ICP-OESInstrumental Analysis of Beryllium

Particulates

Whitney Coffey

ICP-OES…?Inductively Coupled Plasma-Optical Emission Spectroscopy

Properties of berylliumIndustrial uses of berylliumHealth risksSampling methodsInstrumental analysis (ICP-OES)

Overview

Physical Characteristics of Beryllium:

Atomic Number: 4Atomic Weight: 9.012

Period Number: 2Group Number: 2Group Name: Alkaline Earth

Metals

Melting Point: 1560 KBoiling Point: 2744KDensity: 1.85 g/cm3

Solid at room temperature

Good thermal conductorGood electrical conductorNon-magnetic metal

Extremely lightweight, yet very stiff

Sources of Beryllium:

Found in approximately 30 mineral species; the most significant sources are beryl and bertrandite

Aquamarine and emerald are precious forms of beryl

Beryllium has many industrial uses. These include:

Aerospace Space shuttle components Structural material for high-speed aircraft and missiles

Atomic Energy Nuclear weapons components Nuclear reactor components

Ceramics Crucibles Ignition modules Jet engine blades Semi-conductor chips

Electronics Computer parts Telecommunication parts Transistors

Metallurgy Aluminum-, copper-, magnesium-, and nickel-beryllium

alloys

So why analyze for beryllium particulates?

Beryllium-related health issues

Beryllium is safe in natural state and in finished products

Beryllium dust or fumes are unsafe, and can cause illness:

Lungs primarily affected

Other organs may also be affected

1 related condition: Beryllium Sensitization

2 beryllium-related illnesses:Chronic Beryllium DiseaseAcute Beryllium Disease

Beryllium Related Health Risks

Beryllium SensitizationImmune response:

After an individual inhales beryllium dust or fumes, the immune system may see the element as a foreign invader

Cells accumulate in the bloodstream, prepared to mount an attack against any beryllium particles encountered

No outward symptoms

Diagnosis:BeLPT test (beryllium lymphocyte proliferation test):

Blood test to identify immune response to berylliumHighly specific – beryllium only cause of immune responseNormal result: rules out beryllium sensitization as well as CBD

Chronic Beryllium Disease (CBD)Scarring of the lungs that results from immune system attacking foreign beryllium particles

Symptoms: Shortness of breath during activity Persistent dry cough Fatigue Chest and joint pain Increasing loss of appetite

*Symptoms can take a decade or more to develop

Diagnosis: Abnormal BeLPT test Further testing, including:

Chest x-rayPulmonary function testingBlood workExercise tolerance testingBronchoscopy with possible biopsy

Acute Beryllium Disease (ABD)Caused by high dose exposure to dust or fumes

Common symptoms: nausea fatigue night sweats cough breathing difficulties

Onset of symptoms is usually immediate, occasionally delayed a few days following exposure

Cases of acute beryllium disease have become quite rare, thanks to improved safety procedures in the workplace

Beryllium sampling methodsTwo general sampling methods are currently in use:

Air sampling Wipe sampling

Air Sampling A measured volume of air is

drawn through a filter - inhalable dust sampler

Filter and any collected sample then digested and prepared for instrumental analysis

Air sampling rates are typically identified in liters per hour

Wipe Sampling Method for sampling smooth surfaces Analyst can choose

appropriate size for the sampling area per wipe

cm2 is a suitable frame of measurement

Two methods:Dry wipe samplingWet wipe sampling

Dry Wipe SamplingMay be required for some surfaces that:

Can be damaged or compromised by moisture Can be damaged by specific compounds used to moisten the wipes

*Cautionary note:Dry wipes remove only a fraction of the residue from a surface as

wetted wipes do - if wetted wipes can be used without compromising the sampling surface, they are the preferred choice.

