METHOD 6010A INDUCTIVELY COUPLED PLASMA …

1 CD-ROM6010A - 1 Revision 1 July 1992 METHOD 6010 AINDUCTIVELY COUPLED PLASMA - atomic EMISSION AND APPLICATION COUPLED PLASMA - atomic emission spectroscopy (ICP)determines trace elements, including metals, in solution. The METHOD isapplicable to all of the elements listed in Table 1. All matrices, includingground water, aqueous samples, TCLP and EP extracts, industrial and organicwastes, soils, sludges, sediments, and other solid wastes, require digestionprior to analysis. for which METHOD 6010 is applicable are listed in Table limits, sensitivity, and optimum ranges of the metals will vary withthe matrices and model of spectrometer. The data shown in Table 1 provideestimated detection limits for clean aqueous samples using pneumaticnebulization.

2 Use of this METHOD is restricted to spectroscopists who areknowledgeable in the correction of spectral, chemical, and physicalinterferences. OF METHOD to analysis, samples must be solubilized or digested usingappropriate Sample Preparation Methods ( Methods 3005-3050). When analyzingfor dissolved constituents, acid digestion is not necessary if the samples arefiltered and acid preserved prior to analysis. 6010 describes the simultaneous, or sequential, multielementaldetermination of elements by ICP. The METHOD measures element-emitted light byoptical spectrometry. Samples are nebulized and the resulting aerosol istransported to the PLASMA torch. Element-specific atomic -line emission spectraare produced by a radio-frequency INDUCTIVELY COUPLED PLASMA .

3 The spectra aredispersed by a grating spectrometer, and the intensities of the lines aremonitored by photomultiplier tubes. Background correction is required for traceelement determination. Background must be measured adjacent to analyte lines onsamples during analysis. The position selected for the background-intensitymeasurement, on either or both sides of the analytical line, will be determinedby the complexity of the spectrum adjacent to the analyte line. The positionused must be free of spectral interference and reflect the same change inbackground intensity as occurs at the analyte wavelength measured. Backgroundcorrection is not required in cases of line broadening where a backgroundcorrection measurement would actually degrade the analytical result.

4 Thepossibility of additional interferences named in Section should also berecognized and appropriate corrections made; tests for their presence aredescribed in Step - 2 Revision 1 July 1992 TABLE WAVELENGTHS AND ESTIMATED INSTRUMENTAL DETECTION LIMITS Detection EstimatedElement Wavelength(nm) Limit (ug/L)ab Aluminum Antimony Arsenic Barium 2 Beryllium Cadmium 4 Calcium Chromium 7 Cobalt 7 Copper 6 Iron 7 Lead Lithium 5 Magnesium Manganese 2 Molybdenum 8 Nickel Phosphorus 51 Potassium note cSelenium Silver 7 Sodium Strontium Thallium Vanadium

5 8 Zinc 2 The wavelengths listed are recommended because of their sensitivity andaoverall acceptance. Other wavelengths may be substituted if they can provide theneeded sensitivity and are treated with the same corrective techniques forspectral interference (see Step ). In time, other elements may be added asmore information becomes available and as estimated instrumental detection limits shown are taken from Referenceb1 in Section below. They are given as a guide for an instrumental limit. Theactual METHOD detection limits are sample dependent and may vary as the samplematrix varies. Highly dependent on operating conditions and PLASMA - 3 Revision 1 July Spectral interferences are caused by: (1) overlap of a spectral linefrom another element at the analytical or background measurement wavelengths; (2)unresolved overlap of molecular band spectra; (3) background contribution fromcontinuum or recombination phenomena; and (4) stray light from the line emissionof high-concentration elements.

6 Spectral overlap can be compensated for bycomputer-correcting the raw data after monitoring and measuring the interferingelement. Unresolved overlap requires selection of an alternate contribution and stray light can usually be compensated for by abackground correction adjacent to the analyte line. Users of all ICP instruments must verify the absence of spectralinterference from an element in a sample for which there is no instrumentdetection channel. Recommended wavelengths are listed in Table 1 and potentialspectral interferences for the recommended wavelengths are given in Table 2. Thedata in Table 2 are intended as rudimentary guides for indicating potentialinterferences; for this purpose, linear relations between concentration andintensity for the analytes and the interferents can be assumed.

7 Element-specific interference is expressed as analyteconcentration equivalents ( false analyte concentrations) arising from100 mg/L of the interference element. For example, assume that As is to bedetermined (at nm) in a sample containing approximately 10 mg/L ofAl. According to Table 2, 100 mg/L of Al would yield a false signal for Asequivalent to approximately mg/L. Therefore, the presence of 10 mg/Lof Al would result in a false signal for As equivalent to mg/L. The user is cautioned that other instruments may exhibitsomewhat different levels of interference than those shown in Table 2. Theinterference effects must be evaluated for each individual instrumentsince the intensities will vary with operating conditions, power, viewingheight, argon flow rate, etc.

8 The user should be aware of the possibilityof interferences other than those specified in Table 2 and that analystsshould be aware of these interferences when conducting analyses. The dashes in Table 2 indicate that no measurableinterferences were observed even at higher interferent , interferences were discernible if they produced peaks, orbackground shifts, corresponding to 2 to 5% of the peaks generated by theanalyte concentrations. At present, information on the listed silver and potassiumwavelengths is not available, but it has been reported that second-orderenergy from the magnesium wavelength interferes with the listedpotassium line at - 4 Revision 1 July 1992 TABLE CONCENTRATION EQUIVALENTS ARISING FROMINTERFERENCE AT THE 100-mg/L LEVEL Interferent a,b Wavelength------------------------------ ---------------------------- Analyte (nm)AlCaCrCuFeMgMnNiTl V Dashes indicate that no interference was observed even when interferents wereaintroduced at the following levels.

9 Al -1000 mg/L Mg - 1000 mg/L Ca -1000 mg/L Mn - 200 mg/L Cr - 200 mg/L Tl - 200 mg/L Cu - 200 mg/L V - 200 mg/L Fe -1000 mg/LThe figures recorded as analyte concentrations are not the actual observedbconcentrations; to obtain those figures, add the listed concentration to theinterferent - 5 Revision 1 July interferences are effects associated with the samplenebulization and transport processes. Changes in viscosity and surface tensioncan cause significant inaccuracies, especially in samples containing highdissolved solids or high acid concentrations. Differences in solution volatilitycan also cause inaccuracies when organic solvents are involved.

10 If physicalinterferences are present, they must be reduced by diluting the sample or byusing a peristaltic pump. Another problem that can occur with high dissolvedsolids is salt buildup at the tip of the nebulizer, which affects aerosol flowrate and causes instrumental drift. The problem can be controlled by wetting theargon prior to nebulization, using a tip washer, or diluting the the nebulizer and removing salt buildup at the tip of the torch sampleinjector can be used as an additional measure to control salt buildup. Also, ithas been reported that better control of the argon flow rate improves instrumentperformance; this is accomplished with the use of mass flow controllers. interferences include molecular compound formation,ionization effects, and solute vaporization effects.