---
type: "WebPage"
title: "Isoelectric Point (pI) – laboratory protein analysis"
description: "Isoelectric Point (pI) Determination: characterization of your protein charge The Isoelectric Point (pI) is a fundamental physicochemical parameter in the development of therapeutic proteins (monoclonal antibodies, enzymes, hormones). It correspond to the pH at which the net charge of the..."
resource: "https://filab.fr/en/sectors-of-activity/biopharmaceutical/protein-isoelectric-point-pi-determination/"
tags: ["EN", "pll_69b01cfc3b921"]
timestamp: "2026-03-12T08:17:03Z"
published: "2026-03-10T13:30:36Z"
language: "en"
author: "Filab"
---

# Isoelectric Point (pI) – laboratory protein analysis

## Isoelectric Point (pI) Determination: characterization of your protein charge

The **Isoelectric Point (pI)** is a fundamental physicochemical parameter in the development of therapeutic proteins ([monoclonal antibodies](https://filab.fr/en/sectors-of-activity/biopharmaceutical/biotherapeutic-recombinant-protein-characterization/analysis-characterization-monoclonal-antibodies-mabs.md), enzymes, hormones). It correspond to the pH at which the net charge of the protein is zero.

Mastering the pI is necessary to ensure the stability, solubility, and biological activity of your biomolecules. Any variation in pI can reveal post-translational modifications (deamidation, sialylation, C-terminal lysine clipping) that directly impact the homogeneity and safety of your product.

**FILAB** laboratory supports you in the precise measurement of pI and the study of charge heterogeneity, in compliance with [ICH Q6B](https://filab.fr/en/sectors-of-activity/biopharmaceutical/protein-characterization-ich-q6b-laboratory.md) guidelines.

### Our isoelectric point analysis services

  Services
## Isoelectric Point

 FILAB offers tailored analytical solutions to characterize the charge profile of your proteins:
**Experimental pI measurement**: Precise determination of the isoelectric point value for the protein of interest.

**Charge heterogeneity profiling**: Identification and quantification of acidic and basic variants (charge variants).

**Stability and degradation studies**: Monitoring pI evolution under stress conditions (temperature, pH, light).

**Comparability studies**: Assessment of biosimilarity between a reference product and a biosimilar candidate.

## Our technical resources

 [### UPLC/HPLC](https://filab.fr/en/high-performance-liquid-chromatography-hplc-analysis-testing-services-2.md) [### LC-MS/MS](https://filab.fr/en/our-technical-resources/laboratory-analysis-uplc/laboratory-analysis-hplc-lcms.md) [### Fluorometer](https://filab.fr/en/our-technical-resources/laboratory-fluorometer-analysis.md) [### Nanopore](https://filab.fr/en/our-technical-resources/nanopore-sequencing.md)
### Our other biopharmaceutical analysis services

[Intact mass analysis](https://filab.fr/en/sectors-of-activity/biopharmaceutical/intact-mass-analysis-laboratory.md)

[Peptide mapping](https://filab.fr/en/sectors-of-activity/biopharmaceutical/biotherapeutic-recombinant-protein-characterization/peptide-analysis-biopharmaceutical-services.md)

Identification and quantification of PTMs

Elemental impurities ([ICH Q3D](https://filab.fr/en/our-services/our-analysis-services/analysis-ich-q3d-context.md) and [USP 233](https://filab.fr/en/our-services/our-analysis-services/analysis-usp-233-laboratory.md))

Analysis according to ICH Q6B guideline

Analysis and localisation of [disulfide bridge](https://filab.fr/en/sectors-of-activity/biopharmaceutical/disulfide-bridge-analysis.md)[s](https://filab.fr/en/sectors-of-activity/biopharmaceutical/disulfide-bridge-analysis.md)

[Analysis of HCP (Host Cell Protein)](https://filab.fr/en/sectors-of-activity/biopharmaceutical/host-cell-protein-hcp-testing-analysis-laboratory.md)

Protein analysis using the following methods: [BCA method](https://filab.fr/en/sectors-of-activity/biopharmaceutical/protein-analysis-bca-method.md), [Lowry method](https://filab.fr/en/sectors-of-activity/biopharmaceutical/protein-analysis-lowry-method.md), [CBQCA method](https://filab.fr/en/sectors-of-activity/biopharmaceutical/protein-analysis-cbqca-method.md), [Bradford method](https://filab.fr/en/sectors-of-activity/biopharmaceutical/protein-analysis-bradford-method.md)

### Why choose FILAB ?

- **Multidisciplinary expertise**: a team of PhDs and engineers specializing in analytical chemistry and biochemistry.
- **Dual chemistry / materials expertise**
- **ISO 17025 accreditation** by COFRAC.
- **5,200 m²** state-of-the-art analytical facility
- **GMP environment**