In-line sampling

Heuer and Schweehten [15] designed a sampler for installation with a fluidized bed jet mill where the entire classifier product passed through a Sympatec laser measuring device. This system is suitable for use with 

---

Garn, M. B., Gisin, M., Gross, H., King, P., Schmidt, W. and Thommen, C., Extensive flow-injection dilution for in-line sample pre-treatment, Anal. Chim. Acta, 207, 225, 1988. 

FIA star 5010 Modular, semi- or fully automatic operation. May be operated with process controller microprocessor. Can be set up in various combinations with 5017 sampler and superflow software which is designed to run on IBM PC/XT computer 60-180 samples h Dialysis for in-line sample preparation and in-line solvent extraction.Thermostat to speed up reactions. Spectrophotometer (400-700nm) or photometer can be connected to any flow through detector, e.g. UV/visible, inductively coupled plasma, atomic absorption spectrometer and ion-selective electrodes... 

J. R. Hutchinson, P. Zakaria, A. R. Bowie, M. Macka, N. Avdalovic, and P. R. Haddad, Anion-Exchange Capillary Electrochromatography and In-Line Sample Preconcentration in Capillary Electrophoresis, Anal. Chem. 2005, 77, 407. 

We monitored the pH and Eh of the column effluents by means of in-line sampling cells equipped with glass and platinum electrodes, respectively. Effluent samples were collected with a fraction collector. Three separate tests were conducted with columns of identical diameter but different lengths 11, 22, and 44 cm. The different column lengths allowed us to investigate the effect on solution chemistry of residence time in the column and surface area of minerals contacted by the solution. At the flow rates used in our experiment, the residence times were approximately 1, 2, and 4 days, respectively, for the three columns. The mineral surface area contacted by the solutions is proportional to the column lengths. 

Measurement biases were assumed constant for each simulation of the system. It should be noted that the measurement performance assumed corresponds to a clean, well-maintained system in which the pH probes are placed in an in-line sampling system rather than in the CSTR. 

Both GC- and LC-MS have been performed on several nucleosides, especially after persilylation, but several problems related to the trimethylsi-lylation of the N-4 position of cytosine as well as 2 -fluoronucleosides have been reported. An interesting study of nucleosides using LC-CIMS (ammonia) has been presented. That study, along with those of VestaP and Melera concluded that good spectra of nucleosides can be obtained from in-line sample introduction. The best spectra were obtained by spotting a solution of a nucleoside directly onto the LC interface. 

Mixing chambers have often been used in flow analysis, mainly to improve mixing conditions, attain a high degree of sample dispersion, provide exponential dilution, separate different immiscible phases and / or establish fluidised beads. They are essential for some specific tasks such as in-line sample preparation [65], reagent dissolution [66], analyte separation/concentration [67] and integrated reaction/detection [68]. Moreover, they are inherent to some modes of flow analysis, such as flow batch analysis. 

Manifold components used for accomplishing specific steps such as analyte separation/concentration, in-line sample preparation and reagent dissolution can have relatively large inner volumes, thus behaving as mixing chambers. 

Flow analysis has been used to investigate the fundamental chemistry of chemiluminescence and bioluminescence reactions, to optimise post-column chemiluminescence reaction conditions for liquid chromatographic detection and to quantify analytes in relatively simple or synthetic matrices [68]. In recent years, there has been a pronounced increase in the application of these methods to the analysis of real sample matrices [69]. This has usually been achieved by a combination of efficient in-line sample treatment, e.g., use of solid-phase reagents for concentrating selected analytes and/or for removing the sample matrix and exploitation of more inherently selective reactions [70,71],... 

M.B. Gam, M. Gisin, H. Gross, P. King, W. Schmidt, C. Thommen, Extensive flow-injection dilution for in-line sample pretreatment. Comparison between single-stage and dual-stage modules, Anal. Chim. Acta 207 (1988) 225. 

It is interesting to note that in-line sample filtration can be implemented in all of the above configurations. The characteristics and potential of in-line sample filtration are emphasised in Section 8.4. 

Flow analysis is associated with wet chemistry thus, solid samples of diverse origin, e.g., alloys, soils, sediments, sludges and foodstuffs, are normally subjected to in-line treatment in order to form a liquid analyte zone. The two most common examples are in-line sample electrolytic dissolution, where the analyte zone is formed as a consequence of applying a direct electric current to the solid sample, and sequential extractions of soils and sediments. 

The analyte concentration in the portion of the sample zone yielding the analytical signal should match the dynamic concentration range of the flow-based analytical procedure. To this end, in-line sample dilution is often required, and this step is efficiently accomplished in a flow analyser. As emphasised in Chapter 1, calibrated devices such as burettes, volumetric flasks and pipettes are not required, as the sample and reagent volumetric fractions are maintained for all of the assayed sample and standard solutions. 

The degree of in-line sample dilution can be defined in real-time and this is a key benefit of expert flow systems (see 8.7). 

It is a difficult task to define broad terms related to sample preparation, sample (or analyte) extraction and analyte separation/concentration, which becomes even more difficult when physico-chemical processes, e.g., microwave, UV or ultrasound irradiation, are involved. In this monograph, in-line sample digestion, bleaching, hydrolysis, oxidation and related approaches are therefore discussed under the general term sample treatment. 

Due to the pronounced heating effect of microwave irradiation, most applications refer to in-line sample preparation for the determination of metals in biological and clinical matrices. This approach has also been exploited to accelerate the development of, e.g., hydrolysis, extraction and leaching, as well as for the photo-degradation of organic matter (Table 8.1). 

An unsegmented conditioning stream (Ri, Fig. 8.16) can also be added by confluence before the mini-column, and this option is useful for procedures requiring an in-line sample conditioning step. 

Alternatively, the flow system can be exploited for in-line sample conditioning prior to chromatographic separation, as demonstrated by the determination of benzoic and sorbic acids in food products [243]. The flow system comprised an electro-osmotic pump, five solenoid valves and a homemade SPE unit, combined with capillary zone electrophoresis. Tetrabutylammonium bromide was used as an ion pair reagent to improve analyte retention on a Cs-bonded silica sorbent. 

Glucose, ethanol, ammonia, phosphate Fermentation medium Filtration UV—Vis 5, 5, 50,1 mg L-1 after 200-fold in-line sample dilution Flow injection system steriliseablecrossflowmicrofilter process monitoring [538]... 

Iodide Pharmaceutical formulations GD UV-Vis 1.0 mg I L 1 Flow injection system merging zones exploitation of the iodine-starch reaction possibility of using dialysis for in-line sample dilution [539]... 

Phosphorus (dissolved) Waters, sediment extracts Gel filtration UV-Vis 1.1 (low range) or 12 (high range) pgiu1 Flow injection system speciation Sephadex G-25 mini-column UV-assisted in-line sample preparation two dynamic concentration ranges [546]... 

In some instances, the flow manifold is designed for sample preparation prior to, e.g., HPLC or gas chromatography. Protocols for in-line sample filtration and dilution in sequential injection chromatography are presented elsewhere [315]. 

The discussion above demonstrates that in-line sample treatment in flow analysis presents endless possibilities. 

A.R. Wheeler, H. Moon, C.A. Bird, R.R. Orgazalek Loo, C-J Kim, J.A. Loo and R.L. Garrell, Digital microfluidics with in-line sample purification for proteomics analyses with MALDI-MS. Anal Chem 77, 534-540 (2005). 

M. Abdelgawad, M.W.L. Watson and A.R. Wheeler, Hybrid microfluidics a digital-to-channel interface for in-line sample processing and chemical separations. Lab Chip, 9, 1046-1051 (2009). 

---