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Table 2 Extraction methods used in 4 participating laboratories

From: A round robin approach to the analysis of bisphenol a (BPA) in human blood samples

  Laboratory #1 Laboratory #2 Laboratory #3 Laboratory #4
Volume used in analysis 200 μL 500 μL 250 μL 1000 μL for spiked samples, 550 - 1000 μL for environmental samples
Extraction protocol Protein precipitation used Honeywell Burdick & Jackson LC-MS grade acetonitirile containing 10 ng/mL [d6]-BPA. Solid phase extraction: A Strata® NH2 cartridge (#8B-S009-FBJ; 200 mg/3 cc; Phenomenex, Torrance, CA) mounted on an Oasis® MCX cartridge (#186000254; 60 mg/3 cc; Waters, Milford, MA) was used. Solid phase extraction: Waters Oasis HLB cartridge, 1 cc, 10 mg REF 18600383. Solid phase extraction: Thermo Hypersep C18 (Thermo Fisher Scientific, cat # 60108–518), pre-washed with 15 ml methanol.
Vortex mixed, centrifuged and removed 900 μL of supernatant; evaporated supernatant to dryness under stream of nitrogen. Formic acid (98.2%; #F-4636) Ammonium acetate (98%; #0596-01), acetic acid (99.9%; #V194-04), hydrochloric acid (HCl, 37%; #H611), ammonium hydroxide (NH4OH, 29.5% assayed as NH3; #1177-04), and methanol (HPLC grade; #9093-03) Honeywell B&J Methanol REF BJ230-4 HPLC-grade methanol (Fisher A452-4), water (Fisher W5-4) and ammonium acetate (≥97%, Fisher A639-500). Cartridges were washed with 25 mM ammonium acetate and water. Analytes were eluted with MeOH and dried under N2.
Aqua Solutions Ultra Pure Water, HPLC grade, BPA free REF W1089-10 L
Reconstituted in 50 μL acetonitrile/water (50:50; v/v) (Honeywell Burdick & Jackson) and immediately analyzed using LC-MS-MS. SPE column was washed with 5 column volumes methanol
Column activated with 1000 μL BPA free water
Load sample  
Wash with 1000 μL 5% (v/v) methanol
Elute with 1000 μL pure methanol
Extraction pH not monitored 5.0 7 – 7.5 5.0
Containers for extraction Fisher polypropylene micro-centrifuge tubes 16 × 100 mm Borosilicate Glass Disposable Culture Tube (#73500-16100, Kimble Chase). VWR 16X100 mm Test Tubes REF 60825–425 Kimble and Chase 13x110 Conical Tubes REF 73785–5 Borosilicate glass tubes (Fisher Scientific cat#14-961-26).
Drying agent for extraction Nitrogen Nitrogen Nitrogen Nitrogen
Water type & source Honeywell Burdick & Jackson LC-MS grade Milli-Q water was purified by an ultrapure water system (Barnstead International, Dubuque, IA) and verified to be BPA free BPA-free water (verified to be BPA free) HPLC-grade water from Fisher Scientific. It has always tested BPA-free.
Temperature for extraction RT RT for extraction, 30°C for concentration with nitrogen Ambient RT (20-25°C) RT for extraction, 37°C for concentration with nitrogen