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Determination of Lead in Drinking Water Using Graphite Furnace Atomic Absorption Spectroscopy (GFAA)
Published in Paul R. Loconto, Laboratory Experiments in Trace Environmental Quantitative Analysis, 2022
Of the three modes of calibration used in instrumental analysis, external, internal, and standard addition, the latter provides for the most accurate analytical results for samples that exhibit a matrix interference. The external mode of calibration is used to convert the instrumental response to concentration when matrix interferences are not considered a factor. A series of standard solutions that contain the metal of interest are prepared from careful dilution of a certified standard stock solution. The calibration curve is obtained and a least-squares regression is performed on the x, y data points. The best-fit line is used to establish the calibration curve. Samples that contain the metal at an unknown concentration level in a sample matrix nearly identical to that used to prepare the serial standards can be run and the data interpolated to give the concentration. In contrast, the standard addition mode of calibration requires that calibration and analysis be performed on the sample itself. Standard addition can be used provided that (1) a linear relationship exists between the physical parameter measured and the concentration of analyte, (2) the sensitivity of the method is not changed by the additions, and (3) the method blank can be corrected for. A typical standard addition calibration follows:
Student-Tested Laboratory Experiments
Published in Paul R. Loconto, Trace Environmental Quantitative Analysis, 2020
Of the three modes of calibration used in instrumental analysis, external, internal, and standard addition, the latter provides for the most accurate analytical results for samples that exhibit a matrix interference. The external mode of calibration is used to convert the instrumental response to concentration when matrix interferences are not considered a factor. A series of standard solutions that contain the metal of interest are prepared from careful dilution of a certified standard stock solution. The calibration curve is obtained and a least squares regression is performed on the x, y data points. The best-fit line is used to establish the calibration curve. Samples that contain the metal at an unknown concentration level in a sample matrix nearly identical to that used to prepare the serial standards can be run and the data interpolated to give the concentration. In contrast, the standard addition mode of calibration requires that calibration and analysis be performed on the sample itself. Standard addition can be used provided that (1) a linear relationship exists between the physical parameter measured and the concentration of analyte, (2) the sensitivity of the method is not changed by the additions, and (3) the method blank can be corrected for. A typical standard addition calibration follows:
Methods for Analysis of Solid Samples
Published in Somenath Mitra, Pradyot Patnaik, Barbara B. Kebbekus, Environmental Chemical Analysis, 2018
Somenath Mitra, Pradyot Patnaik, Barbara B. Kebbekus
For simultaneous multielement analysis, ICP-AES is the method of choice because it is a rapid and sensitive method and has a long linear dynamic range. Attention should be paid to interference if the concentrations are above 1500 mg/L. The sample digest is nebulized directly into the ICP torch. Suggested wavelengths for Pb, Cr, Fe, Cd, and Ba are 220.35, 267.72, 259.94, 226.5, and 455.4 nm respectively. However, if spectral interference occurs, other wavelengths can be used. The method of standard addition can be used for calibration, because it reduces matrix interference. The amount of added standard should be between 50% and 100% of the analyte concentration. This ensures that precision is not sacrificed, and spectral interferences which depend upon element/interferent ratios are similar for both the sample and the standard. Standard addition can be used for all the elements in the sample if the added standards do not cause serious spectral interference.
Naphthenic acid removal in model and real aviation kerosene mixture
Published in Chemical Engineering Communications, 2021
Débora F. Santos, Andréa R. Chaves, Indianara C. Ostroski
In the model mixture, naphthenic acids were represented by n-dodecanoic carboxylic acid (ACD) (C12H24O2 - Purity 99%, Merck, Sigma-Aldrich). This was selected because of its similarity to the acid compounds present in aviation kerosene (Nascimento et al. 2017). N-dodecane (C12H26 - Purity 99%, Merck, Sigma-Aldrich) was used as a solvent and also to represent the model fuel due to its similarity to kerosene and diesel (Shah et al. 2015; Khan et al. 2017). In the real mixture, the standard addition method was employed, that is, a determined amount of the standard solution containing the analyte is added to a portion of the real sample (Skoog et al. 2013). In this way, the model mixture was added to the real fuel in a 1:1 (v/v) ratio. This technique was necessary because aviation kerosene was supplied by a local distributor. Therefore, the fuel, which had already passed through different filtration systems and the quantities of naphthenic acids were minimal, it was the closet product to be acquired directly from the refinery.
The use of non-adapted anaerobic consortium in batch reactors enable to couple polychlorinated biphenyl degradation and community adaptation
Published in Environmental Technology, 2020
Mara Rúbia de Lima e Silva, Paulo Clairmont Feitosa de Lima Gomes, Dagoberto Yukio Okada, Isabel Kimiko Sakamoto, Maria Bernadete Amancio Varesche
In order to avoid the matrix effect and false positive results, the standard addition method for complex matrices was used [35]. The standard addition method is the performance of the analytical curve with the addition of known quantities of the substance of interest. The extrapolation of this curve gives the actual concentration of the substance of interest. Thus, four to six standard addition points were evaluated for each congener with the successive addition of PCBs represented by the addition of 0.03 mg L−1, 1.0 mg L−1, 1.5 mg L−1, 2.0 mg L−1 and 3.0 mg L−1 of PCB, respectively, and without PCB (Figure SM-1).
Inexpensive spectrophotometric determination of nitrite with a laboratory-constructed flow cell
Published in Instrumentation Science & Technology, 2023
Mohsen Salimi, Siavash Nouroozi
To evaluate the accuracy of the fabricated fluidic system, three samples with nitrite concentrations of 0.50, 0.70, and 1.00 mg/l were prepared and introduced to the system. The concentrations were determined with the standard addition technique. Table 1 shows the results. The t-test shows that there are no differences between actual and calculated concentrations at the 95% confidence level, demonstrating the accuracy of the developed method.[40]