Samples preparation, for analysis

Reduction of 17a-EthynyI to 17a-Ethyl °° A solution of 5 g of 17a-ethynyl-androst-5-ene-3j9,17j5-diol in 170 ml of absolute alcohol is hydrogenated at atmospheric pressure and room temperature using 0.5 g of 5 % palladium-on-charcoal catalyst. Hydrogen absorption is complete in about 8 min with the absorption of 2 moles. After removal of the catalyst by filtration, the solvent is evaporated under reduced pressure and the residue is crystallized from ethyl acetate. Three crops of 17a-ethylandrost-5-ene-3) ,17j9-diol are obtained 3.05 g, mp 197-200° 1.59 g, mp 198.6-200.6° and 0.34 g, mp 196-199° (total yield 5.02 g, 90%). A sample prepared for analysis by recrystallization from ethyl acetate melts at 200.6-202.4° [aj, —70° (diox.). 

The mycelium (56 g dry weight) was filtered off and the steroidal material was extracted with methylene chloride, the methylene extracts evaporated to dryness, and the resulting residue chromatographed over a Florisil column. The column was packed with 200 g of Florisil and was developed with five 400-ml fractions each of methylene chloride, Skelly-solve 8-acetone mixtures of 9 1, 8 2, 7 3, 1 1, and methanol. The fraction eluted with Skellysolve 8-acetone (7 3) weighed 1.545 g and on recrystallization from acetone gave, in three crops, 928 mg of product of MP 210° to 235°C. The sample prepared for analysis melted at 245° to 247°C. 

Sample preparation for analysis by hyphenated methods requires some additional planning when compared to nonhyphenated methods. All steps, extraction, concentration, and final solvent selection must take into consideration and be compatible with all the components of the hyphenated instrumentation. For gas chromatographic methods, all the components in the mixture must be in the gaseous state. For liquid chromatography (LC) or high-performance liquid chromatography (HPLC), the samples of the analytes of interest can be solids or liquids, neutral or charged molecules, or ions, but they must be in solution. If the follow-on analysis is by MS, then each of the analytes may require a different method of introduction into the MS. Metals and metal ions may be introduced by HPLC if they are in solution but commonly are introduced via AAS or inductively coupled plasma (ICP). Other analytes may be directly introduced from HPLC to MS [2],... 

When round robin tests were performed to test the reproducibility of these standard procedures, large coefficients of variation between laboratories were obtained for tin-free paints (78-80% and 24-32% for the ISO and ASTM methods respectively Haslbeck and Holm, 2005). These discrepancies have multiple sources such as the analytical method (Haslbeck and Holm (2005) report 4-54% deviations when different laboratories measuring samples of known concentration), the sea water conditions both in the holding tank and the measuring tank (Haslbeck and Holm, 2005), the sample preparation for analysis... 

The sample preparation for analysis of free amino acids generally involves two steps. The first step is to ensure complete dissolution of the target amino acids. For beverages, this might al-... 

Table 19.8 presents information on the application of microwave radiation as an enhancing factor for other operations associated with sample preparation for analysis. 

Applications of Microwave Radiation in Sample Preparation for Analysis... 

US can be used as an enhancing agent during different steps of sample preparation for analysis ... 

Table 19.9 compares various solvent extraction techniques with regard to the duration and the amount of the solvent used (per 1 sample), and Figure 19.7 presents basic information on the main groups of solvent-free techniques in the context of sample preparation for analysis. 

M.-L. Kuitunen, Sample preparation for analysis of chemicals related to the chemical weapons convention, Encyclopedia of Analytical Chemistry, John Wiley Sons, Ltd, Chichester, 2000, 1055-1071. 

Sample Preparation for Analysis of Chemicals Related to the Chemical Weapons Convention in an Off-site Laboratory... 

Pawliszyn, J. New directions in sample preparation for analysis of organic compounds. Trends Anal. Chem. 14, 113-122 (1995)... 

Sample Preparation for Analysis of Anthocyanins Monomer in Skins Extract... 

Sample Preparation for Analysis of HCTA and Flavonols in Grape Extracts and Juice... 

A method of sample preparation for analysis of grape flavonols is... 

Figure 3.20 A method of sample preparation for analysis of pyranoanthocyanidins and anthocyanin-derivatives in wine (Alcade-Eon et al., 2004)...

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