Methods and related systems are described for high pressure chromatographic analysis. The described system includes a flowpath adapted to flow a mobile phase and the sample at high pressures, an injector adapted to inject the fluid sample into a flowpath, a separation column adapted to operate at high pressures for separating various components, a detector and a processor that calculates the amount of at least one component of the fluid sample. The system can operate a pressures above 20 atm or even 100 atm, and temperatures above about 100 degrees Celsius. The system can deployed in a wellbore in a subterranean rock formation, and include fluid collection system for obtaining the fluid sample downhole. The system can also be located close to a wellhead and includes a tap in fluid communication with a surface flowline carrying produced fluids and the injector.