made by micro-drilling, etching, photolithography or laser erasing, and different channel profiles can be obtained at a reasonable cost. 

On the other hand, sequential injection with the lab-on-valve approach (5.5.3) does not exploit the strategy of downscaling the channel diameter but decreases the channel length and maintains the same approach as used in conventional sequential injection systems. 

In flow-based analytical procedures where the chemical reactions involved and/or the steps of analyte separation/concentration are relatively slow, the analytical signal can be attenuated by reducing the mean available time for the development of these physico-chemical processes. From a practical point of view, the result is equivalent to in-line analyte dilution. This possibility has been exploited in the spectrophotometric determination of hydrogen peroxide in contact lens care solutions using a sequential injection lab-on-valve system [60]. In view of the high sensitivity of the reaction between the analyte and 2,2,-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) in the presence of the enzyme... 

Hydrogen peroxide Lens care solutions Dialysis UV-Vis Up to 342 mg L 1 Sequential injection lab-on-valve system low dialysis efficiency (1.25 %) to promote in-line dilution, thus sensitivity reduction enzymatic assay [60]... 

Pyrolysis can also be used in flow-based determinations with electrothermal atomic absorption spectrometry, as demonstrated in the determination of nickel in environmental and biological reference materials using a sequential injection system with renewable beads [313]. After analyte sorption, the beads were directed towards the furnace of the spectrometer and stopped there pyrolysis was accomplished as usual in order to release the analyte and destroy the beads. This innovation has often been exploited in the lab-on-valve system, but spectrophotometric applications have not been proposed to date. 

Mono-segmented flow system. The sample mono-segment behaves as a titration vessel to which exact titrant amounts are added [328,329]. This innovation has also been implemented in the lab-on-valve system [330]. 

S.S.M.P. Vidigal, I.V. Toth, A.O.S.S. Rangel, Sequential injection lab-on-valve system for the on-line monitoring of hydrogen peroxide in lens care solutions, Microchem. J. 91 (2009) 197. 

J.H. Wang, E.H. Hansen, M. Miro, Sequential injection—bead injection—lab-on-valve schemes for on-line solid phase extraction and preconcentration of ultra-trace levels of heavy metals with determination by electrothermal atomic absorption spectrometry and inductively coupled plasma mass spectrometry, Anal. Chim. Acta 499 (2003) 139. 

J. Jakmunee, L. Pathimapomlert, S.K. Hartwell, K. Grudpan, Novel approach for mono-segmented flow micro-titration with sequential injection using a lab-on-valve system a model study for the assay of acidity in fruit juices, Analyst 130 (2005) 299. 

Lab-on-valve is another development of FIA and SIA this is discussed further in the section on miniaturisation of analytical instruments. 

Lab-on-a-chip (LOG) and lab-on-valve (LOV) devices are versions of pTAS where fluids are manipulated to give a complete assay on a microfabricated chip. Their main goal is the scaling down of laboratory processes onto a chip-based platform. 

Lab-on-valve (LOV) is a development of FI A whereby a microchannel chip (microconduit) is combined with a switching valve. It is a type of pTAS system. The function of the... 

Figure 10.6 The FIAlab Lab-On-Valve integrates all connections, sample loop and flow cell into one simple manifold (Image provided by kind permission of FIAlab Instruments).

Some of the interesting applications of LOV inclnde the manipnlation of beads and microcolnmns for sample clean-up or separation. In particnlar, one version of the system has received considerable attention and is called microseqnential injection-lab-on-valve (pSl-LOV). The J,SI-LOV device can be used for sample pretreatment alone or in seqnence with analysis and detection (usually absorbance or flnorescence). It has also been employed as the front end of a miniaturised CE system. An interesting nse of J,SI-LOV has been in conjunction with suspensions of specially coated beads. These beads can be manipulated by the multiport valve to flow into the holding coil and from there into the detector flow cell to form a temporary microcolnmn. The sample is then mixed with the bead column and any reactions are detected, e.g. adsorption over time. After measurements have been made, the beads are sent to waste. The formation and removal of these temporary microcolumns has advantages over the nse of fixed colnmns snch as ... 

Miro M, Jonczyk S, Wang J and Hansen EH (2003) Exploiting the bead-injection approach in the integrated sequential injection lab-on-valve format using hydrophobic packing materials for on-line matrix removal and preconcentration of trace levels of cadmium in environmental and biological samples via formation of non-charged chelates prior to ETAAS detection. J. Anal Atom Spectrom 18 BOOB. 

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