Wet Wipe SamplingMoistened wipes remove greater percentage of residues than dry wipes

Wipes typically moistened with:Distilled waterMethanol

methanol-wetted wipes have proven most efficient

* In any of the above methods, the collected samples are subjected to an acid digestion, resulting in a liquid sample that can be analyzed via ICP-OES*

Brief definitionInstrument components and functionsParticulate Analysis Spectral interferencesMSF: correction software for spectral

interferences

ICP-OES

What is ICP-OES?ICP-OES, or inductively coupled plasma optical emission spectroscopy,

is a multi- element technique featuring:Moderately low detection limits (~0.2-100ppb)Variety of sampling options for organic or liquid matricesAbility to run up to 60 samples in a single run time of <1min Few chemical interferencesSome spectral interferences that can be corrected via softwareICP source for more complete dissociation of samples

Basic function of ICP-OES: Atoms of the sample in the ICP plasma emit photonsPhotons of each element have characteristic wavelengthPhoton emission recorded by optical spectrometerPhotons emission calibrated against standard emissionsProvides quantitative results of sample

Process OverviewSample typically injected as a liquid (solid samples prepared via acid digestion)

Nebulizer converts liquid sample into an aerosolSpray Chamber transports aerosol sample to the plasma torchPlasma torch vaporizes, atomizes, and ionizes aerosol sampleTransfer Optics focus plasma image onto entrance slit of spectrometerWavelength dispersive device of the spectrometer isolates proper

emission lineDetector and its components measure intensity of the emission lineComputer software compiles data, produces spectral plots of data

NebulizerThe nebulizer converts the liquid sample into an aerosol

Aerosol is then transported to plasma torch via spray chamber

Aerosol droplets must be very small:Prevents clogging of apparatusProvides complete desolvation of sample for accurate resultsNebulizer partly responsible for droplet size

Pneumatic nebulizers most common: to create an aerosol, pneumatic nebulizers rely upon high-speed gas

flow

Peristaltic PumpSample solution pumped into nebulizer by peristaltic pumpSolution is pushed through tubing via process called peristalsis:

Series of rollers push solution through tubingOnly tubing comes in contact with solution

Prevents contamination of sample by the pumpTubing material varies with types of samples being analyzedFlow rate of solution into nebulizer is fixed by peristaltic pump

Spray ChamberSpray chamber is placed between nebulizer and torch

Primary function is to remove droplets too large to pass through torch

Typically allow droplets no larger than 10 m in diameter to pass through

~1-5% of sample will be passed to torch~95-99% drains into waste container

Spray chambers usually made of corrosion-resistant material, to withstand hydrofluoric acid and corrosive organics

Argon plasma most commonly used

ICP plasma source frequently referred to as a torch

ICP Plasma SourceDefinition: a plasma is an electrical conducting gaseous mixture containing considerable concentrations of electrons and cations – net charge approaches zero

Basics of the ICP source:

ICP consists of 3 concentric quartz tubes

Argon gas streams through quartz tubes:

Carries sample through central tube

Also spirals around wall of outer tube:

Centering plasma radially

Cooling inside walls of center tube

Water-cooled induction coil:

Surrounds top of outer tube

Powered by RF generator

Produces fluctuating magnetic field

Ions and electrons interact with magnetic field

Interaction causes flow of particles

Plasma:

Very intense, white, nontransparent core topped by a tail

Core extends a few mm above quartz tubes

Results from recombination of argon and other particles

Optically transparent tail 10-30mm above core

Tail resembles a flame

Spectra typically obtained 15-20mm above induction coil

Transfer Optics:ICP radiation usually collected by a focusing optic, typically

a convex lens or concave mirror

Optic focuses image of the plasma onto entrance slit of spectrometer or wavelength dispersive device

Transfer optics can analyze in three general modes:Radial (side-on) viewAxial (end-on) viewDual view

Wavelength Dispersive DeviceDifferentiates emission radiation of the elements and moleculesEmission radiation is sorted by wavelengthCommon dispersing device: combination of echelle grating and prism

Echelle grating Separates radiation by wavelengths Produces multiple overlapping spectral orders

PrismSeparates the overlapping orders into 2-dimensional patternPattern called ‘echellogram’

Selected emission line transmitted to the detector.

