Environmental Express HotBlock Pro - Manual (Page 25)

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HotBlock™: Operation and Instruction Manual EPA Method 365.2
3. Add 30mL of 3% HNO3 solution.
4. To each tube add 0.5mL of concentrated HNO3 and 2.0 mL of concentrated HCl.
5. Place watch glass or reflux cap on top of digestion vessel and digest at 95°C for 10 minutes.
Note: When using a watch glass, adjust the set point temperature of the HotBlock™ so that a 50mL sample is heated to 85°C BEFORE
placing the watch glass over the sample. Laboratory tests have proven that the addition of the ribbed watch glass will add 10°C to the
sample temperature, bringing the sample temperature up to 95°C. Refer to page 7 of the operations manual for instructions on HotBlock™
temperature adjustment.
6. Add 3mL of 5% KMnO4 and let stand for 15 minutes. If sample does not maintain purple or brown color, add an additional 3mL
of KMnO4 solutions to all samples, blanks and standards. If the sample still does not maintain color, discard set and dilute the
sample prior to digestion. Heat samples at 95°C for 30 minutes.
7. Let samples cool to room temperature and add 3.0mL of 12% NaCl/NH2OH solution.
8. Cap tubes and shake. If color does not dissipate, incrementally add 0.5mL of 12% NaCl/NH2OH solution until color is gone.
All QC samples, concentration limitations, elemental lists and reagent specifications are addressed in depth in EPA Methods 245.1, 7470 and
7471. Safety concerns are also part of the EPA Methods. These steps should only be used as a guide to help improve the performance of your
HotBlock™.
Adaptation of EPA Method 365.2, Phosphorus ALL FORMS
Colorimetric, Ascorbic Acid, Single Reagent
for use with the Environmental Express HotBlock™ Digestion System
Revised 05.05
Scope and Application:
The following procedures have been written as an aid to EPA Method 365.2 for use with the Environmental Express HotBlock™. EPA
Method 365.2 is for the determination of phosphorous in drinking water, surface water and saline water and in domestic and industrial
wastes. Use EPA Method 365.2 for reference while following the sample preparation steps outlined below. Range is 0.01 to 0.5 mg/L.
Apparatus and Materials:
1. HotBlock™ for metals digestions — Model Numbers SC100, SC150*, or SC154
2. Polypropylene Digestion Vessels — Part Number SC475 (or SC490 for use with HotBlock™ SC150)
3. FilterMateTM — Part Number SC0401 (or appropriate FilterMate™) for sample filtration if necessary
* Note: For all procedures, when using the SC150 block with the SC490 digestion vials with a 100mL sample, double the volume of
all reagents and acids added.
Procedure, Aqueous Sample Preparation:
1. For each digestion procedure, transfer 50mL of sample (or appropriate volume for your lab) into the SC475
polypropylene vessel.
2. Add 1mL of H2SO4 solution and swirl. (11 N H2SO4— Slowly add 310mL concentrated H2SO4 to 600mL distilled water. When
cooled dilute to 1 liter.)
3. Add 0.4g of ammonium persulfate.
4. Heat the sample in the HotBlock™ at approximately 100°C for 40 minutes. The sample should slightly boil.
Note: Adjust the HotBlock™ temperature so that the sample obtains a temperature of 100°C. Please refer to page 7 of the HotBlock™
Operation Manual for temperature adjustment and principles of operation.