|| 50 mL (10 mL min.) aliquot of random urine. Add 50% HCl drop by drop to bring the pH between 1–2. Do not use concentrated HCl. Ship refrigerated or frozen. Patient should strictly avoid bananas, wallnuts, tomatoes, pineapples, plums, gooseberries, mirabelles, melons, avocados, aubergines, kiwi fruits and drugs like methocarbamol, mephenesin, guaiphenesis, paracetamol, salicylic acid and strenuous exercise at least 48 hours before and during specimen collection.. .