Instrumentation compatibility, method

A major advantage of static SIMS over many other analytical methods is that usually no sample preparation is required. A solid sample is loaded directly into the instrument with the condition that it be compatible with an ultrahigh vacuum (10" —10 torr) environment. Other than this, the only constraint is one of sample size, which naturally varies from system to system. Most SIMS instruments can handle samples up to 1-2 inches in diameter. 

The choice of the method is governed by what is suitable for the given species (reactants or products), by the availability of instrumentation, and by the experience and familiarity of the investigator with the different methods. As mentioned, the time scale of the reaction must be compatible with the analytical method, and its response, precision, and sensitivity must be appropriate for the concentrations chosen. Generally speaking, it is best to select a method that can provide concentrations to a precision of at least 1-2%. 

Based on Table 3.2, we can deduce from the available flow rates that some manufacturers clearly optimized their systems for 2.1 mm inner diameter (ID) columns, namely the Jasco X-LC, the Thermo Accela, and the Waters Acquity. By sacrificing flexibility in column ID, these systems have been completely optimized to these 2.1 mm columns. Achieving that will be explained below. The instruments of Agilent and Dionex mentioned in Table 3.2 involve a more flexible approach. The higher flow rate limits of their systems allow the use of columns with larger Ids. Users benefit from the better efficiency obtained with 4.6 or 3.0 mm ID columns instead of 2.1 mm ID columns of similar length and their systems are fully compatible with existing conventional methods. 

The compatibility is excellent with continuous ion sources such as ESI, dynamic SIMS, CF-FAB, ICP, El, Cl, etc. Sector instalments are not well-suited for pulsed ionization methods, although there are examples where MALDI sources have been utilized [225-229]. Sector instruments are usually larger and more expensive than other mass analyzers, such as TOFs, quadrupole filters, and traps. 

Sample preparation for analysis by hyphenated methods requires some additional planning when compared to nonhyphenated methods. All steps, extraction, concentration, and final solvent selection must take into consideration and be compatible with all the components of the hyphenated instrumentation. For gas chromatographic methods, all the components in the mixture must be in the gaseous state. For liquid chromatography (LC) or high-performance liquid chromatography (HPLC), the samples of the analytes of interest can be solids or liquids, neutral or charged molecules, or ions, but they must be in solution. If the follow-on analysis is by MS, then each of the analytes may require a different method of introduction into the MS. Metals and metal ions may be introduced by HPLC if they are in solution but commonly are introduced via AAS or inductively coupled plasma (ICP). Other analytes may be directly introduced from HPLC to MS [2],... 

Graphite furnace Flame graphite furnace Varian Associates SpectrA A30 + 40 multi-element analysis Method storage SpectrA AI0 (low cost, single beam) SpectrA A20 (medium cost, double beam) SpectrA A300/400 multi-element analysis, centralized instrument control STA 95 and GTA 96 graphite tube atomizer units - compatible with ail SpectrA A instruments... 

Finally, the analytical method should be selected depending on the sensitivity reqnired, the compatibility of the sample matrix with the specific analysis techniqne, and the availability of facilities. Sample preparation, if it is required, can present problems. Significant losses can occur, especially in the case of organometallic complexes, and contamination of environmental sample is of serious concern. The precision of the analysis depends on the metal itself, the method nsed, and the standard nsed for calibration of the instrument. 

Level 1 sampling provides a single set of samples acquired to represent the average composition of each stream. This sample set is separated, either in the field or in the laboratory, into solid, liquid, and gas-phase components. Each fraction is evaluated with survey techniques which define its basic physical, chemical, and biological characteristics. The survey methods selected are compatible with a very broad spectrum of materials and have sufficient sensitivity to ensure a high probability of detecting environmental problems. Analytical techniques and instrumentation have been kept as simple as possible in order to provide an effective level of information at minimum cost. Each individual piece of data developed adds a relevant point to the overall evaluation. Conversely, since the information from a given analysis is limited, all the tests must be performed to provide a valid assessment of the sample. 

The principle approach to immunoassay is illustrated in Figure 1, which shows a basic sandwich immunoassay. In this type of assay, an antibody to the analyte to be measured is immobilized onto a solid surface, such as a bead or a plastic (microtiter) plate. The test sample suspected of containing the analyte is mixed with the antibody beads or placed in the plastic plate, resulting in the formation of the antibody—analyte complex. A second antibody which carries an indicator reagent is then added to the mixture. This indicator may be a radioisotope, for RIA an enzyme, for EIA or a fluorophore, for fluorescence immunoassay (FIA). The antibody-indicator binds to the first antibody—analyte complex, free second antibody-indicator is washed away, and the two-antibody—analyte complex is quantified using a method compatible with the indicator reagent, such as quantifying radioactivity or enzyme-mediated color formation (see Automated instrumentation, clinical chemistry). 

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