DetectorMeasures intensity of emission lineMany types of detectors to choose fromNewest innovation is SCD segmented-array charge coupled device

detectorSCD houses individual collections of small subarrays

20 to 80 pixels eachOver 200 subarrays on a silicon wafer2D pattern of subarrays associated with echellogram

producedSubarrays account for over 236 ICP spectral linesSpectral lines correspond to the 70 elements ICP analyzesGood response to light 160-782nm

ComputerDetector transmits emission intensities to computer

Computer software compiles, stores, and displays dataEmission results for each elementSpectral plots of individual samplesSpectral overlay plots

Software can correct for a variety of spectral interferences

Particulate Analysis70 elements can be analyzed via ICP-OESDetection limits vary for each elementAcid digestion of solid sample creates aqueous solutionAqueous sample injected into ICPInner argon flow rate of 1L/minStandard and sample solutions typically delivered at rate of

1mL/minICP-OES analyzes emission abundance of sample ionsComputer generates spectral plot on monitor Amount of solution required varies

Number of elements being determinedNumber of replicate measurements being takenSpeed of instrument

ICP-OES detection limitsCopyright © Jobin-Yvon Emission

2000

Beryllium Particulates

ICP-OES LOD for beryllium < 1ppbDOE sets beryllium baseline at 0.004ppm for analysesBeryllium crustal abundance 1.6ppm: above this considered “hit”Wavelengths for beryllium analysis:

Be313.042Be313.107

Subarray used for beryllium analysis: 312.968 – 313.180

Computer plots spectrum of emission abundance for beryllium ions in subarray

Calibration blank run with sampleIn specified subarray:

2 hydroxyl peaks1 argon peak2 beryllium peaks

Spectral Interferences

Several elements cause spectral interference in designated subarray:

ZirconiumVanadiumCeriumTitaniumNiobiumMolybdenumChromium

Emission from these elements can hide emission abundance of beryllium, producing false positives or false negatives

Standards of known concentration analyzed along with sample MSF applied

Spectral Correction – MSF

Multi-component spectral fitting

Algebra-based software program:Single-element spectra obtained for each interfering elementConcentration of analyte calculated using scaling factorsScaling factors calculated using interfering single-element spectraSpectral interferences mathematically eliminated

For accurate results, MSF software requires that data be collected in high- resolution mode peaks must be resolved at every 0.001nm

Typical soil sample at low resolution

Spectral overlay at low resolution

Spectral overlay at high resolution

Beryllium spectrum after MSF application

What have we learned?

Strong + lightweight + corrosion resistant = good for industry!

Fumes + dust = bad for lungs!

Conclusion? Find dust and remove it. But how do we find it?

Some instruments = poor LOD’s

Some instruments = too $$$$

ICP-OES = competitive LOD’s, reasonable cost

Sources

National Jewish Medical and Research Center: www.njc.org

Optima 5000 DV Series ICP-OES. www.perkinelmer.com

Boss, Charles B; Fredeen, Kenneth J. Concepts, Instrumentation, and Techniques in Inductively Coupled Plasma Optical Emission Spectrometry, 2nd Edition. Perkin-Elmer. 1997.

Kriebel D, et al. The pulmonary toxicity of beryllium. Am Rev Respir Dis 1988; 137:464-473.

Kreiss K, et al. Risks of beryllium disease related to work processes at a metal, alloy, and oxide production plant. Occup Environ Med 1997; 54:605-612.

Nolte, Joachim. ICP Emission Spectrometry – A Practical Guide. Chapter 4; Method Development. www.wiley-vch.de

Septon, Jerry; Abel, Ray; Simmons, Michael: Metal and Metalloid Particulates in Workplace Atmospheres (ICP Analysis). OSHA Technical Center, www.osha.gov. Sept 2002.

Chris’ instrumental book