Alternative sampling accessories

Installation of the instrument and where it is going to be located does not seem to be an obvious evaluation objective at first, but it could be important, particularly if 

Installation of the instrument and where it is going to be located does not seem to be an obvious evaluation objective at first, but it could be important, particularly if space is limited. For example, is the instrument free-standing or bench-mounted Maybe you have a bench available but no floor space, or vice versa. It could be that the instrument requires a temperature-controlled room to ensure good stability and mass calibration. If this is the case, have you budgeted for this kind of expense If the instrument is being used for ultratrace detection levels, does it need to go into a class 1, 10, or 100 clean room If a clean room is necessary, what is the size of the room and do the roughing pumps need to be placed in another room In other words, it is important to fully understand the installation requirements for each instrument being evaluated and where it will be located. Refer to Chapter 16 for more information on instrument installation. 

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If a microscope facility is not available, there are other special sampling accessories available to allow examination of microgram or microlitre amounts. This is accomplished by using a beam condenser so that as much as possible of the beam passes through the sample. Microcells are available with volumes of around 4 til and pathlengths up to 1 mm. A diamond anvil cell (DAC) uses two diamonds to compress a sample to a thickness suitable for measurement and increase the surface area. This technique can be used at normal atmospheric pressures, but it may also be employed to study samples under high pressures and improve the quality of the spectrum of trace samples. Alternatively, a multiple internal reflectance ceU may also be used as this technique can produce stronger spectra. 

Alternative Sample Introduction Techniques Nonstandard sampling accessories like laser ablation systems, flow injection analyzers, electrothermal vaporizers, cooled spray chambers, desolvation equipment, direct injection nebulizers, and automated sample delivery systans and dilu-tors are considered critical to enhancing the practical capabilities of the technique. Their use has increased significantly over the past few years as ICP-MS is being asked to solve more and more diverse application problems. This chapter reflects the increased interest in sampling accessories, especially in the area of specialized sample introduction and desolvation devices to reduce the impact of conunon interferences. 

FTIR sample preparation equipment can be purchased from FTIR companies, but there are also a number of small, independent companies that supply FTIR sampling accessories. An Internet search of the names of any of the techniques mentioned in this chapter should turn up their Web sites. Alternatively, the author s Web site at www.spectrosl.com maintains links to many of them. 

Repetitive routine analysis of a specific sample (e.g., for Quality Control) will usually require a dedicated instrument. Therefore, the chromatograph and, in particular, the detector will be chosen for that specific analysis. Consequently, only one detector will be necessary and the purchase of an armory of detectors on the basis that they might be needed in the nebulous future is not advised. An alternative detector can always be obtained if and when the demand arises. The same argument applies to multi-solvent reservoirs and multi-solvent gradient programmers and other accessories that are not immediately required for the specific analysis in mind. 

Manufacturers of TLC materials and accessories are well prepared to satisfy the needs for professionally performed PLC. High-quality precoated preparative plates are available from a number of eommercial sources. Alternatively, less expensive or specialty preparative plates ean be homemade in the laboratory, and loose sorbents and coating devices ean be purehased for this purpose. More-or-less-automated devices can also be purehased for band application of higher quantities of sample solutions to preparative layers. At least for some users, sophisticated densitometric and other instrumental techniques are available as nondestructive tools for preliminary detention and identification of separated compounds in order to enhance the effieiency of their isolation. The only aid still missing, and maybe the most important of all, is a comprehensive monograph on PLC that might encourage and instruct many potential users on how to fully benefit from this very versatile, efficient, relatively inexpensive, and rather easy to use isolation and purification technique. This book was planned to fill that void. 

The range of IR bands that can be utilized to assess hydration alludes to the pervasiveness of water absorbance in an IR spectrum Water is a strong IR absorber and thus can pose a particular difficulty in the spectral examination of aqueous samples. The advent of computer-interfaced FT systems allowing spectral manipulation (such as band subtraction) can circumvent these difficulties, as can the use of specialized accessories such as ATR elements [3] and even alternative vibrational spectroscopic techniques, e.g., FT-Raman spectroscopy. FT-Raman spectroscopy, providing complementary information to IR, has in recent years been employed for the characterization of human SC [185-190] and model SC lipids [191], as well as for the noninvasive monitoring of topically applied compounds [192] and the in vitro evaluation of SC-enhancer interactions [193]. 

This design is Intended as a general guideline only and there are many areas where alternative materials may be substituted. All materials described are avaH-able from either model rocket suppliers or firms that sell radio control airplane accessories. A sample list of these firms and their addresses has been Included at the end of the article. 

When it is necessary to record the transmission spectrum of a microquantity of a material or a limited sample area, beam condensers are employed [11]. Alternatively, a diffiise-rellectance (DR) accessory may be used (Fig. 4.6). In this case, the radiation is multiply reflected between mirrors 5 and detected upon passing through the optical system 2. One of two optical schemes may be used ... 

Coarse or hard powders are not well served by either the compressed pellet or mull technique, mainly because of difficulties associated with grinding. In such situations, the best approaches require the use of an accessory, such as a diffuse reflectance or photoacoustic detector. Both diffuse reflectance and photoacoustic methods [99,100] may be applied to most forms of powdered solids. As a rule, photoacoustic measurements, which are the only form of true absorption measurement, are not significantly influenced by sample morphology. An alternative procedure for powders is ATR, especially a horizontal accessory, preferably equipped with a pressure applicator. Note that the use of pressure is recommended to ensure intimate contact between the sample and the IRE (internal reflectance element) surface. Normally, the sample must conform to the surface of the IRE, and because the strength of the IRE is typically limited, the procedure is recommended only for soft powders. However, with the introduction of diamond-based ATR accessories [101-103], it is possible to handle most types of powdered material. 

As an alternative to AutoDilution with two injection loops, automated dilutions can also be carried out using the more sophisticated AS-AP Autosampler in combination with the Dionex Sample Conductivity and pH Accessory [702]. With this device, an in-line sample conductivity measurement is determined prior to injection and, if the measured conductivity exceeds a specified cutoff... 

As previously discussed, liquids ATR cells may be used and, in general, the horizontal ATR format is the most appropriate and convenient—in use and for cleaning. Alternatively, either a boat cell cylindrical ATR accessory or a ATR dipping probe may be used. In all cases, pay careful attention to cleaning. Trace contamination of the surface of the ATR element will result in a major interference to the sample spectrum. 

One other technique, previously described, is the abrasion of the surface of the sample with a silicon carbide paper. The abraded material may be collected as a dust and analyzed as a compressed alkali halide pellet or by diffuse reflectance. Alternatively, the spectrum of the sample from the surface of the abrasive paper may be obtained with a diffuse reflectance accessory. 

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