A Little Too Occupied To Address E-64 ?

Internal standard and PAH standard solutions were spiked directly onto the tissue in the tube. Stock solutions of PAH standards, quality controls, and internal standards were prepared by diluting original solutions in ACN to yield 0.3, 3.0, 15, 30, and 75?ng/��L spiking solutions. Stock solutions of deuterated PAH standards used as internal standards were prepared by diluting original solutions in ACN to yield a spiking solution of 3.75?ng/��L. Adding 20?��L of internal standard to 3.0?g tissue (or 6.0?g of water homogenized tissue) yielded an internal standard concentration of 25?ng/g in tissue. Adding 10?��L of each standard spike level to 3.0?g tissue (or 6.0?g water homogenized tissue) yielded this website spike levels of 1.0, 10, 50, 100, and 250?ng/g. We performed the standard AOAC version of QuEChERS without further optimization by following package insert directions. In brief, DI water was added to samples to normalize final weight at 15?g. Samples were vortexed for 30 seconds and further diluted with 15?mL of ACN JQ1 and vortexed for an additional minute. The contents of the QuEChERS salt packet (6.0?g MgSO4 and 1.5?g sodium acetate) were added to the sample and shaken 1 minute. Samples were mixed on an ATR rotator for 10 minutes and centrifuged at approximately 4000?��g for 5 minutes at 5.0��C. The upper ACN layer was collected and stored up to 48 hours prior to analysis. Prior to use, Twister stir bars were conditioned at 300��C under 80?mL/min zero grade nitrogen flow in the tube conditioner for 2 hours. SBSE was accomplished by transferring 1.0?mL aliquots of the upper ACN layer to a 10?mL headspace vial containing a conditioned, precoated stir E-64 bar and 4.0?mL of 0.1?M NaHCO3 to reduce organic acid interference. Samples were stirred at room temperature for 90 minutes at approximately 1200?rpm. Stir bars were removed with clean tweezers, rinsed briefly with DI water, blotted dry, and placed into clean glass desorption tubes for analysis. Calibration of the thermal desorption unit was performed by spiking a known amount of PAH standard mix onto Tenax TA adsorbent tubes (Supelco, Bellefonte PA, USA) and desorbing under the same conditions as used for the Twister desorption, as described below. The total recovery of the combined QuEChERS/SBSE procedure was determined by using this calibration to quantify the PAHs recovered from the spiked oyster matrix. 2.4. Stir Bar Desorption and GC/MS Conditions Stir bars were thermally desorbed at 100?mL/minute into the GC using the thermal desorption unit in splitless mode heated at 720��C/minute from 40��C (0.2?min) to 300��C (5 minutes). Analytes were refocused in the inlet at ?120��C on a quartz wool-filled liner in solvent venting mode and transferred to the column by heating the inlet at 720��C/minute to 300��C (3 minutes) with a 10?:?1 split ratio.