Multiple standards

No effect at all—this is the reason for preparing a calibration curve with multiple standards. 

Gran-plot (multiple standard addition with 10iE/s vs. concentration) 0.1-3% 0-1-3% less accurate if interfering ions are present best results if many points between 30 and 80% of a titration curve are evaluated and discordant points are eliminated... 

In Section 8.2.8 we have discussed the standard addition method as a means to quantitate an analyte in the presence of unknown matrix effects cf. Section 13.9). While the matrix effect is corrected for, the presence of other emalytes may still interfere with the analysis. The method can be generalized, however, to the simultaneous analysis of p analytes. Multiple standard additions are applied in order to determine the analytes of interest using many q > p) analytical sensors. It... 

Walters [24] examined the effect of chloride on the use of bromide and iodide solid state membrane electrodes, and he calculated selectivity constants. Multiple linear regression analysis was used to determine the concentrations of bromide, fluorine, and iodide in geothermal brines, and indicated high interferences at high salt concentrations. The standard curve method was preferred to the multiple standard addition method because of ... 

Probably the best way to overcome the problem of poor selectivity is via the multiple standard addition approach in which known amounts of analyte are added to the sample in increasingly high concentrations. Using this method, a... 

The multiple standard addition method is time-consuming although it usually yields superior results to those of the other methods outlined in Table 3.3. 

Add additional analyte to the solution to swamp the interferent. The ratio of analyte to interferent will therefore increase, thus improving the precision of the measurement. This method is termed multiple standard addition... 

Employing the method known as multiple standard addition helps when trying to discern the effects of the sample matrix in which an analyte is dissolved. In this technique, the emf is determined as a function of the amount of standard solution added to the sample. 

Figure 4.10 shows a Gran plot which can be used for such a situation. In this figure, the addition values on the right-hand side of the abscissa represent the volumes (i.e. the known additions) of contaminant brought about by adding, e.g. small amounts of hydroxide to a solution in which a fluoride ISE is immersed. The intercept of the plot on the left-hand side represents the equivalent amount of hydroxide within the sample prior to the multiple standard addition process. This intercept tells us the concentration of hydroxide. Therefore, knowing [OH ], we... 

The participants of the interlaboratory validation study also analyzed multiple standard... 

A standard addition is a known quantity of analyte added to an unknown to increase the concentration of analyte. Standard additions are especially useful when matrix effects are important. A matrix effect is a change in the analytical signal caused by anything in the sample other than analyte. You should be able to use Equation 5-7 to compute the quantity of analyte in a standard addition experiment. Equation 5-9 is used with multiple standard additions to construct the graph in Figure 5-6, in which the jc-intercept gives us the concentration of analyte. 

Due to the possible toxic effects of Hg, alternative electrodes have been sought, such as bismuth, which has recently been used by Kadara and Tothill [155,156] for the determination of Pb2+ and Cd2+ at an SPCE. In this investigation, stripping chronopotentiometric measurements were carried out by depositing a metallic film of bismuth in situ with the target metal ions (lead and cadmium). A deposition potential was applied to preconcentrate the analytes, after which, a constant current was applied to strip the preconcentrated analytes until a limit of —0.2 V. The concentrations for Pb2+ and Cd2+ in the wastewater samples and acetic acid extracts of soils were quantified by the use of a multiple standard addition method. 

Multiple standard addition method (three additions of 50ppb of Cd and Pb solution) is used to detect Cd and Pb in the sample. 

Multiple standard addition method (three additions of 50 ppb of Cd and Pb solution) was utilised to recover two concentration levels of 40 and 80 mg/L of spiked metals into the solution composed of lmL tap water and 24 mL electrolytic cell (0.1M acetate buffer, pH 4.5). 

When calibrating with multiple standards, the calibration order is from low to high... 

Cytokinins (multiple) Standards none cation exchange UV-254 nm (55)... 

The PhytoLogix Discovery Process relies upon multiple standardized extraction and fractionation protocols that allow the generation of diversified extracts and fractionation libraries in a high throughput format at a reasonable cost. Each biomass was extracted with a medium polarity solvent combination, such as methylene chloride/methanol in a ratio of 1 1 followed... 

Calibration Process of determining the relationship between recorded output and input. Mostly this involves adjusting the output to agree with a preset value(s) from one or more standards (e.g. solution with known pH = 4). Where there are multiple standards used this will generate data, which can be plotted graphically as a standard curve or calibration curve. 

A unified safety standard for raw and processed foods This amends the Delaney clause in the FFDCA. Under the Delaney clause, a chemical that causes cancer in experimental animals (regardless of dose) shall not be allowed in processed food. Under the FQPA, pesticide residues shown to cause cancer in humans or animals are allowed on food if the EPA determines that the tolerance is safe, meaning that there is a reasonable certainty that no harm will result from exposure to the pesticide. This amendment is necessary mainly because of improved analytical capabilities. Under the Delaney clause, a carcinogen pesticide would be given a zero tolerance in processed food. However, zero tolerance caused many problems. As the analytical sensitivity increased, concentrations that were zero by old methods became measurable. A unified safety standard eliminates longstanding problems posed by multiple standards for pesticides in raw and processed foods. 

Linearity refers to the linear response of the detector to the analyte concentration within a specified range. Range, expressed in the same units as the analytical test results, is the interval between the lower and upper levels of the analyte concentration. To show linearity, a plot of response vs. concentration is provided for at least at five different concentration levels within the range. In addition, the slope and intercept of the regression line with the correlation coefficient are also provided. Normally a single standard is recommended if the intercept is very close to zero. Otherwise, quantitation, based on linear plot of multiple standards, is generally recommended. 

Sample Solutions. The urine sample solutions all originated from one composite urine sample. The latter was made by combining 150-mL aliquots of the entire first-morning voids of 16, presumably healthy, male subjects. Aliquots of the composite were used to prepare three sets of sample solutions as indicated in Table IV. The solutions in each set were "spiked with internal reference elements and with appropriate volumes of multielement stock solution to make a (multiple) standard addition series (12). The final gallium and yttrium internal reference-element concentrations were 1.0 and 0.1 mg/L, respectively, for both the reference and standard addition solutions. The added analyte concentrations for both the reference and standard addition solutions were 0, 2, 4, 10, and 20 times the approximate "normal analyte concentrations for urine, as listed in Table II. 

A comparison of three calibration methods based on the use of CRMs, generalized simplified standard additions and multiple standard additions revealed the last to be the most practical and reliable [72]. 

The thermospray vaporizer control temperature (Tl) is the critical parameter for total ion sensitivity. A temperature study was performed initially using a standard solution, injected by flow injection, without the column. Using a temperature ramp and monitoring the ion signal with multiple standard injections, we determined the optimum temperature for the specific compound. Figure 5... 

Spreadsheet Summary In Chapter 4 of Applications of Microsoft Excel in Analytical Chemistiy, a multiple standard additions procedure is illustrated. The determination of strontium in sea water with inductively coupled plasma atomic emission spectrometry is used as an example. The worksheet is prepared, and the standard additions plot is made. The unknown Sr concentration and its standard deviation are obtained. 

Spreadsheet Summary In Chapter 12 ot Applications of Microsoft Excel in Analytical Chemistry, we investigate the multiple standard additions method for determining solution concentration. A least-squares analysis of the data leads to the determination of the concentration of the analyte as well as the uncertainty of the measured concentration. 

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