Enhanced Productivity Sampling Systems

FIGURE 17,14 A schematic of a commercially available DIHEN system. (Courtesy of Meinhard Glass Products, a part of Elemental Scientific.) 

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There are a number of these enhanced productivity sampling systems on the market, all of which work in a slightly different way. However, they all have one thing in common, and that is they offer at least a two-fold reduction in analysis time compared to traditional autosamplers. Some of the other benefits associated with this time saving include ... 

Since the heterogeneity of gasification feedstocks results in a formation of a wide variety of products of different chemical nature it is envisaged that the sampling system will have to be enhanced and up-dated on a short term basis. Therefore, there is room for improvement in sampling methods in order to meet all the requirements of the different gasification applications. 

There are many other nonstandard sample introduction devices such as laser ablation, ultrasonic nebulizers, desolvation devices, direct injection nebulizers, flow injection systems, enhanced productivity systems, autodilution, and online chemistry techniques, which are not described in this chapter. However, because they are becoming more and more important, particularly as ICP-MS users are demanding higher performance and more flexibility, they are covered in greater detail in Chapter 17. 

Sample Introduction Delivery Systems (USN, Cooled Spray Chambers, Desolvators, Autosamplers, Autodilutors, Enhanced Productivity Systems, Online Chemistry Techniques)... 

The focus of this chapter has been on the synthesis of new catalysts by parallel and combinatorial methods. Another aspect important to the development of new catalysts by these methods is the screening of these large libraries. We will not attempt to cover this topic comprehensively but do feel it is necessary to summarize some of the approaches that have been taken. Methods for screening libraries can be divided into both serial and parallel methods. Generally, the serial methods are adaptations of standard methods that allow for rapid individual analysis of each member of a library. Serial approaches for the analysis of libraries can be as simple as use of an auto sampler on a GC or HPLC system or as advanced as laser-induced resonance-enhanced multiphoton ionization of reaction products above the head-space of a catalyst (16) or microprobe sampling MS (63). The determination of en-antioselectivity in catalysis is a particular problem. Reetz et al. (64) reported the use of pseudoenantiomers and MS in the screening of enantioselective catalysis while Finn and co-workers (65) used diastereoselective derivatization followed by MS to measure ee. 

The use of molecular probes to track specific microbes in the environment, specifically those not easily cultured, has been recently reviewed (95, 97, 98), The sensitivity of these probes may be further enhanced by using amplification strategies (e.g., polymerase chain reaction or PCR), to amplify segments of DNA from samples obtained from production systems (95, 99), However, gene probes for geosmin or MIB synthesis are not currently available. 

If analysis is to be attempted with a detection system of only moderate selectivity, a substantial cleanup procedure may be required in order to enhance the concentration of the extracted trace residue while decreasing die concentration of possible interfering substances in the sample matrix. This is die case with most of the relatively nonspecific physicochemical detection systems used in residue analysis. Occasionally a sample may be suitable for direct physicochemical analysis after an extraction and concentration step. However, the majority of edible animal products need extensive cleanup to separate the compounds of interest from animal lipids and other natural organic substances prior to detection. For such detection systems, there has been a general rule dictating diat the cleaner sample, the better the result obtained. 

MALDI-TOF-MS facilitates the analysis of carotenoids and other natural products with detection limits that are lower than most other techniques. For example, subpicomole quantities can be detected (Wingerath et al., 1999). The enhanced sensitivity is the result of the efficiency of the pulsed ionization and detection system in which a complete mass spectrum is recorded with each laser flash. Like FAB and LSIMS, molecular ions are the most abundant sample ions, although some protonated molecules and [M-H]+ ions may be formed as well. Abundant molecular ions of carotenoid esters have been observed using MALDI-TOF-MS (Kaufmann et al., 1996 Wingerath et al., 1996),... 

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