Steroid Hormone Analysis by LC-MS/MS: Sample Prep for Plasma, Serum, and Water

• Steroid hormones circulate in plasma/serum and occur in environmental water at low (pg/mL to low ng/mL) concentrations, so extraction must both purify and concentrate the analyte before LC-MS/MS (Li & Kannan, 2022).

• Common extraction routes are protein precipitation, LLE (often with MTBE, ethyl acetate, or hexane blends), and SPE (C18 or polymeric cartridges) — the right choice depends on matrix complexity and target sensitivity (Yuan et al., 2020; CDC NHANES Steroid Panel Method).

• Evaporation to dryness under a gentle nitrogen stream, followed by reconstitution in a small, LC-compatible volume, is the standard concentration step across clinical and environmental steroid methods (USGS TM 5-B9; RSC Analytical Methods, 2023).

• Temperature control during nitrogen blowdown matters: many validated methods use 25–55 °C water baths to balance evaporation speed against thermal degradation of labile steroids (Yuan et al., 2020; Yuan et al., 2020).

• The U.S. Geological Survey's steroid hormone water method explicitly specifies a 24-position nitrogen evaporator with a thermostatically controlled water bath (N-EVAP, Organomation Associates Inc.) as the apparatus for its dry-down steps (USGS TM 5-B9).

Testosterone, estradiol, cortisol, and progesterone are measured for different reasons depending on sample type, but all three matrices share one bottleneck: analytes sit at low concentrations in a complex background, so sample prep — not the mass spectrometer — usually determines whether a method hits the required limit of quantitation. Clinical steroid panels support endocrinology and reproductive-health testing (Braun et al., 2022), while the same hormone classes are tracked as endocrine-disrupting contaminants in surface water, where reporting levels sit in the low nanogram-per-liter range (USGS TM 5-B9). Both worlds converge on the same operations: extract, clean up, dry down, and reconstitute in a small volume before injection.

The three workhorse approaches are protein precipitation, LLE, and SPE, often used in combination.

Protein precipitation is the fastest option, frequently paired with LLE or phospholipid-removal cartridges. A validated 15-analyte serum steroid method uses methanolic ZnSO4 precipitation combined with HybridSPE phospholipid removal, injecting directly without a nitrogen dry-down stage — trading some sensitivity for speed (Braun et al., 2022).

Liquid-liquid extraction is the most common approach for multi-steroid serum and plasma panels. A 12-steroid serum metabolome method combines acetonitrile protein precipitation with MTBE LLE, evaporates the organic layer under nitrogen at 55 °C, and reconstitutes in 50% methanol after derivatization (Yuan et al., 2020). A related 19-analyte method uses MTBE/ethyl acetate LLE, evaporates under nitrogen at 25 °C, and reconstitutes in 250 µL methanol (Li & Kannan, 2022). Plasma testosterone methods follow the same logic, evaporating an MTBE extract under nitrogen and reconstituting in a small methanol/water volume (Thermo Fisher testosterone plasma technical note).

Sequential LLE appears in the CDC's NHANES reference method for a serum steroid panel, using three liquid-liquid extractions with different solvent polarities before drying the combined organic layers and reconstituting in a water/methanol/ethanol mixture (CDC NHANES Steroid Panel Method).

Water samples require a concentration step first, because target hormones occur at far lower absolute mass per unit volume than in plasma or serum, so larger sample volumes must be processed to reach detectable levels.

The USGS National Water Quality Laboratory method for 20 steroid hormones and related compounds in filtered and unfiltered water isolates analytes by SPE onto a C18 disk overlain with a glass-fiber filter, then elutes with methanol (USGS TM 5-B9). The methanol eluate is evaporated to dryness, reconstituted, passed through a Florisil cleanup column, and evaporated to dryness again before derivatization and GC/MS/MS analysis (USGS TM 5-B9). Similar SPE-based LC-MS/MS methods for endocrine disruptors in surface water use polymeric cartridges to capture analytes from acidified water, then dry the eluate under a gentle nitrogen stream in a heated bath before reconstitution — often with additional dry-down cycles for derivatization (USGS TM 5-B9). This multi-cycle pattern reflects that each cleanup stage requires a solvent exchange, and nitrogen evaporation accomplishes that without the oxidative risk of open-air drying.

