Spiked standard

Figure 5.7(b) shows the relevant relationships when Sspike is plotted versus the concentrations of the spiked standards after dilution. Standard addition calibration curves based on equation 5.8 are also possible. 

In trace organic analysis there is usually an extraction or clean-up process, rather than a sample dissolution. Here not only must the matrix effect be considered, but also the recovery yield of the extraction. Frequently an external spike standard is added, but there is often no way of knowing if the recovery of the spike standard matches the analyte in question. There is considerable evidence that the U S E P A method for VOA analysis (Minnich 1993) is subject to such error, as reported by Schumacher and Ward (7997). The analyst must always consider the possibility of such an error, especially when using CRMs to control methods that are applied in routine mode. 

BRM3 identified the need for producing different levels of an analyte in a given matrix (spiked standards) to address matrix related measurement problems in foods. 

Reagents, (a) Pesticide standards of acephate, bromopropylate, chlorpyrifos, chlorpyrifos-methyl, chlorothalonil, diazinon, dichlorvos, endosulfan I, endosulfan II, endosulfan sulfate, lindane, methamidophos, phosalone, procymidone, pyrazophos, triazophos, and vinclozoline (purity >98%) were supplied by Riedel de Haen (Seelze, Germany). For each pesticide, a stock standard solution (about 500 mg/L) was prepared in acetone. Spiking standard solution, containing 50 mg/L of each pesticide, was prepared in acetone from the stock standard solutions. 

Spiked standards recovery reported, identification on aglycone RP-HPLC retention times mg/kg fresh weight Accept... 

Use of the resins with samples containing free chlorine residual is not recommended. Cheh (35) suggested that chlorine may produce mutagenic artifacts on XAD-4. Our experiment with 2-mg/L chlorine residual appeared to promote the release of irreversibly adsorbed spiked standards Six model compounds were recovered at levels several times higher than those observed in normal blank runs. In addition, many resin artifacts were eluted after exposure to this chlorine level, primarily aromatic and aliphatic acids, aldehydes, and ketones. Stoichiometric dechlorination (ferrous ion) is therefore recommended in order to avoid cross contamination between samples and inclusion of undesirable resin artifacts in the residue to be bioassayed. 

Extraction to gas phase, liquid phase and solid phase can be used in the preparation of SVOC/POM samples. It is essential to estimate the recovery of each extraction step. One method is spiking the sample with known amounts of internal standards similar to the analytes. The problem of this method is that spiked standards may not bind to the matrix in the same way as the analytes. Another method is to find the method with the highest recovery of a number of methods. Probably a combination of the two methods will give the most reliable results. Finally, use of certified reference materials, if available, will be the best way to determine the total recovery. 

Initial concentration of CN in the aliquot + concentration of CN in the spike standard... 

The mass of the spiked sample is considered as 40 g and not 43 g (to include the mass of 2 mL of spiking solution of approximate density 1.5 g/mL) in the above calculation. This is hue because this 2 mL of solvent which is added onto the soil as spike standard readily mixes into the soxhlet extract. Therefore, the mass of the sample after extraction (i.e., the mass of the solid residue) almost remains the same as it was before its extrachon. 

Samples are grouped within salinity ranges covering no more than 5%o (smaller for low salinity samples). Spiked standards are prepared in representative seawater samples from each of these ranges. 

Figure 3.11 Typical calibration curves for analysis using standard addition method. The full line represents results of sample with known added spiked standard. The dotted line represents the same curve without the sample. The extrapolating negative point for the sample can be used to determine the concentration of analyte in the sample...

A third vessel is also prepared containing the same acid but no sample or metal spike standard. 

FIGURE 9.9 Reconstructed IP HPLC-MS/MS chromatograms of ara-C from (a) blank, (b) the spiked standard mouse plasma at 50ng/mL, and the reconstructed IP HPLC-MS/ MS chromatogram of nicotinic acid as the ISTD from (c) the study mouse plasma sample. (Adapted from Hsieh, Y. et al., Anal. Chem., 79, 3856, 2007. With permission.)... 

Two samples are mn one is 20 mL of pond water, and the other is 20 mL of spiked standard. 1 mL of methanol is added to each sample before passing it through the SPE cartridge. The cartridge is eluted with methanol, diluted to... 

Second method ca. 1 g sample was treated with 25% tetramethylammonium hydroxide followed by hexane extraction and clean-up with an alumina column. TPeT was added as internal standard. Ethylation was performed with 0.6% NaBEt4 solution in acetate buffer (pH 5). Clean-up was carried out on alumina, with hexane elution. The derivatization yield was verified by comparison between the derivatized compounds provided by SM T and un-derivatized compounds (chloride). Separation was by capillary GC (column of 30 m length, 0.25 mm internal diameter, DB-17 as stationary phase, 0.25 pm film thickness). Recoveries were assessed by spiking (standard additions) results were (66 1)% for DBT, (74 + 2)% for TBT and (55 1)% for MPhT. Calibration was by calibration graph and standard additions, using the calibrants provided by SM T. 

It is considered good practice to know the concentration of the spike (although this is not strictly necessary as the IDMS measurement is actually based on a natural calibration standard of the analyte). If a certified spike standard is unavailable, the concentration of the spike is determined by a reverse IDMS measurement using the natural calibration standard. 

Spike standard solution, enriched minor Isotope A Spike standard solution, depleted major isotope B Natural standard solution, minor Isotope A Natural standard solution, major isotope B... 

Blanks should be run with a reduced spike content to reflect their low analyte concentration. Blank blends will not normally be matched to a spiked standard. 

Regular, routine sample recovery measurements can be made by using the method of standard addition. The matrix is spiked with the analytes in a small volume of solvent at a level which is 50%, 100%, 150% and 200% above the estimated level in the sample. A number of independent replicates should be made at each level. Provided that sufficient material is available, the sample can be analyzed prior to spiking. Standard addition to wet samples should be made in a water-miscible solvent (like acetone or methanol). Any convenient solvent can be used to spike waste samples. 

Matrix spike standard solutions and laboratory control standards which are added to one sample per batch to assess matrix effects. 

Matrix Spike Standard consists of a representative set of the targeted analytes whose percent recoveries are evaluated in the sample matrix. For example, if THMs were the targeted analytes, this reference standard would consist of one or more THMs such as chloroform, bromodichloromethane, and chlorodibromomethane. These compounds would be dissolved in a matrix-compatible solvent such as MeOH. A precise aliquot of this solution is added to a sample so that the effect of the sample matrix on the percent recovery can be evaluated. A second standard called a matrix spike duplicate is often required in EPA methods and is used to assess matrix recovery precision. 

Surrogate spiking standard Consists of tetrachloro-w-xylene (TCMX) and decachlorobiphenyl (DCBP) dissolved in MeOH. These two analytes are highly chlorinated and are structurally very similar to OCs and PCB targeted analytes. TCMX elutes prior to and DCBP after the OCs and PCBs, thus eliminating any coelution interferences. A fixed volume (aliquot) of this reference solution is added to every sample, matrix spike, blank, blank spike, and control in the protocol. 

Matrix spike standard Consists of a representative set of the targeted analytes (i.e., OCs and/or PCBs dissolved in MeOH). A precise aliquot of this solution is added to a sample so that the effect of the sample matrix on the percent recovery can be evaluated. 

Wang W, et al. Quantification of proteins and metabolites by mass spectrometry without isotopic labeling or spiked standards. Anal Chem 2003 75 4818-4826. 

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