A research team from TRIUMF and Simon Fraser University has demonstrated a closed-loop, recycling-compatible electroplating method using a tin(IV) chloride bath solution to manufacture enriched tin-119 targets for producing antimony-119, an emerging therapeutic radionuclide for targeted Auger electron therapy. In findings published in EJNMMI Radiopharmacy and Chemistry, the researchers evaluated three distinct tin electrodeposition formulations and established that a simple tin(IV) chloride bath in hydrochloric acid achieved a quantitative electroplating deposition efficiency of 98 ± 3 percent after seventy-two hours of operation, alongside an overall post-purification target material recovery of 84 ± 6 percent when accounting for all dissolution and column extraction stages. The methodology solves a critical economic and radiochemical bottleneck in targeted cancer therapy development by enabling the recovery and direct re-deposition of costly enriched isotope material without requiring complex, yield-diminishing chemical conversions between irradiation cycles.

Antimony-119 has garnered significant clinical interest for targeted Auger electron therapy because of its decay characteristics and manageable nuclear production profile.

Generating isotopically pure antimony-119 directly via the proton-induced 119Sn(p,n)119Sb reaction requires low-energy medical cyclotrons, which are widely installed in hospitals and research facilities worldwide. The reaction cross section is particularly favorable at low proton energies, reaching a prominent peak of approximately 1100 millibarns between 11 and 12 megaelectronvolts, permitting production on cyclotrons operating below 30 megaelectronvolts without necessitating sophisticated regional accelerator infrastructure. However, enriched tin-119 raw material costs upwards of 20,000 Canadian dollars per gram, or roughly 13,000 euros. Given that a single solid cyclotron target incorporates tens to hundreds of milligrams of enriched material to yield microgram or nanogram quantities of radioantimony, direct single-use consumption is economically unviable, making an efficient, repeatable recycling pathway mandatory for sustainable radiopharmaceutical translation.

Physical properties of elemental tin impose strict engineering limitations on cyclotron targetry. Tin possesses a low melting point of 232 degrees Celsius, meaning solid foil targets requiring 500 to 1000 milligrams of material risk structural compromise under beam heating, whereas electroplated coin targets holding thinner deposits within thermally conductive backing recesses can effectively tolerate intense proton bombardment. Historically, researchers have utilized tin(II) sulfate baths or alkaline tin(IV) hydroxide baths to plate cyclotron targets. While capable of generating functional targets, neither formulation easily integrates with modern extraction chromatography using DBE-300 resin, which elutes recovered tin in a concentrated matrix of twelve-molar hydrochloric acid as tin(IV) chloride. Converting this acidic recovery fraction into sulfate or hydroxide forms introduces severe product losses, complicating process automation and leaving recovered material largely unusable.

To overcome these incompatibilities, the researchers systematically tested three distinct electroplating chemistries: a conventional tin(II) sulfate bath, a sol-gel-derived tin(IV) sols bath, and an acidic tin(IV) chloride bath designed to match the recovery stream of DBE-300 extraction chromatography. The sulfate bath utilized sulfuric acid, phenolsulfonic acid, gelatin, and 2-naphthol under a constant potential of 3.0 volts. The sols bath incorporated tin(IV) chloride pentahydrate complexed with acetylacetone, ammonium hydroxide, and boric acid, operated at a constant current density of 1 ampere per square decimeter. The tin(IV) chloride bath utilized metallic tin dissolved in concentrated hydrochloric acid and oxidized with hydrogen peroxide, which was simply diluted with an equal volume of ultrapure water prior to deposition at 1 ampere per square decimeter using a platinum wire anode.

Experimental trials revealed notable performance differences in plating efficiency and operational stability among the three formulations. The tin(IV) chloride bath demonstrated the highest electrodeposition performance, achieving 90 ± 8 percent recovery after 48 hours and 98 ± 3 percent recovery after 72 hours across natural tin trials, while recovering 96.8 percent of material across four enriched tin-119 targets. Conversely, the tin(IV) sols bath demonstrated the lowest deposition efficiency at 60 ± 30 percent after 48 hours; attempts to accelerate sols deposition by increasing current densities to 10 or 100 amperes per square decimeter caused non-adherent tin precipitation at the cathode yielding less than 10 milligrams of adhered metal.

