Ammonium, as one of the most important nutrients, occupies a central role in nitrogen biogeochemical cycles. Accurate and sensitive determination of ammonium is of great interest and challenging for both environmental scientists and oceanographers. The indophenol blue (IPB) method based on Berthelot's reaction is still the most widely used method, and routine analysis based on IPB method is the most popular technique for the automated ammonium measurement. However, the existing analytical methods have the shortages of high toxicity, interference with salinity, high reagent consumption and difficulties in application in-field. Herein, a new analytical method and a relative compact, robust and portable instrument for ammonium determination have been developed. The main contents and results are as follows: (1) A salinity-interference-free indophenol method for the determination of ammonium in natural waters using o-phenylphenol was developed. The normally used toxic and odorous phenol was replaced by the less toxic, stable flaky crystalline compound, o-phenylphenol. The reaction can be finished within 20 min at room temperature and the formed color compound is stable for 24 h. Under the optimized conditions, the method was salinity-interference-free, it shows high reproducibility (relative standard deviations of 0.64–1.71%, n=11), highly linear calibration up to 100 μM and a low detection limit of 0.2 μM. This method was successfully applied to measure ammonium in Min river, Jiulongjiang estuary and Xiamen coastal area. This work has been published on “Ma et al., Talanta, 2018, 179, 608-614”. (2) An integrated syringe-pump-based environmental-water analyzer (iSEA) and its application for spectrophotometric determination of ammonium is presented. The iSEA consisted a mini-syringe pump equipped with a selection valve. The principle of chemistry method was based on method (1). This fully automated analyzer had a detection limit of 0.12 μM with sample throughput of 12 h-1. Relative standard deviations at different concentrations (0-20 μM) were 0.23-3.36% (n=3-11) and 1.0% (n=144, in 24-h continuous measurement, ~5 μM). Calibration curves were linear (R2=0.9998) over the range of 0-20 μM and 0-70 μM for detection at 700 nm and 600 nm, respectively. The iSEA was applied in continuous real-time monitoring of ammonium variations in a river for 14 days and a shipboard underway analysis in Jiulongjiang estuary and Xiamen coastal area. This work has been published on “Ma et al., Analytical Chemistry, 2018, 90, 6431-6435”.