Total carbon in a sample is measured by converting all carbon to CO₂ and quantifying it using spectroscopic detection, typically infrared spectroscopy.

Overview of Total Carbon Measurement

Total carbon (TC) in a sample includes both organic carbon (TOC) and inorganic carbon (TIC), related by the equation TC = TOC + TIC. Accurate measurement requires homogenizing the sample to ensure representativeness and removing interferences such as inorganic carbon when measuring TOC specifically .

Sample Preparation and Oxidation

1. Homogenization: Solid or liquid samples are mixed or ground to ensure uniformity.
2. Inorganic Carbon Removal (for TOC): Acidification converts carbonates and bicarbonates to CO₂, which is then purged from the sample .
3. Oxidation of Organic Carbon: Organic carbon is oxidized to CO₂ using either combustion at high temperatures (650–1200°C) or wet chemical oxidation with oxidants like persulfate under UV or heat .

Spectroscopic Detection

After oxidation, the CO₂ produced is quantified using a spectrometer, most commonly a non-dispersive infrared (NDIR) detector:

• NDIR Principle: CO₂ absorbs infrared light at specific wavelengths. The spectrometer measures the reduction in IR intensity caused by CO₂ absorption.
• Calibration: The detector signal (peak area) is correlated with known TC standards to determine the carbon concentration in the sample . Other spectroscopic methods for carbon analysis include UV-Vis, Raman, and X-ray photoelectron spectroscopy (XPS), which can provide additional information about carbon bonding and chemical state, though NDIR remains the standard for total carbon quantification .

Measurement Approaches

• Direct Method: Measures TC after removing IC (TOC = NPOC).
• Difference Method: Measures TC and IC separately, then calculates TOC as TOC = TC - IC .

Applications

This method is widely used in environmental monitoring, water quality analysis, soil and sediment studies, and industrial quality control, providing rapid, accurate, and reproducible carbon quantification across diverse sample types . By combining oxidation chemistry with infrared spectroscopic detection, total carbon measurement by spectrometer ensures precise determination of carbon content in both organic and inorganic forms.