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Quality Assurance and Validation
Published in Leo M. L. Nollet, Dimitra A. Lambropoulou, Chromatographic Analysis of the Environment, 2017
Roberta Galarini, Simone Moretti, Giorgio Saluti
The IUPAC guidelines for calibration in analytical chemistry (Danzer and Currie, 1998) defines calibration as the operation that determines the functional relationship between measured values (signal intensities), that is, the y variable, and analytical quantities characterizing types of analytes and their amount or concentration, that is, the x variable. Every instrument used in chemical analysis is characterized by a specific calibration function, that is, an equation relating the instrument output signal to the analyte content. This response function may or may not be linear: the exact form depends on the system being measured and the measurement process itself. The calibration curve is obtained by fitting an appropriate equation to a set of experimental data (calibration data) consisting of the measured responses to known concentrations of analyte.
Atomic Absorption Spectrometry and Related Techniques
Published in Grinberg Nelu, Rodriguez Sonia, Ewing’s Analytical Instrumentation Handbook, Fourth Edition, 2019
Bernhard Welz, Maria Goreti R. Vale
The graphical presentation of the calibration function is the calibration curve (or analytical curve). In the optimum working range there is a linear relationship between the absorbance A, the integrated absorbance Aint, or the emission intensity I and the concentration c or mass m of the analyte in the measurement solution. This is an advantage for the evaluation of the measurement as the linear equation represents the simplest of all possibilities. In AAS this linear range typically only extends over one to two orders of magnitude, whereas in AFS and OES it covers typically three to five orders of magnitude.
Determination of gaseous formaldehyde by derivatization using magnetic multiwalled carbon nanotubes (MWCNTs) modified with 2,4-dinitrophenylhydrazine (DNPH) and high-performance liquid chromatography – ultraviolet detection (HPLC-UV)
Published in Instrumentation Science & Technology, 2022
A DNPH solution (0.1 g/L) was prepared by adding 5.05 mg DNPH to a 50-mL flask. The DNPH was solubilized in approximately 10 mL acetonitrile with sonication for several minutes and with acetonitrile to a final volume of 50 mL A stock solution of formaldehyde was prepared by gravimetric dilution of the products of the formaldehyde solution using ultrapure water. The 37% formaldehyde solution (1.4 mL) was added to a 500-mL volumetric flask and diluted with ultrapure water. The stock solution of formaldehyde (1 g/L) was diluted with ultrapure water to produce standard solutions from 0.01 to 5.00 mg/L. All formaldehyde standards were prepared daily by dilution to the desired concentration with ultrapure water. The 5 M Η3PO4 solution was prepared by adding 195 μL of Η3PO4 (85%) to a 50 mL volumetric flask followed by dilution with ultrapure water. The formaldehyde standard or sample (1.0 mL) was transferred into a 2-mL HPLC vial and 20 μL of Η3PO4 and 50 μL of the 100 mg/L DNPH in acetonitrile were added successively. For the MWCNT-DNPH and formaldehyde derivatization, MWCNT-DNPH was used instead of the DNPH solution. The mixture was stirred at approximately 35 °C for at least 30 min. The magnetic solid material was separated using a magnet and the derivative released in triplicate by 1 mL eluent. Each eluate (20 μL) was injected into the HPLC. A calibration curve was obtained by linear regression of the peak area of the formaldehyde derivative as a function of the formaldehyde concentration.
Characterisation, adsorption and desorption of ammonium and nitrate of biochar derived from different feedstocks
Published in Environmental Technology, 2022
Makhosazana P. Aghoghovwia, Ailsa G. Hardie, Andrei B. Rozanov
Once the equilibrium period of 24 h of shaking had lapsed, the samples were filtered under vacuum using 0.45 µm nylon membrane filters. The pH of the supernatant solution was measured and the quantity of and in solution was determined. The concentration of in the solutions was determined colorimetrically using the salicylate method [19]. An ultra violet/visible (UV/VIS) spectrophotometer was used at 667 nm to measure the intensity of the emerald green colour that developed from each sample. The concentration of was calculated based on the linear regression equation of the calibration curve prepared from the analyses of standards. Nitrate in solution was measured using an auto analyser high resolution digital colorimeter [20]. The samples were put through a cadmium column and measured at a wavelength of 520 nm on the UV/VIS spectrophotometer. The amount of and adsorbed on the biochar surfaces was calculated from the difference in the concentration of and in the initial solution before extraction.
Trends and Levels of Perfluorinated Compounds in Soil and Sediment Surrounding a Cluster of Metal Plating Industries
Published in Soil and Sediment Contamination: An International Journal, 2021
Situ Na, Reti Hai, Xiaohui Wang, Nankun Li
PFCs were quantified using ultra-high-performance liquid chromatography coupled with triple quadrupole mass spectrometry (UPLC-MS/MS, Agilent 6470, Santa Clara, CA, USA), with electrospray ionization (ESI) in negative mode. Nitrogen was used in the nebulizer and collision cell. Separation of PFCs was carried out using a Zorbax eclipse plus C18 column (2.1 mm i.d. × 100 mm length, 3.5 µm, Agilent). The mobile phase consisted of acetonitrile (A) and 10 mM ammonium acetate aqueous solution (B) with a flow rate of 0.3 mL·min−1. A gradient elution program with linear ramps was used as follows: t0min 30% A, t5min 75% A, t9min 100% A, and t12min 30% A. The MS conditions were sheath gas flow rate of 8 L·min−1 at 350°C, nebulizer pressure of 40 psi, and capillary voltage of 4 kV. Detailed parameters of MS for individual PFCs can be found in Na et al. (2020). A seven-point internal standard calibration curve for individual PFCs was prepared.