Four anions cover most of the world’s detergent formulations: SDBS (sodium linear alkylbenzene sulfonate), LABSA (the acid form), AOS (sodium alpha-olefin sulfonate) and SLES (sodium laureth sulfate). They are often quoted side by side as if they were interchangeable, but they differ in form, in cost structure, in hard-water tolerance and in what they do to the rest of the formula.
This guide is a decision framework rather than a price list: what each surfactant is, how to compare them on cost per unit of active matter, where each one wins, and how to switch a formula from one to another without wrecking its stability.
The four surfactants at a glance
| Surfactant | CAS | Typical supply form | Active matter | Charge |
|---|---|---|---|---|
| SDBS (LAS-Na) | 25155-30-0 | Powder / granules | 80 +/- 2% | Anionic sulfonate |
| LABSA (LAS acid) | 27176-87-0 / 68584-22-5 | Viscous liquid | approx. 96% | Anionic sulfonic acid |
| AOS | 68439-57-6 | Powder (92%) or liquid (34-36%) | 92% or 34-36% | Anionic sulfonate |
| SLES | 9004-82-4 | Liquid paste / solution | approx. 70% | Anionic sulfate (ethoxylated) |
Cost per unit of active matter, not per tonne
The first mistake in surfactant sourcing is comparing invoice prices. A tonne of 80% SDBS delivers 800 kg of active matter; a tonne of LABSA delivers about 960 kg, but requires caustic, heat, equipment and a drying step before it becomes a usable surfactant. The comparison that survives a cost review is:
- Cost per kg of active matter at the delivery point.
- Plus process cost – neutralisation capital, energy, labour, waste.
- Plus freight volume – a low bulk density powder ships air; a 70% paste ships water.
- Plus reformulation cost if performance differs and the formula must change.
Hard water: the decisive performance difference
Linear alkylbenzene sulfonate is calcium-sensitive. In soft water it is an excellent detergent at the lowest cost; in hard water it precipitates unless a builder keeps calcium in solution. AOS tolerates hard water substantially better, which is why it appears in markets with high water hardness and in formulations that cannot carry a full builder load. SLES sits in between, with better hard-water tolerance than LAS and lower cost than AOS in liquid formats.
| Water hardness | Practical implication |
|---|---|
| Soft (under 60 mg/L as CaCO3) | LAS/SDBS is the value choice; builder demand is low |
| Medium (60-180 mg/L) | SDBS plus a proper builder (zeolite, carbonate, citrate) works well |
| Hard (above 180 mg/L) | Increase builder or shift part of the anionic load to AOS |
Form: powder, paste or liquid
| Product form | Best surfactant choice | Reason |
|---|---|---|
| Laundry powder | SDBS (dry-blended) | Already neutralised and free-flowing; no drying equipment needed |
| Liquid detergent | LABSA neutralised in situ, or SLES | Liquid handling; SLES also gives mildness and viscosity response |
| Hand dishwash | SLES with LABSA or AOS | Foam quality and skin mildness dominate |
| Shampoo / personal care | SLES, AOS | Mildness, foam, low irritation |
| Industrial alkaline cleaner | SDBS | Sulfonate stable at high pH; powder easy to dose |
| Hard-water / EOR applications | AOS | Electrolyte and hardness tolerance |
Mildness and personal care
If the product touches skin regularly, the ranking changes completely. Sulfates such as SLES are milder than sulfonates in typical formulations, and ethoxylation further reduces irritation; LAS is the harshest of the four on skin, which is why it dominates laundry and industrial cleaning but is rarely used in personal care. AOS occupies a middle position with good mildness and excellent hard-water performance.
Electrolyte and stability considerations
| Property | SDBS | LABSA (neutralised in situ) | AOS | SLES |
|---|---|---|---|---|
| Stability at pH above 11 | Excellent | Excellent once neutralised | Good | Hydrolysis risk at extreme pH |
| Stability at low pH | Good (sulfonate) | Not applicable | Good | Hydrolyses to lauryl alcohol and sulfate |
| Salt thickening | Limited | Limited | Moderate | Excellent – the standard viscosity lever |
| Foam | High, dense | High, dense | High, finer | High, creamy |
| Hard water | Moderate | Moderate | Good | Good |
How to switch a formulation
- Match on active matter, not weight. Replacing 10 kg of 96% LABSA needs about 12 kg of 80% SDBS to deliver the same active, plus a caustic credit if you were neutralising.
- Re-check the builder load if you move between LAS and AOS, because the hardness tolerance changes.
- Re-check viscosity in liquid systems, where the surfactant’s salt response is the main thickening mechanism.
- Re-check foam if the application has a foam specification – machine wash, CIP, or high-pressure spray.
- Re-run stability at 40 deg C for four weeks; surfactant swaps often show up first as separation or pH drift.
Frequently asked questions
Which is cheaper, SDBS or LABSA? LABSA per unit of active matter, if you already own neutralisation and drying equipment. If you do not, SDBS is cheaper in total because you are buying the neutralisation as part of the product.
Can AOS replace LAS one for one? On a performance basis in hard water, often yes at slightly lower active; on cost, rarely, because LAS is the cheapest anionic available.
Is SLES a sulfonate? No – it is an ethoxylated sulfate, which is why it hydrolyses at low pH and why it thickens so well with salt.
Why does my powder perform worse in winter? Cold water reduces surfactant solubility and soil removal; increase the nonionic share or add a hydrotrope rather than simply raising anionic loading.
Contact PolyBlueChem for SDBS, AOS and SLES samples with COA.