Standard Operating Procedure for Analysis of Particulate Phase Mercury
June 1, 1994
Version 2.0
Standard Operating Procedure for Analysis of Particulate Phase Mercury
1.0 Introduction/Overview
The objective of the Lake Michigan Loading Study is to assess the contribution of atmospheric
deposition to the concentration of mercury and other toxic trace species found in Lake Michigan.
The atmosphere has been implicated as one of the dominant sources of mercury and trace elements
to bodies of water and it is clear from investigations in remote regions of the globe that long range
transport of mercury and other toxics from source regions is occurring. By quantifying the wet
deposition and ambient concentrations of mercury it will be possible to determine the relative
importance of precipitation and dry deposition in accounting for the atmospheric loading of
mercury to Lake Michigan. In addition, investigating other ambient trace species will aid in the
identification of significant mercury sources.
Particle-phase mercury, Hg(p), generally represents a small but significant fraction of total
atmospheric mercury. Recent advances in analytical chemistry have made quantification of the
extremely low levels of Hg(p) possible, however, tremendous care must be exercised in all phases
of sample handling and analysis. This protocol describes analysis of ‘acid-extractable’ total
mercury from atmospheric particulate samples.
2.0 Sample Analysis
2.1 Summary
The technique described by this protocol is designed for use with glass-fiber or quartz fiber filter
media. When used in conjunction with an open-faced filter pack, these media demonstrate a low
pressure drop and have a very low background level of Hg with proper pretreatment. Sample
filters are stored at -40EC before analysis to prevent volatilization of the collected Hg(p).
Particulate mercury is extracted into a 1.6 M nitric acid solution utilizing a microwave digestion
technique. The mercury forms are then oxidized with bromine monochloride, to Hg2+. Oxidized
mercury forms are subsequently reduced to Hg0 with stannous chloride (SnCl2). In this volatile
form, the metal is purged from solution using an Hg-free nitrogen stream and collected on a goldcoated
bead trap. A mercury-free pretreated soda lime trap is utilized in the purge system to
capture acid gases that may damage the gold-coated bead trap. Quantification is accomplished
using a dual amalgamation technique followed by cold vapor atomic fluorescence spectroscopy
(CVAFS).
All analytical procedures for determination of particulate phase mercury are carried out in a class
100 laminar flow exhaust hood inside a Class 100 Clean Room. Nitrogen utilized for purging is
99.998% pure and is stripped of any mercury using a gold coated trap before use in the purge
system. Clean room gloves are worn at all times and all labware with which the samples and
reagents comes into contact is cleaned weekly using the acid cleaning procedure described in
Standard Operating Procedure for Sampling of Particulate Phase Mercury, Section 2.1.
SOP for Analysis of Particulate Phase Mercury Volume 2, Chapter 2
2-434
2.2 Reagents and Materials
All reagent lot numbers, preparation dates and procedures are recorded for each new batch of
reagent used. A reagent blank is obtained after each new batch of reagent has been prepared.
Bromine monochloride (BrCl), stannous chloride (SnCl2) and hydroxylamine hydrochloride
(NH2OHCHCl) are prepared fresh monthly.
Solid reagents (potassium bromide, potassium bromate, hydroxylamine hydrochloride and stannous
chloride) are stored in the clean room in a desiccator containing silica gel and an open bed of
activated charcoal. The caps of all reagent bottles are Teflon taped to reduce entry of vapor phase
compounds. Even with these precautions, reagents will nevertheless absorb mercury over time and
must be replaced. All reagents are made in the clean room, except the working standard solution.
2.2.1 Hydrochloric Acid
EM Science Suprapur hydrochloric acid is used to prepare BrCl and SnCl2. This acid
characteristically has a very low blank value (20 pg/mL).
2.2.2 Bromine Monochloride
Bromine monochloride is prepared in a class 100 laminar flow exhaust hood by adding
11.0 mg KBr per mL of HCl while the solution is stirred using an acid-cleaned Tefloncoated
magnestir. When the KBr is dissolved, 15.0 mg KBrO3 per mL of HCl is added
slowly and the solution is allowed to continue stirring. This process produces chlorine and
bromine gas and must be performed slowly in a functioning exhaust hood. After addition
of the salts the solution is a deep yellow color. If there is no color (or very faint) then the
BrCl has been substantially reduced and will not have enough oxidizing power for use. In
this case, the solution is remade. Bromine monochloride is stored at room temperature in
the clean room. Fresh bromine monochloride is be prepared monthly or as needed.
2.2.3 Hydroxylamine Hydrochloride
30 grams of NH2OHCHCl is dissolved in MQ-water to make 100 mL in an acid-cleaned
100 mL volumetric flask. This solution is purified by adding 0.5 mL of SnCl2 and purging
overnight with Hg-free N2. The solution is stored in an acid-cleaned, dark Teflon bottle in
the refrigerator. Fresh hydroxylamine solution is prepared every month or as needed.
2.2.4 Stannous Chloride
20.0 gm of SnCl2CH2O is placed into an acid-cleaned 100 mL volumetric flask. Working
in a fume hood, 10 mL of concentrated HCl is added and the solution is then brought to
100 mL with Milli-Q water. The solution is stored in an acid-cleaned, dark Teflon bottle
in the refrigerator. Fresh stannous chloride is prepared every month or as needed.
Volume 2, Chapter 2 SOP for Analysis of Particulate Phase Mercury
2-435
2.2.5 Milli-Q Water
Deionized water, with a resistivity of 18.2 MÙ/cm, is prepared using a Milli-Q system
from a pre-purified (reverse osmosis) water source. Milli-Q water is used for reagent
preparation.
2.2.6 Soda Lime Traps
High purity grade soda lime (EM Science) is utilized in an acid-cleaned glass tube with
glass wool endplugs and Teflon connectors. After packing, this trap is conditioned by
purging a 0.5 M HCl solution through the trap for 30 minutes. The soda lime trap is
changed after analysis of 30 samples.
2.2.7 Preparation of Working Standard Solution
100 µL of the stock Hg solution (1 mg/mL in nitric acid) is pipetted into a 1 L volumetric
flask. 5 mL of concentrated BrCl is added and the flask is brought up to volume with
MQ-water and thoroughly mixed. This is the Secondary Standard solution (100 ng
Hg/mL). Replace this solution as needed (it is stable for at least one year).
The Working Standard (2 ng Hg/mL) is prepared from the Secondary Standard solution by
placing 2 mL of Secondary Standard into a 100 mL volumetric flask, adding 1 mL of BrCl
and bringing the solution to volume with MQ. The Working Standard is replaced monthly.
2.2.8 Nitric Acid Extraction Solution.
The extraction solution is a 10% dilution of concentrated nitric acid (1.6M). A 1000 mL
volumetric flask is filled with about
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