Sample accurate

Maximum accuracy in sampling is desirable. Is maximum accuracy attainable Decisions regarding the total effluent will be based on what was found from a relatively small sample. Only if the sample accurately represents the total will the extrapolation to the entire effluent be valid. 

Saunders, S.R., Herring, D.A. and Boyce, G. 1995 Can skeletal samples accurately represent the living populations they come from The St. Thomas Cemetery Site, Belleville, Ontario. In Grauer, A.L., ed.. Bodies of Evidence. New York, John Wiley and Sons, Inc. 69-89. 

Recently Shihabi and Bishop (93) described a refinement in the preparation of a stable substrate and demonstrated the feasibility monitoring the reaction kinetically. This procedure has been evaluated by Lifton et. al. (9 ), who found that this method correlated well (r 0.914) with the copper soap-lipase method of Dirstine. They concluded that the method was rapid (less than 5 min. per sample), accurate, precise and linear over a clinically useful range. Its simplicity allows its application as an emergency procedure. Attempts to use this assay for urine lipase activity were unsuccessful. 

According to the official method of analysis, hydrochloric acid can be determined by first weighing a given sample accurately, and secondly, by adding carefully a solution of known strength of sodium hydroxide in the presence of an appropriate indicator unless and until the exact equivalent amounts of HC1 and NaOH have undergone the following chemical reaction ... 

To remind yourself how to weigh samples accurately, watch the video clip at www.brightredbooks.net... 

Nickel is normally present at very low levels in biological samples. To determine trace nickel levels in these samples accurately, sensitive and selective methods are required. Atomic absorption spectrometry (AAS) and inductively coupled plasma-atomic emission spectroscopy (ICP-AES), with or without preconcentration or separation steps, are the most common methods. These methods have been adopted in standard procedures by EPA, NIOSH, lARC, and the International Union of Pure and Applied... 

The reaction was followed continuously by measurement of H2 vented, through an electronic pressure controller (Rosemount Inst, model 5866) set at 9 bar, using a wet gas meter. Liquid samples, of 0.5 mL each, preceded by 0.5 mL to flush the line, were removed for NMR analysis at times corresponding to a spread of conversions from 10 to 90% as estimated from the cumulative hydrogen evolution. Spectra were recorded on 0.1 mL samples accurately diluted with 0.5 mL of D2O containing... 

The evaluation of hazards posed to human health by toxic airborne chemicals is one of the common tasks employed in industrial hygiene. This process requires the collection of air samples to estimate air concentrations of specific substances inhaled by workers which can then be compared with standards and guides of acceptable exposure. Thus air sampling directly influences the formulation of important decisions. If air samples underestimate exposures, the consequence may be death or occupational disease. Conversely, overestimating exposures may result in the institution of unnecessary controls. Since either form of error is undesirable, it is fundamentally important that air sampling accurately define the extent of hazard. This requires that air samples be collected according to scientific, unbiased schemes for estimating exposures to toxic airborne chemicals. 

I jAcidity or Alkalinity. Pour two 100 ml samples, accurately measured in a 100 ml graduate, into a 400 ml beaker contg 200 ml distd w. Add 5 drops of methyl-red indicator (prepd by dissolving 0.1 g of MR in 100 ml of 70% alcohol and neutralized to a salmon pink color). If the soln is yel, titrate with N/10 sulfuric acid and if red, titrate with N/10 NaOH soln. Calculate alkalinity as NHj and acidity as nitric acid... 

B) Purity. Dissolve ca 0.5g of sample accurately weighed, by warming with 20ml of 20% NaOH... 

Mix 10 g of ground freeze-dried samples (accurately weighed) with 100 ml of 80% aqueous methanol in a 500-ml Erlenmeyer flask. 

Dissolve about 240 mg of sample, accurately weighed, in 75 ml of glacial acetic acid. Titrate with standardized 0.1 N perchloric acid in acetic acid to a potenticmetric endpoint using glass-calcmel electrodes. Each ml of 0.1N perchloric acid is equivalent to 25.234 mg of cimetidine. 

Transfer about 65 mg of sample, accurately weighed, to a 200 ml volumetric flask. 

Field records document field measurements and field conditions at the time of sampling. These are permanent project records that are stored with the rest of the project files in a central location after the project is completed. A chemist, a geologist, or an engineer often reviews the field records to order to interpret the collected data in context of field conditions during sampling. Accurate and relevant field records allow efficient resolution of issues related to field and laboratory data interpretation and quality, whereas sketchy and inaccurate records raise more questions than they answer. 

PolyPs, which can be detected by NMR spectroscopy are called NMR-visible , and represent a more mobile fraction of the total PolyP content. Lack of an NMR-visible PolyP signal does not indicate the absence of PolyPs in a sample. Accurate values of the chemical shifts of these signals depend on the pH and residual concentrations of divalent cations in the extract (Pilatus et al., 1989). 

Approximately 0.3 g. of sample, accurately weighed, is added to 100 ml. of 5 % aqueous sodium hydroxide contained in a beaker. Three grams of the nickel-aluminum alloy is added in three or four portions over a period of 10 minutes. When the reaction has subsided, the mixture is heated on a steam bath for 1 hour and then filtered, the residue being carefully washed. An aliquot portion of the filtrate may now be analyzed for halogens by any standard procedure. Ethanol may be used to facilitate the reduction of alkali insoluble compounds. 

Nonvolatile Residue Evaporate 19 mL (20 g) of sample, accurately measured, in a tared dish on a steam bath, and dry at 105° for 1 h. 

Assay Transfer about 1 g of sample, accurately weighed, into a 1000-mL flask containing 20 mL of water, and dilute to volume with water. Place 10 mL of this solution into a glass-stoppered flask, add 25 mL of sodium hydroxide TS, and allow the mixture to stand for 5 min. Add 25 mL of 0.1 A iodine, stopper the flask, allow the contents to stand in a cold, dark place for 10 min, and add 30 mL of 1 A sulfuric acid. Titrate the excess iodine with 0.1 A sodium thiosulfate, using starch TS as the indicator. Perform a blank determination (see General Provisions), and make any necessary correction. Each milliliter of 0.1 A iodine is equivalent to 0.9675 mg of... 

Assay Transfer about 200 mg of sample, accurately weighed, into a 250-mL beaker, add 50 mL of 1 10 sulfuric acid, allow to stand for at least 3 min, stirring occasionally, and titrate with 0.1 N potassium permanganate to a light pink color that persists for at least 20 s. Calculate the total peroxides, P, as grams of hydrogen peroxide equivalents per 100 g of the sample, by the equation... 

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