Monitoring nonylphenol ethoxylates (NPE) in milk and milk powder with rapid tests

Aug 23, 2021
Monitoring nonylphenol ethoxylates (NPE) in milk and milk powder with rapid tests

Brief Information 

Nonylphenols (NP) are a family of closely related organic compounds composed of phenol bearing a 9 carbon-tail. Nonylphenol Ethoxylates (NPE) are nonionic surfactants that are used in a wide variety of industrial applications and consumer products. Many of these, such as laundry detergents, are “down-the-drain” applications. Some others, such as dust-control agents and deicers, lead to direct release to the environment. NPEs, though less toxic and persistent than NP, are also highly toxic to aquatic organisms, and, in the environment, degrade into NP.

NP and NPEs are produced in large volumes, with uses that lead to widespread release to the aquatic environment. NP is persistent in the aquatic environment, moderately bioaccumulative, and extremely toxic to aquatic organisms. NP has also been shown to exhibit estrogenic properties in in-vitro and in-vivo assays. NP’s main use is in the manufacture of NPEs. NP and NPEs have been found in environmental samples taken from freshwater, saltwater, groundwater, sediment, soil and aquatic biota. NP has also been detected in human breast milk, blood, and urine and is associated with reproductive and developmental effects in rodents.
NPEs had been banned in EU, US and China for use in textiles for clothing. 

In the dairy industry, NPEs can be found in teat disinfectants, udder washes, milking machine detergents, and commercial laundry products. They are principally used as surfactants, to help liquid solutions spread or cling to other materials and surfaces.

NPE Determination and Rapid Testing

Conventional Methods

In recent years, various methods have been developed for the determination of NPEs in different samples like water, food, textile, etc. These methods are based on chromatography, which is sensitive, precise and accurate. The table below is a summary.

Method Sample Sample Preparation Detection Limit
HPLC-FD Infant formula Acetonitrile-H2O and C8 column 0.010 μg/g 
GC-MS Milk, breast milk N-hexane, methanol, SPE 0.05 μg/kg
LC-ESI-MS/MS Egg, milk MSPD, SPE 0.10 μg/kg

Rapid Testing Methods

Enzyme-linked immunosorbent assay (ELISA) and Lateral Flow Immunoassay (LFIA) are the two main methods that are used widely in food safety, environmental and clinical analysis. Due to the structural similarity of NPEs, monoclonal antibodies against NPE will have a broad spectrum cross-reactivity of different NPEs, which then enable the established immunoassay to detect different NPEs simultaneously. Ringbio has 2 commercial kits based on immunoassay for detection NPEs in milk and milk powder.

Product Sample preparation Detection performance


for quantitative testing of NPE

2ml sample, 
100μl HCl, 
Detection range: 5 – 200ng/mL
Detection time: 25min at 37oC
LOD: 5 ng/mL

NPE Rapid Test Kit

for qualitative testing of NPE

3ml sample,
200μl ethanol,
mix and test

Detection time: 10min at room temp.
LOD: milk: 150 ng/mL, 
milk powder: 200 – 220 ng/mL