Determination of Water-Soluble Polymers Containing Primary Amide Groups Using the Starch-Triiodide Method
Authors: Scoggins M.W. , Miller J.W. 
Published: December 2007

Partially hydrolyzed, water-soluble polyacrylamide Partially hydrolyzed, water-soluble polyacrylamide polymers in oilfield brines were determined by polymers in oilfield brines were determined by oxidation with bromine at pH 3.5 to give a product that oxidized iodide ion to iodine. The iodine was measured spectrophotometrically as the starch-triiodide complex.Analyses of samples containing polyacrylamide polymers ranging from 10 to 100 ppm concentration polymers ranging from 10 to 100 ppm concentration gave results with a pooled standard deviation of 0.91 ppm and an average recovery of 104%. Separate ppm and an average recovery of 104%. Separate calibration for each batch of polymer was required because of the nonuniform composition of the product. product.

Introduction

Water-soluble polymers and copolymers of acrylamide and its derivatives are used to treat water and in oil recovery. These polymers are in the 3 to 15 million number-average molecular weight range and may have up to 50% of the amide groups hydrolyzed. A rapid method for determining less than 100 ppm of these materials in surface water and oilfield brine is described here.Turbidimetric techniques using a quaternary ammonium cation (Hyamine 1622 TM) or the hypochlorite ion as precipitants were applied to both polyacrylic acid and hydrolyzed polyacrylamide polyacrylic acid and hydrolyzed polyacrylamide polymers. While these techniques are rapid and polymers. While these techniques are rapid and sensitive, they are subject to heavy metal ion interference. Measurements used by others but deemed unsatisfactory for our work include total nitrogen, amide nitrogen, solution viscosity, and organic carbon.Post and Reynolds used a hypobromite oxidation-spectrophotometric titration to assay various aliphatic amides. Adapting this technique for analyzing acrylamide-based polymers yielded semiquantitative results. A polymer manufacturer recommended a similar procedure, based on this reaction, to form an N-bromoamide oxidation product. After destroying the excess oxidizing agent product. After destroying the excess oxidizing agent (bromine), the N-bromoamide oxidation product reacted with iodide ion to form iodine. Finally, the iodine was measured as the familiar starch-triiodide complex. Lambert described a superior iodide reagent using a linear A-fraction of potato starch/cadmium iodide solution as both the color reagent and source of iodide ion. We used this reaction to determine water-soluble amides. We have modified the bromine oxidation reaction conditions to make the reaction applicable for samples containing high concentrations of chloride ion. We combined this with the stable Lambert reagent to provide a reliable and sensitive procedure for determining polymers containing the primary amide group.

Experimental

Reagents and Apparatus

Buffer solution was pH 3.5. We dissolved 25 g sodium acetate trihydrate in 0.80 dm3 water, added 0.11 dm3 glacial acetic acid and 0.75 g hydrated aluminum sulfate, adjusted the pH to 3.5 with acetic acid, and diluted the solution to 1 dm3. Starch-CdI2 color reagent was prepared as described in Ref. 7, except that we used J. T. Baker Iodometry Grade potato starch powder. Sodium formate (1 % solution) potato starch powder. Sodium formate (1 % solution) and saturated bromine water were required. Linear starches were obtained from Stein, Hall and Co. Inc. We measured absorbance on a Cary Model 11 spectrophotometer in 1-cm cells.

SPEJ

P. 151