Evaluating full radiochemical recycling confirmed that only the tin(IV) chloride system was chemically compatible with the hydrochloric acid matrix recovered from chromatographic resin purification. Attempts to adapt the recovered tin(IV) chloride fraction to the sols formulation by evaporating hydrochloric acid under heat or airflow caused substantial losses of volatile tin(IV) chloride, which boils at 114 degrees Celsius, while neutralizations using ammonium hydroxide failed to generate adherent electroplated films. No viable chemical pathway was found to convert the recovery fraction to tin(II) sulfate without adding interfering agents. In contrast, the recovered tin(IV) chloride fraction required only water dilution before being electroplated directly into fresh solid targets, delivering an overall recovery yield of 84 ± 6 percent across the combined dissolution, separation, and re-plating cycle.

Target durability and substrate interactions were evaluated using silver and copper backing materials during irradiations on the TRIUMF TR13 cyclotron. Targets electroplated on both metals remained intact without material loss or melting under 13 megaelectronvolt proton beams up to 30 microamperes for durations up to 4 hours. However, copper was found to be unsuitable for multi-cycle recycling because dissolved copper ions from the backing enter the recovery stream, where copper(II) chloride acts as a re-oxidizing catalyst that severely suppresses subsequent tin electroreduction. Furthermore, proton bombardment of copper produces 65-zinc, which emits persistent 1115-kiloelectronvolt gamma rays requiring heavy radiation shielding. Silver backings dissolved far less in acid, generated no electrochemical interference during tin re-plating, and activated primarily to 109-cadmium, whose low-energy emissions below 90 kiloelectronvolts are readily shielded.

Surface characterization by environmental scanning electron microscopy and energy dispersive X-ray spectroscopy revealed distinct structural morphology and purity across the target types. Targets produced via tin(II) sulfate baths displayed irregular, barnacle-like morphologies contaminated with organic carbon flakes and drying fibers. The tin(IV) sols bath produced large clustered aggregates with evident chloride and oxide crystal formation. The tin(IV) chloride bath produced the most uniform, homogeneous surfaces, yielding the highest surface tin purity at 88 ± 2 weight percent. Enriched tin-119 targets exhibited localized micro-porosity caused by hydrogen gas bubbling during prolonged 72-hour electroplating of small 50-milligram batches, but this surface roughness was successfully eliminated without chemical contamination by flattening the malleable tin deposit using a manual hydraulic pellet press.

Comprehensive trace element screening via inductively coupled plasma mass spectrometry verified that the separation and recycling protocol reliably yielded radioantimony of high chemical purity. The radiochemical purification removed between 99.97 and 99.999 percent of bulk tin, leaving as little as 2 micrograms of tin in the final product elute. Non-radioactive antimony contamination in the final fraction was traced to leaching from borosilicate glass beakers during heated dissolution, an artifact successfully suppressed down to 9 nanograms when dissolving targets in inert Teflon vessels. By uniting high-current target durability, superior surface homogeneity, and an efficient target-to-target recycling yield above 80 percent, this electroplating methodology provides a technically practical and economically viable platform for the routine clinical production of pure antimony-119 radiopharmaceuticals.

Subject of Research: Radiochemical target engineering and enriched material recycling for cyclotron production of medical radionuclides

Article Title: Recycling-compatible electroplating of enriched tin-119 targets for the production of antimony-119 for targeted Auger electron therapy

Article References: Grundmane, A., Ramogida, C. F., & Radchenko, V. (2026). Recycling-compatible electroplating of enriched tin-119 targets for the production of antimony-119 for targeted Auger electron therapy. EJNMMI Radiopharmacy and Chemistry, 11(1), Article 67. https://doi.org/10.1186/s41181-026-00468-6

Image Credits: AI Generated

DOI: 10.1186/s41181-026-00468-6

Keywords: antimony-119, tin-119, targeted Auger electron therapy, electroplating, cyclotron targetry, radionuclide production, radiopharmacy, nuclear medicine, material recycling, tin(IV) chloride, energy dispersive X-ray, scanning electron microscopy, inductively coupled plasma mass spectrometry, TRIUMF TR13 cyclotron, radiochemical separation, DBE-300 resin, Auger electrons