Analytical Confirmation Procedure

Range Confirm procedure provides an acceptable degree of linearity, accuracy, and precision when applied to samples containing analyte within or at extremes of the range of procedure specified. Confirmed within the range 25 to 125% of test concentration based on linearity and accuracy data. 

The confirmation of a compound s identity is only one half of the overall confirmation procedure quantitative confirmation is the other half. Compound concentrations calculated from analyses on two columns or two detectors must be in agreement. The EPA recommends a 40 percent difference (calculated as the RPD shown in Equation 1, Table 2.2) as a threshold value for making decisions on the presence or absence of a compound (EPA, 1996a). This means that the concentrations obtained from two columns or two detectors that agree within 40 percent indicate the presence of an analyte, provided that the retention time confirmation criterion has been also met. 

Whenever a measured value exceeds a certain threshold (an internally defined limit or a legal restriction criterion) then a confirmation procedure is recommended or even necessary. The purpose of confirmation analysis is to prove or disapprove the measurement result obtained by the usual analytical method. Generally, the difference from the confirmation procedure compared to the usual test method should be due to only either the use of a completely different separation column (with completely different retention behaviour) in the same detection system or the use of an alternative detection method with sufficient sensivity. For the latter case and especially for GC methods, the prefered procedure should be to apply analyte selective mass spectroscopy (MS) detection. In some cases, derivatisation of the analyte followed by MS detection can also be the method of choice. In the case of HPLC methods, different polarity of another column in connection with full exploitation of modern UV diode array detection systems may be useful to selectively allow confirmation of the analyte. It is extremely important to make sure that the confirmation procedure works at the restriction criterion level or other self-defined concentration limit ... 

When a certain critical concentration value has been measured and found excessive, then it may be recommendable or even necessary to confirm the result or the identity of the quantified analyte by means of another analytical technique, for instance by specific detection using mass spectrometry. This confirmation procedure should be clearly presented in this paragraph. 

In addition to this approach, there is a need for fairly simple, routine tests that can be incorporated into the analytical procedures that every residue chemist can use. Confirmation procedures such as the formation of derivatives by chemical reaction were first applied some years ago, but it is only recently that Cochrane and Chau in Canada 14,15,16,17,... 

Acceptable forensic practice recommends confirmation of the detection of an analyte (drug) by a second or definitive method. For VOCs, two acceptable GC confirmation procedures are re-sampling and re-analysis using a different column or use of mass spectrometry for absolute identification. 

Quantitative mass spectrometry, also used for pharmaceutical appHcations, involves the use of isotopicaHy labeled internal standards for method calibration and the calculation of percent recoveries (9). Maximum sensitivity is obtained when the mass spectrometer is set to monitor only a few ions, which are characteristic of the target compounds to be quantified, a procedure known as the selected ion monitoring mode (sim). When chlorinated species are to be detected, then two ions from the isotopic envelope can be monitored, and confirmation of the target compound can be based not only on the gc retention time and the mass, but on the ratio of the two ion abundances being close to the theoretically expected value. The spectrometer cycles through the ions in the shortest possible time. This avoids compromising the chromatographic resolution of the gc, because even after extraction the sample contains many compounds in addition to the analyte. To increase sensitivity, some methods use sample concentration techniques. 

It is shown, that for assay of substances and prepai ations the different approaches ( Confirming and Inspecting ) should be applied. The criteria to analytical procedures uncertainty for tests Uniformity of dosage units and Dissolution ai e developed. 

The approaches to analytical procedures uncertainty prognosis are developed. The correctness of these approaches is confirmed in 3rd and 4th rounds of pharmaceutical laboratories inter-laboratory testing ( Phamia-Test program of State Inspection for Quality Control of Medicines, Ministry of Health of Ukraine). 

In any form of analysis it is important to determine the integrity of the system and confirm that artefacts are not produced as a by-product of the analytical procedure. This is particularly important in enantiomeric analysis, where problems such as the degradation of lactone and furanon species in transfer lines has been reported (40). As chromatography unions, injectors, splitters, etc. become more stable and greater degrees of deactivation are possible, problems of this kind will hopefully be reduced. Some species, however, such as methyl butenol generated from natural emissions, still remain a problem, undergoing dehydration to yield isoprene on some GC columns. 

Procedure. Weigh out 0.0226 g of hydrated ammonium iron(III) sulphate and dissolve it in 1 L of water in a graduated flask 50 mL of this solution contain 100 g of iron. Place 50.0 mL of the solution in a 100 mL separatory funnel, add 10 mL of a 1 per cent oxine (analytical grade) solution in chloroform and shake for 1 minute. Separate the chloroform layer. Transfer a portion of the latter to a 1.0 cm absorption cell. Determine the absorbance at 470 nm in a spectrophotometer, using the solvent as a blank or reference. Repeat the extraction with a further 10 mL of 1 per cent oxine solution in chloroform, and measure the absorbance to confirm that all the iron was extracted. 

For example, if the internal standard is mnch more volatile than the analyte it is likely that more will be lost dnring storage, if it is mnch more polar it may be extracted either mnch more or less efficiently than the analyte during sample work-np, or if the internal standard is different chemically then derivatization procedures may be more or less efficient (it may be argued that as long as this differential behaviour is reproducible, it can be allowed for in the calcnlation procednres bnt significant extra work wonld be required to confirm such reproducibility). 

Because of the special regulatory position occupied by foods and beverages, a great deal of attention has been given to development and application of analytical procedures for them. Improved procedures have resulted in quantitation and confirmation levels in the range of 1 to 10 ppb with sample amounts of 10 to 250 g. Detection limits for foods are in the 0.1 to 1 ppb range. Detection limits of 0.1 to 1 ppm appear adequate for pesticide formulations (1, > while sensitivity of 0.01,... 

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. 

Third, the bulk of the items in Table 1 address method performance. These requirements must be satisfied on a substrate-by-substrate basis to address substrate-specific interferences. As discussed above, interferences are best dealt with by application of conventional sample preparation techniques use of blank substrate to account for background interferences is not permitted. The analyst must establish a limit of detection (LOD), the lowest standard concentration that yields a signal that can be differentiated from background, and an LOQ (the reader is referred to Brady for a discussion of different techniques used to determine the LOD for immunoassays). For example, analysis of a variety of corn fractions requires the generation of LOD and LOQ data for each fraction. Procedural recoveries must accompany each analytical set and be based on fresh fortification of substrate prior to extraction. Recovery samples serve to confirm that the extraction and cleanup procedures were conducted correctly for all samples in each set of analyses. Carrying control substrate through the analytical procedure is good practice if practicable. 

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