A Sequential Injection System for the Spectrophotometric Determination of Calcium, Magnesium and Alkalinity in Water Samples

Abstract

A sequential injection methodology for the spectrophotometric determination of calcium, magnesium and alkalinity in water samples is proposed. A single manifold is used for the determination of the three analytes, and the same protocol sequence allows the sequential determination of calcium and magnesium (the sum corresponds to the water hardness). The determination of both metals is based on their reaction with cresolphtalein complexone; mutual interference is minimized by using 8-hydroxyquinoline for the determination of calcium and ethylene glycol-bis(β-aminoethyl ether)-N,N,N′,N′-tetraacetic acid (EGTA) for the determination of magnesium. Alkalinity determination is based on a reaction with acetic acid, and corresponding color change of Bromcresol Green. Working ranges of 0.5 -5 mg dm -3 for Ca, 0.5 -10 mg dm -3 for Mg, and 10 -100 mg HCO3 -dm -3 , for alkalinity have been achieved. The results for water samples were comparable to those of the reference methods and to a certified reference water sample. RSDs lower than 5% were obtained, a low reagent consumption and a reduced volume of effluent have been accomplished. The determination rate for calcium and magnesium is 80 h -1 , corresponding to 40 h -1 per element, while 65 determinations of alkalinity per hour could be carried out.

Iron speciation in natural waters by sequential injection analysis with a hexadentate 3-hydroxy-4-pyridinone chelator as chromogenic agent

“…These studies also contributed to set the aspiration order in SI: ligand solution, buffer and sample, this way ensuring a good mixture of the sample with a buffered ligand solution. The buffer volume was set to the minimal reproducible amount of 24 μL [12], to ensure good mixing of the three plugs.…”

“…So, hydrogen peroxide was chosen as the oxidising agent for the determination of total iron with SPE and two steps were added to the analytical cycle (Table 1), in order to sandwich the sample between two oxidant plugs [4]. The volume of oxidant was 24 mL per plug, the reported minimum volume to attain an effective overlapping [12] and the concentration of 12.8 mM was adopted from previous work [4]. Again, calibration curves with iron(III) and iron(II) standards were established and compared.…”

Flow injection analysis as a tool for enhancing oceanographic nutrient measurements—A review

“…Flow analysis versions of this approach have been reported using flow through potentiometric detection [170,171] or spectrophotometric detection using the peak width quantification method [172]. An alternative approach involves the on-line acidification of the sample to ca.…”

A review on sequential injection methods for water analysis

“…This means that by using the same manifold but placing different reagents on the selection valve ports, and changing the operational parameters, more than one analyte can be determined. From the listed papers, over 40% involved the determination of more than one analyte [34-36,39,40,45,49-53,55,59-61,72,74,78,83-85, 94,96,101-104,106,107,114,116,117,119,120,132,135,138,140,141,145, 148,149,153,155], with close to 18% describing the determination of more than two analytes [34][35][36]40,45,[49][50][51]53,74,83,78,102,101,116,140]. Some more detailed examples of bi-parametric determinations will be detailed in Section 3.4.2, as they usually involve quantifying two oxidation states.…”

“…2. Schematic representation of a SIA manifold for the multiparametric determination of calcium, magnesium and alkalinity in natural waters (adapted from [78]): P -peristaltic pump, BG -bromocresol green reagent for alkalinity determination, Qhydroxiquinoline as masking agent for magnesium in calcium determination, EGTA -masking agent for calcium in magnesium determination, CPC -cresolphtalein complexone colour reagent for calcium and magnesium determination, S (alkalinity)/S (Ca, Mg) -sample for alkalinity or calcium and magnesium determination, respectively.…”