Perform all calculations defined in the method and report the concentration values in the appropriate units. Calculate the MDL as follows:. Note: If additional confirmation is desired, reanalyze the seven replicate aliquots on two more nonconsecutive days and again calculate the MDL values for each day. If so, this could result in the calculation of an unrealistically low MDL.
Concurrently, determination of MDL in reagent water represents a best case situation and does not reflect possible matrix effects of real world samples. However, successful analyses of LFMs Section 9. Typical single laboratory MDL values using this method are given in Table 4. The MDLs must be sufficient to detect analytes at the required levels according to compliance monitoring regulation Section 1. MDLs should be determined annually, when a new operator begins work or whenever, in the judgment of the analyst, a change in analytical performance caused by either a change in instrument hardware or operating conditions would dictate they be redetermined.
LRB data are used to assess contamination from the laboratory environment. Calculate accuracy as percent recovery using the following equation:. When sufficient internal performance data become available usually a minimum of analyses , optional control limits can be developed from the mean percent recovery x and the standard deviation S of the mean percent recovery.
These data can be used to establish the upper and lower control limits as follows:. After each five to 10 new recovery measurements, new control limits can be calculated using only the most recent data points. Also, the standard deviation S data should be used to establish an on-going precision statement for the level of concentrations included in the LFB.
These data must be kept on file and be available for review. If the calibration cannot be verified within the specified limits, reanalyze either or both the IPC solution and the calibration blank. All samples following the last acceptable IPC solution must be reanalyzed. The analysis data of the calibration blank and IPC solution must be kept on file with the sample analyses data.
The preparation and required periodic analysis of SIC solutions and test criteria for verifying the interelement interference correction routine are given in Section 7. Special cases where on-going verification is required are described in Section 7. Taking separate aliquots from the sample for replicate and fortified analyses can in some cases assess the effect. Unless otherwise specified by the data user, laboratory or program, the following laboratory fortified matrix LFM procedure Section 9. Also, other tests such as the analyte addition test Section 9.
In each case the LFM aliquot must be a duplicate of the aliquot used for sample analysis and for total recoverable determinations added prior to sample preparation. For water samples, the added analyte concentration must be the same as that used in the laboratory fortified blank Section 7. For notes on Ag, Ba, and Sn see Sections 1.
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Over time, samples from all routine sample sources should be fortified. Note: The concentration of calcium , magnesium , sodium and strontium in environmental waters, along with iron and aluminum in solids can vary greatly and are not necessarily predictable. Fortifying these analytes in routine samples at the same concentration used for the LFB may prove to be of little use in assessing data quality for these analytes. For these analytes sample dilution and reanalysis using the criteria given in Section 9. Percent recovery may be calculated in units appropriate to the matrix, using the following equation:.
The data user should be informed that the result for that analyte in the unfortified sample is suspect due to either the heterogeneous nature of the sample or matrix effects and analysis by method of standard addition or the use of an internal standard s Section The analysis of reference samples is a valuable tool for demonstrating the ability to perform the method acceptably. Reference materials containing high concentrations of analytes can provide additional information on the performance of the spectral interference correction routine.
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Directions for using MSA or internal standard s are given in Section The analyte s addition should produce a minimum level of 20 times and a maximum of times the method detection limit. If recovery of the analyte s is not within the specified limits, a matrix effect should be suspected, and the associated data flagged accordingly.
The method of additions or the use of an appropriate internal standard element may provide more accurate data. If not, a chemical or physical interference effect should be suspected and the associated data flagged accordingly. The method of standard additions or the use of an internal-standard element may provide more accurate data for samples failing this test.
Other wavelengths may be substituted if they can provide the needed sensitivity and are corrected for spectral interference. However, because of the difference among various makes and models of spectrometers, specific instrument operating conditions cannot be given. The instrument and operating conditions utilized for determination must be capable of providing data of acceptable quality to the program and data user.
The analyst should follow the instructions provided by the instrument manufacturer unless other conditions provide similar or better performance for a task. The following procedure is recommended for vertically configured plasmas. The purpose of plasma optimization is to provide a maximum signal-to-background ratio for the least sensitive element in the analytical array. The use of a mass flow controller to regulate the nebulizer gas flow rate greatly facilitates the procedure. Allow the instrument to become thermally stable before beginning. This usually requires at least 30 to 60 minutes of operation.
Divide the spent volume by the aspiration time in minutes and record the uptake rate.
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Set the peristaltic pump to deliver the uptake rate in a steady even flow. Collect intensity data at the wavelength peak for each analyte at 1 mm intervals from mm above the top of the work coil. This region of the plasma is commonly referred to as the analytical zone. Determine the net signal to blank intensity ratio for each analyte for each viewing height setting.
Choose the height for viewing the plasma that provides the largest intensity ratio for the least sensitive element of the four analytes. If more than one position provides the same ratio, select the position that provides the highest net intensity counts for the least sensitive element or accept a compromise position of the intensity ratios of all four analytes.
If a mass flow controller is being used, it should be reset to the recorded optimized flow rate. The required data and procedure is described in Section 9. This data must be generated using the same instrument operating conditions and calibration routine Section These documented data must be kept on file and be available for review by the data user.
A general description concerning spectral interference and the analytical requirements for background correction and for correction of interelement spectral interference in particular are given in Section 4. To determine the appropriate location for background correction and to establish the interelement interference correction routine, repeated spectral scan about the analyte wavelength and repeated analyses of the single element solutions may be required.
Criteria for determining an interelement spectral interference is an apparent positive or negative concentration on the analyte that is outside the 3-sigma control limits of the calibration blank for the analyte. The upper-control limit is the analyte IDL.https://rotciotoftspid.ga
How should a sample intended for total metals analysis be digested?
Once established, the entire routine must be initially and periodically verified annually, or whenever there is a change in instrument operating conditions Section Only a portion of the correction routine must be verified more frequently or on a daily basis. Test criteria and required solutions are described in Section 7.
Initial and periodic verification data of the routine should be kept on file. Special cases where on-going verification are required is described in Section 7. Cap the tube and mix. The sample is now ready for analysis Section 1. Allowance for sample dilution should be made in the calculations. Section 1. If a precipitate is formed during acidification, transport, or storage, the sample aliquot must be treated using the procedure described in Sections For the determination of total recoverable analytes in all other aqueous samples or for preconcentrating drinking water samples prior to analysis follow the procedure given in Sections When necessary, smaller sample aliquot volumes may be used.
Place the beaker on the hot plate for solution evaporation. See the following note.
The beaker should be covered with an elevated watch glass or other necessary steps should be taken to prevent sample contamination from the fume hood environment. This step takes about two hours for a mL aliquot with the rate of evaporation rapidly increasing as the sample volume approaches 20 mL. A spare beaker containing 20 mL of water can be used as a gauge. Slight boiling may occur, but vigorous boiling must be avoided to prevent loss of the HCl-H 2 O azeotrope.
Quantitatively transfer the sample solution to a 50 mL volumetric flask, make to volume with reagent water, stopper and mix. If after centrifuging or standing overnight the sample contains suspended solids that would clog the nebulizer, a portion of the sample may be filtered for their removal prior to analysis. However, care should be exercised to avoid potential contamination from filtration. The sample is now ready for analysis. Because the effects of various matrices on the stability of diluted samples cannot be characterized, all analyses should be performed as soon as possible after the completed preparation.
The sieve, mortar and pestle should be cleaned between samples. From the dried, ground material weigh accurately a representative 1.
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