Preparation reagents, cleaning procedures

The polystyrene samples were used as received. Examination by XPS showed only carbon on the surface (XPS does not detect hydrogen). The pyrolytic carbon samples were prepared by a "steady state" fluidized bed process (j ). The carbon samples were polished by the manufacturer using 7-alumina. Before use in this study the pyrolytic carbon samples were ultrasonically cleaned in reagent grade methanol for five minutes. Examination by XPS of both the as received and ultrasonic methanol cleaned samples showed removal of small amounts of chlorine, magnesium, silicon, and sulfur by the cleaning procedure. 

This section presents an overview of the cold-trap pre-concentration gas phase detection method for the determination of mercury in seawater. A more thorough and complete discussion of the analytical details (e.g., cleaning procedures, reagent preparation, analytical manipulations) can be found in Fitzgerald et al (21). 

Alumina supported sodium metaperiodate, which can be prepared by soaking the inorganic support with a hot solution of sodium metaperiodate, was also found to be a very convenient reagent for the selective and clean oxidation of sulphides to sulphoxides79. The oxidation reaction may be simply carried out by vigorous stirring of this solid oxidant with the sulphide solution at room temperature. As may be expected for such a procedure, solvent plays an important role in this oxidation and ethanol (95%) was found to be... 

Even inside the controlled conditions of a research laboratory, analyzing clean and standardized test samples PCR procedures requires careful quality control, taking into consideration differences in sample preparation, variation in pipetting, differences in reaction tube thickness, poor calibration or instability of the thermal cycler, and reagent quality. 

All reagents and solvents that are used to prepare the sample for analysis should be ultrapure to prevent contamination of the sample with impurities. Plastic ware should be avoided since these materials may contain ultratrace elements that can be leached into the analyte solutions. Chemically cleaned glassware is recommended for all sample preparation procedures. Liquid samples can be analyzed directly or after dilution when the concentrations are too high. Remember, all analytical errors are multiplied by dilution factors therefore, using atomic spectroscopy to determine high concentrations of elements may be less accurate than classical gravimetric methods. 

A very reactive form of a finely divided metal is a so-called Rieke powder [79]. These materials are produced as fine powders by chemical precipitation during the reduction of various metal halides ivith potassium metal in refluxing tetrahydrofuran. Obviously this is a potentially hazardous laboratory procedure and ultrasound has provided an alternative method of preparation of these extremely valuable reagents [80]. The sonochemical technique involves the reduction of metal halides with lithium in TH F at room temperature in a cleaning bath and gives rise to metal powders that have reactivities comparable to those of Rieke powders. Thus powders of Zn, Mg, Cr, Cu, Ni, Pd, Co and Pb were obtained in less than 40 min by this ultrasonic method compared with reaction times of 8 h using the experimentally more difScult Rieke method (Tab. 3.1). 

The selectivity that can be gained by using labeling reagents of varied reactivity and perhaps also with favourable spectral qualities. This becomes important in the analysis of a complex matrix such as encountered in polluted water samples, biological specimens, pharmaceutical preparations, etc. The derivatization step can then also serve as a clean-up procedure. 

New polymer-supported reagents for sulfide transfer have been developed to avoid exposure to malodorous and toxic sulfur reagents. Ley et al.15 prepared a stable aminothiophosphate polystyrene resin for the conversion of secondary and tertiary amides to thioamides in high conversion and purity (Table III, entry 11). This procedure is extremely clean and affords the desired product with short reaction times in comparison to Law-esson s reagent. In addition, the aminothiophosphate resin dehydrates primary amides to nitriles. 

Polymer-supported hypervalent iodine compounds in general are readily prepared and they have gained recently considerable popularity as reagents for clean oxidations. However, they are not newcomers since they have been known since 1961. A detailed procedure for the iodination of polystyrene and its conversion to poly[(diacetoxyiodo)styrene] appeared in 1972 [85]. However, this and other related methods were time consuming and despite encouraging results did not gain popularity. 

The aluminum isopropoxide is prepared by dissolving cleaned amalgamated aluminum in anhydrous isopropyl alcohol. Although the resulting solution is dark because of suspended particles, in many cases it may be used for the reduction without purification.6 This procedure is often convenient where single reductions are to be carried out with ketones which are known to be reduced satisfactorily in this manner (see tables at end of chapter). However, with aldehydes or ketones which are new or not readily available, or with those which are known to give anomalous results with unpurified reagent, it is advisable to use distilled aluminum isopropoxide, either as the solid or as a molar solution in isopropyl alcohol. 

Osmium tetroxide was supplied by Matthey-Bishop, Inc. in 1-g amounts in sealed glass ampuls. The procedure that we describe below should be followed to prepare the osmium tetroxide catalyst solution. Work in a well-ventilated hood. One ampul is scored in the middle, broken open, and the two halves are dropped into a clean, brown bottle containing 39.8 mL of reagent grade terf-butyl alcohol and 0.20 mL of 70 or 90% terf-butyl hydroperoxide (Aldrich). The bottle is capped (use caps with Teflon liners) and then swirled to ensure dissolution of the Os04. These solutions are stored in the hood at room temperature and seem to be very stable. 

---