Amount of sample required

As a rough guide, the amounts recommended for 8 in diameter sieves are given in Table 4.6a. Alternatively, the sample weight may be based on the median particle size (Table 4.6b), but this neglects to take into account that the narrower the distribution, the smaller the sample required [80]. 

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The amount of sample required is quite small as little as 10 mole is typical So many peptides and proteins have been sequenced now that it is impossible to give an accurate count What was Nobel Prize winning work m 1958 is routine today Nor has the story ended Sequencing of nucleic acids has advanced so dramatically that it is possible to clone the gene that codes for a particular protein sequence its DNA and deduce the structure of the protein from the nucleotide sequence of the DNA We 11 have more to say about DNA sequencing m the next chapter... 

Miniaturisation of various devices and systems has become a popular trend in many areas of modern nanotechnology such as microelectronics, optics, etc. In particular, this is very important in creating chemical or electrochemical sensors where the amount of sample required for the analysis is a critical parameter and must be minimized. In this work we will focus on a micrometric channel flow system. We will call such miniaturised flow cells microfluidic systems , i.e. cells with one or more dimensions being of the order of a few microns. Such microfluidic channels have kinetic and analytical properties which can be finely tuned as a function of the hydrodynamic flow. However, presently, there is no simple and direct method to monitor the corresponding flows in. situ. 

In conclusion, it may be stated that Py-GC/MS is the method of choice for chemical characterization of synthetic polymers used in artworks or as conservation materials. The chemical information is generally specific for the individual component, and the amount of sample required is practically negligible, thus allowing application of the technique even... 

The optimum amount of sample required to produce detectable spots with a minimum of spreading due to overloading is about 0.01 pg to 50 pg. With samples much larger than this, isotherms become nonlinear, the Iit values alter significantly with sample size and resolution suffers because of increased tailing or fronting. 

In a typical FT-ICR experiment, after ion detection, a voltage spike is used to eject all ions from the cell in preparation of a new experiment. However, instead of being ejected from the cell, the ions can be allowed to relax to the center of the cell through collisions with background gases. These ions can then be re-excited and measured several times.This remeasurement process may reduce the amount of sample required for FT-ICR analysis, a capability that is very important in biological applications. 

Sensitivity is generally taken to signify the limits of detectability of a chromophore. Some methods (e.g. NMR) detect all chromophores accessible to them with equal sensitivity while in other techniques (e.g. UV) the range of sensitivity towards different chromophores spans many orders of magnitude. In terms of overall sensitivity, i.e. the amount of sample required, it is generally observed that ... 

Many papers have described methodologies useful for characterizing ligand-protein interactions (63-67). However, among these methods, ACE has been the subject of much attention recently for the evaluation of affinity interactions because of both its high resolution and the extremely small amounts of sample required. 

Infrared spectroscopy is a widely used technique in the field of art and art conservation due to its versatility and ability to provide structural information on both inorganic and organic materials, the small amount of sample required, and minimum pretreatment. 

Analysis of errors [234] indicated that the optimal conditions for standard addition experiments correspond to values of Ga/Gr and m/m, of unity. The main limitation of the method is, obviously, the relatively large amounts of sample required (about 1-2 mg) for weighting in conventional analytical balances. This is a... 

All samples and eluents must be filtered to prevent obstruction of flow through the system, especially at inlets to the columns. For manual injection 1-2 mL of sample are required to assure good rinse of the injection loop. For automatic injection, as with the WISP autosampler, the amount of sample required is relatively less since only the volume injected is actually used. 

The type (e.g., liquid, solid, powder, gel, syrup, emulsion, granule) and range of food samples (raw ingredients to final products) for water activity measurement are immense. The amount of sample required for measurement is typically 5 to 10 ml. A homogeneous and representative sample should be prepared and placed into the sample cup. For the majority of samples, no preparation is necessary the sample is simply placed into the cup. Multicomponent (e.g., muffin with raisins or pizza) and coated samples (e.g., breaded foods or chocolate-covered bar) may have to be sliced, crushed, or ground in order to obtain a representative sample. If sample preparation is necessary, then a consistent technique must be used with each sample to ensure reproducible results. 

