Distillation; Vigorous Digestion Volumes; General Digesdahl Digestion (Not Usepa Accepted) - Hach DR2400 Manual

2.3.3 General Digesdahl Digestion (Not USEPA accepted)

2.4 Distillation

5940022LabPrac.fm
7. Warm the beaker. Add 5 mL of 5.0 N sodium hydroxide and quantitatively
transfer the sample with deionized water to a volumetric flask. See Table 3
below for the suggested final volume.
8. Adjust the sample to pH 4 by drop-wise addition of 5.0 N Sodium Hydroxide
Standard Solution; mix thoroughly and check the pH after each addition.
Dilute to volume with deionized water. Multiply the result by the correction
factor in Table 3. A reagent blank also should be carried through the digestion
and measurement procedures.
Table 3 Vigorous Digestion Volumes
Suggested
Expected Metal
Sample Vol.
Concentration
for Digestion
1 mg/L 50 mL
10 mg/L 5 mL
100 mg/L 1 mL
Many samples may be digested using the Digesdahl Digestion Apparatus
(Cat. No. 23130). It is designed to digest many types of samples such as oils,
wastewater, sludges, feeds, grains, plating baths, food, and soils. In this
procedure the sample is oxidized by a mixture of sulfuric acid and hydrogen
peroxide. Digestion of a dry sample requires less than ten minutes, while
liquid samples require about 1 minute/mL. The digestion is done in a special
flat-bottomed 100-mL volumetric flask. Aliquots (sample portions) are taken for
analysis using colorimetric methods.
Procedures for digestion and using the Digesdahl Digestion Apparatus are
based on the type and form of the sample, and are found in the Digesdahl
Digestion Apparatus Instruction Manual, which is included with each Digesdahl
Digestion Apparatus.
Distillation is an effective, easy, and safe method of separating some chemical
components for analysis. Hach Company offers the following equipment for
distillation: the General Purpose Distillation Apparatus (Cat. No. 22653-00),
shown in Figure 2; the Arsenic Distillation Apparatus Set (Cat. No. 22654-00); the
Cyanide Distillation Apparatus Set (Cat. No. 22658-00); and the General Purpose
Heater and Support Apparatus, which comes in a 115 VAC, 60 Hz model
(Cat. No. 22744-00) and a 230 VAC, 50 Hz model (Cat. No. 22744-02).
The Hach Distillation Apparatus is suitable for water and wastewater that
requires sample pretreatment by distillation. Applications for the General
Purpose Apparatus include: fluoride, albuminoid nitrogen, ammonia nitrogen,
phenols, selenium, and volatile acids. The General Purpose Heater and Support
Apparatus provides efficient heating and anchoring of the glassware.
Laboratory Practices
Suggested Suggested Final
Volume of 1:1 Volume After
HCl Digestion
10 mL 200 mL
10 mL 200 mL
25 mL 500 mL
Correction
Factor
4
40
500
Laboratory Practices
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