Minimization of matrix effects with environmental samples using ICP-OES

Introduction Matrix effects with environmental applications –Instrumental and analytical approach to avoid/reduce those effects Hardware, Optic and introduction systems Summary Conclusion 2

CONSISTENCY IS KEY! Know your HARDWARE! Know your INTRODUCTION SYSTEM SETUP!! Know the WORST CASE SAMPLE SENARIO!!! Only then can you OPTIMIZE your methodology…. 3

Internal Standard usage Background Correction Points / Models Atypical IEC’s (Carbon?) Sample diversity (drinking waters are not waste waters or brines, etc.) SPEED! Getting the best data WHILE trying to follow a regulated methodology (EPA)…problems of second and third source standards 4

Environmental Applications – Challenges Emission spectra of environmental samples is typically not extremely line rich and thus environmental work is often described as being “easy” But The matrix composition can vary considerably The amount of TDS in the final solution can be high vary strongly: Ca– 3000 mg/lMg– 500 mg/l Al– 1000 mg/l Fe– 1000 mg/l Na– 100 mg/l K– 100 mg/l P– 1000 mg/l 5

Axial Plasma Observation – The choice for environmental work Axial plasma observation was introduced in the mid 1990s. The development driven by requirements for higher sensitivity, particularly for the toxic, heavy metals. Today, axial plasma observation still plays an important role as it provides much higher matrix tolerance as compared to ICP-MS. 6

Axial Plasma Observation – Challenges Axial plasma observation improves the sensitivity due to the larger observation volume by sampling the emitted light from the entire excitation channel However, it also suffers from stronger influences, since all phenomena present in the excitation zone including the plasma tail above the plasma, are viewed The most relevant effects are: –Recombination effect –Influence of the plasma load –Self absorption –Easy ionizable element effect 7

Recombination effect In the cooler temperature regions, within the plasma tail, ions and electrons recombine.  The energy required for their ionization and any excess energy the electrons carry is then again released, which produces additional continuum-like radiation. 8

Removal/ minimization the recombination effect “Removal” of the recombination zone from the optical path –The OPI to minimizes the effects from the recombination zone by radial deflection from the light path Optical light path to spectrometer Adjustable argon jet Recombination matrix effects Plasma

Removal/ minimization the recombination effect 10 Radial plasma viewing completely eliminates the effect

Influence of the plasma load –With higher plasma loads, the excitation efficiency decreases, which results in lower background to peak rations.  With varying matrices the achievable sensitivity greatly varies.  At 1100 W and 10 L/min Ar, the sensitivity difference between a water- and a 1 % Ca matrix is more than a factor of two 11

Optimization of the Plasma Power –Operating of the plasma with robust plasma conditions and appropriate line selection the effect can be minimized  Using robust conditions at 1400 W and 13L/min and As at 193 nm (less influenced by recombination) the sensitivity difference can be reduced to a factor of 1.18  With radial plasma observation the effect is further reduced 12

Calibration at 1100 W 13

Calibration at 1400 W 14

Self absorption –Self absorption is the effect where cooler atoms and ions absorb the radiation, they would, under higher temperature conditions, emit –The effect, reduces the measured light intensity the more of the respective element is present in the sample  Calibration functions become non linear or even reverse, (self reversal of emission lines) 15

Elimination of self absorption effects High dynamic range detector readout  0.1 m sec phase interval to utilize the full potential of the emission line  Does not influence the self absorption behavior, but enables maximum concentration coverage with a minimum number of lines Multi line calibration  Selection of appropriate lines providing a linear calibration within the relevant concentration range  Automatic, concentration dependent line switching Radial plasma observation  Less effected by self absorption  Further expansion of the linear dynamic range 16

100 mg/l nm – Axial Plasma Observation

Multi line calibration nm and using Axial View 18 R 2 = R 2 =

19 Multi line calibration nm and using Radial View R 2 = R 2 =

Easy ionizable element effect –Group 1 and 2 elements cause the strongest effect. Those elements are almost exclusively present as ions –If introduced at “higher” concentrations, this leads to a massive increase of the electron density and thus a shift of the equilibrium –It often leads to an enhanced emission for atomic lines and respectively higher than normal intensities for the alkali and earth alkali elements 20 Effect of 50 ppm Na on 0.2 ppm K using axial plasma observation