Evaporating the extract to dryness and reconstituting in a small volume delivers the sensitivity gain that makes trace steroid quantitation possible — extraction alone only separates analyte from matrix, but dry-down concentrates it. A serum extract diluted in several milliliters of organic solvent would place many steroids, particularly estradiol at sub-ng/mL levels, below the limit of detection if injected directly (Yuan et al., 2020). Drying to residue and reconstituting in a much smaller volume — 100–250 µL is typical for serum methods — concentrates the analyte proportionally and standardizes solvent composition for reproducible chromatography (Li & Kannan, 2022; Li & Kannan, 2022).

A gentle, indirect nitrogen stream over a temperature-controlled water bath is preferred over open-air evaporation for documented reasons: nitrogen displaces oxygen over the sample surface, reducing oxidative degradation during extended low-temperature drying, and a thermostatically controlled bath keeps evaporation steady across many samples at once — which is why the USGS water method specifies a 24-position nitrogen evaporator with a thermostatically controlled water bath, identified in the report as an N-EVAP unit from Organomation. (USGS TM 5-B9). Bringing every sample to the same dry endpoint before reconstitution also avoids variable solvent carryover.

Temperature choice is a real trade-off: faster evaporation at higher bath temperatures shortens turnaround but raises thermal-degradation risk. Several validated methods use 55 °C for organic-layer evaporation but drop to 25 °C for the final dry-down, reflecting analyte-specific stability testing (Yuan et al., 2020; Li & Kannan, 2022). Over-drying past visible dryness can also degrade certain steroids or promote loss through adsorption onto tube walls, so tightly timed, monitored dry-down is a documented best practice (RSC Analytical Methods, 2023).

For labs running plasma, serum, and water methods side by side, a benchtop nitrogen evaporator built for tubes and vials — such as Organomation's N-EVAP — handles the higher-volume LLE and SPE eluates typical of these workflows, while a plate-format evaporators like the MICROVAP suits smaller-volume, higher-throughput serum panels processed in microplates.

Yes. Nearly every validated steroid hormone method — clinical or environmental — includes an evaporation and reconstitution step, because trace-level steroids in dilute organic extracts fall below practical LC-MS/MS sensitivity without it (Yuan et al., 2020; USGS TM 5-B9). Skipping it generally means accepting a higher limit of quantitation — rarely acceptable for endocrinology or environmental monitoring work.

Common causes are over-drying past visible dryness, excessive bath temperature for heat-labile steroids, and adsorption of nonpolar residue onto tube walls during extended evaporation (RSC Analytical Methods, 2023; RSC Analytical Methods, 2023). Monitoring dry-down time and using validated bath temperatures per analyte class minimizes these losses.

What extraction method is best for steroid hormones in plasma?
LLE with MTBE or similar nonpolar solvents is the most widely reported approach for plasma testosterone by LC-MS/MS, followed by nitrogen evaporation and reconstitution in a small methanol/water volume (Thermo Fisher testosterone plasma method).

Why does the USGS steroid hormone water method specify a nitrogen evaporator by name?
The USGS method documents its exact apparatus for reproducibility, specifying a 24-position nitrogen evaporator with a thermostatically controlled water bath, identified as an N-EVAP unit from Organomation. (USGS TM 5-B9).

Can serum steroid panels skip the nitrogen dry-down step?
Some streamlined methods combine protein precipitation with phospholipid-removal cartridges and inject directly, trading sensitivity for speed (Braun et al., 2022). Panels targeting low-abundance steroids like estradiol generally still need a dry-down and reconstitution step (Yuan et al., 2020).

How low are steroid hormone concentrations in environmental water?
Interim reporting levels for the USGS method range from about 0.8 to 8 nanograms per liter across the 20 target compounds (USGS TM 5-B9).

Does temperature matter during nitrogen blowdown of steroid extracts?
Yes. Validated methods use bath temperatures between roughly 25 °C and 55 °C, balancing faster solvent removal against thermal stability of specific steroids (Yuan et al., 2020; Li & Kannan, 2022).

What is the difference between SPE and LLE for steroid hormone sample prep?
SPE suits water samples because it processes large volumes efficiently through a small cartridge or disk, while LLE is more common for plasma and serum, where volumes are smaller (USGS TM 5-B9; Yuan et al., 2020).

Whether you're building a clinical steroid panel or an environmental endocrine-disruptor method, the sample prep bottleneck is almost always the concentration step, not the chromatography. For guidance on matching a nitrogen evaporator to your extract volume and throughput — from tube-based evaporation systems to plate-based evaporation workflows — contact an Organomation application specialist to discuss your specific steroid hormone method.