Easy Standard Nebulization of Aqueous Samples in Combination with Hydride Vapour Generation (ICP-OES) Jan Knoop1, Uwe Opppermann1, Jürgen Schram2 1 Shimadzu Europa GmbH, Spectroscopy, Duisburg, Germany 2 Niederrhein University of Applied Sciences, Faculty of Chemistry, Krefeld, Germany

■ Overview For nowadays applications in the field of elemen-tal analysis, the request always is to lower down the limits of detection. Thereby the origin for this request can vary: The source is legislation, e.g. to protect the environment or alternative this is caused by industry/company demands, e.g. to optimize product behaviors due to higher pureness of utilized materials and so on. The resulting question always is, how to reach this new requirements. A robust basic technique can be atomic absorption spectroscopy. With the use of dual atomizer instruments like the AA-7000 (Shimadzu) laboratory bench space can be saved and analyses can be performed from high ppm to ppt range. But every time this means to measure element per element, as the technique is not working simultaneously. Fig. 1: AA-7000 wit AAC (Automatic Atomizer Changer) to perform measurements in flame and furnace mode within one instrument. The next step then is to look for simultaneous methods, to analyze all requested elements at once. For this approach the ICP-OES and ICP-MS techniques are most suitable. As there are many request from different industries to have a robust and most user-friendly instrumentation, this poster focuses how easy it is to perform trace analysis for many elements, including critical ones like mercury and arsenic, simultaneously, without compromises in sensitivity. ■ ICP-OES: Common Sample Injection Two different sample injection techniques are regarded, the typically used direct nebulization of the sample (A) and the hydride vapour technique (B). Commonly this techniques are performed separately. Both techniques have advantages and disadvantages. The direct nebulization (Fig. 2) is easy to perform, and no special additionally chemicals are in use. The technique is sensitive enough for many critical elements, like to achieve the LOD of 1 ppb for lead according to the European drinking water directive.[1] But this technique is not sensitive enough for mercury and arsenic. Figure 2: Direct nebulization of the sample

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Therefore the hydride vapour technique is applied (Fig. 3), where in acid milieu the sample gets in contact to a sodium borohydride solution. This causes ions like arsenic and mercury to change from liquid to the gas phase. By the liquid/gas separator it is managed to forward this gas phase with the analytes to the plasma torch, matrix-free, resulting in a higher sensitivity. Figure 3: Hydride vapour technique line diagram [2] ■ Combined techniques: Hydride vapour + Nebulization As already indicated in Fig. 3, for the easiest combination of this two sample injection techniques, the exit line of the liquid/gas separator (Fig. 3) is directly connected to the carrier gas line of the coaxial nebulizer (Fig. 2), so both, the hydrides and the aspirated sample reach the spray chamber. After passing, the sample is injected to the plasma mini torch. For this study the ICPE-9820 was used (Fig. 4). Fig. 4: New ICPE-9820 for axial and radial plasma observation.

Fig. 5: Calibration and spectra for mercury using hydride vapour technique combined with direct nebulization.

■ Optimized Sensitivity By using the combined techniques for sample injection, the sensitivity, esp. of the hydride vapour elements (Hg, As), is increased. This is documented by the LOD values (tab. 1). For the elements, not sensitive to hydride vapour technique (Cd, Cu, Pb) the sensitivity is comparable to the common direct nebulization. Table 1: LOD values for different sample aspiration techniques. In addition to sensitivity check, some reference material was measured, showing good recovery within a range of ±10% (Tab. 2). Especially the hydride sensitive element arsenic results in excellent recoveries of ±3 %. Table 2: Recovery for drinking water samples for direct nebulization and combined method: *TMDW, trace metals in drinking water, High Purity Standards (North Charleston, SC, USA). Hg not specified.

■ Discussion The purpose of this study was to evaluate the easiest combination of two sample injection techniques; the hydride vapour technique coupled with the direct nebulization. The sensitivity data already shows the selected hydride elements are more sensitive than using hydride technique, only. For the elements Cd, Cu and Pb sensitivity is not increased, reasonable on the one hand by the fact they are typically not sensitive for hydride vapour technique and on the other hand the carrier gas flow is a bit more varying, as it depends furthermore on the reaction of sample solution with the NaBH4-solution and the formed amount of gaseous compounds. But in the end, the method is robust enough to achieve recovery rates of water reference material in the range of ±10% and this gives the reason to follow this easy combination, to accelerate sample throughput once more without a compromise in sensitivity. ■ References [1] 98/83/EC Drinking Water Directive on the quality of water

intended for human consumption [2] ESI Elemental Scientific, User Manual: hydrideICP

Element A) Direct Nebulization

B) Hydride Vapour

A + B Combined

Hg ≤ 1.0 µg/L ≤ 0.10 µg/L ≤ 0.02 µg/L As ≤ 3.0 µg/L ≤ 0.80 µg/L ≤ 0.30 µg/L Cd ≤ 0.10 µg/L - ≤ 0.16 µg/L Cu ≤ 0.15 µg/L - ≤ 0.15 µg/L Pb ≤ 1.0 µg/L - ≤ 1.0 µg/L

In cooperation with

0.0 2.5 5.0Concentration (ug/L)

0

25

50

75

100

125

150

175

200

Inte

nsity

Hg 184.950 nm (1)

r = 0.99996

Equation:

Factor:b = 0.0000000

Conc = a * I ̂3 + b * I ̂2 + c * I + d

a = 0.0000000 c = 0.0285862d = 0.0262817

Weight: NoneOrigin: None

Detection Limit (3s) = 0.0132932 Limit of Quantity (10s) = 0.0443106

Element A) Direct Nebulization A + B Combined

TMDW* TMDW-A* TMDW* TMDW-A* As - - 99.9 % 103 % Cd 101 % 99,4 % 93.7 % 93.6 % Cu 99,5 % 100 % 99.5 % 98.5 % Pb 95,0 % 101 % 90.0 % 90.0 %