Worldwide Solutions - February 2008 - (Page 12) GERSTEL Solutions Worldwide Application Method parameters Automated MPS SPE • Cartridges: 6 mL / 1000 mg silica gel • Syringe: 1 mL • Sample vials: 1.5 mL or 4 mL • Collection vial: 10 mL CIS 4 • Temperature program: 10 °C – 12 °C/s – 300 °C (15 min) • Pneumatic setting: Solvent Vent GC • Oven program: 45 °C (1 min) – 10°C/min – 325°C (1 min) • Carrier Gas: Helium, 1.2 mL/min, constant flow • Column: HP5-MS 30 m x 0.25 mm x 0.25 µm Detection system • MSD: SIM/SCAN 50 – 285 amu For the determination of the 16 PAH compounds in the EPA standard test mix, the following GC system was used: GERSTEL MultiPurpose Sampler (MPS), GERSTEL Solid Phase Extraction (SPE), GERSTEL Cooled Injection System (CIS 4) with LN2 Option, GC 6890 and MSD 5975, both from Agilent Technologies. Calibration standard: 100 ng/mL EPA PAH standard test mix extracted using the GERSTEL SPE and analyzed by LVI GC/MS in SIM Mode. Chromatogram of a real sample (Roofing extract diluted 1:100), analyzed in SIM mode. Automated Sample Prep Steps The GERSTEL SPE preparation steps can be easily selected from pull-down menus in the GERSTEL MAESTRO software. The following steps were performed for each sample: • • • • • • • • Place an empty 10 mL eluate collection vial in the SPE station Place a new 6 mL / 1000 mg silica gel cartridge in the SPE sliding carriage Condition the cartridge using 10 mL of a dichloromethane/ hexane mixture (1:1) followed by 10 mL hexane Introduce the sample to the SPE cartridge at a speed of 10 µL / sec and collect the eluate or waste liquid Further elute the cartridge using 8 mL of a dichloromethane/ hexane (1:1) mixture. Speed: 10 µL/s Clear out the liquid from the cartridge by pumping through 3 mL of air Discard the used cartridge into the waste receptacle Return the collection vial to the autosampler tray ing the initial injection temperature at 10 °C. After completing the injection, the split vent was closed and the CIS heated to 300 °C using a temperature program, transferring the analytes to the GC column. New method provides answers faster Oliver Lerch was extremely happy with the results. The customer’s application was easily transferred to the GERSTEL SPE and automated. The LVI-GC/MS method gave good results. „The relative standard deviation (RSD) of the complete method certainly pleased the customer”, said Oliver Lerch, “for most of the analytes, RSDs were between 0.8 and 2.8 percent using a 20 ng/L standard.” For the roofing extract samples (1:100), RSDs were between 0.4 and 9.7 percent. The required limits of determination of 0.01 µg/ mL (equal to 10 ng/mL) were easily reached. In the range between 0.5 and 1000 ng/mL calibration curves were linear with correlation coefficients around 0.999. Two calibra- tion curves were created, one for each of the sample volumes (500 µL and 1000 µL) initially extracted by the SPE cartridges. Concentrations were calculated with and without taking the d10-Phenanthrene internal standard into account. A blank extraction right after the highest standard produced a slight carry-over. Naphthalene was the only compound that showed higher RSDs and blanks. The reasons are probably twofold: Hexane and dichloromethane are not ideal solvents for naphthalene – and the GERSTEL Solutions Worldwide – February 2008 12
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