Alkaline CuO Oxidation with a Microwave Digestion System:  Lignin Analyses of Geochemical Samples

Abstract

A novel approach for the analysis of lignin in geochemical samples has been developed as an alternative to the alkaline CuO oxidation procedure first developed in 1982. The new procedure utilizes microwave digestion technology, as opposed to conductive heating, to carry out oxidative hydrolysis of six samples in an oxygen-free atmosphere at 150 degrees C for 90 min. Ethyl acetate is used as the extraction solvent in place of diethyl ether. Additionally, the new method incorporates a simplified extraction procedure that minimizes solvent handling and the amount of glassware needed. Under these novel conditions, the yields and compositions of lignin phenols from four different samples (modern and ancient sediments; woody and nonwoody tissues) match those obtained by the "traditional" procedure. The significant advantages of this new alkaline CuO oxidation method include faster reaction times, the ability to accurately measure and control reaction conditions, added flexibility for the analyst, and a marked increase in the achievable sample throughput.

Analysis of cooking spices in natural waters

“…The LLE technique had poor recoveries of vanillin (35.3%) and ethyl vanillin (43.6%), and 4 of 14 tested compounds had recoveries <70%. Using LLE, Goni and Montgomery (2000) reported slightly higher yields than we achieved for some compounds. The C-18 column had poor recovery of 4-hydroxybenzoic acid (4.9%), vanillic acid (19.6%), 3,4 dihydroxybenzoic acid (15.1%), and 6 of the 14 compounds had recoveries <70% (Table 2).…”

“…3). Also, a number of these spices are liberated from macromolecules during cupric oxide oxidation [the "lignin" technique; (Goni and Montgomery 2000)], prompting the question of whether the monomer compositions would mimic that of macromolecular substrates. Comparison of our SPE-extracted monomer concentrations with compound distributions resulting from the analysis of "Lake Washington Standard Mud" illustrate that the monomer compositions do not mimic that routinely observed for macromolecular lignin (data not shown).…”

“…Two popular approaches include liquid-liquid extraction (LLE) (Barber et al 2000) and C-18 solid-phase extraction (Castillo et al 1999). These are also the two techniques most commonly used to isolate individual lignin phenols after cupric oxide oxidation (Goni and Montgomery 2000;Louchouarn et al 2000). Since several spices are liberated from woods after alkaline oxidation, and thus their extraction efficiencies by LLE or C18-SPE are well documented for aquatic samples, we compared the new technique to these two well-established techniques.…”

Refractory dissolved organic nitrogen accumulation in high-elevation lakes

“…Samples for DIC were collected before June/July 2010 but are not reported due to sample storage issues. Lignin-phenol analysis followed established protocols 68,69 . Further details are provided in the Supplementary Methods.…”

Chemical characteristics of particulate organic matter from a small, mountainous river system in the Oregon Coast Range, USA

“…The fine and coarse fractions of suspended sediments were analyzed by alkaline CuO oxidation (Goñi and Montgomery 2000;Goñi et al 2009) to obtain the yields of a variety of products derived from different biochemical precursors and biological sources. The analytical precision and variability of this technique was evaluated by oxidizing well-characterized standardized materials (vegetation and sediment samples) as well as replicate analyses of selected samples.…”