Sample introduction systems flow injection analysis

In 1985, mono-segmented flow analysis was proposed [64] as a means of achieving extended sample incubation times without excessive sample dispersion. The sample was inserted between two air bubbles into an unsegmented carrier stream therefore the innovation combined the favourable characteristics of both segmented and unsegmented flow systems. Further development revealed other potential applications, especially with regard to relatively slow chemical reactions, flow titrations, sample introduction to atomic absorption spectrometers, liquid-liquid extraction and multi-site detection (Chapters 7 and 8). This innovation was also referred to as segmental flow injection analysis [65]. 

Sample insertion relying on time-based introduction is inherent to segmented flow analysis and was the preferred approach before the advent of flow injection analysis. Manual injection using syringes with [50] or without [1] needles was used in the earliest flow injection systems (Fig. 6.7) but is now rarely used, except when very small sample volumes are available. 

A current trend is the coupling of another technique with AES, such as liquid chromatography, ion chromatography, or flow injection analysis, to enhance the capability of the plasma, particularly in the field of speciation (the so-called hyphenated techniques). This coupling can be considered as a highly sophisticated sample introduction system. In... 

Online analysis Online sample processing techniques such as flow injection provide advantages such as reliability, sample economy, ease of automation, measurement standardization, high speed, optional sample dilution, and the ability to derivatize the analyte so as to suit the analyzer/detector. These procedures facilitate the online monitoring of fermentation substrate materials, respiratory gases, and biomass. The modifications to flow injection analysis for accurate discontinuous flow operation include sequential injection analysis and bead injection spectroscopy. The most recent invention in online techniques is the introduction of the Lab-on-a-Valve, which opens the way to development of a novel type of microflow analytical system monitored by UV-visible spectrophotometry using fiber optics. This system is an ideal tool for fermentation monitoring. 

A flow injection analysis system (FIAS) for direct analysis of raw nrine was mentioned earlier (Lorber et al. 1997). No sample preparation was carried ont so the probability of cross contamination was negligible. The response profile of the ICPMS detector is typical of the FIAS sample introduction method, as shown for a calibration solution containing 100 ng L" uranium (top frame of Figure 4.11) and an actual raw urine sample containing 3.8 ng L (bottom frame). 

Several instrument manufacturers supply flame photometers designed specifically for the determination of sodium, potassium, lithium, and sometimes calcium in blood serum, urine, and other biological fluids. Single-channel and multichannel (two to four channels) instruments are available for these determinations. In the multichannel instruments, each channel can be used to determine a separate element without an internal standard, or one of the channels can be reserved for an internal standard such as lithium. The ratios of the signals from the other channels to the signal of the lithium channel are then taken to compensate for flame noise and noise from fluctuations in reagent flow rate. Flame photometers such as these have been coupled with flow injection systems to automate the sample-introduction process (see Section 33B-3). Typical precisions for flow-injection-analysis-based flame photometric determinations of lithium, sodium, and potassium in serum are on the order of a few percent or less. Automated flow injection procedures require l/KIO the amount of sample and 1/10 the time of batch procedures. -... 

A novel method of valveless sample introduction in flow analysis systems called flow-diffusion analysis (FDA) is described Due to the reduction of mechanical parts, i e an injection valve is dispensable, the system becomes very simple and its transformation into the micro-scale should require less effort than the respective transfer of conventional flow-injection systems Additionally, due to the time based sampling, the method is more flexible in terms of sensitivity and linear range compared to established volume based methods... 

For those techniques, a dissolved sample is usually employed in the analysis to form a liquid spray which is delivered to an atomiser e.g. a flame, or electrically generated plasmas). Concerning optical spectrometry, techniques based on photon absorption, photon emission and fluorescence will be described (Section 1.2), while for MS particular attention will be paid to the use of an inductively coupled plasma (ICP) device as the atomisation/ionisation source (Section 1.3). The use of on-line liquid sample introduction systems, such as flow injection manifolds and chromatography, will be dealt with in Section 1.4, because they have become commonplace in most laboratories, opening up new opportunities for sample handling and pretreatment as well as to obtain element-specific molecular information. 

The first hyphenated approach to be considered is the on-line combination of MS and MS, i.e. tandem mass spectrometry (MS-MS). A variety of combinations of different mass analysers have been described, including quadrupole and magnetic-sector analysers as MS], and quadrupole, magnetic-sector, ion-trap and time-of-flight analysers as MS2. Instruments like triple-quadrupoles are widely used for MS-MS, either as stand-alone systems with sample introduction via a solids insertion probe or flow-injection analysis, or in on-line combination with GC or LC. The work of Yost and co-workers and of Hunt and colleagues exemplify these methods. 

Principles and Characteristics As mentioned already (Section 3.5.2) solid-phase microextraction involves the use of a micro-fibre which is exposed to the analyte(s) for a prespecified time. GC-MS is an ideal detector after SPME extraction/injection for both qualitative and quantitative analysis. For SPME-GC analysis, the fibre is forced into the chromatography capillary injector, where the entire extraction is desorbed. A high linear flow-rate of the carrier gas along the fibre is essential to ensure complete desorption of the analytes. Because no solvent is injected, and the analytes are rapidly desorbed on to the column, minimum detection limits are improved and resolution is maintained. Online coupling of conventional fibre-based SPME coupled with GC is now becoming routine. Automated SPME takes the sample directly from bottle to gas chromatograph. Split/splitless, on-column and PTV injection are compatible with SPME. SPME can also be used very effectively for sample introduction to fast GC systems, provided that a dedicated injector is used for this purpose [69,70],... 

Organophosphate esters have been analyzed mainly in the indoor air samples. SAE has been relatively popular in the extraction of organophosphates from air samples, which have been collected either on filters or adsorbents. Both static and dynamic extraction can be used. An example of dynamic SAE (DSAE) is the extraction of OPEs from quartz filters by hexane MTBE (7 3). The flow rate was 0.2 ml/min, and the total extraction time was only 3 min, at a temperature of 70°C. The recoveries were compared with static SAE (2 X 20 min) and PEE and the recoveries obtained with DSAE (>95%) were at the same level or better than those obtained with other methods. No further purification or concentration was needed before GC-NPD analysis of organophosphates. The GC column was a 30 m X 0.32 mm i.d. DB% column with a phase thickness of 0.1 /rm. Splitless injection was applied in the sample introduction. The LODs were better than 0.4 ng/m. The system was developed further, and the DSAE was connected online with GC using PTV and large volume injection during the transfer. The most abundant compound found in the air was tri(w-butyl) phosphate. ... 

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