Recovery, analyte

An analytical method vahdation study should include demonstration of the accuracy, precision, specificity, limits of detection and quantitation, linearity, range, and interferences. Additionally, peak resolution, peak tailing, and analyte recovery are important, especially in the case of chromatographic methods (37,38). 

The sfe of chlorpyrifos methyl from wheat followed by on-line Ic/gc/ecd has been investigated (93). Extraction profiles were generated to determine the maximum analyte recovery and the minimum extraction time. Using pure CO2, a 65% recovery of chlorpyrifos methyl spiked onto wheat at 50 ppb was reported. When 2% methanol was added to the CO2, the recovery from a one gram sample averaged 97.8% (n = 10, 4.0% RSD). 

Following this procedure urea can be determined with a linear calibration graph from 0.143 p.g-ml To 1.43 p.g-ml and a detection limit of 0.04 p.g-ml based on 3o criterion. Results show precision, as well as a satisfactory analytical recovery. The selectivity of the kinetic method itself is improved due to the great specificity that urease has for urea. There were no significant interferences in urea determination among the various substances tested. Method was applied for the determination of urea in semm. 

Accuracy (systematic error or bias) expresses the closeness of the measured value to the true or actual value. Accuracy is usually expressed as the percentage recovery of added analyte. Acceptable average analyte recovery for determinative procedures is 80-110% for a tolerance of > 100 p-g kg and 60-110% is acceptable for a tolerance of < 100 p-g kg Correction factors are not allowed. Methods utilizing internal standards may have lower analyte absolute recovery values. Internal standard suitability needs to be verified by showing that the extraction efficiencies and response factors of the internal standard are similar to those of the analyte over the entire concentration range. The analyst should be aware that in residue analysis the recovery of the fortified marker residue from the control matrix might not be similar to the recovery from an incurred marker residue. 

In addition, each workbook contained a summary table of all results and limit of detection (LOD) determinations. The table was organized with sample identifications in the left-hand column. Eor each analyte, the analytical result and the LOD appeared in adjacent columns, and analyte recoveries appeared above the results columns. The summary table was generated automatically from the analytical results in the individual worksheets, without operator intervention or re-entry of any information. 

The method was validated in numerous matrices, both animal and crop, at levels ranging from 0.01 to 0.50 mg kg in acetochlor equivalents for each of the two metabolite analytes. Analytical recoveries were >70%. No apparent trends were observed for either the level of fortification or the matrix analyzed. 

Untreated (control) soil is collected to determine the presence of substances that may interfere with the measurement of target analytes. Control soil is also necessary for analytical recovery determinations made using laboratory-fortified samples. Thus, basic field study design divides the test area into one or more treated plots and an untreated control plot. Unlike the treated plots, the untreated control is typically not replicated but must be sufficiently large to provide soil for characterization, analytical method validation, and quality control. To prevent spray drift on to the control area and other potential forms of contamination, the control area is positioned > 15 m away and upwind of the treated plot, relative to prevailing wind patterns. 

Once test sites have been identified, control soil should be collected and returned to the laboratory. This soil is used to (1) verify soil texture and related properties, (2) ensure adequate analytical recovery of target analytes, and (3) determine the presence of potential background interferences in the soil. 

During evaporation of organic solvents, the temperature of the water-bath should be kept at 40 °C or lower. Once the solvent is evaporated, continued rotary evaporation may lead to reduced analyte recovery. 

In general, new sample preparation technologies are faster, more efficient and cost effective than traditional sample preparation techniques. They are also safer, more easily automated, use smaller amounts of sample and less organic solvent, provide better target analyte recovery with enhanced precision and accuracy. Attention to the sample preparation steps has also become an important consideration in reducing contamination. A useful general guide to sample preparation has been published [3]. A recent review on sample preparation methods for polymer/additive analysis is also available [4]. 

It can be shown that multistep extraction is advisable, i.e. it is always better to use several small portions of solvent (e.g. 5 x 20 cm3) to extract a sample than to extract with one large portion (e.g. 1 x 100 cm3) [77]. As mentioned already, for general purposes a recovery of greater than 90% is usually considered acceptable in polymer/additive analysis no analytical recovery is required. A flow-chart for LSE is available [3]. 

High analyte recoveries as a result of few sample transfers... 

In the mid-to-late 1990s, SFC became an established technique, although only holding a niche position in the analytical laboratory. The lack of robust instruments and the inflexibility of such systems has led to the gradual decline of SFE-SFC. Only a small group of industrial SFE-SFC practitioners is still active. Also the application area for SFC is not as clearly defined as for GC or HPLC. Nevertheless, polymer additives represent a group of compounds which has met most success in SFE-SFC. The major drawbacks of SFE-SFC are the need for an optimisation procedure for analyte recovery by SFE (Section 3.4.2), and the fair chance of incompatibility with the requirements of the chromatographic column. The mutual interference of SFE and SFC denotes non-ideal hyphenation. 

