Submilligram samples

High resolution two-dimensional electrophoresis allows hundreds of proteins to be separated and characterized in submilligram samples of complex protein mixtures. Applications of this method to the analysis of agriculturally important products, including milk, meat, and wheat are reviewed. In a model study we analyzed 100 individual kernels of the wheat cultivar Newton (Triticum aestivum L.) for electrophoretic variants. One variant protein was found in 47 kernels, while three variant proteins occurred together in two of the kernels. The implications of two-dimensional electrophoresis for cultivar identification and the problem of relating electrophoretic protein variants to genetic variants are discussed. 

Exemplary of this performance are thin-layer microbore LCEC chromatograms taken from submilligram samples of rat brain (Fig. 52). It is obvious that detection limits on the order of 0.1 -0.2 pg are obtained. Thus, using a... 

Coulometry can be classified as a macro method, involving grams of sample. The use of submilligram samples in coulometry, on the other hand, classifies it equally well as a micro method. High-precision coulometry has been widely used for the determination of major constituents of various materials. Determination of trace impurities, e.g., dopants such as chromium in ruby lasers, has been performed at the nanogram level. It has been used successfully for the determination of stoichiometry of materials such as GaAs, for measurement of physical constants such as the faraday and atomic weights, for determination of major constituents of Standard Reference Materials, and for the analysis of important research materials such as separated isotope solutions. 

There have recently been significant advances in the technique of carbon 14 measurements, which have permitted the determination of the concentration ratio C14/C12 in samples of small size. Two developments have occurred the first is an entirely new mass-spectrometric separation of Cl4 and Cl2 ions and their subsequent estimation by counting [1-8]1, while the second is simply the extension of conventional proportional counter operation to very small size carbon samples [9]. The first method is very fast, precise, and capable of treating samples of even submilligram size, but requires an expensive installation. The second method is slow (counting times of two months or more are necessary), can probably be made sufficiently precise to handle most problems, works down to sample sizes of 10 mg carbon, and is relatively inexpensive, especially to install in already-existing radiocarbon laboratories. 

Coupling a screening system with an analytical fraction collector can be helpful when very small amounts (submilligrams to single-digit milligrams) are required. It often also provides the first opportunity to isolate enriched samples for further use in the method development, for example, as retention time markers. The choice of stationary phases in the method development system can be based on... 

Preparative liquid chromatography. Any scale of operation in which the objective is the collection of sample components for subsequent identification or use. Preparative LC may involve submilligram or multigram quantities. 

Figure 3.6 shows the relationship between the relative peak intensity in the tetramer region and the average tacticity calculated from the blending composition for various mixtures of iso- and syn-PS. It is noted that this relationship shows a fairly good linearity. Furthermore, the plot for an at-PS sample also nearly falls on the line. Thus the tacticity of an unknown PS sample could be determined using only a small sample size in the order of submilligram. 

In the split/pool method of combinatorial synthesis, mixtures of compounds are made that are difficult to characterize. The LC/CLND of a nominally equimolar pool (based on nitrogen) should yield equal-sized chromatographic peaks of compounds. In the early stages of a lead development project, weighable quantities of authentic pure samples of a compound are not available, and yet quantitative measurements such as IC50, solubility, or plasma stability need to be made. LC/CLND can be used to calibrate solutions made from submilligram synthetic samples. LC/CLND is an important new technique to add to the arsenal of the organic analytical laboratory. 

In the modern drug discovery laboratory, analysts are asked to quantify the amount of target compound in hundreds of novel samples each day. These molecules are made in submilligram amounts and have never been synthesized before. The only information available is the structure of the molecule and properties that can reliably be calculated from the structure. The... 

Kim SH, Kelly PB, Clifford AJ. Accelerator mass spectrometry targets of submilligram carbonaceous samples using the high-throughput Zn reduction method. Anal Chem 2009 81(41) 5949-5954. 

In contrast to FAAS not only liquid but also solid samples can be analyzed in ETAAS. However, one of the problems is the reliable introduction of solid samples into the atomizer. The high sensitivity of the technique makes it necessary to handle samples in the submilligram range. The most reliable procedure was shown to be the slurry technique [14] whereby a finely powdered and/or homogenized solid sample is kept in suspension by ultrasonic agitation so that it can be introduced into the atomizer with a conventional autosampler. This technique has the significant advantage that a solid sample can be treated like a liquid, i.e., it can not only be pipetted but can also be diluted, mixed with a modifier, and several aliquots can be taken reproducibly. 

The above-mentioned problem with the high sensitivity of ETAAS which makes it necessary to handle submilligram masses of sample can be of advantage if microsamples have to be analyzed. Typical examples are the analysis of hair segments [15], finger nails, or other forensic samples. 

This effect can be illustrated for clonidine, a potent hypotensive agent in man. Clonidine is normally administered in submilligram doses and investigation of its metabolism and kinetics requires a sensitive analytical method. The gas chromatographic behaviour of small quantities (< 10 ng/ml) of clonidine is variable. If quantities (40 ng) of i -clonidine (Fig. 10) are added to the sample then levels down to 200 pg of clonidine could be reproducibly quantitated (Relative standard deviation 10%) by SIM (32). 

Chemical purity measurements are often not performed on tritiated compounds of high specific activity. Such materials are usually prepared in submilligram quantities, and, even if it were feasible to weigh samples accmately enough to prepare solutions of known mass concentration, the required manipulations would increase the risk of decomposition of the compound (see Section 1.5). Fortunately, high specific activity tritiated compounds are... 

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