Figure 5
From: Analysis of free chlorine in aqueous solution at very low concentration with lateral flow tests
(a,b) Chlorine loss due to contact with substrate samples over time in a 2 ppm chlorine solution (12 mg substrate per ml solution). The chlorine concentration was determined by the absorbance of the oxidized DPD at 551 nm. “Blank” stands for the concentration of the initial chlorine solution at the beginning and the end of the experiment. (c) Images of 9 cm long tests made of buffer-impregnated paper substrates after 5 and 1 ppm free chlorine solution flowed through for the time given below the test. (d) Images of 9 cm long tests made of alternative, non-cellulosic substrates without buffer impregnation after 5 ppm free chlorine solution flowed through for the time given below the test. (a,c) Samples consist of the following paper substrates: Schleicher & Schüll 2992, Schleicher & Schüll 2992 hornified in an oven at 120 °C, lab-made cotton linters paper, TEMPO catalysed pre-oxidized lab-made cotton linters paper, free chlorine pre-oxidized lab-made cotton linters paper (Cl2) and DBS paper from Ahlstrom-Munksjö. (b,d) Samples consist of the following alternative substrates: PET substrates from Ahlstrom-Munksjö 6613 (pure PET), 6613 H (with surfactant) and 6614 (with binder), Spec-Wipe 3 from VWR with 45% polyester and 55% cellulose, glass fibre 691 from VWR and glass fibre MN 85/90 BF from Macherey-Nagel. The flow time is given below each test photo. Please note that the flow time for the Schleicher & Schüll 2992 paper is different for (c,d) because in (c) the paper was used in cross direction (7:30 min) and in (d) in machine direction (5:30 min), whereby only the flow time was reduced, and the colour intensity did not decrease significantly. The colour intensity difference here is due to the fact that all tests shown in (c) were impregnated with buffer prior printing, all tests in (d) not.
