Sample preparation proficiency-testing

After arrival, checking, and coding, the proficiency test samples and corresponding matrix blanks are usually divided into portions to allow application of multiple sample preparation methods for the different analytical techniques prior to analysis (9). 

Handling and preparation of authentic/proficiency test samples is preferably performed in a laboratory room dedicated to this purpose. The key advantage of a separate room is limitation of the possibilities of sample contamination. In previous tests, several participants have experienced cross-contamination, often with the consequence of false positive identifications and subsequent failure of the test. 

Parallel to the preparation of proficiency test samples, some laboratories do prepare quality control samples by the same methods, to check... 

Controls are used to ensure proper technique and the specificity of the stain. The use of similarly processed positive and negative staining controls is essential for interpretation of immunohistochemical reactions and must he done for each anti-hody. These controls may he commercially prepared, previously tested patient samples or proficiency testing specimens for which results have heen confirmed. 

There are proficiency testing programs that are geared toward clinical sensitivity or specificity by seeking to determine whether a disease can be detected versus other types of controls that are use to test sensitivity, selectivity, and most importantly, reproducibility and precision. With mass spectrometry, the controls are and should be no different than those used for other assays, with one interesting exception. Quality assurance materials prepared for MS/MS may not be useful in other assays that are less selective. The example is newborn screening where quality assurance/control QA/QC materials have a mixture of compounds present in the blood specimens. However, in less selective immunoassays, the mixture creates interferences. In addition, material is used to spike a blood sample is key and one should ensure there is no enzyme activity. We have encountered such a problem with a d/1 mixture of metabolites where one form was degraded in the prepared blood. 

Residue-testing laboratories might also need to review their sample preparation processes and consider modifying or eliminating tissue homogenization prior to residue extraction. Suppliers of proficiency-testing services should also question whether certain drugs are appropriate to include in such studies. For example, liver spiked with sulfaquinoxaline, sulfadiazine, or sulfamerazine is not suitable for preparation of spiked interlaboratory check samples or reference materials. 

Figure 6.11 shows the pseudo-on-flow NMR chromatograms of a soil sample extracted with water. The soil sample was prepared by a Polish laboratory as part of the sixth proficiency test. It was spiked with five compounds, with two of them (compounds 3 and 4) being related to chemical weapons. 

Quality control sample, often chosen randomly, from a batch of samples and undergoing separate, but identical sample preparation and analysis whose purpose is to monitor method precision and sample homogeneity. Duplicate testing also aids in the evaluation of analyst proficiency. Volume 1(10). 

To conduct a proficiency test, a reference laboratory will prepare a quantity of material appropriate for distribution to all the laboratories under test. Requirements for the material will include that it is well characterized, and that it is sufficiently stable and homogeneous that no tested laboratory will be put at disadvantage by receiving a sample not representative of the lot. Further, the material should be typical of that of interest, and have constituents with concentrations within the ranges of interest. Additionally, it is important that concentration values be kept confidential during the period of the test, so that no participant will have an unfair advantage. 

Work Instruction for the Preparation of Test Samples for OPCW Proficiency Tests , QDOC/LAB/WI/PRO002 (7) and... 

The proficiency test is conducted with the assistance of two laboratories, one preparing the test samples... 

Figure 4. Sample preparation flowchart of an organic liquid sample in the eighth proficiency test...

Lewisite 1 was used for spiking in the sixth and in the ninth proficiency test. The participants that failed to identify lewisite 1 did not describe an effective lewisite 1 sample preparation procedure (12) in their analysis report, which could indicate that no such procedure had been employed. The participants performances in the identification of lewisite 1 are summarized in Table 3. 

Methylphosphonic acid was used for spiking in the fifth and in the tenth proficiency test. Many participants, in particular, failed to identify methylphosphonic acid in the tenth test for reasons that are difficult to trace from their analysis reports. It can only be speculated that the high concentration of salt ( %% NaCl) in the sample has been the cause most of these participants did not describe an effective sample preparation procedure (e.g. cation exchange) for the removal of salts, and employed GC/MS as an indirect analysis technique. Indirect GC/MS analysis of methylphosphonic acid requires derivatiza-tion salts are known to influence the derivatization reaction negatively. The participants performances in the identification of methylphosphonic acid are summarized in Table 6. 

