Strategies for Eliminating Interferences in Optical Emission Spectroscopy Best practices to optimize your method and correct for interferences to produce accurate results National Environmental Monitoring Conference Washington DC

Anything that causes an inaccurate signal for your analyte of interest What is an Interferent Anything that causes an inaccurate signal for your analyte of interest Know your interferences Collect information Frequently from multiple sources Have specific, identifiable, and correctable causes Examples: Contaminated Method Blank, Incorrect Standard Concentration. Quantify your interferences Obtain information quantitatively or semi-quantitatively How significantly do the interferences affect your accuracy

Accuracy can also be expressed as Percent Relative Error Interferences may Affect Accuracy or Precision Accuracy: Usually expressed as error. The difference between a measurement and the True Value is its absolute error (mg/L). Accuracy can also be expressed as Percent Relative Error Precision: Simply the degree of reproducibility of a set of replicate measurements. Precision can expressed by Standard Deviation (SD) or Percent Relative Standard Deviation (%RSD)

ICP Interferences that may Affect Accuracy or Precision Plasma density Interferences Physical Spectral Matrix Ionization Environment User Plasma Lab cleanliness Unwanted light Sample introduction User error

PerkinElmer Avio 500 Simultaneous ICP Instrumentation PerkinElmer Avio 500 Simultaneous ICP Vertical Plasma Torch Design Flat Plate™ Plasma Technology Dual View PlasmaShear™ System Universal Data Acquisition Color PlasmaCam™ Syngistix™ for ICP Software

Spectral Interferences in ICP-OES The most severe problems: line rich matrix element(s) few analytical wavelengths of analyte Possible solutions: Improve resolution Matrix match Use an alternate i.e. cleaner wavelength if possible Interelement correction Multivariate correction (MSF)

Indirect Overlaps vs. Indirect Overlaps Interferent Emission Line

Spectral Interference Correction Software Based Interference Correction Techniques Multicomponent Spectral Fitting (MSF) Interelement Corrections (IEC)

IEC Correction The IEC correction factor is a measurement of the effect of an interfering element upon the observed concentration of an analyte The correction factor is simply the correlation between interferent concentration and the apparent or “false” analyte concentration Relationships established between analyte and interferent IEC Correction Factor Ratios determined based on this relationship Ratios highly dependent on plasma conditions 200 Fe 500 Fe 2 5 Analyte Conc.

Analytical Considerations for IEC IEC standards – Single element standards of all suspected interferences Interferent Standards must not contain the analyte Choose analytes and concentrations that are likely to be in the unknown samples Interferent needs to be in the linear range Plasma conditions must be constant

Interferences on Arsenic 50ppb As in the presence 100ppm Aluminum, Calcium, Iron, and Magnesium

Arsenic Blanks in a Matrix of 100ppm Aluminum and Iron Improper Peak Integration Proper Peak Integration Fe on As -6ppb Fe on As -525 ppb Al on As -110ppb Al on As -22ppb

Interferences Causing Erratic Baseline and False Concentrations Aluminum; 100ppm produces an false concentration of -243 ppb Accuracy Calcium; 100ppm spectra mimics the blank, but poor baseline Precision Iron; 100ppm produces an false concentration of -104 ppb Accuracy Magnesium; 100ppm spectra mimics the blank, but poor baseline Precision

Software Generating an IEC Table IEC Factor = False analyte concentration (ppb) / Apparent concentration of the interferent (ppm)

Software Generates an IEC Summary Table Units: ppb False Analyte / ppm Interfering Element Set correction factors Look at values: if numbers are getting large, check background points

IEC Review Mathematical ratio between the analyte and the interference Highly dependent on Plasma conditions Highly dependent on analyte integration parameters Table must be generated from analyte free interfering standards The interferences must be analyzed The Interferences must be within the linear range. Alternate wavelengths can be used to extend the linear range of the interferent Interferent usually quantitated in the radial mode May add noise to the signal Can correct for direct spectra overlaps

MSF – An Alternate to IEC’s Multi-Spectral Fitting Does not depend on plasma conditions Interferences do not need to be quantitated Does not correct for direct spectral overlaps

MSF Modeling Analyte Spectra 40 ppb As in Combined Matrix Matrix 200ppm Al, Ca, Fe Mg Blank Spectra Analyte Spectra 40 ppb As in Combined Matrix

Components of the Matrix Combined Matrix Spectra Aluminum Spectra Calcium Spectra Magnesium Spectra Iron Spectra

Defining the Components in Syngistix

Entering the Model into the Method MSF is now the peak integration algorithm Reference the model created in “Examine Spectra” in the method

Improving Detection Limits / Precision With MSF 10ppb As in 2% HNO3 Data can be reprocessed with either peak integration methods

Detection Limit Calculation Sample ID ( matrix 200ppm Al, Ca, Fe, and Mg, 10ppb As with Background Points 10ppb As with MSF interference corrections of the Blank MDL Sample #1 0.005 0.009 MDL Sample #2 0.006 0.008 MDL Sample #3 0.010 MDL Sample #4 MDL Sample #5 MDL Sample #6 0.011 MDL Sample #7 Calculated MDL (3.14* STDEV Sample 1-7) 0.007 0.003

1 ppm Indium in 100ppm Cobalt Matrix Severe Co spectral interference on all usable Indium Wavelengths Modeling a Cobalt Standard in MSF can eliminate matrix contribution. Indium Can Successfully be Analyzed in a Cobalt matrix using MSF In 325.609 In 451.131

Indium Spike Recoveries With and Without MSF

Review IEC MSF Interferences must be calibrated for and within the Linear range Once MSF Model is generated interferences do not need to be contained within the Method Corrects for Direct Spectral overlaps Interference must not be a direct spectra overlap Factors are dependent on plasma conditions, power etc. Model is valid for different plasma conditions Background Point and Peak Integration is Critical Automatically integrates Peak

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Thank You for Your Attendance! Contact information: Dan Jones Daniel.Jones@PerkinElmer.Com