Calibration blank

The measurement of F and F is accomplished by two pressurizations, one with the sample cell empty (Fp = 0) and one with a calibrated blank of known volume in the sample cell. For an empty cell equation (21.1) becomes... 

When a calibrated blank of known volume is used, its volume, can be... 

The Karl Fischer titration requires 20 to 45 min (depending on sample being tested) to complete calibration, blank determination, sample equilibration (extraction in Karl Fischer solvent), and final testing. 

Note C, counts at specified mass (calibration blank subtracted). 

Laboratories calibrate ICP-AES instruments according to manufacturer s instructions by analyzing a calibration blank and one standard to span the full dynamic linear range of the instrument. 

Remember the basic rules organic methods typically require a five-point calibration trace element AA methods use a calibration blank and three standards the ICP-AES instruments are calibrated with one standard and a calibration blank inorganic analysis methods use three- to five-point calibration curves. 

The calibration blank in trace element analysis is prepared by acidifying reagent water with the same concentrations of the acids used in the preparation of standards and samples. It serves as a calibration point in the initial calibration. As part of an analytical batch, the calibration blank is analyzed frequently to flush the analytical system between standards and samples in order to eradicate memory effects. Calibration blanks are also used in inorganic compound analysis, where they are prepared with the chemicals specified by the method. 

The instrument blank is the reagent used in the final preparation of the samples, which is injected into the analytical system after high level standards and samples have been analyzed. Analysis of instrument blanks removes memory effects from the analytical system. A calibration blank used for flushing the system in trace element analysis is an example of an instrument blank. 

Calibration blank ICP-AES the results of the calibration blank are to agree within three times the IDL. 

Three calibration blank standards should be analyzed to establish a representative blank level, after which the calibration standards are analyzed. After calibration, the quality control standard should be analyzed to verify the calibration. The sample introduction system is flushed with rinse blank, and the blank solution is analyzed to check for carry-over and the blank level. If the blank level is acceptable, the samples can be analyzed. If the blank values are too high, the flushing of the sample introduction system and analysis of the blank solution should be repeated until an acceptable blank level is reached. The calibration blank value, which is the same as the absolute value of the instrument response, must be lower than the method s detection limit. 

Calibration Blank Solution Tare a clean, dry 4-oz polyethylene bottle (or equivalent). Add approximately 50 g of High-Purity Water. Slowly add 28 1 g of concentrated nitric acid, mix thoroughly, slowly add 12 1 g of concentrated hydrochloric acid, and mix thoroughly again. Dilute the solution to 100.0 0.1 g with High-Purity Water, and mix thoroughly. 

Analyze the Calibration Blank Solution. Results for cadmium should indicate a concentration of less than 0.01 mg/ kg. If the results are not less than 0.01 mg/kg, repeat the analysis. In the event that reanalysis is unsuccessful, take steps consistent with the manufacturer s recommendations to identify and remediate the sources of contamination or interference. Do not proceed with the analysis until the sources of contamination or interference have been identified and corrected. 

Next, analyze the prepared samples, digestion blanks, and digestion fortification samples in groups of no more than ten. At a minimum, each group should contain a digestion blank, a prepared sample, a second replicate of the prepared sample, and that same sample prepared as a fortification sample. Analyze the Calibration Blank Solution followed by any of the Cadmium Calibration Standards between each group of ten samples. 

To determine the calibration curve, aspirate the Cadmium Calibration Standards and the Calibration Blank Solution. If possible, use the calibration function incorporated in the ICP-AES instrument s soft- or firmware. If necessary, plot instrument response versus concentration of cadmium Fit this line with a linear equation of the form y = mx + b, in which y is instrument response, m is the slope of the best-fit line, x is concentration, and b is the y intercept of the best-fit line. The correlation coefficient for the best-fit line should be >0.99. Concentrations of cadmium in the calibration blanks, calibra-... 

Rinse and calibration blank solutions were prepared from 18 Mfl Milli-Q water with 5% HN03 as per the instructions provided by the approval program. 

Analytical sample Any solution or media introduced into an instrument on which an analysis is performed, excluding instrument calibration, initial calibration verification, initial calibration blank, continuing calibration blank. The following are all analytical samples undiluted and diluted samples, predigestion spike samples, duplicate samples, serial dilution samples, analytical spike samples, postdigestion spike samples, interference check samples, laboratory control samples, preparation or method blank, and linear range analysis samples. 

As previously discussed, all nutrients are quantified by spectrophotometry. Calibration in the context of spectrophotometric analysis means comparison of the sample absorption after chemical reaction with the absorption of a standard (Le., an artificial sample) of known concentration, which has been treated in exactly the same manner. The reliability of calibrations decreases with increasing concentration differences between sample and standard. Consequently, the best calibration and thus the best analytical results are obtained with exactly matched sample and calibration ranges. Since the methods for calibration, blank determination and calculation of results follow the same procedures for all nutrients discussed here, the different steps to be taken simultaneously are outlined in the following. 

Before a suite of samples can be analyzed, a set of protocols, similar in design to other U.S. EPA ICP-MS analytical procedures such as Method 200.8, must be followed to ensure the instrument is working at its optimum performance. A summary of these protocols is shown in Table 20.2. The analytical run sequence outlined should be performed on a daily basis in order to meet all quality control requirements. (Note The samples shown in the top portion [sequence 1-19] must be run once per sequence, while the 10 samples [sequence 20-22] and the final continuing calibration verification [CCV] and continuing calibration blank [CCB] samples must be repeated.)... 

Instrument detection limit (IDL) Prepare 10 separate calibration blanks. Analyze the 10 blanks in triplicate on three nonconsecutive days, for each analyte. The IDL is equal to three times the standard deviation of the 10 blank measurement results, expressed as pg/L. 

Calibration standards of the 18 elanents and a calibration blank were prepared from multielement standards in 2% NaCl + 1% HNO3, using an external linear-through-zero calibration graph. A different blank (1% HNO3) was subtracted from all samples due to the fact that some contaminations were present in 2% NaCl. Concentrations of the six multielement standards were 25, 50,100, 500,1000, and 5000 ppt. 

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