Spike solutions

Note isoxaflutole will degrade to RPA 202248 in solution. Standard solutions are stable for approximately 3 months when kept under refrigeration. A solution containing only isoxaflutole may be monitored for formation of RPA 202248 when maintained under the same storage conditions as the spiking solutions and standards used. 

Isotope dilution mass spectrometry (IDMS) can be applied with most of the ionisation methods used in mass spectrometry to determine isotope ratios with greater or lesser accuracy. For calibration by means of isotope dilution, an exactly known amount of a spike solution, enriched in an isotope of the element(s) to be determined, is added to an exactly known amount of sample. After isotopic equilibration, the isotope ratio for the mixture is determined mass spectrometrically. The attraction of IDMS is its potential simplicity it relies only on the measurement of ratios. The... 

The primary sample types used for field spiking were freshly prepared soapy distilled water (soapy water), air filter cassettes set up with 2.0 L/min. of air flow, and foil-backed patches of underwear cloth with a cover flap of coveralls cloth. The spiking solution was applied to the underwear material and the coveralls patch was then folded down to cover the spiked area. The patch was then exposed to air and sunlight for the duration of the trial in an area upwind from the trial site. The washwater samples for spiking consisted of 50-mL samples of soapy water prepared by putting on latex examination gloves and washing with Ivory soap in deionized water prior to the trial in the same way the operator would wash his hands. 

Sullivan et al. [69] studied the loss of phthalic acid esters and chlorinated biphenyls from seawater whilst stored in glass containers. Equilibrium was essentially reached in 12 h at 25 °C. Labelled compounds were used in some of the studies. Table 1.10 shows that between 2.2 and 49.9% of the organic solutes were lost from the spiked solutions. 

The limit of detection (LoD) has already been mentioned in Section 4.3.1. This is the minimum concentration of analyte that can be detected with statistical confidence, based on the concept of an adequately low risk of failure to detect a determinand. Only one value is indicated in Figure 4.9 but there are many ways of estimating the value of the LoD and the choice depends on how well the level needs to be defined. It is determined by repeat analysis of a blank test portion or a test portion containing a very small amount of analyte. A measured signal of three times the standard deviation of the blank signal (3sbi) is unlikely to happen by chance and is commonly taken as an approximate estimation of the LoD. This approach is usually adequate if all of the analytical results are well above this value. The value of Sbi used should be the standard deviation of the results obtained from a large number of batches of blank or low-level spike solutions. In addition, the approximation only applies to results that are normally distributed and are quoted with a level of confidence of 95%. 

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. 

Recovery — Overall procedural recovery was evaluated. The results from spiked plasma QC (evaluation) samples that went through the analytical procedure were compared to the results from neat spiking (control) solution samples. The neat spiking solutions used to prepare the plasma evaluation samples were evaporated and reconstituted at the same volumes as the extracted samples. The analyte was tested at three concentration levels and the internal standard was tested at one. Mean recovery for the analyte was approximately 122.9% the level was 55.2% for the internal standard. 

Each participant received nine ready-to-elute cartridges corresponding to three replicates for each sample, a spiking solution containing 1000 mg L-1 of NPEO and LAS (total concentration), respectively, and standards of NPEO and a commercial mixture of LAS with the proportional composition of different homologues as follows C10, 13.8% On, 36.6% C12, 29.2% and C13, 19.1%. 

Using the three measured ratios, Ca/ Ca, Ca/ " Ca and Ca/ " Ca, three unknowns can be solved for the tracer/sample ratio, the mass discrimination, and the sample Ca/ Ca ratio (see also Johnson and Beard 1999 Heuser et al. 2002). Solution of the equations is done iteratively. It is assumed that the isotopic composition of the Ca- Ca tracer is known perfectly, based on a separate measurement of the pure spike solution. Initially it is also assumed that the sample calcium has a normal Ca isotopic composition (equivalent to the isotope ratios listed in Table 1). The Ca/ Ca ratio of the tracer is determined based on the results of the mass spectrometry on the tracer-sample mixture, by calculating the effect of removing the sample Ca. This yields a Ca/ Ca ratio for the tracer, which is in general different from that previously determined for the tracer. This difference is attributed to mass discrimination in the spectrometer ion source and is used to calculate a first approximation to the parameter p which describes the instrumental mass discrimination (see below). The first-approximation p is used to correct the measured isotope ratios for mass discrimination, and then a first-approximation tracer/sample ratio and a first-approximation sample CeJ Ca... 

The accuracy of an analysis can be determined by several procedures. One common method is to analyze a known sample, such as a standard solution or a quality control check standard solution that may be available commercially, or a laboratory-prepared standard solution made from a neat compound, and to compare the test results with the true values (values expected theoretically). Such samples must be subjected to all analytical steps, including sample extraction, digestion, or concentration, similar to regular samples. Alternatively, accuracy may be estimated from the recovery of a known standard solution spiked or added into the sample in which a known amount of the same substance that is to be tested is added to an aliquot of the sample, usually as a solution, prior to the analysis. The concentration of the analyte in the spiked solution of the sample is then measured. The percent spike recovery is then calculated. A correction for the bias in the analytical procedure can then be made, based on the percent spike recovery. However, in most routine analysis such bias correction is not required. Percent spike recovery may then be calculated as follows ... 

