Blank Preparation

A blank prepared in the laboratory that accompanies a set of sample containers in the field and laboratory. 

A calibration curve for the range 0.2-10 mg fluoride ion per 100 mL is constructed as follows. Add the appropriate amount of standard sodium fluoride solution, 25 mL of 2-methoxyethanol, and 10 mg of a buffer [0.1 Af in both sodium acetate and acetic (ethanoic) acid] to a 100 mL graduated flask. Dilute to volume with distilled water and add about 0.05 g of thorium chloranilate. Shake the flask intermittently for 30 minutes (the reaction in the presence of 2-methoxyethanol is about 90 per cent complete after 30 minutes and almost complete after 1 hour) and filter about 10 mL of the solution through a dry Whatman No. 42 filter paper. Measure the absorbance of the filtrate in a 1 cm cell at 540 nm (yellow-green filter) against a blank, prepared in the same manner, using a suitable spectrophotometer. Prepare a calibration curve for the concentration range 0.0-0.2 mg fluoride ion per 100 mL in the same way, but add only 10.0 mL of 2-methoxyethanol measure the absorbance of the filtrate in a 1 cm silica cell at 330 nm. 

After refluxing, disconnect the trapping tube, and transfer the yellow solution into a 25-mL volumetric flask. Rinse the mbe with ethanol, and adjust the solution to volume with ethanol. Measure the absorbance of the solution at 435 nm against a blank prepared by diluting 15 mL of color reagent to 25 mL with ethanol. Determine the carbon disulflde content from a calibration curve obtained by plotting carbon disulfide concentrations of different standard solutions on the abscissa versus the absorbance on the ordinate. 

Titrate one blank prepared from 3 drops of indicator plus 50 mL of 0.05 M NaCl. Subtract the blank volume of HCI from that required to titrate Na2C03. 

The calendering process and its conditions are developed or modified according to the requirements of subsequent operations and the purpose for which the sheet is used. Thus for sheets which are to be open cured, such as in chemical plant lining and custom built items such as inflatables and ebonite pipes, roll coverings for paper and steel mills, the calendering needs to be more exact than the sheets which are used for blank preparation for molding of... 

If the sample is distilled, neutralize a 50 mL portion of boric acid distillate with NaOH and then add 1 mL Nessler reagent. Let the solution stand for 10 min, after which measure the absorbance or transmittance against a reagent blank. Prepare a calibration curve under same conditions as samples. The reagent blank and the standards should be distilled, neutralized, and Nesslerized before color measurements. 

The term sample or blank preparation refers to a series of steps pertinent to TEM analysis. These include filter fusing, plasma etching, carbon coating, and specimen washing. Some of these steps may not be required if polycarbonate filters are used. 

Trip blanks prepared in vials and containing aliquots of methanol or analyte-free water accompany soil samples collected in a similar manner for low concentration VOC analysis according to EPA Method 5035. In this case, field samples and trip blanks have the same contamination pathway when exposed to airborne contaminants and the same VOC transport mechanism. These trip blanks provide important information, which may enable us to recognize the artifacts of improper sample handling, storage, or shipping. 

If compounds that are not contaminants of concern are present in the blanks, but not in the samples, then they most likely came with the water used in the blank preparation. 

Prepare one sample tube for the enzyme activity measurements. Add 1.0 mL of reagent cocktail and 0.7 mL of distilled water. Next, add 0.2 mL NADP+ solutions. Be careful to pipet exactly 0.2 mL NADP+. Mix the contents of the sample tube. Readjust the spectrophotometer with the Blank (prepared in step no. 3) to read 0.00 absorbance or 100.00% transmission. Remove the Blank and save it for future readjustments. 

Unless particulates are being collected in a grossly polluted atmosphere, large volumes of air must be filtered to give sufficient amounts of material for analysis by flame spectrometry. The filters are then ashed and/or digested prior to analysis. Unused filters are usually used for blank preparation. Pio and Hall18 have published a useful concise review of atmospheric particulate sampling, and a more detailed account has been written by Spurny.19... 

Digestion Blank Preparation Transfer 5.0 mL of concentrated nitric acid into a digestion vessel that has been cleaned according to the manufacturer s specifications, seal, and heat the vessel for 8 to 16 h at 210° 5°. Allow the vessel to cool to room temperature, and quantitatively transfer its contents into a clean, dry, tared 1-oz polyethylene bottle. Slowly add concentrated hydrochloric acid to achieve a final concentration of 10% (w/w), and dilute to an appropriate final mass with High-Purity Water. 

Procedure Determine the absorbance of the Sample Solution at 490 nm against a blank prepared using identical reagents. 

Procedure Concomitantly determine the absorbance of the Blank Preparation, the Standard Preparation, and the Test Preparation at the lead emission line at 283.3 nm with a suitable atomic absorption spectrophotometer equipped with a lead hollow-cathode lamp and an air-acetylene flame, using 4-methyl-2-pentanone to set the instrument to zero. In a suitable analysis, the absorbance of the Blank Preparation is not greater than 20% of the difference between the absorbance of the Standard Preparation and that of the Blank Preparation. The absorbance of the Test Preparation does not exceed that of the Standard Preparation. 

Standard Preparation and Blank Preparation Transfer 1.0 mL of Lead Nitrate Stock Solution into a 100-mL volumetric flask, dilute with water to volume, and mix. Transfer 2.0 mL of the resulting solution into a 50-mL volumetric flask. Add 10 mL of 9 IV hydrochloric acid and about 10 mL of water to both the volumetric flask and a second, empty, 50-mL volumetric flask (Blank Preparation). Add 20 mL of Ascorbic Acid-Sodium Iodide Solution and 5.0 mL of Trioctyl-... 

Atomic Absorption System Apparatus Use a suitable atomic absorption spectrometer equipped with a nickel hollow cathode lamp and an air-acetylene flame to measure the absorbance of the Blank Preparation, the Standard Preparations, and the Test Preparation as directed under Procedure (below). 

Blank Preparation Prepare in the same manner as in the Test Preparation, but omit the sample. 

Procedure Zero the instrument with the Blank Preparation. Concomitantly determine the absorbances of each of the Standard Preparations and of the Test Preparation at least three times each, and record the average of the steady readings for each. Between each measurement, aspirate the Blank Preparation, and ascertain that the reading returns to its initial blank value. 

Blank Preparation Pipet 20.0 mL water in a 100-mL Erlenmeyer flask. 

Procedure To the flasks containing 20.0 mL of each Test Preparation and to the Blank Preparation, add 5.00 mL of Acetate Buffer. At zero time, and at regular time intervals so that each test sample is analyzed in the same elapsed time, place the flasks containing the Test Preparations and the Blank Preparation in a circulating water bath maintained at 30.0° 0.1°. Equilibrate the samples for 10 min in the water bath. In the same order and with the same time intervals, rapidly pipet 25.00 mL of equilibrated Sucrose Substrate Solution into the test flasks. Incubate for 30.0 min, and stir continuously. Terminate the reaction by adding 10.00 mL of Sodium Carbonate Solution, and swirl to mix. Place the flasks containing the Test Preparations and the Blank Preparation in a water bath maintained at 20.0° 0.1° for 30 min. Use a... 

Procedure To 0.1 ml of cytoskeleton preparation containing between 10 to 100 pg protein is added 5 ml of the protein reagent. The absorbance at 595 nm is measured after 5 min and before 20 min against a reagent blank prepared from 0.1 ml isotonic 5 mM phosphate buffer, pH 7.4, and 5 ml of the protein reagent. 

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