[HB+plasma] = [H+plasma] + [Bplasma] ∼ {BBB} ∼ [Bcsf] + [H+csf] = [HB+csf]
pKa –pHplasma = log([HB+plasma]/[Bplasma])		pKa – pHcsf = log ([HB+csf]/[Bcsf])
2.6 = log ([HB+plasma]/[Bplasma])		2.7 = log([HB+csf]/[Bcsf])
	Antilog of equations
398 = [HB+plasma]/[Bplasma]		501 = [HB+csf]/[Bcsf]
	[Bplasma] ∼ [Bcsf]
[HB+plasma]/398 = [Bplasma]		[Bcsf] = [HB+csf]/501
	[HB+plasma]/398 = [HB+csf]/501
	[HB+csf]/[HB+plasma] = 501/398 = 1.26