The OPCW has created the following quality system documents to control the proficiency testing. The documents are Standard Operating Procedure for the Organization of OPCW Proficiency Tests (QDOC/LAB/SOP/PT1), Work Instruction for the Preparation of Test Samples for OPCW Proficiency Tests (QDOC/LAB/WI/PT2), and Work Instruction for the Evaluation of the Results of OPCW Proficiency Tests (QDOC/LAB/WI/PT3). 

Sample preparation procedures and analytical techniques for the off-site laboratories of the CWC have been developed and tested in five international interlaboratory comparison (round-robin) tests (1 5), in two trial proficiency tests, and in more than 14 official proficiency tests (see Chapter 6). The Recommended Operating Procedures (ROPs) for sampling and sample preparation (6,7) were written and updated on the basis of the results of the round-robin tests. The ROPs (see Table 1) were designed to be comprehensive enough to allow the analysis of all CWC-related chemicals. Accordingly, some of the procedures contain many sample preparation steps. It is also recommended that the ROPs should be used as first choice in the analysis, with other approaches not excluded. 

The ROPs include sampling, sample preparation, and analysis instructions for low-volume Tenax and XAD-2 air samples. Only the preparation of an XAD-2 low-volume air sample is presented in this article, while the thermal desorption of a Tenax tube is described in the context of gas chromatographic analysis see Chapter 10). Active charcoal is such a strong adsorbent that it requires more effective extraction methods than XAD-2 resin or Tenax tubes. Thus, the recoveries of CWC-related chemicals tend to be lower from active charcoal than from other air sampling materials. Furthermore, active charcoal is not usually used for the collection of organophosphorus chemicals. The sample preparation methods for active charcoal samples have not been validated in international round-robin or proficiency tests. 

This article reviews the sample preparation methods for analytical techniques used in offsite laboratories. The procedures described are from the ROPs (7) and procedures followed at the Finnish Institute for Verification of the Chemical Weapons Convention, VERIFIN. The usefulness of the methods as demonstrated in international comparison and proficiency tests is noted. 

In both the trial and official proficiency tests, the ROPs for sample preparation validated in the round-robin tests proved themselves useful methods to recover CWC-related chemicals spiked at trace level. The participating laboratories had prepared the samples following the ROPs, though sometimes with slight modifications. Many of the laboratories were also able to identify degradation products... 

Dimethyl-2-butanol (DMB, pinacolyl alcohol, CAS 464-07-3) was a spiking chemical in the water sample in the first official proficiency test. One laboratory missed it because of insufficient sample preparation the water sample was not extracted with dichloromethane, in which the chemical is soluble, but was merely evaporated and the residue... 

Twenty-five laboratories participated in the sixth official proficiency test where lewisite 1 (CAS 541-25-3) was used as spiking chemical in the organic liquid sample. Five of the seven laboratories that performed sample preparations to derivatize the... 

In the tenth official proficiency test, five laboratories did not find divinyl sulfoxide (CAS 1115-15-7) in the decontamination solution sample Dl The chemical should have been recovered from the organic extract of the sample. Concentration of the extract, if undertaken, could have helped two laboratories identify this chemical. In one laboratory, false sample preparation was the probable reason for missing it. The laboratory extracted the sample with dichloromethane, evaporated the extract to dryness, dissolved the evaporation residue, and finally sily-lated it. Usually, organic solvents should not be evaporated to dryness in the recovery of a volatile chemical, and this might be the reason for missing the chemical. Perhaps for this same reason the laboratory missed ethyl 2-methoxyethyl methylphospho-nate (CAS 170082-62-9) in the Dl sample. 

The soil sample was problematic in the second trial proficiency test. Only six of the 15 participating laboratories successfully identified both N,N-diethylaminoethanol (CAS 100-37-8) and A-ethyl-diethanolamine (EDEA, CAS 139-87-7). For these particular spiking chemicals, efficient TEA/methanol extraction followed by a silylation procedure was essential in the sample preparation. One laboratory missed both spiking chemicals, probably because TEA/methanol extraction was not carried out. Another laboratory also missed them but for a different reason. Instead of TEA, ethyldimethy-lamine (EDMA, CAS 598-56-1) was used as an extractant, and although this should not have had a dramatic effect on the recoveries of the spiking chemicals, since EDMA should be as good a modifier as TEA, the laboratory then derivatized the 1 % EDMA/methanol extract with BSTFA, thus removing any chance of success. Chemicals in alcohol solutions cannot be silylated, and this must... 

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