Reference materials spiking solutions

Filter samples can be prepared to airborne workplace concentrations by spiking each filter with aqueous solution containing elements with concentrations gravimetrically traceable to ultrapure metals or stoidiiometricaUy well defined oxides. The amormts correspond for some of the materials to current threshold limit values of contaminants in workroom atmospheres provided that the simulated filter has been exposed to one cubic meter of air. The certified values are based on a gravimetric procedure, i.e. weight per volume composition of the primary reference material dissolved in high purity sub-dis-tiUed acids. The National Institute of Occupational Health in Oslo, Norway, has produced several batches of such materials certified for 20 elements. Additionally, information values are reported for four other elements see Table 6.2. 

The limit of quantitation (LoQ) is the lowest concentration of analyte that can be determined with an acceptable level of uncertainty. This should be established by using an appropriate reference material or sample. It should not be determined by extrapolation. Various conventions take the approximate limit to be 5, 6 or 10 times the standard deviation of a number of measurements made on a blank or a low-level spiked solution. 

For application in the isotope dilution technique and for tracer experiments using isotope enriched spikes, Merck (Darmstadt, Germany) have launched the production of new sets of isotopically enriched materials, such as 53Cr or mCd enriched spike calibration solutions, which were characterized by the Institute for Reference Materials and Measurements (IRMM, Geel, Belgium).52... 

The main goal of every procedure for analytical quality control is to allow data within assigned values of accuracy and precision to be obtained. Analytical quality control is primarily achieved by the use of Certified Reference Materials (CRMs) and participation in intercomparison exercises, though calibration solutions and spiked samples can also be used (43, 63, 64). 

The pesticides spiking solution for RM15 was prepared using pesticides reference materials (Pestanal ) from Riedel de Haen in form of neat crystals (apart from chlor-fenvinphos which is liquid). Stock solutions were properly diluted with acetonitrile to the final concentrations. The stock solution for simazine was prepared in methanol. 

The results obtained within the SWIFT-WFD project, dealing with the preparation of water reference materials, will contribute to the future developments of such materials, especially for the analysis of pesticides and PAHs at low concentration levels. The two different strategies employed, direct fortification in the laboratory by using spiking solutions following detailed protocols, and fortification of the material before dispatch, led to homogeneous and satisfactory stable reference materials for quality control purposes. 

The introduction of pyrolytically coated graphite tubes and the L vov platform technique in GF-AAS as well as of the Zeeman-GF-AAS technique offer improved possibilities to reduce matrix effects when measuring tooth lead in aqueous solutions. Where these techniques are available calibration with lead-spiked tooth solutions can be applied. Otherwise the analyses must be carried out by means of internal standard addition. The accuracy of the analytical procedure should be assessed by interlaboratory comparison, since, at present, no reference material of human teeth is available. 

Third method 0.2 g sample was extracted with 8 mL acetic acid/H20. Ethylation was performed with 0.75% NaBEt4 solution, simultaneously extracting with 1 mL nonane during a 3 min microwave exposure (40 W). TPrT was added as internal standard. The derivatization yield was verified with ethylated compounds. Clean-up was performed with an alumina column followed by elution with diethyl ether. Separation was by capillary GC (25 m column length, dimethylpolysiloxane as stationary phase, 0.17 pm film thickness as carrier gas injector temperature at 250 °C column temperature ranging from 120 to 280 °C). Detection was by FPD (detector temperature of 350 °C). Recoveries were evaluated by spiking the reference material at three different levels results were (71 + 6)% for MBT, (104 + 7)% for DBT, (94 7)% for TBT and (81 8)% for TPhT. Calibration was by standard additions. 

The extent to which a digestion procedure brings the uranium into solution cannot be assessed through spiked experiments or addition of a yield monitor, as the spike is not representative of the actual sample. However, there are standard procedures published by the American Society for Testing and Materials (ASTM) and the Environmental Protection Agency (EPA) of the USA. Certified reference materials are also available from the International Atomic Energy Agency/NIST. 

In order to obtain reliable results for quantification purposes, the quality parameters of the methods developed need to be studied. Only two developed UHPLC-MS/ MS methods have been validated in the literature. One study was validated by using the National Institnte of Standards and Technology (NIST) Certified Reference Material (CRM) [18], and the second by spiking the extraction solution with different concentrations of procyanidin and alkaloid [29]. The LOQs obtained for catechin and epicatechin were 11.2 and 65.5 pg/g of chocolate when the NIST CRM was nsed [18], On the other hand, when the extraction solution was spiked with the target analytes standards, the detection limits (LODs), and LOQs of the procyanidins (catechin, epicatechin, and the dimer Bj) were between 7 and 30 pg/L and 10 and 90 pg/L, respectively, and for the caffeine and teobromine alkaloids, these values were below 30 and 100 pg/L, respectively [26]. 

Meanwhile, metrological institutions, such as the Institute of Reference Materials and Measurements (IRMM) in Geel, Belgium, and the Bundesanstalt fur Materialforschung und -priifung (BAM) (the Federal Institute for Materials Research and Testing) in Berlin, Germany, distribute certified spike solutions [18, 19], for example, for boron, uranium, plutonium, copper, and zinc. 

After microwave-assisted digestion of the sample with a mixture of nitric acid and hydrogen peroxide, during which equilibration with the isotopically enriched spikes added also took place, formic acid was used to convert the isotope-diluted elements into volatile compounds in a photo-reactor. In the case of iron and nickel, the corresponding volatile carbonyl compounds are most likely formed, whereas in the case of selenium, hydride compounds are obtained. A schematic representation of the UV-PVG-ICP-IDMS setup is shown in Figure 8.10. The good accuracy of results was demonstrated by the successful analysis of certified reference materials. Extremely low LODs of 0.18, 1.0, and 1.7 pgg were found for Ni, Fe, and Se, respectively, which are improvements of a factor of 30 for the two metals and 150 for Se compared with conventional pneumatic solution nebulization. 

The accuracy of this type of simultaneous spedes-spedfic multi-element GC-ICP-IDMS determination of five elemental species of high relevance for toxicological assessment of marine food samples was demonstrated by the excellent agreement of the results obtained with the corresponding certified values for different reference materials. LCDs of 1.4 ng g for MMM, 0.06 ng g for TML, 1.2 ng g for DBT, and 0.3 ng g for MBT and TBT were obtained, which are much lower than the limits required for adequate control of seafood. The tolerable weekly intake of MMM for humans as recommended by the US Environmental Protection Agency (EPA) is <0.7 Jg kg body weight and the tolerable MMM content in fish as recommended by the EU is < 1 xg g . With resped to the relative simple sample preparation and the commerdal availability of certified spike solutions of MMM and the butyltin compounds, multi-spedes spedes-spedfic GC-ICP-IDMS has a high... 

The calibration curve of HTO analysis is usually done using artificial standard solutions of nitrate salts, or nitrate plus ammonium salts, in zero-grade laboratory water. Natural samples can be analyzed as reference materials when spiked with primary inorganic N-standards [149]. 

As part of the quality control programme and to support accreditation according to the EN lEC/ISO 17025 2005 [6], each batch of samples should contain a reference material to validate the results. As there are currently no suitable and traceable certified reference materials available, several in-house reference materials (RMs) were developed. One iron ore and one sinter dust were selected to be developed as RMs for the alpha spectrometry method and the same sinter dust along with a blast furnace dust were selected for the gamma spectrometry method. When analysing stack emission samples, one blank filter was spiked with a known amount of a certified Pb standard solution (R22-02, National Physical Laboratory, UK) and used as a reference for result validation. 

---