Laboratory analytical recoveries and field spike recoveries were acceptable for all substrates encountered in this series of studies. Calculated penetration factors were similar to penetration factors reported in the literature. 

The study concluded that Once wash steps are optimized, samples prepared by solid phase extraction are cleaner than those prepared by protein precipitation. Samples prepared by extraction with a Multi-SPE plate resulted in lower LOQs than samples prepared by solvent precipitation. Drug recoveries were acceptable (>80%) for both the SPE and the solvent precipitation methods. Well-to-well reproducibility of samples was slightly better with extraction with a Multi-SPE plate. Evaporation and reconstitution, while more time-consuming, yield better chromatographic performance, allow analysis of lower concentration samples, and require optimization for good analyte recovery. 

Matrix effect — To demonstrate that the assay performance was independent from the sample matrix, QC samples were prepared using two different lots of matrix. The QC samples were evaluated using the same calibration curve. With regard to analytical recovery, no significant difference was observed for the QCs prepared in two lots of plasma. 

Matrix effect is a phrase normally used to describe the effect of some portion of a sample matrix that causes erroneous assay results if care is not taken to avoid the problem or correct for it by some mechanism. The most common matrix effects are those that result in ion suppression and subsequent false negative results. Ion enhancement may lead to false positive results.126 127 Several reports about matrix effects include suggestions on what can cause them and how to avoid them.126-147 While various ways to detect matrix effects have been reported, Matuszewski et al.140 described a clear way to measure the matrix effect (ME) for an analyte, recovery (RE) from the extraction procedure, and overall process efficiency (PE) of a procedure. Their method is to prepare three sets of samples and assay them using the planned HPLC/MS/MS method. The first set is the neat solution standards diluted into the mobile phase before injection to obtain the A results. The second set is the analyte spiked into the blank plasma extract (after extraction) to obtain the B results. The third set is the analyte spiked into the blank plasma before the extraction step (C results) these samples are extracted and assayed along with the two other sets. The three data sets allow for the following calculations ... 

Figure 12.5. Extracted analyte recovery with time.

Breast adipose (endrin) Placement of adipose into extraction cell between layers of alumina followed by SFE with C02 and C02 modified with 5% dichloromethane analyte recovery into cyclohexane clean-up using neutral alumina GC/ECD 10 ppb 73 Djordjevic et al. 1994... 

Sorption. Any reduction in analyte recovery in the presence of solid media may be a reflection of losses through sorption or actual degradation, and in reality it is difficult to quantify degradation due to the unknown extent of the sorption processes. Sorption can be by intercalation (absorption), and/or electrostatic attraction and covalent... 

The precision of the assay for nonreduced samples was demonstrated by the evaluation of six independent sample preparations on a single day (repeatability) and the analysis of independent sample preparations on three separate days by two different analysts (intermediate precision). The RSD values for the migration time were 0.9%. The RSD values for peak area percent of the main peak and the minor peaks in the profile were 0.6 and 12.6%, respectively. The higher variability observed with the minor peaks was determined to be primarily related to the sample heating during preparation for the analysis. These results demonstrate that the use of uncoated fused-silica capillaries in combination with a sieving matrix can provide adequate precision and analyte recovery. 

For projects needing stringent QC, control charts are recommended to monitor analyte recoveries throughout an investigation (see Taylor, 1987, for a detailed discussion). Briefly, during each quarter of a project, the last 20 observations of recoveries from QC spikes are used to generate a control chart. Control limits are established for the analytical process as described by Taylor (1987). When control limits are exceeded, sample analyses are suspended until the problem step(s) can be identified and corrected. These actions must follow an appropriate protocol for corrective action. The results of this type of investigation or procedure modification become a part of the permanent record of the sample set and the project. 

SPMDs. Use of this type of blank is generally limited to laboratories that assemble SPMDs. If the numbers of SPMD-fabrication blanks are inadequate, SPMD-process blanks can be used to determine analyte recovery and the precision of the overall analytical method. Also, this type of QC sample can be used for other purposes, such as determining potential effects of storage or changes in batches or lots of SPMD materials. 

These type of spikes are used when a rapid and independent assessment of individual steps in sample processing and enrichment is desired. The spikes used are radiolabeled ( " C- or H- labeled) compounds, which typically consist of a high molecular weight PAH or a chlorinated compound. For assessment of the dialytic step of overall analyte recovery from SPMDs a procedural blank is spiked directly... 

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