Standard reagents and procedures

Caution All procedures should be carried out in a well-ventilated fume-hood and chemical resistant gloves and safety glasses should be worn at all times. 

To a two-necked round-bottomed flask (50 mL) equipped with a magnetic stirrer, rubber septum and under a nitrogen atmosphere, add (ethoxy-carbonylmethylidene)triphenylphosphorane (2.62 g, 7.5 mmol) and dry dichloromethane (15 ml). 

Remove the solvent by rotary evaporation. Purify the residue by column chromatography on silica gel (9 1 petroleum ether ethyl acetate v/v as eluant) to give the desired product as a colourless oil (quantitative yield, Z ratio 14 1). 

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If the analysis is to be carried out in a similar way to total N in herbage, by acid-digestion in test tubes in an aluminium block followed by a colorimetric autoanaiysis procedure, then take a 0.5-g sample of air-dry soil. If serious frothing occurs, take 0.2 g soil, and adjust the calculation accordingly. Reducing the amount to 0.1 g may give peaks which are too small to be read with confidence. See Chapter 7 (pp. 138-141) for details of standards, reagents and method. 

Procedure. Pipette 1 ml of the AOAC extract (increase appropriately if the peaks are too small) into a 20-ml volumetric flask. Using a pipettor, carefully add 1 ml H SO (approximately 98% m/m), swirl slowly to mix and allow to cool. Make up to the mark with 50% (v/v) H SO (approximately 98% m/m), stopper and invert several times to mix. The water soluble P, present in the sample solution as orthophosphate, can be determined by autoanaiysis see Chapter 7 for details of standards, reagents and method. 

The requirements for the laboratory control of reference standards was embedded in the Code of Federal Regulations. Title 21 CFR Part 211 section 194 subsection 8b states Complete records shall be maintained of any testing and standardization of laboratory reference standards, reagents, and standard solutions. It falls to the individual firm to develop procedures to give inspectors the best possible assurance of compliance to the regulation. The central role of reference standards in the assurance of patient safety makes them a common focal point for regulatory inspections. Development of sound procedures and the strict adherence to such procedures is therefore critical. 

All procedures are carried out at room temperature allow all standards, reagents, and samples to equilibrate to room temperature before using. Universal precautions should be taken at all times, as samples are potentially infectious. 

Procedure. Prepare a 0.25 per cent solution of diphenylcarbazide in 50 per cent acetone as required. The test solution may contain from 0.2 to 0.5 part per million of chromate. To about 15 mL of this solution add sufficient 3M sulphuric acid to make the concentration about 0.1M when subsequently diluted to 25 mL, add 1 mL of the diphenylcarbazide reagent and make up to 25 mL with water. Match the colour produced against standards prepared from 0.0002M potassium dichromate solution. A green filter having the transmission maximum at about 540 nm may be used. 

Preparation of the standard solutions. For procedure (i) it is necessary to incorporate a releasing agent in the standard solutions. Three different releasing agents may be used for calcium, (a) lanthanum chloride, (b) strontium chloride and (c) EDTA of these (a) is the preferred reagent, but (b) or (c) make satisfactory alternatives. 

Most methods of oxidation to sulphones involve classical reagents and the standard procedure has been to use a measured amount of oxidation reagent in excess and to determine the unused amount by back-titration, nearly always with iron(II). Sub-classification is most convenient according to the reagent ... 

Subpart E - Testing Facilities Operation Sec. 58.81 Standard operating procedures. Sec. 58.83 Reagents and solutions. 

A practical problem in solution preparation usually requires a different strategy than our standard seven-step procedure. The technician must first identify a suitable conjugate acid-base pair and decide what reagents to use. Then the concentrations must be calculated, using pH and total concentration. Finally, the technician must determine the amounts of starting materials. The technician needs a buffer at pH = 9.00. Of the buffer systems listed in Table 18-1. the combination of NH3 and NH4 has the proper pH range for the required buffer solution. 

All reagents and chemicals were commercially available materials purified by standard laboratory procedures. 

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