- Electrolyte solution for PYO, HHQ, and PQS detection:
50 mM acetate buffer (pH 5.0) with 20 % ACN. Prepare a
stock solution of 0.2 M sodium acetate (CH 3 COONa). Weigh
1.640 g of sodium acetate and transfer to a 100 ml volumetric
flask. Add DW up to 90 ml. Sonicate until the sodium acetate is
dissolved and then adjust the final volume to 100 ml with DW.
Also, prepare a stock solution of 0.2 M acetic acid
(CH 3 COOH). Add about 25 ml of DW to a 100 ml volumetric
flask. Add 1.144 ml of acetic acid (99.7 %) to the volumetric
flask (seeNote 12). Then, make up to 100 ml with DW. 50 mM
acetate buffer at pH 5.0 can be obtained by diluting 0.2 M
sodium acetate and 0.2 M acetic acid. Add about 40 ml of DW
to a 250 ml graduated cylinder, then add 17.85 ml of 0.2 M
acetic acid, 32.15 ml of 0.2 M sodium acetate, and make up to
200 ml with DW. Similarly, 50 mM acetate buffer (pH 5.0)
with 20 % ACN can be obtained by diluting 0.2 M sodium
acetate and 0.2 M acetic acid. Add about 20 ml of DW to a
100 ml graduated cylinder; then add 8.925 ml of 0.2 M acetic
acid, 16.07 ml of 0.2 M sodium acetate, and 20 ml of 100 %
ACN; and make up to 100 ml with DW. - Prepare daily electrolyte of acetate buffer and formate buffer as
will evaporate and affect the desired concentration. - Run the DPV control using the only electrolyte 50 mM acetate
buffer (pH 5.0) consisting of 20 % ACN prior to the electro-
chemical detection of PYO, HHQ, and PQS. This step aims to
ensure that the BDD electrode is clean, uncontaminated, and
ready for analysis. In a blank electrolyte, DPV should give a
clean background. If the DPV shows any oxidation/reduction
peaks in the blank buffer, polish and clean the BDD electrode
with CV (seeNotes 2and 4 ). - Run the DPV for the standard mixture of 5μM PYO, 20μM
HHQ, and 20μM PQS. 5μM PYO, 20μM HHQ, and 20μM
PQS can be obtained by diluting 2 mM stock solutions of PYO,
HHQ, and PQS (seeNote 1). 12.5μl of the 2 mM PYO stock
solution, 50μl of the 2 mM HHQ stock solution, 50μl of the
2 mM PQS stock solution, and makeup with 5 ml of 50 mM
acetate buffer (pH 5.0) consisting of 20 % ACN (seeNote 5). - The acetic acid is added to ethyl acetate to release any complex
metal ion from PQS and facilitate the partitioning of PQS into
the ethyl acetate layer [17] (PQS is a ferric iron chelator [18]). - The MCX sorbents have a polymeric structure (hydrophilic N-
vinylpyrrolidone and lipophilic divinylbenzene (PVP-DVB))
that is modified with sulfonic groups. The MCX SPE was the
best cartridge to extract PYO, HHQ, and PQS based on the
electrostatic interaction between the positively charged ana-
lytes at low pHs and the negatively charged stationary phase.
114 Alyah Buzid et al.