I am using the human interferon-gamma ELISA kit (Cat. No. KAC1231). What is the conversion from units per milliliter to picograms per milliliter?
The format of this ELISA is a three member solid phase sandwich (capture antibody coated on the plate, antigen, and HRP conjugated detection antibody). The procedure for this kit is very straightforward. The standards are provided in individual vials. When you are ready to perform the assay, you reconstitute each of the vials of standard with 1 mL water to the final concentration. There are 6 vials of standard provided. Standard 1 is reconstituted to a concentration of 0 units/mL. Standard 2 is reconstituted to a concentration of 1 unit/mL. Standard 3 is reconstituted to a concentration of 2 units/mL. Standard 4 is reconstituted to a concentration of 5 units/mL Standard 5 is reconstituted to a concentration of 10 units/mL. Standard 6 is reconstituted to a concentration of 30 units/mL. Then one simply pipettes 50 microliters of sample or standard into the wells immediately followed by 50 microliters of the HRP conjugated detection antibody.
Then the wells are incubated for 2 hours at room temperature on a shaker. After the incubation, the wells are washed. Then 200 microliters of chromogen solution are added, incubated for 15 minutes in the dark, then 50 microliters of stop solution are added. The wells are then read at 450 nm. The interferon-gamma concentration is determined by interpolation from the standard curve. This kit is calibrated in units per milliliter.
A question that comes up frequently on this kit is the conversion between units per milliter and picograms per milliliter. For this kit, 1 unit of the standard preparation is equivalent to 1 IU of NIH reference preparation Gg-901-530. For this standard, 20 IU = 1 ng. Therefore 1 IU = 0.050 ng = 50 pg. We indicate in the protocol that the statistical sensitivity of the kit is 0.03 IU/mL, which is equivalent to 1.5 pg/mL. The standards converted from IU/mL to pg/mL as follows: 0 IU/mL = 0 pg/mL, 1 IUmL = 50 pg/mL, 2 IU/mL = 100 pg/mL, 5 IU/mL = 250 pg/mL, 10 IU/mL = 500 pg/mL, 30 IU/mL = 1500 pg/mL.
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Then the wells are incubated for 2 hours at room temperature on a shaker. After the incubation, the wells are washed. Then 200 microliters of chromogen solution are added, incubated for 15 minutes in the dark, then 50 microliters of stop solution are added. The wells are then read at 450 nm. The interferon-gamma concentration is determined by interpolation from the standard curve. This kit is calibrated in units per milliliter.
A question that comes up frequently on this kit is the conversion between units per milliter and picograms per milliliter. For this kit, 1 unit of the standard preparation is equivalent to 1 IU of NIH reference preparation Gg-901-530. For this standard, 20 IU = 1 ng. Therefore 1 IU = 0.050 ng = 50 pg. We indicate in the protocol that the statistical sensitivity of the kit is 0.03 IU/mL, which is equivalent to 1.5 pg/mL. The standards converted from IU/mL to pg/mL as follows: 0 IU/mL = 0 pg/mL, 1 IUmL = 50 pg/mL, 2 IU/mL = 100 pg/mL, 5 IU/mL = 250 pg/mL, 10 IU/mL = 500 pg/mL, 30 IU/mL = 1500 pg/mL.
Find additional tips, troubleshooting help, and resources within our Antibodies and Immunoassays Support Center.