Behavioral Variability in ABA Chemical Pretreatment Close to the 14C Age Limit

Abstract

ABSTRACT. The acid-base-acid (ABA) procedure is a common chemical pretreatment used on most organic matter samples. Although this pretreatment is straightforward, there is no consensus among labs about the optimum strength of the chemicals, or even the temperature, to be used for digestions. Comparisons between 14 C results obtained by samples undergoing ABA against other wet oxidations, such as acid-base oxidation followed by stepped-combustion (ABOX-SC) or -cellulose on wood, have sometimes suggested that ABA does not always remove all contaminating carbon. In addition, if not all ABA protocols are the same, could it be said that one procedure is better than others or comparable to wet-oxidation pretreatments, if rigorously applied? To determine whether 14 C-free samples showed any fraction modern carbon (FmC) deviations due to pretreatment strategies, 3 experiments were carried out. The first compared 14 C results for wood samples at or near the limit of 14 C dating, pretreated with a standard ABA protocol used at UC Irvine's Keck Carbon Cycle Accelerator Mass Spectrometry (KCCAMS) facility, with those obtained from ABA-and ABOX-SC-prepared aliquots of the same samples performed at Australian National University (ANU) in 2001. The second experiment subjected wood samples, ranging from ~12 ka BP to 14 C-free, to 5 selected published ABA pretreatments. Third, we evaluated whether the ABA protocol needs a higherstrength final acid step (particularly important for removing CO 2 absorption when samples are submerged in alkaline solutions). We are able to show that rigorous ABA treatments exist that can provide robust, reproducible results for many wood samples that are known to be >>50 ka BP, implying that a lack of control over the procedure's outcome might be samplerelated, rather than due simply to inadequacies in the chemical pretreatment.

Bag of Tricks: A Set of Techniques and other Resources to Help 14C Laboratory Setup, Sample Processing, and Beyond

“…However, the typical procedure involves a series of warm acid and alkaline washes, and rinsing with deionized water. Santos and Ormsby (2013) made a compilation of several ABA treatments to evaluate their weaknesses and strengths, and found that most of them are suitable even when 14 C ages are close to the 14 C limit (>50 ka BP). Organic samples that are difficult to clean may require a more aggressive treatment, such as wet oxidation (also termed ABOX, e.g. acid, base, oxidation treatment) with or without the stepped-combustion procedure (Bird et al 1999a; Santos et al 2001; Brock and Higham 2009; Haesaerts et al 2013), stepped-combustion alone (McGeehin et al 2004), or hydropyrolysis (Ascough et al 2010).…”

“…acid, base, oxidation treatment) with or without the stepped-combustion procedure (Bird et al 1999a; Santos et al 2001; Brock and Higham 2009; Haesaerts et al 2013), stepped-combustion alone (McGeehin et al 2004), or hydropyrolysis (Ascough et al 2010). Regardless of the chemical strategy adopted, note that those harsh digestions may require several milligrams of organic material (more than usual); therefore, the risks of the procedure should be evaluated carefully (Higham et al 2009; Santos and Ormsby 2013). ABA pretreatments (as well as holocellulose extractions, Southon and Magana 2010) can be carried out in large batches when using 13×100mm disposable borosilicate glass tubes coupled with heat blocks up to ~200°C maximum.…”

“…However, the typical procedure involves a series of warm acid and alkaline washes, and rinsing with deionized water. Santos and Ormsby (2013) made a compilation of several ABA treatments to evaluate their weaknesses and strengths, and found that most of them are suitable even when 14 C ages are close to the 14 C limit (>50 ka BP).…”

Wood14C Dating with AixMICADAS: Methods and Application to Tree-Ring Sequences from the Younger Dryas Event in the Southern French Alps

“…The classical ABA (acid-base-acid) method described by de Vries and Barendsen (1954) is routinely used in many laboratories for the pretreatment of various organic samples, including wood. Largely modified in the different 14 C laboratories (Santos and Ormsby 2013), this method isolates the wood cellulose and lignin and removes exogenous inorganic and organic carbon. Nevertheless, the ABA treatment can leave behind a residual contamination in very old samples (i.e.…”

Improved radiocarbon analyses of modern human hair to determine the year‐of‐death by cross‐flow nanofiltered amino acids: common contaminants, implications for isotopic analysis, and recommendations

“…In order to avoid disintegration of the keratinized material under alkaline conditions, this chemical treatment was performed at room temperature. [50] The samples were then dried at 40°C. This pretreatment procedure is designed to remove molecules adsorbed or transferred onto the surface of the keratinized material by endogenous-exogenous pathways.…”