Environmental Express HotBlock Pro - Manual (Page 23)

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HotBlock™: Operation and Instruction Manual EPA Method 200.8
Procedure, Aqueous Sample Preparation — Dissolved Analytes (EPA Method 200.8, Paragraph 11.1):
1. For the determination of dissolved analytes in ground and surface waters, pipet a 20mL or greater aliquot of filtered,
acid-preserved sample into the SC475 digestion vessel.
2. Add an appropriate volume of (1+1) HNO3 to adjust the acid concentration of the aliquot to approximate a 1% (v/v) nitric acid
solution. If the direct addition procedure is being used, add internal standards, cap and mix.
Note: If a precipitate is formed during acidification, transport or storage the sample aliquot must be treated using procedures for
Total Recoverable Analytes.
Procedure, Aqueous Sample Preparation—Total Recoverable Analytes
(EPA Method 200.8, Paragraph 11.2):
Note: This section applies to water samples containing turbidity of greater than 1 NTU.
1. For each digestion procedure, transfer 50mL of well-mixed, unfiltered, acid-preserved sample into the SC475 polypropylene vessel.
2. Add 1.0mL (1+1) HNO3 and 0.5mL of (1+1) HCl and swirl. Heat in the HotBlock™ at a sample temperature of 95°C. The HotBlock™
set temperature should be approximately 115°C. The temperature of a reference blank should be tested to ensure
correct temperature.
3. Reduce the volume of the sample aliquot to about 20mL at this temperature. This should take about 2.5 hours.
4. Place a ribbed watch glass (SC505) over the digestion vessel to reduce additional evaporation.
Note: When using a watch glass, adjust the set point temperature of the HotBlock™ so that a 50mL, 5% acid solution 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 approximately 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.
5. Gently reflux the sample for 30 minutes.
6. Using the polycarbonate transfer racks, remove samples from the HotBlock™ and allow them to cool.
7. Add reagent water to bring the sample to the 50mL mark on the digestion vessel. Cap and mix.
8. If necessary, filter with SC0401 (or appropriate FilterMate™) to remove insoluble material.
Note: The filtration step should be performed slowly with little pressure placed on the plunger. If excessive back pressure occurs,
stop filtration and allow sediments to “settle out.” Applying pressure to the plunger may cause sample “blow through” allowing
sediment to pass through the filter into the digestate.
9. Prior to analysis, adjust the chloride concentration by pipetting 20mL of the prepared solution into another SC475 digestion vessel
and bring up to 50mL volume with reagent water. If the dissolved solids in this solution are >0.2%, additional dilution may be
necessary to prevent clogging of the extraction and/or skimmer cones. Note the dilution factor for concentration calculations. If
the direct addition procedure is being used, add internal standards, cap and mix.
Procedure, Solid Sample Preparation:
1. For each digestion procedure, transfer 0.5 g ± 0.01 g of a dried sieved sample into the SC475 polypropylene vessel.
2. Add 2.0mL (1:1) HNO3 and 5mL (1:4) HCl and swirl. Heat in the HotBlock™ at a sample temperature of 95°C.
3. Heat the sample for 30 minutes. Allow to cool and bring to 50mL volume with DI water.
4. Filter with SC0401 (or appropriate FilterMate™) to remove insoluble material.
All QC samples, concentration limitations, elemental lists and reagent specifications are addressed in depth in EPA Method 200.8. Safety
concerns are also part of the full method. Follow the instructions listed in EPA Method 200.8. These steps should only be used as a guide to
help improve the performance of your HotBlock™.