Method performance terms recovery

The complexity of the method in terms of number of steps and solvents needed depends on the sorbent chemistry. The development in a simplified scenario involves running an analyte in several concentrations in multiple replicates and assaying for recovery and performance. This procedure is described in detail for several silica and polymeric sorbents by Wells.42 However, if a number of sorbents are to be evaluated, the process becomes time-consuming if multiple 96-well plates (each with one sorbent packed in all the wells) must be screened separately. This process may take a week or more and consume an analyst s precious time as well. The most plausible solution is to pack different sorbents in the same well plate and use a universal procedure that applies to all of them. An example of such a multisorbent method development plate is the four-sorbent plate recently introduced by Phenomenex demonstrated124 to require only 1 to 2 hr to determine optimal sorbent and SPE conditions. 

The combined uncertainty for quinizarin, which is significantly greater than that calculated for the other markers, is dominated by the precision and recovery terms. The results of the precision study indicated variable method performance across different matrices and analyte concentrations. The uncertainty, u(Rs), asso-... 

Method performance in air analysis involves terms such as accuracy, storage stability, capacity, sampling rate, recovery, and sensitivity. To evaluate the performance of a developed method, certified reference materials for particulate matter, such as urban dust SRM 1649a particulate matter from NIST (Gaithersburg, MD, USA) can be purchased. In addition, a standard reference material has been recently developed for the determination of organic compounds in house dust the SRM 2585 is intended for using in method validation for the analysis of PAHs, PCBs, chlorinated pesticides, and PBDEs (Poster et al. 2007). 

During crop gathering, some parts of Solanaceae plants may be occasionally included. A method for the simultaneous determination of tropine, atropine, scopolamine, homatropine, anisodamine, a-solanine, and a-chaconine in grains and seeds (wheat, rye, maize, soybean, linseed) has been reported by Jandric et al. [84]. The analytes were separated by isocratic HPLC on a Chirobiotic V column and detected by ESl-MS/MS detector operating in the MRM mode. The method performances were presented in terms of linearity in the range 5-80 ng g, specificity, selectivity, accuracy (recoveries from 61 % to 111 %), precision (CV <5 %), and ruggedness. The limits of quantitation (LOQ) were in the range 2.2-4.9 ng g . ... 

If analytical methods are validated in inter-laboratory validation studies, documentation should follow the requirements of the harmonized protocol of lUPAC. " However, multi-matrix/multi-residue methods are applicable to hundreds of pesticides in dozens of commodities and have to be validated at several concentration levels. Any complete documentation of validation results is impossible in that case. Some performance characteristics, e.g., the specificity of analyte detection, an appropriate calibration range and sufficient detection sensitivity, are prerequisites for the determination of acceptable trueness and precision and their publication is less important. The LOD and LOQ depend on special instmmentation, analysts involved, time, batches of chemicals, etc., and cannot easily be reproduced. Therefore, these characteristics are less important. A practical, frequently applied alternative is the publication only of trueness (most often in terms of recovery) and precision for each analyte at each level. No consensus seems to exist as to whether these analyte-parameter sets should be documented, e.g., separately for each commodity or accumulated for all experiments done with the same analyte. In the latter case, the applicability of methods with regard to commodities can be documented in separate tables without performance characteristics. 

Another result of the requirements to distribute homogeneous test material is that some pretreatment steps usually performed on routine samples are not done on the interlaboratory sample. For example, in interlaboratory rounds for the determination of metals by inductively coupled plasma, the test material is often a solution of the metals in water. Often a method requires extraction of the metals by acid digestion of the field sample, a procedure that will have significant uncertainty in terms of recovery of analyte. 

LC-MS/MS methods are usually subjected to a validation procedure before they are used for routine analysis. In case of GLP studies or clinical studies, a validation is considered to be mandatory. During the validation procedure, the assay is evaluated with respect to the overall performance. Parameters tested are the limit of quantification (5 1 signal/noise ratio), within batch and inter batch reproducibility (accuracy and precision), recovery, specificity and long-term sample stability in matrix (Shah 2000, EEC Guidance on validation 1994, EEC Guidance on validation 1996, FDA Guidance for Industry 2001). 

Water used in the experiments was doubly distilled and passed through an ion exchange unit. The conductivity was approximately 1 x 10"6 S/m. Simulated HLLW consisted of 21 metal nitrates in an aqueous 1.6 M nitric acid solution as shown in Table 1 and was supplied by EBARA Co. (Tokyo, Japan). Concentrations were verified by AA for Na and Cs with 1000 1 dilution and by ICP for the other elements with 100 1 dilution. Total metal ion concentration was 98,393 ppm. The experimental apparatus consisted of nominal 9.2 cm3 batch reactors (O.D. 12.7 mm, I.D. 8.5 mm) constructed of 316 stainless steel with an internal K-type thermocouple for temperature measurement. Heating of each reactor was accomplished with a 50%NaNO2 + 50% KNO 2 salt bath that was stirred to insure uniform temperature. Temperature in the bath did not vary more than 1 K. The reactors were loaded with the simulated HLLW waste at atmospheric conditions according to an approximate calculated pressure. Each reactor was then immersed in the salt bath for 2 min -24 hours. After a predetermined time, the reactor was removed from the bath and quenched in a 293 K water bath. The reactor was opened and the contents were passed through a 0.1 pm nitro-ceflulose filter while diluting with water. Analysis of the liquid was performed with methods in Table 1. Analysis of filtered solids were carried out with X-ray diffraction with a CuK a beam and Ni filter. Reaction time was defined as the time that the sample spent at the desired temperature. Typical cumulative heat-up and cool-down time was on the order of one minute. Results of this work are reported in terms of recoveries as defined by ... 

Fatty acid ethyl esters may be clinically important, independent of whether FAEEs induce cytotoxicity, because they can serve as a marker for ethanol intake. We performed a study to determine the clinical utility of FAEE in the blood as a short-term confirmatory marker for ethanol intake and as a long-term marker for ethanol intake after ethanol is no longer detectable (Doyle, 1996), To isolate FAEEs from plasma for quantitation by gas chromatography-mass spectrometry (GC-MS) in these clinical studies, we developed a two-step method using solid-phase extraction with a recovery of 70 3%, using ethyl oleate as a recovery marker (Bernhardt, 1996). 

Experiments may be performed in the laboratory to obtain both T and Tj for fluids in porous media. It is possible to measure Ti in a single experiment using the CPMG spin-echo method. This is faster than performing a series of inversion-recovery experiments to measure Ti. For this reason, time constraints in well logging applications usually mean that only Ti can be determined. From Eqs (8) and (9) it can be seen that measurements of T and Tj may be used to obtain surface area to volume ratios of the pores present. If spherical pores are assumed, then the pore radius, r, may be obtained as S/F= 3/r. However, the actual pores of rocks are not spherical and are interconnected. We shall simply use the term pore size to imply a quantity inversely proportional to S / F at a particular location in the pore space. 

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