Confirmatory sampling

The confirmatory procedure should be developed for the same tissues for which the determinative procedure was developed, preferably using the same extraction procedure as used for the determinative portion of the method. Storage and stability data are necessary for dried or liquid sample extracts if MS analyses of the confirmatory samples are to be conducted in a laboratory other than the laboratory of sample preparation. Analytes present in sample extracts must be stable long enough for the samples to be shipped to the MS laboratory and analyzed. 

For petroleum and petroleum product releases in a nonsensitive area (if there is such an area), the analytical methods preferred to determine the concentration of total petroleum hydrocarbons in environmental media is the standard EPA test method (EPA 418.1). For initial delineation of the area, test field kits may be used in nonsensitive areas, provided that the results are comparable to laboratory data. Final confirmatory sampling and analyses should be carried out using laboratory analyses. 

Preliminary Plans for Performance Monitoring and Confirmatory Sampling... 

Presence/absence sampling is used for confirmatory sampling, for example, for a flare pit evacuation. It is also used for exploratory sampling. Presence/absence sampling uses discrete grab samples. 

Confirmatory sampling is used by the decontamination crews to determine the effectiveness of the cleaning technique being employed. If a cleaned surface tests clean, the surface should be isolated from further airborne deposition. 

The FDA mandates that of all the calibration concentrations included in the validation plan, the lowest jc for which CV < 15% is the LOD (extrapolation or interpolation is forbidden). This bureaucratic rule results in a waste of effort by making analysts run unnecessary repeat measurements at each of a series of concentrations in the vicinity of the expected LOD in order to not end up having to repeat the whole validation because the initial estimate was off by + or - 20% extrapolation followed by a confirmatory series of determinations would do. The consequences are particularly severe if validation means repeating calibration runs on several days in sequence, at a cost of, say, (6 concentrations) x (8 repeats) x (6 days) = 288 sample work-ups and determinations. 

Reliable analytical methods are available for determination of many volatile nitrosamines at concentrations of 0.1 to 10 ppb in a variety of environmental and biological samples. Most methods employ distillation, extraction, an optional cleanup step, concentration, and final separation by gas chromatography (GC). Use of the highly specific Thermal Energy Analyzer (TEA) as a GC detector affords simplification of sample handling and cleanup without sacrifice of selectivity or sensitivity. Mass spectrometry (MS) is usually employed to confirm the identity of nitrosamines. Utilization of the mass spectrometer s capability to provide quantitative data affords additional confirmatory evidence and quantitative confirmation should be a required criterion of environmental sample analysis. Artifactual formation of nitrosamines continues to be a problem, especially at low levels (0.1 to 1 ppb), and precautions must be taken, such as addition of sulfamic acid or other nitrosation inhibitors. The efficacy of measures for prevention of artifactual nitrosamine formation should be evaluated in each type of sample examined. 

The extent of validation of confirmatory techniques is currently under consideration. Qne approach is that the extent of validation may be smaller than for the enforcement method. In principle, validation in triplicate at the relevant concentration level (LOQ or MRL) is sufficient. In the case where an MRL is set for multiple crops, a single validation in all representative crop groups is sufficient. A confirmatory method for residues in air is not required if a corresponding method was submitted for the other sample matrices. This approach is realized in Germany. ... 

Other considerations could include availability of reagent(s) or equipment, method for routine analyses vs limited samples, and confirmatory method vs multi-residues. Plan for method validation and/or analytical quality control. 

A method should be able both to quantify the amount of marker drug residue present in the sample and to identify the compound unambiguously. Historically, this required two distinct procedures a determinative procedure used to quantify the analyte, and a confirmatory procedure used to unequivocally identify the analyte. The need for two procedures was driven by the limitations of available technology. Most determinative methods over the last two decades have been based on liquid chromatography, usually with ultraviolet (UV)/visible or fluorescence defection. Limitations of cost. 

For confirmatory procedures, the fortified sample sets at half and twice the tolerance... 

Standards should be analyzed contemporaneously for both determinative and confirmatory procedures. The method developer needs to describe fully the preparation of all the standards and the calibration procedure to be used, such as calibration prior to sample analysis, interspersed standards, or bracketing standards (confirmatory only). 

