Bar: 1 Bar=14.5037738 psi.  1 Bar= 100 kilopascals  1 kilopascal = 0.001 Megapascals

Crossflow Velocity:  refers to the velocity of the fluid across the top of the membrane surface. A “flow” is usually given in terms of volume per unit membrane area per unit time as with liters/m2/h (LMH). CF=Pi-Po where Pi is pressure at the inlet and Po is pressure at the outlet and is related to the retentate flow rate .It provides the force that sweeps away larger molecules that can clog the membrane .

Delta p: is pressure drop from retentate inlet to outlet. It is (pi-p0) where pi is the inlet pressure and p0 is the outlet pressure. 

Depth filtration: see outline

Direct flow filtration device (DFF): is a filtration device that has one inlet and one outline. DFF devices are tpyically single use devices. Depending upon the selected pore size, molecules smaller than the aerage membrane pore size will pass through the filter. In contrast, tangential flow filtraiton (tff) devices have one inlet, one retentate outlet and at least one permeate outlet (see outline for TFF). 

Filtrate Flux (J): is the rate at which a portion of the sample has passed through the membrane.

Flow: is typically given in terms of volumn per unit membrane area per unit time as in liters/m2/h (LMH). A cross flow, for example, might be given as ml/min for a membrane area of xm2.

Flux (permeate flow): the flow of fluid across the membrane (i.e., through the pores of the membrane).

Log reduction value (LRV):  LRV is obtained by calculating the cahnge in viral concentration in say an antibody solution between before and after filtration with a virus removing membrane. LRV=Log10(C0/CF) where C0=viral concentration in an antibody solution before filtration with the virus removing removing membrane and CF=viral concentration in the antibody solution after filtration with the virus removing membrane.

nanofiltration: is a special kinda of ultrafiltration (Bachacher “Purification of intravenous immunoglobulin G from human plasma – aspects of yeild and virus safety” Biotechnol. J. 2006, 1, 148-163).

Nominal Molecular Weight Cut Off (NMWCO): is the size (kilodaltons) designation for the ultrafiltration membranes. The MWCO is defined as the molecular weight of the globular protein that is 90% retained by the membrane. 

Percent Solids by Weight (% w/v): is defined as the weight of dry solids in a given volume of a susension divided by the total weight of that volume of the suspension, multipled by 100.  (Menyawi, US 17/054,018, published as US 2021/0246162)

Retentate: is the portion of the sample that does not pass through the membrane, also known as the concentrate. Retentate is typically re-circulated during TFF. 

Surface (Zeta) potential: When the zeta potential of monoclonal antibodies under given solution conditions is designated as Eil (mV) and the zeta potential of a virus removing membrane under given solutios conditions is designated as Em (mV), the two desirably have the following relationship: 0 mV≤Eil-Em≤20mV. When the result of Eil-Em is within the range that allows interaction between the antibodies and the membrane to decrease, it is thought to have an effect of improving the filtration rate of the membrane. A value for Eil-Em of more than 20 mV causes electrostatic interaction between antibodies and the membrane to increase, having an adverse effect on filtration. Also, when the virus removing membrane is negatively charged within a certain pH range and the antibodies are positively charge, the relationship between the zeta potential Eil of antibodies and the zeta potential Em of a membrane is desirably represented by -4% x Em ≤Eil1≤-550% x Em. Hongo (US 13/260419). 

Transmembrane pressure (TMP): refers to the pressure which is applied to drive the solvent and components smaller than the cut-off value of the filtration membrane through the pores of the filtration membrane. In tangential flow systems, highest TMP’s are at the inlet (beginning of flow channel) and lowest at the outlet (end of the flow channel). TMP is calculated as an average pressure of the inlet, outlet, and filtrate prots. The TMP is the force that actually pushes molecules through pores of the filter. TMP can be calculated as TMP [bar]=(PF + PR)/2-Pf where PF is the feed pressure, PR is the retentate pressure and Pf is the filtrate pressure. In other words, the driving force (transmembrane pressure or TMP) is the difference between the average of the membrane feed pressure (P1) and the retentate pressure (P2) minus the permeate pressure (P3); TMP=(P1+P2)/2-P3). Schilog (WO 02/00331)

Volume concentration factor (VCF): refers to the ratio of the initial feed volume to the retentate volume. For examplke, if 20 L of feedstock are processed until 18 L have passed through to the filtrate and 2 L are left in the retentate, a 10 fold concentration has been performed so the VCF is 10.