Excellent resolution 21  Higher accuracy in line rich matrices Al 168 nm Cd 214 nm 8 pm Resolution 23 pm Resolution

Ionization buffering and Internal standardization –The EIE effect can be reduced by providing an excess of easy ionizable elements in the plasma –Matrix differences are additionally compensated by the use of an internal standard On-line introduction, Sc or Y used as internal standard, Cs used as ionization buffer Peristaltic Pump ICP To nebulizer From spray chamber drain Waste Sample Buffer/InternalStandard “ orange-orange” peristaltic tubing “orange-green”

Calibration of Alkali and Earth Alkali Elements Calibration Standards Elem. Std.1 [mg/L] Std.2 [mg/L] Std.3 [mg/L] Std.4 [mg/L] Std.5 [mg/L] Std.6 [mg/L] Na K Mg Ca Al Fe Cs2000 Sc10 Elem. CS7 [mg/L] CS8 [mg/L] CS9 [mg/L] CS10 [mg/L] Na K Mg Ca Al Fe Cs2000 Sc10 AxialRadial Power1450 W Coolant flow12 L/min Auxiliary flow0.8 L/min Nebulizer flow0.95 L/min Plasma TorchQuartz, fixed, 2.5 mm Injector tube Quartz, fixed, 1.8 mm Injector tube Spray ChamberCyclonic NebulizerModified Lichte Sample aspiration rate2.0 mL/min Replicate read time50 sec per replicate Plasma Parameters Check Standards

Recoveries of Alkali and Earth Alkali elements using ionization buffering and internal standardization SampleAlCaFeKMgNa [mg/l] Meas. CS CS CS CS Given CS CS CS CS Recov.[%] CS793%101%100%115%101%103% CS896%98% 106%99%98% CS9104%108%106%102%98%111% CS1097%98%101%104%101%98% 24 SampleAlCaFeKMgNa [mg/l] Meas CS CS CS CS Given CS CS CS CS Recov.[%] CS799% 97%111%96%93% CS8101%97% 109%99%97% CS9100%102%97%98% 99% CS10100%98%95%97%98%94% Axial ViewRadial View Slightly better average recoveries are achieved in radial mode (99% versus 102%)

Influence of an Alkali Matrix (50 ppm Na )on Alkali Elements (K) using Axial and Radial Plasma Observation 25 Axial: Strong Effect Radial: Effect visible, but greatly reduced Axial Radial Depth of field Viewing volume Induction area Induction coil Viewing volume Viewing height Central channel Induction coil

Twin Interface Plasma Observation Accurate determination of alkali elements in the presence of a varying alkali/earth alkali matrix (e.g. mineral waters) with axial ICP- OES  The EIE (Easy Ionizable Element) effect is greatly reduced since the alkali/earth alkali elements are measured in radial mode  No need for the use of an ionization buffer  Cost reduction, reduced risk of contamination  Toxic elements can still be determined with great sensitivity since they are measured in axial mode  Dynamic range and linearity can be further expanded

Twin Interface (TI) – (Dual View) 27

SPECTROBLUE Twin Interface - Principle 28 Coupling mirrorOptic window Control mirror Mirror, plain Mirror, concave Torch Entrance slit optic Radial view Axial view

SPECTROBLUE Twin Interface - Design 29

Twin Interface - Design 30 Small, light throughput optimized light path Periscope optic rigidly connected to the optic and the torch. Plasma sided, easy to clean/change, window to avoid the contamination of optical components Self adjusting, pneumatic control mirror All components easily exchangeable

New OPI Flange and Locking Mechanism The OPI can be disassembled without removal of the torch Novel, easy to use locking mechanism

Twin Interface - Properties Switchable 3-Mirror Periscope Optimized for smallest size and maximum light throughput using “Reverse Ray Tracing” Self adjusting, pneumatic control mirror Robust construction. Rigidly coupled to the optical system and the plasma torch 45°- viewing angle to reduce contamination Plasma sided protection windows to avoid contamination of optical components All components easy to maintain Separate, computer controlled light path purge flows 32

