Sample Masking

Since corrosion rate must be normalized to the exposed area, it is critical to know and control the area of exposure. Furthermore, for electrochemical tests, an electrical connection must be made to the sample. 

Sliding oring seal-Adapter to cell neck- 

ASTM G150 is a new standard for the determination of critical pitting temperature (GPT) [4]. That standard describes a flushed port cell, in which the sample is pressed against an o-ring attached to a cell. 

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Signal intensity (sample/mask) Avg. intern, precision (%STD) Avg. extern, precision (%STD)... 

Hence, the ratio of PJ Pr F) gives pj(l — FJ. The factor F can be determined from techniques discussed in Section V,D or by measuring the ratio of the power incident diffusely on the sample mask without a conformal matched plug in the viewing port to that with a plug. 

In resolving complex metal-ion mixtures, more than one masking or demasking process may be utilized with various aliquots of the sample solution, or applied simultaneously or stepwise with a single aliquot. In favorable cases, even four or five metals can be determined in a mixture by the application of direct and indirect masking processes. Of course, not all components of the mixture need be determined by chelometric titrations. For example, redox titrimetry may be applied to the determination of one or more of the metals present. 

An alloy of chromel containing Ni, Fe, and Cr was analyzed by a complexation titration using EDTA as the titrant. A 0.7176-g sample of the alloy was dissolved in ITNOa and diluted to 250 mb in a volumetric flask. A 50.00-mb aliquot of the sample, treated with pyrophosphate to mask the Fe and Cr, required 26.14 mb of 0.05831 M EDTA to reach the murexide end point. A second 50.00-mb aliquot was treated with hexamethylenetetramine to mask the Cr. Titrating with 0.05831 M EDTA required 35.43 mb to reach the murexide end point. Einally, a third 50.00-mb aliquot was treated with 50.00 mb of 0.05831 M EDTA, and back titrated to the murexide end point with 6.21 mb of 0.06316 M Cu +. Report the weight percents of Ni, fe, and Cr in the alloy. 

Thin-Layer Chromatography. Chiral stationary phases have been used less extensively in tic as in high performance Hquid chromatography (hplc). This may, in large part, be due to lack of avakabiHty. The cost of many chiral selectors, as well as the accessibiHty and success of chiral additives, may have inhibited widespread commerciali2ation. Usually, nondestmctive visuali2ation of the sample spots in tic is accompHshed using iodine vapor, uv or fluorescence. However, the presence of the chiral selector in the stationary phase can mask the analyte and interfere with detection (43). 

Eor toxic materials, it usually is advisable to provide ventilated sampling hoods or breathing-air stations and masks, to assure that the sampler is adequately protected from toxic or flammable vapors and dusts. Special provision for access to and exit from sampling points also may be needed at elevated locations and to avoid tripping or bumping ha2ards and to ensure that the sampler does not transverse areas not intended as walkways, eg, tank covers or roofs. 

Many different materials can be used to spatially mask an implant on the semiconductor surface. Such masks include photoresist, dielectrics, and metals. In order to be an effective implant mask the material should be thick enough to prevent the implant from penetrating the mask and entering the sample. A minimum thickness for stopping 99.99% of the ions in the masking material is + 3.72Ai p (168). 

As the result of the performed investigations was offered to make direct photometric determination of Nd microgram quantities in the presence of 500-fold and 1100-fold quantities of Mo and Pb correspondingly. The rare earth determination procedure involves sample dissolution in HCI, molybdenum reduction to Mo (V) by hydrazine and lead and Mo (V) masking by EDTA. The maximal colour development of Nd-arsenazo III complex was obtained at pH 2,7-2,8. The optimal condition of Nd determination that was established permit to estimate Nd without separation in solution after sample decomposition. Relative standard deviations at determination of 5-20 p.g of Nd from 0,1 g PbMoO are 0,1-0,03. The received data allow to use the offered procedure for solving of wide circle of analytical problems. 

The first element, dynamic dilution, provides a reproducible sample for each panelist. The system must minimize the loss of the odorant to the walls of the delivery apparatus, provide clean dilution air of odor-free quality, maintain a constant dilution ratio for the duration of a given test, and have no memory effect when going from high to low concentrations or switching between odorants of different character. The type of mask or port and the delivery flow rate have been found to influence the response of panelists in determining odor threshold and intensity. 

Let us consider the separation of polymethylmethacrylate (PMMA) on a nonmodified silica column as an example. In THE (medium polar eluent) the PMMA eludes in size exclusion mode because the dipoles of the methylmethacrylate (MMA) are masked by the dipoles of the THE. Using the nonpolar toluene as the eluent on the same column, the separation is governed by adsorption because the dipoles of the carbonyl group in the PMMA will interact with the dipoles on the surface of the stationary phase. The separation of PMMA in the critical mode of adsorption can be achieved by selecting an appropriate THF/toluene mixture as the eluent. In this case all PMMA samples... 

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