Potentiometric, Amperometric, and Polarographic Methods for Microanalysis

Abstract

A review is given of various practical methods for the microdetermination o f common constituents in petroleum products by potentiometric, amperometric, and polarographic means. A brief description or mention is included of the equipment used in these methods, together with typical applications to microanalysis. Methods are outlined for the determination of acidity, basicity, saponification number, and halogens .by potentiometric titration; sulfate ion, halogens, silver, lead, iron, and copper by amperometric titration; and lead, aluminum, and sodium by polarographic analysis.ANY investigators have, recognized the value of electro-M metric methods in the determination of small amounts of material (3, 6, 9, 10, 28, 89, 30). Benedetti-Pichler, for example, points out the general advantages of a potentiometric end point in microanalysis when dealing with colored or very dilute solutions ( 3 ) . Stock (89) recently reviewed microchemical applications of potentiometry with emphasis on special apparatus used for very small volumes (drop-scale analysis). Polarographic methods are inherently suited to microchemical VI ork bzcaiise they utilize dilute solutions (10-0 to lo-* molar). Majer has described various cells for the polarographic examination of very small volumes of solution (81 ). Amperometric titrations, either a t a dropping mercury or a rotating platinum electrode, are useful in the analysis of small volumes of dilute solutions (28).

Determination of Organically Bound Chlorine in Petroleum Fractions with Oxyhydrogen Burner

“…This has been advantageous on several occasions, when samples submitted for chlorine analysis were found to contain bromine as well as chlorine. Potentiometric and am- perometric methods for the determination of halide ions recovered from petroleum products are discussed by Parks and Lykken (8). Titrations were performed at about 5 0 C. to take advantage of the lower solubility of silver chloride (5) at lower temperatures.…”

“…Procedures for determining small quantities of chloride ion in aqueous solution include nephelometry (11), amperometry (10,12), differential potentiometry (4), mercuric nitrate titrimetry (6), and a microdiffusioncolorimetric method (7,8,17). Each procedure was investigated for measuring less than 100 y of chloride-the amount obtained from 10 to 15 grams of naphtha.…”

Determination of Iron in Used Lubricating Oils: Spectrochemical Analysis by the Buffered Direct Current Arc

“…MAXYr procedures for the quantitative estimation of iron in used lubricating oils have appeared in the literature (12). In most cases the sample is completely oxidized by wet ashing or is simply ignited and burned to an inorganic ash.…”

“…The former procedure involves the possible introduction of proportionately large amounts of iron from the oxidizing acids, and work carried out in this laboratory indicates that dry ashing occasionally leads to loss of iron; both methods are time-consuming. Published methods involve colorimetric determination of iron in the residue after oxidation (3,9,13,(15)(16)(17), subjecting the inorganic ash to polarographic analysis (8,14), or estimating the iron content by means of amperometric titration (12). In nearly all the procedures cited, separation of iron from interfering cations is necessary.…”

Amperometric Titrations

“…FROM the number of papers that have appeared since the first review in 1949 (4%), it is evident that the amperometric titration method is gaining momentum and is rapidly attaining maturity as a widely accepted analytical method. Several general and review papers have been published (3,10,23,31,32,35,40,59,65,80).…”