Series 200 lc quaternary pump

The analytical reference standards of 8-oxoGua. 8-oxodGuo and 8-oxoGuo were purchased by Spectra 2000 s.r.l (Rome, Italy). The isotope labeled internal standards (¹³C¹⁵N₂) 8-oxodGuo and (¹³C¹⁵N₂) 8-oxoGuo were obtained from CDN Isotopes Inc. (Pointe-Claire, QC, Canada). (¹³C¹⁵N) 8-oxoGua (98%) was obtained from Cambridge Isotope Laboratories Inc. (Tewksbury, MA, USA).
Glacial acetic acid 30% NH₃. Dimethyl sulfoxide. Sodium hydroxide solution (50%–52% in water) and CHROMASOLV^® gradient grade ≥99.9% Methanol and Acetonitrile for HPLC/MS ≥99.9% carbon disulfide low benzene content were obtained from Sigma Aldrich (Saint Louis, MO, USA). Purified water was obtained from a Milli-Q Plus system (Millipore Milford, MA, USA). Anotop 10LC syringe filter device (0.2 µm pore size, 10 mm diameter) were purchased from Whatman Inc. (Maidstone, UK). A Kinetex Polar C18 column 100 A. (150 × 4.6 mm, 2.6 µm) supplied by Phenomenex (Torrance, CA, USA) were used throughout the study.
The urine samples were analyzed on a Series 200 LC quaternary pump (PerkinElmer, Norwalk, CT, USA) coupled with an AB/Sciex API 4000 triple-quadrupole mass spectrometry detector equipped with a Turbo Ion Spray (TIS) probe.

Urine samples were collected at the end-shift of the same Wednesday of blood and buccal cell sampling in sterile plastic containers, were divided into three aliquots in polypropylene screw-cap tubes and stored frozen at −20 °C until analysis. The urine samples were analyzed on a Series 200 LC quaternary pump (PerkinElmer, Norwalk, CT, USA), coupled with an AB/Sciex API 4000 triple-quadrupole mass spectrometry detector equipped with a turbo ion spray (TIS) probe.
The method described in Andreoli et al. [28 (link)] with some modifications [29 (link)] was applied to the urine samples to assess the concentrations of 8-oxoGua, 8-oxodGuo, 8-oxoGuo and their internal standards, ((¹³C¹⁵N₂) 8-oxoGua), ((¹³C¹⁵N₂) 8-oxodGuo) and ((¹³C¹⁵N₂) 8-oxoGuo), using the isotopic dilution method. The 1.5 version of Analyst® software (AB Sciex, Framingham, MA, USA) was employed for instrument control.
To normalize the results for the dilution grade of urine, the results were expressed as the ratio to the concentration of urinary creatinine. The method of Jaffe using alkaline picrate test with UV-vis detection at 490 nm [30 (link)] was applied to determine the urinary creatinine. Samples with creatinine concentrations lower than 0.3 g/L or higher than 3.0 g/L were excluded from statistical analysis according to the American Conference of Governmental Industrial Hygienists (ACGIH) recommendation [31 ].