Diphenylamine

The current smoking rate is based on the definition of a smoker as someone who has smoked at least 100 individual cigarettes in his or her lifetime and who, at the time of interview, reported smoking every day or some days. Measurements of UCC are taken using gas chromatography–mass spectrometry, specifically with the detector model Clarus 600 T of Finland PerkinElmer. The indicators used in the measurement are cotinine and diphenylamine (Aldrich, USA). The UCC threshold for identifying smokers is generally set at 20–100 ng/ml [7 (link),13 (link),14 (link)], but the Society for Research on Nicotine and Tobacco has suggested that the standardized threshold of urinary cotinine be set at 50 ng/ml [15 (link)]. It should be noted that this suggestion for standardization reflects a Western model that does not necessarily apply to the characteristics of South Korea or other Asian countries. In South Korea, for instance, studies involving interviews and longitudinal observations of certain populations have suggested UCC thresholds as low as 20 ng/ml can indicate smokers [9 ]. Admittedly, however, such a low threshold is not sensitive to the detection of cotinine owing to unrelated factors such as secondhand smoking. Therefore, the present research used one of the generally accepted threshold levels of UCC ≥ 30 ng/ml [16 (link)].

H, xanthine solution, xanthine sodium salt, H₂O₂, thiobarbituric acid (TBA),diphenylamine, pyrogallol, standard SOD, GSH, GSSG and all chemicals were obtained from Sigma-Aldrich, St Louis, MO, USA.

Smoking-related factors included smoking status, urinary cotinine level, and pack-years of smoking. Smoking status was determined using the questionnaire and categorized as non-smoker, ex-smoker, or current smoker (including smoking often). Urinary cotinine levels were analyzed in 2010 and 2011 and measured using gas chromatography and mass spectrometry with a Perkin Elmer Clarus 600T (PerkinElmer, Turku, Finland), cotinine (Sigma, St. Louis, MO, USA), and diphenylamine (Aldrich, St. Louis, MO, USA) (threshold of detection, 0.25 ng/mL) [21 ]. We corrected for urine dilution by using urinary creatinine concentrations and calculated creatinine-standardized cotinine concentrations (vs. non-standardized) by dividing individual urinary cotinine concentrations by creatinine concentrations. Pack-years of smoking (Equation (1)) were calculated using information collected with the questionnaire and the following formula:
$Pack-yearsofsmoking=\frac{Numberofcigarettessmokedperday}{20\left(thenumberofcigarettesinapack\right)}\times thenumberofyearsmoked$

HPS (Purolite Int., Llantrisant, UK), used as catalyst support, was of two types: hyper-cross-linked nonfunctionalized polystyrene, Macronet MN270 (BET SSA 1337 m²/g), and HPS containing tertiary amino groups, MN100 (BET SSA 724 m²/g), designated here as HPS-NR₂. Both supports were washed with distilled water and acetone and then dried under vacuum as described elsewhere [34 (link)]. Benzene (BZ, 99.8%), toluene (TOL, 99.8%), naphthalene (NL, 99%), aniline (AN, 99%), anthracene (ANC, 97%), phenylacethylene (PHA, 98%), phenol (PL, ≥99%), propiophenone (PP, 98%), diphenylamine (DPA, 99%), tetrahydrofuran (THF, ≥99.9%), methanol (MeOH, 99.8%), acetone (≥99.5%), hydrogen peroxide (H₂O₂, 35%), isopropanol (i-PrOH, ≥99.5%), butanol (BuOH, ≥99%), hexane (≥99%), and dodecane (≥99%) were obtained from Sigma-Aldrich. Chloroplatinic acid hydrate (H₂PtCl₆·6H₂O, Pt content 38.41%), palladium acetate (Pd(CH₃COO)₂, Pd content 47.68%), and ruthenium hydroxychloride (Ru(OH)Cl₃, Ru content 45.05%) were purchased from JSC “Aurat” (Moscow, Russia). Sodium hydroxide (NaOH) was obtained from Reakhim (Moscow, Russia). Reagent-grade hydrogen of 99.999% purity was received from AGA (Tver, Russia). All chemicals were used as received. Distilled water was purified with an Elsi-Aqua water purification system.