Buck Scientific, Inc.

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Buck Scientific, Inc.

• Seminar in ANALYTICAL INSTRUMENTATION for
  Spectroscopy Chromatography

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ATOMIC ABSORPTION (AAS)
Theory Principle of OPERATION

• Using a LIGHT SOURCE made from a Pure METAL
  ELEMENT, the CONCENTRATION of that METAL in a
  Solution can be determined by the ABSORBANCE of
  this Light by Excited ATOMS of the same METAL

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Basic AA Theory

• There are THREE Primary Modes of measuring an
  ATOMIC SIGNAL
• Emission
• Absorption
• Fluorescence

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Basic AA Theory

• While PLASMA EMISSION was also being
  investigated at the same time, several companies
  developed WORKING AAS instruments rapidly, within
  2 years

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Basic AA Theory
The COMPLEX nature of Atomic FLUORESCENCE made it
difficult to FULLY develop as a working
Analytical technique for Quantitative Analytical
Chemistry
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Basic SPECTROMETER Design

• ALL Analytical Spectrometers have several BASIC
  design components in common
• Light Source
• Sample Chamber
• Optical System
• Detector
• Output

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Basic AA Design

• The BASIC Instrument was developed back in 1947
  as part of a U.S. Government Grant

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Basic AA Design

• First instruments were DIRECT Current, SINGLE
  Beam designs
• Next generation were ALTERNATING Current to try
  to compensate for high Drift Instability
• Final designs had to split the signal into a
  DOUBLE Beam path to fully correct for Noise,
  Drift Errors

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Basic AA Design

• Light Source
• Buck lamps have the highest output (energy) at
  the lowest current for best stability and
  lifetime
• Amp-hours will determine HCL operating life

Lamp Power effects on Line Signal quality
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Basic AA Design

• BUCK Scientific manufactures its OWN
  Hollow-Cathode Lamps to provide the BEST possible
  Energy to achieve the highest Sensitivity and
  Reproducible Sample Data

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Basic AA Design

• SAMPLE chamber to deliver the Solution is made
  of a DYNAMIC NEBULIZER, a SPRAY CHAMBER and a
  BURNER HEAD Assembly

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Basic AA Design

• BURNER HEAD uses Dynamic Impact-Bead NEBULIZER
  for maximum Sample Aerosol delivery to Flame for
  ALL types of Solutions (high salt, organic)

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Basic AA Design

• OPTICAL SYSTEM for the BUCK AAS consists of a
  compact, med-high Resolution, SINGLE-BEAM, 1/4M
  Ebert Monochromator with variable Slits to
  maximize separation of Resonance Lines that come
  from the Hollow-Cathode Lamps

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Basic AA Design

• Adjustable SLITS are used to increase the
  Resolution / Separation of HCL signals from
  Metals with rich Spectra (many lines) such as
  Fe, Ni, Mn Co

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Basic AA Design

• The DETECTOR used to measure the Absorbance
  SIGNAL is a high-Gain / low-Noise
  Photo-Multiplier Tube (PMT) that is OPTIMIZED for
  the UV region

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Basic AA Design

• DATA OUTPUT can be read directly from the
  Graphics LCD, sent to a Printer or be transferred
  to a Computer as an ASCII file to process in
  Excel, Lotus, etc.

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BUCK AA Hardware

• The features of high-energy, compactness
  economy developed into the 210-series AAS

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BUCK AA Hardware

• 3-Lamp Turret with Self-Aligning Lamps, high
  Safety Auto-Gas Box Ignition...

precision Wavelength and Slit adjustments for
Rapid, Simple Reliable analyses
low-cost manual controls...
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AA Techniques

• There are several MODES of Analysis for Atomic
  Absorption Spectroscopy
• Flame AAS
• Graphite Furnace AAS
• Hydride Generation AAS
• Cold-Vapor Mercury AAS

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AA Techniques

• FLAME AAS
• Air-Acetylene (1800oC) or Nitrous Oxide
  (2300oC) Flames allow the determination of most
  Metals with high-PPB / low-PPM Detection Limits

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AA Techniques

• GRAPHITE FURNACE uses extremely SMALL sample
  volumes (20µL), then runs a Temperature PROGRAM
  to DRY any liquid, then CHAR or ASH away any
  organic or matrix, then ATOMIZE the Analyte for
  PPB levels

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AA Techniques

• GFAAS requires a source of Cooling Water and
  Argon Gas to operate

The BUCK 220-GF used a proprietary
high-frequency, back-mounted Power Supply for
maximum Efficiency
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AA Techniques

• For Environmental work, the low-level HYDRIDE
  GENERATION method is excellent for some Metals
  such as As, Se, Sb and occassionally Bi, Ge
  Sn. A carefully controlled Reaction with a
  STRONG Reducing Agent is used.

Hydride Generation Reaction
To FLAME
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AA Techniques

• The Metal, MERCURY, has the unique ability to
  ABSORB light in the Vapor state at ROOM
  Temperature. Since it does not require any HEAT
  to generate an ABS signal, this method is called
  COLD-VAPOR or Flameless AAS

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BACKGROUND Correction

• In AAS, there are several types of INTERFERENCES
  that can affect the Accuracy and Precision of the
  Data due to various effects on the Metal or the
  Instrument

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BACKGROUND Correction

• SPECTRAL Interferences are addressed by using a
  good quality HCL.
• PHYSICAL effects are corrected by using proper
  Sample Preparation.
• CHEMICAL errors are minimized by using Matrix
  Modifiers and Reagents

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BACKGROUND Correction

• IONIZATION can be reduced by adding a Buffer to
  the Solutions.
• Non-Specific absorbances, or NSA, are due to the
  BACKGROUND signal from the Sample matrix, and are
  corrected using a DEUTERIUM D2 Lamp

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BACKGROUND Correction D2
ABSORBANCE signals for Elements are Narrow
Sharp while signals from BACKGROUND radiation is
Broad. A DEUTERIUM Lamp is used to ISOLATE
Background signals.
Pb-283nm.
HCL generates a narrow band radiation, that
sees BOTH Element-Specific AND Background
Non-Specific Absorbances

• 180-400nm.

