Sample preparation units

TABLE 3.3 A Comparison of Nanocapillary and Conventional LC-MS for the Amount Injected and UV and MS Responses  

LC/MS Volume Injected, nL Amount Injected, ng UV Response MS Response 

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Marsh et al. [47] have described an apparatus based on an autoanalyser system for the automatic preparation of soil extracts for mineral nitrogen determination. It consists of a reagent adder, which adds the correct volume of extractant for an approximately weighed amount of soil, and a sample preparation unit, which mixes, filters, dilutes and loads samples on to an autoanalyser sampler. A labour saving of 60% is achieved in this method compared to manual method. Examples are given of the determination of nitrate plus nitrate nitrogen and ammonium nitrogen. 

Tests were carried out to compare the efficiency of extraction results obtained using a manual weighing and sample preparation method, and the reagent adder and sample preparation unit. Extracts of four replicates of ten soils were prepared by each method and analysed for nitrate- plus nitrite-nitrogen by a diazotisation and coupling reaction with sulphanilic acid and N-(l-naphthyl)ethylenediamine and ammonium-nitrogen by an indophenol method. These methods are described fully by Greaves et al. [48]. 

Flow injection analysis is based on the injection of a liquid sample into a continuously flowing liquid carrier stream, where it is usually made to react to give reaction products that may be detected. FIA offers the possibility in an on-line manifold of sample handling including separation, preconcentration, masking and color reaction, and even microwave dissolution, all of which can be readily automated. The most common advantages of FIA include reduced manpower cost of laboratory operations, increased sample throughput, improved precision of results, reduced sample volumes, and the elimination of many interferences. Fully automated flow injection analysers are based on spectrophotometric detection but are readily adapted as sample preparation units for atomic spectrometric techniques. Flow injection as a sample introduction technique has been discussed previously, whereas here its full potential is briefly surveyed. In addition to a few books on FIA [168,169], several critical reviews of FIA methods for FAAS, GF AAS, and ICP-AES methods have been published [170,171]. 

Figure 5.5 Schematic representation of online hyphenation of microdialysis sample preparation unit with NCE [80].

The system is fitted with a sample preparation unit (Fig. 51) (the use of which depends on the methods to be employed). The analysis apparatus is... 

The SPR biosensor systems for analysis of complex samples in the field have to integrate several key elements. These include, in particular, a sample preparation unit, a fluidic system, a biorecognition element, and an SPR optical platform (Fig. 1). 

In this biosensor system, a sample is pretreated in the sample preparation unit and dehvered by the fluidic system into contact with the biorecognition element immobihzed on the sensor surface. The SPR optical platform converts its specific interaction with the analyte into the sensor output. 

SPR biosensors are devices that are suitable for analysis of aqueous samples. Therefore, in order to detect target analytes in different real-world matrices (e.g., tissue, meat, soil, and air) the analyte has to be transferred to a liquid by a sample preparation unit. Numerous sample pretreatment methods for gas, solid, and crude liquid samples compatible with SPR biosensors are available. For detection in gas environments such as air, real-time trapping of analyte into an aqueous solution is possible by using collectors such as a wetted-wall cyclone particle collector [1]. Several optical biosensors have been integrated with these collectors and installed on aerial vehicles for real-time detection... 

Coupled systems include multidimensional and multimodal systems. Multidimensional chromatography involves two columns in series preferably two capillary columns, with different selectivity or sample capacity, to optimize the selectivity of some compounds of interest in complex profiles or to provide an enrichment of relevant fractions. In multimodal systems, two chromatographic methods or eventually a sample preparation unit and a chromatographic method are coupled in series. Coupled systems that received much interest in recent years are multidimensional CGC (MDCGC), the combination of high-performance liquid chromatography with CGC (HPLC-CGC) and the on- or off-line combination of supercritical fluid extraction with CGC (SFE-CGC). Multidimensional and multimodal techniques in chromatography arc described in detail in [65],... 

Beta Scientific make three analyzers, the 4200, the 4201 and the 4203. These instruments were designed for unattended and fully automatic operation, complete analyses in less than 10 minutes, cost effectiveness and an ASCII, R232 interface for computer or LIMS connection [196]. The model 4200 is a single channel instrument with no R232 interface and manual calibration the model 4201 also includes an R232 interface, and the moel 4203 is a three channel version without sample preparation but with an R232 interface. The model 4210 is a th station sample preparation unit, a required accessory for model 4203. 

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