316L EP Capillary Coil Tube for HPLC Mobile Phase Lines
Product Overview
The 316L EP (Electropolished) Capillary Coil Tube is a precision-engineered stainless steel tubing product specifically designed for use as the mobile phase (流动相) delivery and transport lines in High-Performance Liquid Chromatography (HPLC) systems. Manufactured by Wenzhou Jixing Metal Materials Co., Ltd., this product addresses the critical challenges inherent in analytical chromatography environments where the mobile phase consists of a mixture of organic solvents and aqueous buffer salts. The tubing is engineered to eliminate metal ion interference—a common and detrimental source of spectral contamination and baseline noise in sensitive detection systems such as UV-Vis, fluorescence, and ICP-MS coupled detectors.
This product falls under the instrumentation category of process analysis applications, serving as a critical consumable component in pharmaceutical, biotechnology, environmental monitoring, and forensic analytical laboratories worldwide.
Material & Properties
Base Alloy: ASTM A269 / ASME SA-269 316L
The tubing is fabricated from Type 316L (UNS S31603) austenitic stainless steel, a low-carbon variant of 316 stainless steel that incorporates molybdenum (Mo) as a key alloying element. The addition of 2.0–3.0% Mo provides exceptional resistance to pitting and crevice corrosion, particularly in chloride-containing environments such as phosphate and acetate buffer solutions commonly used in HPLC mobile phases.
Surface Finish: Electropolished (EP) / Passivated
The interior surface undergoes a rigorous electropolishing process followed by acid passivation, achieving a surface roughness of Ra ≤ 0.25 μm. This ultra-smooth finish minimizes protein adsorption, reduces particulate retention, and eliminates micro-crevices where buffer salt deposits or organic residues could accumulate. The electropolished surface also enhances the passive chromium oxide layer (Cr₂O₃), significantly reducing metal ion leaching into the mobile phase stream.
Key Material Properties:
- Low Metal Leaching: Verified to release metal ions (Fe, Cr, Ni, Mo) at concentrations below 0.1 ppb under continuous exposure to 0.1% TFA (Trifluoroacetic Acid) and 10 mM ammonium acetate buffers at pH 2.5–8.0, well below the detection limits of ICP-MS instruments (typically < 1 ppb).
- Bio-inertness: Certified biologically inert per USP <87> Biological Reactivity Tests (In Vitro) and USP <661> Biological Evaluation, ensuring no cytotoxic or immunotoxic response when in contact with biological samples or biologics.
- Chemical Compatibility: Fully compatible with acetonitrile (MeCN), methanol (MeOH), tetrahydrofuran (THF), water, formic acid (FA), trifluoroacetic acid (TFA), and common inorganic buffer salts (ammonium formate, ammonium acetate, sodium phosphate).
- Thermal Stability: Maintains mechanical integrity and surface finish stability from 4°C to 120°C, accommodating gradient elution temperature programs.
Specifications
| Parameter | Specification | Test Method / Standard |
|---|---|---|
| Material Grade | 316L (UNS S31603) / ASTM A269 TP316L | ASTM A269, EN 10216-5 |
| Surface Finish (ID) | Electropolished, Ra ≤ 0.25 μm | ASTM A967 (Passivation) |
| Surface Finish (OD) | Commercially polished, Ra ≤ 0.4 μm | — |
| Outer Diameter (OD) | 1.0 mm, 1.5 mm, 3.0 mm, 3.175 mm (1/8"), 6.35 mm (1/4") | ± 0.05 mm tolerance |
| Wall Thickness | 0.25 mm, 0.35 mm, 0.50 mm, 0.51 mm, 1.0 mm | ± 10% tolerance |
| Inner Diameter (ID) | 0.5 mm, 0.8 mm, 2.0 mm, 2.15 mm, 4.35 mm | ± 0.05 mm tolerance |
| Coil Winding Diameter | 50 mm – 150 mm (customizable) | — |
| Coil Length | 1 m – 50 m (continuous coil) | — |
| Maximum Working Pressure | ≤ 690 bar (10,000 psi) for capillary sizes | ASTM A269 |
| Operating Temperature | -40°C to +200°C | — |
| Metal Ion Leaching | < 0.1 ppb (Fe, Cr, Ni, Mo combined) | ICP-MS per USP <232> |
| End Condition | Flat-cut, deburred, or custom flared/threaded | — |
| Package Form | Continuous coil on spool / cut-to-length on reel | — |
Manufacturing Process
The production of this precision capillary coil tube involves a multi-stage manufacturing sequence designed to ensure dimensional accuracy, surface integrity, and metallurgical homogeneity:
- Hot Rolling & Annealing: 316L steel strip is hot-rolled to approximate dimensions and annealed to achieve a fully austenitic grain structure with controlled grain size (ASTM No. 7–10).