D2 Lamp creates a continuum of BROAD band
radiation, that ONLY sees other BROAD band
signals, such as BACKGROUND
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BKG Correction VGP

• For any Analytical wavelengths outside the
  180-400nm. Range for the D2 Lamp, Variable GIANT
  PULSE Correction will work for many applications

Pb-283nm. _at_ 5mA
Low CURRENTS for Analytical Measurements create a
narrow band source of radiation
Pb-283nm. _at_500mA
High CURRENTS (gt500mA) are used to form the GIANT
PULSE as a broad, wide band to make it SIMILAR
to the D2 Continuum for reading ONLY signals from
the BACKGROUND
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BACKGROUND Correction

• Passing the HCL Beam through a D2 Lamp plasma
  coil allows the Analysis of Trace Metals in
  Complex Samples such as Cadmium in Fertilizers
  without the high levels of Light LOSS from
  Beamsplitters

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ATOMIC ABSORPTION (AAS)
Sample PREPARATION Applications

• Careful techniques must be used to Collect,
  Preserve and then PREPARE the Sample so it can be
  run on the AAS Instrument.
• This is an OVERVIEW of the Common method for
  Sample Preparation

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SAMPLE PREPARATION

• Samples MUST be in the form of a clear,
  particle-free Solution
• These Solutions can be based on an Aqueous
  (water) or Organic (solvent) matrix
• Calibration materials (Blank and Standards) must
  be prepared with the SAME procedures as the
  Samples

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Sample PREPARATION

• Some of the common procedures for AAS
• Open Beaker Acid Digestion
• Closed Vessel Pressure Digestion
• Soxhlet Solvent Extraction
• Muffle-Furnace Ashing
• Sonication
• Centrifugation
• Simple Filtration

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PREPARATION Equipment

• For the highest Accuracy in the Analysis, it is
  important to use Lab-ware that is Calibrated and
  Certified!
• Balances and Pipets are the major sources of
  Analytical error in AAS work

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PREPARATION Equipment

• A reliable source of Pure WATER is very important
  for doing low-level Trace Analysis, such as GFAAS
  work.
• A bad Blank can cause as much as a 50 error!!

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Calibration Equipment

• The proper STORAGE containers should be used to
  minimize any LOSS of the Sample METALS or
  Contamination from the Environment

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Calibration Equipment

• STANDARD Solutions for Calibration of all Atomic
  Absorption instrumentation should be NIST/NBS or
  ISO / IUPAC Certified for true Accuracy

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APPLICATIONS

• 50 Metallic Elements of the Periodic Table can
  be determined by Flame or Furnace AAS from the
  0.0001 to 100 concentrations

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APPNOTE - Environmental

• SAMPLE Factory Effluent / Discharge
• PREPARATION Digest w/ 100ml. W/ 10ml. HNO3
  boil down to 100ml. filter and run directly (no
  dilution factor)
• ANALYSIS Air- Nitrous Flames w/
• 2-point Calibration

RESULTS mg/L or PPM in Sample
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APPNOTE - Environmental

• ELEMENT Original Treated
• As Hyd 85 PPB 17 PPB
• Cr6 Air 3.7 PPM 0.55 PPM
• Ag Air 212 PPB lt 10 PPB
• Pb GFAA 1.9 PPM 0.05 PPM
• Ba N2O 450 PPM lt 50 PPM
• AAS can monitor the Pollution in any Water, and
  any Treatment. Meets ALL USEPA requirements.

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APPNOTE - Metallurgical

• SAMPLE Automotive Parts Plating
• PREPARATION Simple 120 and 1500 dilution of
  Plating Bath w/ DI Water
• ANALYSIS Air- Nitrous Flames w/
• 1-point Calibration

RESULTS Percent (v/v) or mg/L (PPM) in the Bath
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APPNOTE - Metallurgical

• Element New Bath Old Bath
• Cu (acid) 1.72 1.29 -
• Zn (alkali) 0.35 0.42
• Ag (cyanide) 1250 PPM 490 PPM --
• Cr (acid 6) 0.60 0.57 OK
• Ni (sulfamate) 4800 PPM 3870 PPM -
• AAS can be used for both the MAJOR MINOR Bath
  components, contamination build-up and for
  Discharge Monitoring to avoid penalties

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APPNOTE - Agricultural

• SAMPLE Rice / Corn Fertilizer Plants
• PREPARATION 1100 dilution of Fertilizer.
  Digest 2 gram wet Plant w/ 15ml HNO35ml
  H2SO42ml 30 H2O2
• ANALYSIS Air-Flames w/ 1-pt CAL

RESULTS PPM in both Samples, look at metal
RATIO in Plant
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APPNOTE - Agricultural
Element Fertilizer Rice Corn Magnesium
0.15 47 PPM 280 PPM Potassium 1.15 195
PPM 2250 PPM RATIO 7.7 4.2 - 8.0
OK Copper 65 PPM 12 PPM 39 PPM Molybdenum
15 PPM 3.1 PPM 14.6 PPM RATIO 0.23
0.25 OK 0.37 AAS D2 correction gives
the BEST Accuracy for Trace Minerals in these
Complex Samples