Optimization of Dynamic Headspace Sampling Conditions for the Identification of Palaeolithic Adhesives

Peaktables of untarget DHS-GC×GC-TOFMS analysis of pine resin and hide glue. Both are used as a proxy for Palaeolithic adhesives. This is the start of an extensive library for VOCs extracted with DHS on adhesives used in prehistory. ____SAMPLES____The pine resin (Pinus nigra subsp. laricio (Corsican pine)) was collected in Corsica in September 2009, stored in a plastic container until the measurements in October 2022. The hide glue was produced in-house from a deer hide by an experienced experimenter (C. Lepers, TraceoLab), see SI1 for more information. All samples (5 mg of pine resin and 10 mg of hide glue) were placed in 20 mL screw cap headspace vials with a 1.3 mm PFTE septa (Gerstel®, Kortrijk, Belgium). Any instrumental variances were checked by measuring a Cannabis terpenes standard (#1 and #2, 2500 ppm) (Restek® Corporation, Bellefonte, PA, USA). The standard was diluted to 25 ppm in methanol (≥ 99.8%, HPLC grade, Fisher scientific, Loughborough, UK) and 40 µL was pipetted in a 20 mL screw cap headspace vial. No internal standard was added, due to the solid nature of the samples. A n-alkane standard solution (C7-C30, Sigma Aldrich, Saint louis, USA, 1000 ppm) was diluted in MeOH to 20 ppm and 2 µL was pipetted inside a 20 mL vial.____EXTRACTION____DHS was automated using a MultiPurposeSampler autosampler (MPS, Gerstel K.K, Mülheim an der Ruhr, Germany), connected to the GC system. The DHS parameters were: timeincu: 20 min, Tincu: 50°C, Fpurge: 22.5 mL.min-1 and Vpurge: 450 mL. VOCs were trapped in a thermal desorption tube filled with Tenax TA. During the trapping, the temperature of the tubes was 30°C. The needle temperature was set at 120°C. After the DHS extraction, VOCs were desorbed in the thermal desorption unit (TDU, Gerstel K.K.), the TDU was heated from 40°C to 280°C at 300°C.min-1, and held isothermal for 3 min. The desorption was conducted in splitless mode, and VOCs were trapped on a liner filled with Tenax TA at -20°C in a cooled injector system (CIS, CIS4 Gerstel K.K.). Subsequently, VOCs were released into the GC by heating of the CIS to 250°C at 12°C.s-1 and held for 3 min. The CIS was operated in split mode (5:1). Before the sequence starts and after each run, the tube was reconditioned for 15 min in the TDU at 300°C.____CHROMATOGRAPHY____All samples were analysed on a Pegasus GC-4D (LECO® Corporation, St. Joseph, MI, USA) GC×GC-TOFMS equipped with a secondary oven and a quad-jet, dual stage thermal modulator. The column set was ch