Another difference between determinative and confirmatory method trial procedures is the way in which sample extracts are prepared for analysis. Most current methods submitted for review use the same sample extraction technique for both the determinative and confirmatory procedures. In those cases where the same extraction technique is used, the sponsor may provide the prepared extract to the FDA laboratory for analysis. Any problems with the extraction procedure will have been corrected during the determinative method trial. 

For confirmatory methods, the confirmatory procedure criteria described previously should be met. All negative control samples should fail to meet the confirmation standard established in the procedure. All samples fortified at or above the tolerance and all incurred residue samples at or above the tolerance should meet the confirmation standard (to confirm) described in the SOP. It has been argued that it is not necessary for incurred samples containing the marker residue at a concentration below the tolerance to meet established confirmatory criteria. However, failure to confirm the marker residue in these samples may indicate a lack of robusmess of the procedure. Any procedure that had this problem would be closely examined to ensure that the method would meet the needs of the Agency. 

To demonstrate the validity of an analytical method, data regarding working range/ calibration, recovery, repeatability, specificity and LOQ have to be provided for each relevant sample matrix. Most often these data have to be collected from several studies, e.g., from several validation reports of the developer of the method, the independent laboratory validation or the confirmatory method trials. If the intended use of a pesticide is not restricted to one matrix type and if residues are transferred via feedstuffs to animals and finally to foodstuffs of animal origin, up to 30 sets of the quality parameters described above are necessary for each analyte of the residue definition. Table 2 can be used as a checklist to monitor the completeness of required data. 

Origin of sample Matrix type Main study Independent lab. validation" Confirmatory method"... 

Experience has shown that confirmatory data relating to the amount of test item applied can be gained by the collection of samples immediately following the final application. 

The method using GC/MS with selected ion monitoring (SIM) in the electron ionization (El) mode can determine concentrations of alachlor, acetochlor, and metolachlor and other major corn herbicides in raw and finished surface water and groundwater samples. This GC/MS method eliminates interferences and provides similar sensitivity and superior specificity compared with conventional methods such as GC/ECD or GC/NPD, eliminating the need for a confirmatory method by collection of data on numerous ions simultaneously. If there are interferences with the quantitation ion, a confirmation ion is substituted for quantitation purposes. Deuterated analogs of each analyte may be used as internal standards, which compensate for matrix effects and allow for the correction of losses that occur during the analytical procedure. A known amount of the deuterium-labeled compound, which is an ideal internal standard because its chemical and physical properties are essentially identical with those of the unlabeled compound, is carried through the analytical procedure. SPE is required to concentrate the water samples before analysis to determine concentrations reliably at or below 0.05 qg (ppb) and to recover/extract the various analytes from the water samples into a suitable solvent for GC analysis. 

The method for chloroacetanilide soil metabolites in water determines concentrations of ethanesulfonic acid (ESA) and oxanilic acid (OXA) metabolites of alachlor, acetochlor, and metolachlor in surface water and groundwater samples by direct aqueous injection LC/MS/MS. After injection, compounds are separated by reversed-phase HPLC and introduced into the mass spectrometer with a TurboIonSpray atmospheric pressure ionization (API) interface. Using direct aqueous injection without prior SPE and/or concentration minimizes losses and greatly simplifies the analytical procedure. Standard addition experiments can be used to check for matrix effects. With multiple-reaction monitoring in the negative electrospray ionization mode, LC/MS/MS provides superior specificity and sensitivity compared with conventional liquid chromatography/mass spectrometry (LC/MS) or liquid chromatography/ultraviolet detection (LC/UV), and the need for a confirmatory method is eliminated. In summary,... 

To determine the residue levels of dinitroaniline herbicides, GC/NPD or GC/ECD is used in general. An aliquot of GC-ready sample solution is injected into the gas chromatograph under the conditions outlined below. Further confirmatory analysis is carried out using gas chromatography/mass spectrometry (GC/MS) in the selected-ion monitoring (SIM) mode. 

As with GC, the combination of MS and MS/MS detection with LC adds an important confirmatory dimension to the analysis. Thermospray (TSP) and particle beam (PB) were two of the earlier interfaces for coupling LC and MS, but insufficient fragmentation resulted in a lack of structural information when using TSP, and insufficient sensitivity and an inability to ionize nonvolatile sample components hampered applications using PB. Today, atmospheric pressure ionization (API) dominates the LC/MS field for many environmental applications. The three major variants of API... 

---