Axial Plasma Observation – The choice for trace analytical work Axial plasma observation was introduced in the mid 1990s The development driven by requirements for higher sensitivity, particularly for the toxic, heavy metals Axial plasma observation still plays an important role as it provides much higher matrix tolerance as compared to ICP-MS 33

Axial Plasma Observation – Challenges Axial plasma observation improves the sensitivity by sampling the emitted light from the entire excitation channel However, it also suffers from stronger influences, since all phenomena present in the excitation are viewed Pros and Cons: –High sensitivity –Stronger matrix effects –Less suitable for high TDS and applications with organic solutions 34 Viewing volume

Radial Plasma Observation – The choice for high stability, high matrix loads and organic solutions Radial plasma observation provides lower sensitivity since the central channel is only partially view However, it provides high stability and freedom from matrix effects since the affected zones in the plasma are blanked out Pros and Cons : –High stability –High matrix tolerance –High linear dynamic range –Freedom from matrix effects –Lower sensitivity Viewing volume

“Dual View” – really the best of both worlds? “Dual View” appears to solve the dilemma having to make a choice between axial and radial plasma observation But! Only one view uses the direct light path, the other is compromised  Sensitivity loss due to additional optical components  Sensitivity loss in the UV since the light path cannot be purged effectively 36 Coupling mirror Optic window Mirror, plain Mirror, concave Torch Entrance slit optic

“Dual View” – really the best of both worlds? For highest sensitivity, instrument using a “Dual View” technique typically have a horizontal torch orientation  Disadvantages with higher matrix loads and organic solutions Compared to a dedicated radial interface the sampling volume using a periscope is smaller  Ultra high stability and precision as compared to a dedicated radial systems cannot be achieved  The “dual view” technique serves a purpose, but does not provide the highest possible performance 37

Other hardware options? Turn the plasma! Using MultiView, the plasma orientation can be changed  The instrument can be used as a dedicated radial as well as a dedicated axial instrument 38

MultiView - Radial/Axial Plasma in one Instrument 39 Analytical performance without compromise  Highest sensitivity  Highest stability and precision  Highest dynamic range  Highest matrix compatibility  Freedom from matrix interferences  Other techniques or instruments are not anymore required

TI Analytical Performance: LODs TI axial mode 40 Integration time 60s per replicate TI-Torch with slit –No visible wear after 200h of operation TI/DV in axial mode achieves the exact same sensitivity as a dedicated axial (EOP) system BUT the radial mode is less sensitive and throughput reduced!

TI Analytical Performance: Linearity, K nm 41 The linearity is drastically reduced for elements effected by the EIE Linearity: R 2 =0.99 Rel. deviation of the standards up to 25% TI Radial: Linearity, R 2 = Rel. deviation of the standards < 5% Axial modeRadial mode

Analytical Performance: Linearity radial mode 42 Linearity: R 2 = Rel. deviation of the standards < 7%

Matrix effects with environmental applications can effectively addressed –Recombination effects can be minimized by a deflection of the recombination zone (OPI) or eliminated by radial plasma observation –Robust plasma conditions minimize the differences in excitation properties in the plasma caused by a varying and higher TDS matrix –Self absorption effects can be avoided by multi line calibration and an appropriate line selection. A high dynamic range read out helps to reduce the required number of lines Self absorption effects are drastically reduces by radial plasma observation –The EIE effect can be well reduced by the use of an ionization buffer –Twin Interface Plasma Observation eliminates the EIE and further expands the dynamic range 43

EOP, the axial interface version, provides high sensitivity and detection limits for superior analysis of industrial and environmental trace elements. SOP radial interface version offers precise performance at higher sample concentrations, exhibiting excellent tolerance for high saline and organic fractions plus superb analysis of suspensions and slurries. TI twin-interface version automatically performs both axial and radial viewing of the plasma. This “eliminates” the EIE effect, optimizes linearity and dynamic range, while enabling high-sensitivity measurement of toxic elements. MV, Multi View interface allows the end user to SWITCH between a DEDICATED Radial AND Axial system (without the drawback of a periscope or complicated entrance optics). This offers the best of both worlds in a systems that is optimized for Axial and Radial viewing, something NO DUAL VIEW system can achieve! 44

45 Thank You for Your Attention!