The main differences are that the Hach method calls for 25 mL samples and use of ionic strength adjuster pillows. Hach ammonia standards are used for calibration. Hach nitrate standards are used for calibration. For samples with significant turbidity, the samples are first filtered through glass-fiber filters before being filtered through the membrane filters. Standard Method 4500-P B Persulfate Digestion Method is used to prepare the samples.
Digestion occurs in an autoclave.
A Hewlett Packard 8452A Diode Array Spectrophotometer is used. Preliminary Acid Hydrolysis is used to prepare samples and digest in an autoclave. The Hewlett Packard 8452A Diode Array Spectrophotometer is used. A Dohrman DC-180 Carbon Analyzer with an automatic sampler is used, so sample injection is not required. The equipment does a one-point calibration.