Based on the linear enhancement of formaldehyde (FA) within 7.0~1000 pmol l -1 on luminol-bovine serum albumin (BSA) chemiluminescence (CL) system, FA determination in air and beer samples using CL with flow injection (FI) was proposed. The detection limit was 2.5 pmol l -1 (3s) and the relative standard deviations were less than 4.5% (n = 7). At a flow rate of 2.0 mL min -1 , a whole analysis from sampling to washing only needed 32 s, offering a sample throughput of 112 h -1 . This proposed method was successfully utilized to determine FA vapor pressure in liquid (121.8 ± 3.8 Pa), FA content in real air sample (8.93 ± 0.03 mg m -3 ), and FA levels in beer (199.5 ± 5.6~225.2 ± 3.5 mg l -1 ), giving determination recoveries from 90.7% to 109.3%. The mechanism of BSA-FA interaction was also investigated, showing FA binding to BSA was a spontaneous process mainly through hydrogen bonding and van der Waals force by FI-CL, with binding constant K of 1.89 × 10 6 l mol -1 and the number of binding sites n of 0.86. Molecular docking analysis further revealed FA could enter into the pocket at subdomain IIA of BSA, with K of 1.71 × 10 5 l mol -1 and DG of -29.68 kJ mol -1 .Keywords: Formaldehyde; Vapor pressure; Real air sample; Beer samples; Bovine serum albumin; Luminol; FI-CL.
INTRODUCTIONFormaldehyde (FA), a colorless pungent chemical with high water solubility, is usually released as a fixative for pathologists, a byproduct of combustion and off-gassing of various building products, leading to wide existence in foods, industry and environment.1,2 It has attracted intensive attention in public 3-5 because of its negative impacts on human health. Chemiluminescence (CL) in combination with FI technique has also been favorably utilized in FA determination, 42-44 due to its conspicuous merits in terms of high sensitivity, low limit of detection (LOD), wide dynamic concentration response range, automatability and less reagent consumption. [45][46][47][48][49] However, so far no FI-CL using luminol-bovine serum albumin (BSA) system has been described for FA determination. In this current work, it was found that FA can remarkably enhance CL intensity from luminol-BSA system, and the CL intensity increments were linear with FA concentrations from 7.0 to 1000 pmol l -1 . Based on the good linear enhancement, a simple FI-CL method using luminol-BSA system was first developed to determine FA.
RESULTS AND DISCUSSIONThe relative CL intensity-time profile of luminol-BSA-FA system The relative CL intensity-time profile of luminol-BSA-FA system was given in Fig. 4 (I max referred to the maximum CL intensity, and T max referred to the time for the I max ). The studied concentrations of luminol, BSA and FA were 5.0 × 10 -5 , 5.0 × 10 -9 and 3.0 × 10 -10 mol l -1 , respectively. It can be seen that the I max of luminol-BSA system (curve ¡) is 219 with the T max of 4.1 s, and then vanishes in the following 28 s; however in the presence of FA (curve l), the I max of luminol-BSA system strikingly increases about 1.92-fold to 420 with the...
