You can dissolve 500g crystal phenol in 500 ml 1M tris pH 8.0 (if you want phenol solution for DNA extraction) or 50 mM Sodium acetate pH 4.0 (when prepare acid Phenol for RNA extraction). Keep in mind check pH of phenol solution before use and discard this solution when phenol turns red/brown. Some authors prefer the use of commercial kits, prior to the use of phenol-chloroform extraction isoamyl alcohol.

Annex some references that could guide you.

Exp Parasitol. 2011 Jun;128(2):159-62. doi: 10.1016/j.exppara.2011.02.001. Epub 2011 Feb 17.

Giardia intestinalis: DNA extraction approaches to improve PCR results.

Babaei Z1, Oormazdi H, Rezaie S, Rezaeian M, Razmjou E.

Author information

Abstract

Difficulty in disrupting cysts of Giardia intestinalis, a cosmopolitan protozoan parasite, decreases the yield of DNA extracted and reduces the effectiveness of the polymerase chain reaction (PCR). To improve the detection of the Giardia Glutamate Dehydrogenase (gdh) gene, we re-evaluated the effects of deoxyribonucleic acid (DNA) extraction methods. Purified and concentrated cysts from 33 fecal samples were disrupted using conventional methods, and DNA extraction was conducted using two protocols: the QIAamp Stool Mini Kit and phenol/chloroform/isoamyl alcohol (PCI). PCR amplification was successful for 12 extracted DNA samples (36%) using PCI following a glass bead and freeze/thaw pretreatment and for all 33 samples (100%) using the QIAamp Stool Mini Kit following the aforementioned pretreatment. Consequently, the pretreatment of cysts with glass beads and freeze/thaw cycles followed by extraction of DNA with the QIAamp Stool Mini kit was the more effective protocol.

Thank you so much Jose Ramon Vielma