Method: Carbohydrate in Produced Water (Colorimetric)

Abstract

Author(s): Stringfellow, William; Lee, Ji Yeon | Abstract: Standard method for the measurement of guar gum and other carbohydrates in produced water from the oil and gas industry. Written in compliance with USEPA protocols for the State of California agencies ANALYTE: D-Glucose, CAS#50-99-7 D-Mannose, CAS# 3458-28-4 D-Galactose, CAS#59-23-4 D-Lactose, CAS#63-42-3 Guar Gum, CAS#9000-30-0 INSTRUMENTATION: PerkinElmer Lambda 35 UV/VIS Spectrophotometer 1.0 Scope and Application 1.1 This method covers the determination of mannose, guar gum and other carbohydrates in produced water samples. 1.2 Sugars have varying response factors by this method (Figure 1) and the carbohydrate used for calibration must be specified in the result. 1.3 The method is based on standard curves that are specific for mannose, one of two sugars in commercial guar gum, such that the final carbohydrate concentration is expressed as mannose, mg/L. 1.4 Commercial guar gum should not be used as a calibration standard, due to variability in chemical composition and purity. 1.5 Glucose is not a structural component of guar gum and is therefore not recommended as a calibration standard. 1.6 The method is usable in the 6 to 1000 mg/L as mannose range. Detection range may be variable according to the instrument used. 2.0 Summary of Method Guar gum, a polysaccharide of galactose and mannose, is a common ingredient for hydraulic fracturing fluids [7]. Standard methods for measuring carbohydrates in flow-back and other produced water are needed, particularly in the context of reporting water quality data to regulatory agencies [6]. This method describes standard procedures for carbohydrate measurement that have been validated for use in produced water. Heating produced water with sulfuric acid hydrolyzes polysaccharides and dehydrates monosaccharides to form 2-furaldehyde from pentoses and 5-(hydroxymethyl)-2-furaldehyde from D-glucose and other hexoses [2, 8]. 2-Furaldehyde and 5-(hydroxymethyl)-2-furaldehyde reacts with anthrone to form a green colored compound [1, 2, 3, 5]. Total carbohydrate is quantified by measuring absorbance of known and unknown samples at 625 nm [2].