| |
.
Metals
analysis:
Methods for
metals analysis of solid samples can be classified in two categories:
| 1. |
Direct
Analytical Method: |
| |
Solid Sample
-->
Mechanical Sample Preparation (Grinding, Sieving, Weighting,
Pressing, Polishing, etc.) -->
Multielement
Analysis by XRF.
Philips
PW2400 X-Ray Fluorescence Spectrometer -
XRF
Used
for multi-element, qualitative, quantitative and/or semiquantitative
determinations from ppm (ca. 0.1%) to high weight percentages
level elements ranging from carbon to uranium in sample
matrices that include liquids (water (high concentrations),
oil, organic liquids), powders (e.g., dry plants, coal,
oxides, sulfides, carbides) and solids (e.g., metals &
alloys, plastics, rocks). Being a non-destructive technique,
X-ray fluorescence spectrometry has become one of the most
efficient instrumental means to detect the elemental composition
of inorganic, ceramic, mineral, and alloy samples.
|
Niton
XRF Spectrum Analyzer (XL723s) -
Portable XRF
This is a field portable XRF analyzer used for the detection
and measurements of the arsenic, barium, copper, lead, zinc,
iron, cadmium, mercury and antimony according to EPA Method
6200 in both bulk (such as soil, sludge, etc.) and thin
(such as films, coatings, etc.) samples. It is able to conduct
in situ soil screening and testing and ex situ
prepared soil-sample analysis without site-specific calibrations.
|
|
| 2. |
Combined
Analytical Methods: |
|
Solid
Sample --> Mechanical Sample Preparation (Grinding,
Drying, Weighing) -->
Decomposition -->
Filtration, Dilution -->
Multielement analysis (AAS, GFAAS, ICP-MS).
In order to analyze metals using combined analytical
method, the solid sample (e.g., soil, sewage sludge, mixed waste,
oil, plastics, metals and alloys, rocks, etc.) should be transferred
into solution prior to testing. Wet digestion is a classical technique
that requires complex mixtures of acids for sample decomposition.
Microwave digestion is a convenient and timesaving closed-vessel
method compared to the traditional approach of open beakers on hot
plates. Samples are digested for metals analysis in sealed TFE-lined
bombs placed in a microwave oven.
CEM MDS-2100 Microwave Digestion
Oven
EPA methods:
Method 3015 - Microwave assisted acid
digestion of aqueous samples and extracts;
Method 3031 - Acid digestion of
oils for metal analysis by flame atomic absorption or ICP
spectroscopy;
Method 3050B - Acid digestion of sediments, sludges,
and soils;
Method 3051 - Microwave assisted
Acid Digestion of Sediments, Soils, Sludges, Soils, and
Oils;
Method 3052 - Microwave Assisted
Acid Digestion of Silicious and Organically Based Matrices;
Method 3060 - Alkaline Digestion
for Hexavalent Chromium.
|
Once a solid sample has been digested, the resulting
solution can be analyzed using one of the following analytical instruments
available in the Material Characterization Laboratory:
Thermal-Jarrel Ash Atomic Absorption
Spectrophotometers (Model 12) - AAS
EPA Methods:
Method 7000A - Atomic absorption method
|
Perkin Elmer 4110 ZL Zeeman-Corrected
Graphite Furnace Atomic Absorption
Spectrometer with AS-72 Autosampler - GFAAS
EPA Methods:
Method 200.9 - Determination of trace elements by stabilized
temperature Graphite Furnace Atomic Absorption Spectrometry
Atomic absorption, direct aspiration:
| 7041-Sb |
7081-Ba |
7091-Be |
7131-A |
7191-Cr |
7201-Co |
| 7211-Cu |
7381-Fe |
7421-Pb |
7461-Mn |
7481-Mo |
7521-Ni |
| 7740-Se |
7761-Ag |
7841-T1 |
7911-V |
7951-Zn |
|
|
Agilent 7500i Benchtop Inductively
Coupled Plasma-Mass Spectrometer System - ICP-MS
EPA
methods:
Method 6020 -Inductively Coupled - Mass
Spectrometry;
Method 200.8 -Determination of trace elements
in waters and wastes by Inductively Coupled - Mass Spectrometry.
|
All above-listed instruments serve the same purpose:
to perform metals analysis on solution. They can be used for the
determination of metals in a wide variety of sample types (drinking
water, groundwater, other aqueous samples, industrial wastes, soils,
sludge, sediments, and other solid samples) in different application
areas such as Environmental, Chemicals/Petrochemicals, Pharmaceutical,
Semiconductor Manufacturing, Metallurgy, etc. However, there is
no universal single technique, which will suit all of analytical
needs. Your choice of technique/instrument should be based on the
criteria summarized in the following table.
| .
|
AAS
|
GFAAS
|
ICP-MS
|
|
Detection
Limit
|
Very
good for some elements
(in the sub-ppm range)
|
Excellent
for some elements
(in the sub-ppb range)
|
Excellent for most elements
(typically, 1-10 ppt)
|
|
Speed/Sample
Throughput
|
Fast
(10-15 secs per element)
|
Slow
(3-4 mins per element)
|
Fast
(All elements in <1 min)
|
|
Dynamic
Range
|
103
|
102
|
109
|
|
Interferences:
Spectral
Chemical
(matrix)
Physical
(matrix)
|
Very
few
Many
Some
|
Very
few
Many
Very
few
|
Few
Some
Some
|
|
Multi-Element
|
No
|
No
|
Yes
|
|
Elements
Applicable to
|
68+
|
50+
|
82 (all metals from lithium to uranium)
|
|
Sample
Volumes Required
|
Large
(ml)
|
Very
small (µl)
|
Very small (µl or ml)
|
|
Semiquantitative
Analysis
|
No
|
No
|
Yes
|
|
Isotopic
Analysis
|
No
|
No
|
Yes
|
|
Ease
to Use
|
Very
easy
|
Moderately
easy
|
Moderately easy
|
|
Method
Development
|
Easy
|
Difficult
|
Difficult
|
|
Running
Costs
|
Low
|
Medium
|
High
|
| .
|
|
|
|
|
|
