Specification decides price, not the product name

Two vials carrying the same analyte name can differ in price by a factor of ten. The difference is never the name — it is the specification behind it. This page sets out what each variable actually buys you, so you can specify deliberately instead of buying the cheapest vial that carries the right word on the label.

1. Purity grade

Grade	Where it is used	What you are paying for
≥80%	Screening, method scouting, non-quantitative work	Lowest cost; impurities may interfere with sensitive detection
≥90%	General immunoassay development	Reduced background from host-cell proteins and aggregates
≥95%	Calibrators, controls, antibody pairing	The usual working grade for quantitative assay development
≥98%	Reference material, structural and binding studies	Highest characterisation cost; tightest lot-to-lot control

A note on methods: SDS-PAGE (reducing) reports subunit purity by molecular size, while SEC-HPLC reports how much of the protein is monomeric in solution. A preparation can read 97% by SDS-PAGE and 91% by SEC-HPLC — they measure different things. Always ask which method a quoted purity figure came from.

2. Endotoxin level

Endotoxin level	Suitable for	Why the price differs
< 1.0 EU/µg	Standard immunoassay and biochemical work	Routine quality-control level
< 0.1 EU/µg	Cell-based assays, primary cells, stimulation and signalling studies	Requires stricter process control and additional testing per lot

3. Tag format

Format	Strengths	Trade-offs
Carrier-free / untagged	Closest to the native analyte; no tag interference in calibrators or binding studies	Harder to express and purify, therefore the most expensive format
His-tag	Simple purification; convenient for detection and immobilisation	Tag can affect folding or block an epitope; not ideal where the natural analyte is expected
hFc-tag	Dimerisation improves avidity; easy detection with anti-human-Fc reagents	Large tag alters molecular weight and can complicate calibrator preparation

4. Expression system

Expression system	Glycosylation	Typical fit
E. coli	None	Small, non-glycosylated proteins and peptides — fastest and least expensive
HEK293 (mammalian)	Human-like	Glycosylated receptors and biomarkers where correct folding drives activity
CHO (mammalian)	Human-like	Scale-up and formats intended for longer development programmes
Baculovirus / insect	Partial	Selected targets where insect glycosylation is acceptable

5. Source: recombinant versus plasma-derived

Source	Example	Cost profile
Recombinant protein	sST2, cTnI, NT-proBNP, CRP, IL-6	Per-milligram cost is high because expression and purification are costly, but lot control is strong
Purified from human plasma	D-dimer antigen	Material is comparatively inexpensive because it is isolated rather than manufactured — expect an order-of-magnitude lower price and different handling

How we quote

Because these variables move the cost by a wide margin, we quote per order rather than publishing a single list price. Tell us the downstream application — antibody pairing, calibrator, cell stimulation, structural work — and we will recommend the grade that fits. If your protocol already specifies a purity and endotoxin level, send that and we will quote against it.

For research use and in-vitro diagnostic development only. Not for human or animal therapeutic use.

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