Flow injection analysis sample volume study

Duarte and colleagues used a factorial design to optimize a flow injection analysis method for determining penicillin potentiometricallyd Three factors were studied—reactor length, carrier flow rate, and sample volume, with the high and low values summarized in the following table. 

Micro flow control devices open new possibilities for the miniaturization of conventional chemical and biochemical analysis systems. The micro total analysis system (pTAS) including microfabricated detectors (e.g. silicon based chemical sensors, optical sensors), micro flow control devices and control/detec-tion circuits is a practical micro electro mechanical system (MEMS). pTAS realize very small necessary sample volume, fast response and the reduction of reagents which is very useful in chemical and medical analysis. Two approaches of monolithic and hybrid integration of these devices have been studied. Monolithic and hybrid types of flow injection analysis (FIA) systems were already demonstrated [4, 5]. The combination of the partly integrated components and discrete components is useful in many cases [6]. To fabricate such systems, bonding and assembling methods play very important roles [7]. 

Flow injection analysis is a continuous flow method in which highly precise sample volumes are introduced into a stream using segmented or unsegmented flow. The method must be accurate, precise and reproducible before it can be considered as a useful technique and the following test proves that this technique does meet all the requirements. Tyson [3], carried out several studies involving flow injection techniques and atomic spectroscopy with considerable success. 

A flow injection system with a micro-column of strong anion exchanger has been interfaced with an ICP-mass spectrometer via a microconeentrie nebulizer to perform on-line separation and trace determination of bromate in drinking waters (Elwaer, 1999 Elwaer et al, 2000). Method development studies examined the effect of sample injection volume, carrier stream flow rate and eluent concentration on system response. B asic performance data for this method were limit of detection, 0.13 ag/L (500 p-L sample injection) analysis time, 5 minutes per sample precision, 2.6%RSD (at5 g/L). 

The volume of biofluid needed for NMR analysis ranges between 0.3 to 0.4 or 1.5 to 2.5 mL with 5 or 10 mm tubes respectively. This can be a hindrance for pharmacokinetic studies which require numerous plasma samples or for difficult-to-obtain biofluids such as bile, cerebrospinal fluid (CSF) or those from neonates. Recent progress in the use of flow-injection NMR probes will alleviate this disadvantage. 

If the mass spectrometer is equipped with an LC system, then fast fingerprint MS analyses can be performed by injection of a series of different samples by the autosampler unit. This system will allow automated operation of a large series of samples. In addition, it is possible to utilize the flexibility that lies in the use of different mobile phases and the fast variation between them. The LC-MS system is simply operated as an ordinary LC-MS system, but without an analytical column. Typical injection volumes would be between 0.1 and 3 pL, and mobile phase flows between 0.1 and 0.2 mlV min. With this flow, a chromatographic peak will appear between 0.3 and 0.8 min after injection. Total time per analysis will be 1-2 min per injection. With a scan range of m/z 65-1500, a sufficient number of scan spectra (>15 spectra) will be captured for further data processing. Normally, it is preferred to perform multiple injections from the same sample, and the number of injections could be from 3 up to 10, depending on the study. With multiple injections, the precision of the analytical system can be controlled directly from the score plots and, of course, be evaluated relatively to the differences between the samples. 

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