Potentiometric titrations of sulfate using an ion-selective lead electrode

Abstract

melts, are susceptible to attack by metals such as lead and arsenic that can drastically reduce the life of the crucible. Either graphite crucibles (#A2260 Fusion Crucible, Ultra Carbon Corp., Bay City, Mich.) or vitreous carbon crucibles (#170 Crucible, Beckwith Carbon Corp., 16140 Raymer St., Van Nuys, Calif.) are well suited for this flux-fusion technique. Vitreous carbon crucibles are employed when reduction of sample components is a problem or when melts tend to wet graphite crucibles. Although vitreous carbon crucibles are rather expensive, 20 to 25 melts can be made in one crucible before it is destroyed by oxidation.Mixtures consisting of 90 wt % flux and 10 wt % sample give good characteristic X-ray yields for the lighter elements. The flux/sample ratio can be changed within reasonable limits to suit particular needs. All samples should be ground to pass at least -100 mesh.Preparation of Flux-Fusion Glasses. After mixing the flux and sample, the mixture is transferred to the proper crucible and fused according to the schedule depicted in Figure 1. An initial 5-minute fusion at 1100 °C will completely dissolve all but the most refractory samples, in which case the initial fusion time may be increased or the melt swirled in the crucible to promote solution of the sample. A mediumsized muffle furnace is satisfactory for either single or multiple fusions. After the initial fusion, a short carbon rod is placed on top of the melt to flatten the surface and an additional 5-minute heating period is begun (no carbon rod is used with vitreous carbon crucibles.) The crucible, melt, and flattening rod are then removed from the furnace intact and are cooled for 10 or 15 minutes to room temperature. The glass disks can be removed easily by lifting off the flattening rod and tapping the inverted crucible against a flat surface. Machining about a 2°t aper on graphite crucibles which

Determination of Sulfonate Groups and Total Sulfur

“…The sulfur dioxide evolved is determined by iodometric titration (Canadian Pulp and Paper Association useful method G.7U, March 1959). Sulfate can be determined by titration with barium chloride (Ora 1960), backtitration with sulfuric acid after addition of barium perchlorate (Aldrich 1974), potentiometric titration with lead perchlorate using an ion-selective electrode (Ross and Frant 1969), or ion chromatography (Douek and Ing 1989).…”

Potentiometric Titration of Sulfate in Water and Soil Extracts Using a Lead‐Mercury Amalgam Indicator Electrode

“…This permitted development of a procedure that could be used with an automatic titrator. The use of automatic titrators have not been reported with the potentiometric titration procedures cited (2,5,11,12). Carbonate and HCO"-interfere with Ph 2+ titration of SO42 -since PbCO" is less soluble than PbSO 4 .…”

“…Several solvents have proved effective in lowering the PbSO 4 solubility when added to aqueous solution (2,5,11,12). Methanol, ethanol, and isopropanol were compared and found to be suitable for use with the automatic titration procedure.…”

“…Cortellessa (2) used a lead-sensitive electrode prepared by immersing a Ag electrode in a K 4Fe(CN),3 -3H20-K3Fe-(CN), solution to measure SO42 -in solutions low in interfering ions. Ross and Frant (11) introduced a lead-sensitive Ag, Ag2S, PbS electrode (10) that has been used to measure SO42-in saturated soil extracts (4) and SO42-oxidized from organic compounds (10 subject to interferences from Cl -, CO32 -HCO3 -, NO3 -, PO43 -, Cu + , Hg-h , and Ag-h (5, 10,11,12). Many of these ions are present in natural waters and soil extracts.…”

Honey as a bioindicator for environmental pollution with SO2

“…The amount of sulphate was determined in a 25 mL aliquot of each sample by titration with The end-point of titration was determined potentiometrically (Ross and Frant, 1969) with an indicator lead ion selective electrode (Pb-ISE) (Orion 94-82) and a reference electrode (Orion 90-02) on an Orion 960 autochemistry system. Constant ionic strength was achieved by addition of 1 mL of 5 M aqueous NaClO 4 .…”