Removable surface contamination

Ingots of EGS are evaluated for resistivity, crystal perfection, and mechanical and physical properties, such as she and mass. The iagots are sHced iato wafers usiag at least 10 machining and polishing procedures. These wafers are sHced sequentially from the iugot, and evaluated for the correct surface orientation, thickness, taper, and bow. As a final procedure, the wafers are chemically cleaned to remove surface contaminants prior to use. 

Silica [7631-86-9 (colloidal)-, 112945-52-5 (fumed)]. Purification of silica for high technology applications uses isopiestic vapour distillation from cone volatile acids and is absorbed in high purity water. The impurities remain behind. Preliminary cleaning to remove surface contaminants uses dip etching in HF or a mixture of HCl, H2O2 and deionised water [Phelan and Powell Analyst 109 1299 1984],... 

Because of the extreme surface sensitivity of static SIMS, care should always be exercised not to handle the samples. Clean tools and gloves should be used always to avoid the possibility of contaminating the surface. While it is possible to remove surface contamination with solvents like hexane, it is always desirable not to clean the surface to be analyzed. 

Surface samples were collected in snow pits under ultra-clean conditions described elsewhere [13] with the exception that samples for anion analysis were collected in polystyrene cups precleaned without the use of acids. Ice core samples were cleaned to remove surface contamination using the "dry-core" procedure involving rinsing and melting of exterior surfaces with ultra-pure water [13]. Shallow-depth firn cores are permeable and the dry-core rinsing is unsuitable. Therefore an inner core of 2.5 cm diameter was taken from intervals of the 7.6 cm diameter South Pole firn core using a specially-built precleaned stainless steel corer within a -15 °C cold room. Prior to this coring, exposed ends of core sections were shaved away with precleaned stainless steel chisels. 

In these studies, samples of approximately 20 irradiated or 5000 unirradiated particles were leached with hot 13M HN03 for about 1 hour to remove surface contamination (uranium) and then activated at ambient temperatures in the TRIGA reactor to produce inventories of the... 

Washing. Washing with water-detergent combinations or with solvents can be used to remove surface contamination from environmental samples such as fruits or plants or from a worker s hands, if dermal exposure from industrial chemicals or pesticides is suspected. 

CsCl at 200°C for 14 days, is shown in Figure 4. Before this spectrum was collected, the cube was sputtered with Ar ions to remove surface contamination. Two Cs MNN transitions arise at 554 and 566 eV (6) and the larger 0 KLL peak is at 506 eV. Superimposed on Figure 4 is a spectrum of natural pollucite, recorded under the same instrument conditions and corrected for a -4 eV positional difference observed in each of the three peaks. The same charging shift was observed in the Si peaks (not shown in Figure 4), which were found at 76 eV (cube) and 72 eV (natural pollucite). Transitions from four elements, Al, Si, 0, and Cs, were observed in both spectra. Potassium was not detected in either spectrum. 

To obtain optimum adhesion onto a wide range of materials, chemical treatment of the surface is often recommended. The first action, as with the mechanical treatment, is to remove surface contamination such as grease with a clean solvent. The surface of the material is then modified to provide... 

Losses of metals from dilute aqueous solution on storage are well documented. To prevent this it is usually necessary to acidify the sample after collection and filtration to pH 1. If the sample is to be analysed subsequently by flame AAS hydrochloric acid should be used (Section III.C.2) alternatively, prior to flameless electrothermal atomic absorption analysis, nitric acid should be added to preserve the sample (IV.B). The type of storage container is also important and high-density polyethylene is the preferred material for sample bottles. Here the adsorptive losses of metals appear to be lower than on glass. To avoid container contamination of the sample the container should be leached with dilute nitric acid for several days prior to use. This will remove surface contamination from the container material. Subsequent to the acid-leach, containers are washed in distilled-deionised water and then with a portion of the sample. Storage of samples for mercury analysis requires special conditions and these will be discussed later. 

In 1980, Klug reported a method to detect morphine in head hair of drug abusers by TLC. He dissolved the hair in sodium hydroxide and hydrolyzed the solution with HCL. He extracted the solution with amyl alcohol and separated the components by TLC. Detection and quantitation were made by fluorimetry. The findings were between traces and 4 ng/mg. A HPTLC method was used to determine morphine in human hair. From 20 to 200 mg of hair were washed four times with water to remove surface contamination. Then the hair was incubated in sodium hydroxide and subsequently in HCL at 80°C in both cases. After SPE (type "Extrelut 3"/Merck) the solution was dansylated, analyzed by HPTLC (methanol (MeOH)/ammonia 99 1), and quantitated by densitometry. 

Sample Preparation. Copper samples weighing 100 mg were cut from larger samples using a carbide-tipped drill. These samples were cleaned in reagent-grade HCl (IN) and rinsed in triple distilled water to remove surface contaminants. Sample material was placed in polyethylene vials and thermally sealed. Four USGS standards— numbers AGV-1, BRC-1, DTS-1 and W-1— were weighed and placed in similar vials to be used as absolute standards. 

E.W. Hoppe, et al., "A method for removing surface contamination on ultra-pure copper spectrometer components," submitted for publication to J. Radioanal Nucl Chem., 2006. 

The method is very precise when some experimental conditions are fulfilled. The ring is usually made of platinum wire and should be kept as horizontal as possible. A decline of 1° causes an error of 0.5%. Care must be taken to provide that the ring is in the horizontal position and to avoid any disturbance of the surface when the critical point of detachment is approached. The ring is usually heated to red glow before use to remove surface contaminants. A zero or near zero contact angle is necessary, otherwise wrong values of surface tension could be measured. 

To make a plan-view sample by cleaving, first cut the sample into a 1 mm wide strip. Then cut the sample at the edge and parallel with this as shown in Fig. 4.1(b). The cleaved sample often contains large thin areas suitable for diffraction contrast imaging and HREM. Since the thin-film surface side is not a cleaved surface, a short time of ion milling of the surface side can reduce sample thickness and remove surface contamination. 

Few samples in the real world can be analyzed without some chemical or physical preparation. The aim of aU sample preparation is to provide the analyte of interest in the physical form required by the instrument, free of interfering substances, and in the concentration range required by the instrument. For many instruments, a solution of analyte in organic solvent or water is required. We have already discussed some of the sample preparation steps that may be needed. Solid samples may need to be cmshed or ground, or they may need to be washed with water, acid, or solvent to remove surface contamination. Liquid samples with more than one phase may need to be extracted or separated. Filtration or centrifugation may be required. 

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