Environmental Express HotBlock CURRENT - Manual (Page 22)

800.745.8218 / 843.576.1147 / www.environmentalexpress.com Environmental Express • 20
HotBlock™: Operation and Instruction Manual EPA Method 200.8
4.3 Reduce the volume of the sample aliquot to about 10mL at this
temperature. This should take about 2.5 hours.
4.4 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.
4.5 Gently reflux the sample for 30 minutes.
4.6 Using the polycarbonate transfer racks, remove samples from the
HotBlock™ and allow them to cool.
4.7 Add reagent water to bring the sample to the 50mL mark on the
digestion vessel. Cap and mix.
4.8 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.
4.9 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.
5.0 Procedure, Solid Sample Preparation
5.1 For each digestion procedure, transfer 0.5g ± 0.01g of a dried sieved
sample into the SC475 polypropylene vessel.
5.2 Add 2.0mL (1:1) HNO
3
and 5mL (1:4) HCl and swirl. Cover the vessel with
a disposable watch glass (catalog # SC505) and reflux an additional 30
minutes at a sample temperature of 85°C.
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.
5.3 Allow to cool and bring to 50mL volume with DI water.
5.4 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™.