A third possibility to estimate the bias component of the uncertainty is to perform a recovery experiment, where a sample is spiked with the analyte. The nncertainty of the nominal valne (i.e. the spiked amount) has to be calcnlated from the uncertainty of the volume added and the concentration of the spike solution. In the example in the slide the spiking is done using a micropipette. The uncertainty of the concentration of the spike solution is taken from the certificate of the manufacturer of the standard solution used and the uncertainty (repeatability and max. bias) of the micropipette is delivered by the respective manufacturer. Both components are combined to the uncertainty of the spike. 

Recovery Study. Spiking solution. A 10 mg/mL spiking solution was prepared by dissolving 0.500 g of sodium dichloro-isocyanurate dihydrate in 50 mL distilled water. (It may take up to 2 hours to dissolve all the material.)... 

Alternatively, the spike solution can be diluted serially to lower concentrations. The S/N ratio at each concentration level is determined. The concentration level (in percent related substance) that gives an S/N value of about 10 will be reported as the QL. 

Intrinsic Accuracy. Intrinsic accuracy indicates the bias caused by sample matrix and sample preparation. In this approach, a stock solution is prepared by using known quantities of related substance and drug substance. The stock solution is further diluted to obtained solutions of lower concentrations. These solutions are used to generate linearity results. In addition, these linearity solutions of different concentrations are spiked into placebo. The spiked solutions are prepared according to the procedure for sample analysis. The resulting solutions, prepared from the spiked solution, are then analyzed. If the same stock solution is used for both linearity and accuracy and all of these solutions are analyzed on the same HPLC run, the response of linearity (without spike into matrix) and accuracy (with spike into matrix) can be compared directly. Any differences in response indicate the bias caused by matrix interference or sample preparation. To determine the intrinsic accuracy at each concentration level, one can compare the peak area of accuracy (with matrix) with that of linearity (without matrix) at the same concentration (Figure 3.11). This is the simplest approach, and one would expect close to 100% accuracy at all concentration levels. 

This is a more stringent approach, as this indicates the bias caused by matrix interference, sample preparation, and calculation. For example, related substance (found) = 1.20% and related substance (theory) = 1.40% (calculated from the weight of authentic sample used in the spiked solution) therefore,... 

Figure 8.3 Transient signals of 63 Cu and 65Cu in protein spots of Alzheimer s brain samples measured by LA-ICP-MS (isotopic-enriched 65Cu spike solution was doped to the gel after 2D gel electrophoresis). (J. Su. Becker et al, Int. ). Mass Spectrom., 242, 135 (2005). Reproduced by permission of The Royal Society of Chemistry.)...

Gas chromatographic-mass spectrometric (GC-MS) calibration standard mixes for quantitation were prepared in ethyl ether at concentrations of 20, 50, and 75 ppm. Internal standard spiking solution containing 1-chlorohexane, 1-chlorododecane, and 1-chlorooctadecane was prepared from individual stock solutions in methanol of each component. Two hundred microliters of each solution were added to ethyl ether and diluted to 2 mL. Forty microliters of this internal standard mix was added to the column extracts before diluting to 2 mL to yield a final concentration of 100 ppm per internal standard component. 

Because interfering peaks could not be completely removed from parfait eluates, blank (unspiked) columns were routinely run in parallel with each spiked sample, and only peaks that could be unequivocally ascribed to the spiked solute were quantified. 

The extraction of the 19 haloethers from sand spiked at 600 ng/g (per analyte) was performed at 250 atm/70°C/60 min (dynamic) using carbon dioxide only (Experiments 5 through 8 in Figure 4). Sample size was 2.5 g. In Experiments 5 and 6, two sand samples (spiked in an aluminum cup with 150 / L of 10 ng// L spiking solution) were extracted in parallel. In Experiments 7 and 8, two other sand samples (spiked directly in the extraction vessel to avoid losses due to compound volatilization and sample transfer) were extracted in parallel. In Experiments 9 and 10, two soil samples (spiked in an aluminum cup as in Experiments 5 and 6) were extracted in parallel at 150 atm/50°C/60 min (dynamic). 

A wastewater sample was found to contain 3.8 mg/L cyanide. A 100 mL aliquot of this sample was spiked with 10 mL of 50 mg/L cyanide standard solution. The concentration of this spiked solution was measured to be 8.1 mg/L. 

The total mass of CN ions in 110 mL of sample and spike solution... 

Unlike aqueous samples, spike recovery for soil and solid wastes often does not require ary correction to be made in the volume of spike solution. Because the analysis of all soil and solid matrice requires that the analyte in the solid sample be extracted into a definite volume of solvent, there is no need to make ary volume or mass correction for the spike in solution added. This is shown in Example 6. 

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. 

The above formula may be directly used without any volume correction, if the volume of spike added is very small, i.e., <1% sample volume. However, if the volume of the spike solution added to the sample is large (>5% of the volume of the sample), the true (or expected) concentration in the above formula may be determined as follows ... 

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