Collision/Reaction Cell Technology Made Routine

Agilent’s ORS has revolutionized collision/reaction cell ICP-MS by bringing effective interference removal capability into the routine analytical lab. The ORS is easy to set up and use for routine trace analysis of complex, variable, and unknown sample matrices, without compromising the multi-element capability of ICP-MS. Analysts familiar with conventional (non-cell) ICP-MS will find the ORS is much simpler to operate.

Uniquely, the ORS removes interferences independently of the analyte (the same cell conditions remove interferences on multiple elements) and independent of the sample matrix (the same cell conditions remove multiple interferences on each element). This means that unknown samples can be analyzed, without requiring matrix-specific or element-specific optimization,and without requiring any interference correction equations. And unlike other reaction cells, there are no cell scanning voltages to set up or optimize.

The ORS is standard on the 7500ce and 7500cs and available as an on-site upgrade for the 7500a. The 7500ce and 7500cs share the same ORS technology, but with different sample introduction systems, interfaces, and ion lenses. These differences address the different requirements of ultratrace analyte measurements in high-purity sample matrices, such as those analyzed in semiconductor labs (7500cs), and of trace and major analyte measurements in complex and variable sample matrices (7500ce).

Schematic showing ORS featured in 7500ce and 7500cs models. Sample introduction system, interface, and ion lenses are different but are interchangeable between models. Off-axis ion lens can be removed for cleaning without breaking vacuum. Reaction cell is mounted on-axis with analyzer for increased ion transmission.

Any Analyte, Any Matrix

In complex and variable sample matrices, the ORS is typically operated in He (collision) mode, using pure He cell gas. This is a major advantage over the use of reactive or mixed cell gases: since He is inert, no new interferences are formed in the cell and no analytes are lost by reaction. The complete absence of new, cell-formed reaction product ions avoids the need for a dynamic, or scanning cell, which means that method setup is simplified and consistent operating conditions can be applied to multiple analytes and multiple sample types. If variable, high-matrix samples are analyzed on a cell system that uses highly reactive molecular gases, the sequential chemistry that is characteristic of these gases will generate many new interferences, the levels of which will vary depending on the levels of other analyte and matrix components present. This inevitably leads to errors in the results.

Screen Uncharacterized Samples with He Collision Mode

In He collision mode, interference removal is not matrix or interference-specific, which also makes He mode a very powerful screening tool, enabling interference-free semiquantitative analysis of unknown, high matrix samples. Freedom from matrix interferences means that semiquantitative data is much more accurate, even in unknown matrices. Interference correction equations are not needed, which in turn means that method setup is simpler and faster and that no analysis time is wasted performing daily checks and adjustments of correction equations.

High Efficiency Reaction Mode

In addition to the wide applicability of the He mode for complex sample matrices and multi-elemental analysis, a few elements have predictable, high intensity plasmabased interferences, which are more efficiently removed using reaction mode. These elements include Ca at its major isotope (m/z 40, which is overlapped by 40Ar) and Se at m/z 78 and 80 (overlapped by Ar2 polyatomic species). In these and several other cases, H2 is an ideal reaction gas, since it reacts quickly and efficiently with the Ar-based interfering species, but reacts slowly or not at all with the analyte. Thus, interferences can be reduced to the level of baseline noise, permitting single or sub-ng/L (ppt) detection limits to be achieved for these difficult elements.

Consistent interference reduction in a variable, complex matrix using He mode. Comparison plots showing Std mode (no cell gas - red) and He mode (green) spike recovery data for 5 ppb Cr in a variable matrix (up to 1% each of HCl, H2SO4 and Butanol). Potential interferences on 52Cr include ArC, ClOH and SO. All are removed, regardless of reactivity, under a single set of conditions, allowing accurate quantification of Cr at the main isotope, despite the variable matrix composition.

Standard addition calibration of Se using H2 reaction mode showing good linearity even at 5 ppt. BEC is 1.9 ppt Se. While He collision mode can also be used for trace Se, H2 mode offers unmatched performance.