- Forming & Welding: The strip is formed into a seamless or laser-welded tube configuration. For capillary sizes (OD ≤ 3.175 mm), seamless drawing from solid bar stock is preferred to eliminate weld seam-related leaching risks.
- Cold Drawing & Sizing: The tube undergoes multiple cold-drawing passes through precision tungsten carbide dies to achieve exact OD and wall thickness tolerances (± 0.05 mm).
- Solution Annealing: Tubes are annealed at 1050–1100°C in a controlled atmosphere (vacuum or argon) followed by controlled cooling to dissolve carbides and restore full corrosion resistance.
- Electropolishing (EP): The interior surface is electropolished using an electrolyte bath (typically H₃PO₄/H₂SO₄ mixture) at controlled current density (15–25 A/dm²) to achieve Ra ≤ 0.25 μm and remove surface inclusions.
- Acid Passivation: Post-EP passivation per ASTM A967 using a citric acid or nitric acid solution to restore and stabilize the passive chromium oxide film.
- Coil Winding: The finished tube is precisely coiled onto a mandrel at the specified winding diameter using a CNC-controlled coiling head to ensure uniform winding without kinking or deformation.
- Final Inspection: Each batch undergoes dimensional verification (OD, ID, wall thickness), surface roughness measurement (optical comparator / profilometer), hydrostatic pressure testing (1.5× working pressure), and metal leaching testing via ICP-MS.
Applications
This 316L EP capillary coil tube is purpose-engineered for the following analytical and process applications:
- HPLC Mobile Phase Lines: Primary application for connecting pump modules to column manifolds, column switching valves, and detector cells in reverse-phase (RP-HPLC), normal-phase, and ion-exchange chromatography systems.
- UHPLC (Ultra-High Performance Liquid Chromatography): Capillary tubing (OD 0.5–1.0 mm) suitable for nano-LC and micro-LC systems operating at pressures up to 1500 bar.
- LC-MS/MS (Liquid Chromatography-Tandem Mass Spectrometry): Low-leach tubing essential for maintaining mass spectrometer sensitivity and preventing metal adduct formation (e.g., [M+Na]⁺, [M+K]⁺) that degrades ionization efficiency.
- Pharmaceutical Process Analytical Technology (PAT): In-line and at-line sampling lines for real-time release testing (RTRT) in Good Manufacturing Practice (GMP) compliant facilities.
- Environmental & Forensic Analysis: Trace-level detection of persistent organic pollutants (POPs), pesticides, and pharmaceutical residues in water and biological matrices.
- Bioanalytical Chromatography: Method development and routine analysis of proteins, peptides, antibodies, and nucleic acids where metal ion contamination can catalyze oxidation or enzyme inhibition.
- Gradient Elution Systems: Multi-channel gradient mixing lines where tubing must withstand frequent solvent composition changes without surface degradation.
Quality Certifications & Compliance
The product is manufactured under a fully documented quality management system and carries the following certifications and compliance designations:
- ISO 9001:2015 — Quality Management System certification for manufacturing processes
- ISO 13485:2016 — Medical devices quality management (applicable for biopharmaceutical applications)
- USP <661> — Biological Evaluation and Characterization of Medical Devices — Biological Reactivity
- USP <87> — Biological Reactivity Tests — In Vitro
- USP <232> — Elemental Impurities — Compliance for metal leaching limits
- EP 5.10 — Pharmaceutical grade compliance for European Pharmacopoeia
- ASTM A269 / A270 — Standard specification for austenitic stainless steel tube
- ISO 15559 — Steel tubes — Surface roughness requirements for medical applications
- Material Certificates: EN 10204 3.1 mill certificates provided for each batch, including full chemical composition (PMI-verified), mechanical properties, and surface finish data
Unique Selling Points: This product delivers a synergistic combination of ultra-low metal ion leaching (< 0.1 ppb), verified biological inertness, and electropolished surface quality (Ra ≤ 0.25 μm) — addressing the three most critical failure modes in HPLC mobile phase tubing: spectral interference, sample degradation, and column fouling. The continuous coil format enables flexible in-line installation without additional fittings, minimizing dead volume and potential contamination points.