ELISA Four Parameter Inversion

Invert a caller-fitted four-parameter logistic ELISA standard curve.

Description

A four-parameter logistic inversion converts response into concentration using a previously fitted standard curve.

A four-parameter logistic inversion converts response into concentration using a previously fitted standard curve. Its asymptotes define the admissible response interval.^[1]

Invert a caller-fitted four-parameter logistic ELISA standard curve.

When to use ELISA Four Parameter Inversion

Use this tool to invert a caller-fitted four-parameter logistic ELISA standard curve.

Prepare the canonical sequence, peptide assignments, fitted assay parameters or upstream measurements requested. Keep corresponding entries aligned, use the stated mass and signal units, and remove FASTA headers before entering sequence text.

How to use ELISA Four Parameter Inversion and understand its results

Prepare the canonical sequence, peptide assignments, fitted assay parameters or upstream measurements requested. Keep corresponding entries aligned, use the stated mass and signal units, and remove FASTA headers before entering sequence text.
Enter absorbance, upperAsymptote, lowerAsymptote, midpointConcentration, hillSlope using the field table and calculation rules, then run the tool.
Read concentration, normalizedResponse. The explanation below defines the units, signs, ordering and any flags or placeholder values.
If the tool reports an input issue, correct the values and run it again. Apply the stated assumptions when interpreting a successfully returned result.

Input field	Meaning	Value type; see rules below	Requirement
absorbance	Absorbance	number	Required
upperAsymptote	Upper asymptote	number	Required
lowerAsymptote	Lower asymptote	number	Required
midpointConcentration	Midpoint concentration	number	Required
hillSlope	Hill slope	number	Required

Enter upper a greater than lower d, positive midpoint c, nonzero signed slope b and response strictly between d and a. Return modeled concentration and normalized response.

concentration=c×[(a−d)/(y−d)−1]^(1/b); normalized=(y−d)/(a−d)

Units, indexing, boundary conditions and exceptional cases are defined in the calculation rules above.

Output field	Meaning	Value type
concentration	Concentration	number
normalizedResponse	Normalized response	number

json

{
  "input": {
    "absorbance": 5,
    "upperAsymptote": 10,
    "lowerAsymptote": 0,
    "midpointConcentration": 2,
    "hillSlope": 1
  },
  "output": {
    "concentration": 2,
    "normalizedResponse": 0.5
  }
}

Limitations and assumptions

The curve convention places a at the upper asymptote and d at the lower. No fitting, blank correction, uncertainty or dilution adjustment is performed; use concentration units from the fitted midpoint.

Numeric inputs must be finite. Follow the calculation-specific rules for overflow, underflow and exceptional cases. Missing required fields, extra fields, wrong value types and violations of the calculation rules are input errors.

Alternative or Complementary methods

Use BCA Blank Correction: Subtract the matched assay blank from BCA absorbance. For a complementary task, use Protein Dilution Backcalculation: Back-calculate original protein concentration after dilution.

References

ELISA Four Parameter Inversion — tool.io

Similar or alternative tools

BCA Blank Correction
Subtract the matched assay blank from BCA absorbance.
Protein Dilution Backcalculation
Back-calculate original protein concentration after dilution.