The remarkable versatility of NMR as an analytical method has diminished the importance of IR analysis in modern laboratories but it remains a very useful technique. The very small amount of sample required and the prominence of functional group absorption means that the progress of a reaction can be monitored very conveniently. For example, the reduction of an aldehyde to an alcohol will be accompanied by the disappearance of the prominent C=0 peak and the appearance of a C—OH absorption. Because both peaks are so readily identifiable in a small sample, the reaction is easy to follow and its completeness can be assayed. 

The injection of the sample into the LC-NMR system can be carried out by an autosampler or a manual injection valve. The only difference which has to be considered is the fact that the amount of sample required for the NMR system is larger than that required for UV detection. Therefore, it is often necessary to inject sample volumes which exceed 100 jjlL In such cases, it is mandatory to dissolve the sample in the starting solvent phase in order to avoid additional LC gradients created by the sample solvent being injected. 

Differential Scanning Calorimetry (DSC) was used for a long time in the field of process safety [21-23], This is essentially due to its versatility for screening purposes. The small amount of sample required (micro-calorimetric technique) and the fact that quantitative data are obtained, confer on this technique a number of advantages. The sample is contained in a crucible placed into a temperature controlled oven. Since it is a differential method, a second crucible is used as a reference. This may be empty or contain an inert substance. 

There are two main approaches to the oxidation of OC in water samples to C02 combustion in an oxidizing gas and UV-promoted or heat-catalyzed chemical oxidation. Other approaches are sometimes used, but are much less widespread.11 Carbon dioxide, which is released from the oxidized sample, can be detected in several ways, including conductivity detection, nondispersive infrared (NDIR) detection, or conversion to methane and measurement with a flame ionization detector (FID).1213 The limits of detection in TOC determination can be as low as 1 pg L 1, and the dynamic range can span many orders of magnitude. The precision of the method is usually very good, and the analysis can be completed in a few minutes. Another advantage is the very small amount of sample required—from 10 to 2000 pL. 

One of the first applications of HPLC in the clinical field was the quantitation of theophylline in asthmatic infants. This highly accurate measurement was an important test because of the very low amount of sample required and the accuracy of the determination (see Fig. 1-10). More recent clinically related HPLC separations include drugs and drug metabolites, neurochemicals and their metabolites, histamines, thyroid hormones, and enkephalins. The earliest bioresearch applications of HPLC included the determination of peptides, proteins, and amino acids. Application of HPLC to the analysis of these compounds remains important, as indicated by the rapid growth in references (Fig. 1-11). Bioresearch remains one of the most rapidly expanding growth areas of LC. 

Larger diameter sample tubes (usually 8—10 mm in diameter), usually with susceptibility-matching plugs, may be used to gain some sensitivity at the expense of a larger total amount of solution. At the other extreme, smaller diameter tubes (principally 1.7 or 3 mm) reduce inherent sensitivity but require smaller samples. For tubes of 3, 5, and 8 mm, S/N for a 0.1% ethylbenzene solution varies approximately in the ratio 1 2 3, but the total amount of sample needed is far less for the smallest tube. Microcells, in which the sample is contained in a spherically shaped cavity of 25—50 jil can also be used to reduce the total amount of sample required, and capillary sample tubes of outer diameter 355 pan, containing only about 10 p.1, have come into use with specially wound receiver coils of very small diameter. Special flow-through sample tubes are also used in... 

The amount of sample required to obtain a spectrum is of the order of 0.01 mg (direct sample introduction system) to 1 mg (indirect sample introduction system). Purity of the sample is desirable, but in many cases not essential. Usually up to 10% of impurity (much more even of low molecular weight compounds) does not seriously interfere with the interpretation. In some instances, information about the structures of the different compounds may be obtained even from mixtures. 

Selective cleavage of ether bonds is useful to determine the contribution of carbon-carbon bonds for polymer lignin. Pivaloyl iodide [90] is known to cleave a-ether bonds selectively and trimethylsilyl iodide [91,92] can cleave a- and P-ether bonds quite effectively under the proper reaction conditions. Because of the very small amount of sample required, pyrolysis GC-MS may be applied for the analysis of a specific morphologi region of a cell wall. 

Table 4.6 Amount of sample required for a sieve analysis on an 8 in...

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