Determination of Sr in soil by tungsten coil atomic emission spectrometry Arthur L. Salido a, ⁎, Bradley T. Jones b a Western Carolina University, United States b Wake Forest University, United States abstract article info Article history: Received 13 September 2011 Accepted 18 September 2011 Available online 29 September 2011 Keywords: Tungsten coil Atomic emission spectrometry Strontium Aluminum Soil Radioactive dispersion device Dirty bomb Strontium was determined in soil by tungsten coil atomic emission spectrometry (WCAES). Since aluminum enhances strontium emission and is a common component of soil, it was first necessary to develop a method to remove aluminum from digested soil solutions. This was accomplished by buffering solutions to a pH of 5.5 with ammonium bicarbonate. Each buffered solution was filtered through a 0.45 μm syringe filter. Twenty- five μL of the filtrate were injected into a WCAES instrument and analyzed. The method effectively removed aluminum from digested samples. The next goal was to develop a fast soil digestion method that could be used in field analyses. A potential application for a fast method is the detection of radioisotopes after the de- tonation of a radioactive dispersion device ("dirty bomb"). Such devices could potentially contain strontium- 90, and a field method would be necessary to quickly determine the concentration of strontium. Two differ- ent soil digestion methods were tested. The first (method A) was a typical method using aqua regia, hydrogen peroxide, and heat. The second (method B) was a faster method that involved shaking soil with concentrated acid for 30 s. Strontium "spike" recoveries showed that method B was not as effective at recovering strontium from soil. The % strontium recoveries (method B) were 87% compared to 93% for method A. A NIST SRM "San Joaquin Soil" was analyzed using both soil digestion methods. Strontium recoveries were 76% and 59% for methods A and B respectively, suggesting that digestion conditions needed to be more thorough. © 2011 Elsevier B.V. All rights reserved. 1. Introduction A new form of atomic emission spectrometry using tungsten coil atomization has been described in recent publications [1–4]. Most re- cently, tungsten coil atomic emission spectrometry (WCAES) has been used to determine total carbon in soft drinks [5], iodide [4] and trace metals in soil and water samples [2–4]. There are several advantages as- sociated with WCAES. The instruments have low power requirements and can be operated with a 12 V DC battery. Multiple elements can be detected simultaneously. The use of gasses is minimal compared to ICP-based instruments. The components are inexpensive. Detection limits are often in the low ng/mL range for many elements. WCAES instruments can easily be made portable, which is crucial if field analyses are necessary. The atomizer achieves 3000 K at low- power (250 W). The emission detectors can be powered and con- trolled by a small notebook computer. In the event of a radioactive dispersion device (RDD or “dirty bomb”) attack, a portable instru- ment would be critical. It would enable law enforcement, public safe- ty groups, and media to quickly know the types and concentration of elements present. A portable instrument would prevent further con- tamination of vehicles, lab buildings, and personnel because analyses would be accomplished on-site. Strontium-90 is a likely radioisotope for inclusion in a dirty bomb [6]. 90 Sr is used in radioisotope thermoelectric generators (RTGs), which are typically positioned in remote locations to power radio beacons, lighthouses, and weather stations. Unfortunately, many RTG locations are unknown or are not secured, making them poten- tial tools for criminal or terrorist activity [7]. Strontium has been characterized in water by WCAES [2]. The sys- tem described in that article reported a detection limit of 0.1 ng/mL. The work that will be described in this article used a similar WCAES system but with an inexpensive and portable detector. The goal of this research was to develop a field method for the determination of strontium in soil samples by WCAES. The determination of strontium by WCAES is not straightforward. In previous research, it was found that aluminum and potassium en- hance the strontium emission signal that is monitored at the 460.7 nm analytical line [1]. The enhancement effect is much more pronounced for aluminum than potassium. The effect can be consid- ered beneficial in some cases. For example, aluminum and potassium can be used as matrix modifiers to improve instrument sensitivity to- ward strontium. However, this effect can be problematic. Soil can contain aluminum and potassium concentrations that reach several percent. High concentrations of these elements would complicate and potentially prolong Sr determinations. In order to correct or account for the enhancement effects of alu- minum or potassium in soil, several sample treatment methods were investigated. This article will describe a sample treatment that Microchemical Journal 101 (2012) 1–4 ⁎ Corresponding author. Tel.: + 1 8282272587. E-mail address: salido@wcu.edu (A.L. Salido). 0026-265X/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.microc.2011.09.008 Contents lists available at SciVerse ScienceDirect Microchemical Journal journal homepage: www.elsevier.com/locate/microc