PFA Cross Flow Nebulizer (X-Flow)PFA Cross Flow Nebulizer (X-Flow)

Technical Features

Cross flow nebulizers have been available for many years and the design is extremely simple. A nebulizer gas orifice is positioned at 90 degrees to sample orifice through which sample is pumped. Ar gas exiting the gas orifice shears the liquid, generating a fine aerosol. Typically, cross flow nebulizers use a mixture of platinum, alumina or sapphire for the gas and sample orifices. This leads to increased background for some elements, and some limitations on chemical compatibility. The X-Flow is unique in that both orifices are made from PFA. A schematic diagram of the X-Flow is shown here: the pink insert is the sample orifice and the blue insert (yellow in the close up image) is the gas orifice. The upper inlet is the optional make up gas port which can be used to add O2 for organics analysis, or when it is required to operate at higher total gas flows (>1L/min) while keeping the nebulizer gas flow at the optimum flow of approx. 1L/min. The yellow fitting in the main diagram is the sample uptake line connector which is a zero dead volume fitting. This keeps washout time to a minimum since there is no dead space in the sample uptake path to be washed out.

Nebulizer gas and make up gas fittings accept standard 4mm OD tubing. The nebulizer gas orifice is 0.5mm which means it is virtually impossible to clog and even the highest salt content and high particulate content samples can be aspirated. Typically the X-Flow is used with an 400µl/min uptake line with ICP-MS and with the 1000µl/min uptake line with ICP-OES, however the requirement for a Scott-type chamber limits its applicability to ICP-OES since most ICP-OES instruments are used with a cyclonic chamber. The 100µl/min uptake line is used with microvolume samples.


The available sample uptake lines
for the X-Flow are as follows:
Free aspiration uptake
rate (µ/min)
Inner Diameter
(mm)
100 0.38
400 0.51
1000 0.76
 

Performance

Due to the higher efficiency of the C-Flow, the sensitivity of the X-Flow with 400µl/min uptake line is comparable (actually about 10-20% lower) to a C-Flow 200, although the X-Flow has a slightly lower oxide ratio in ICP-MS.

In comparison with a conventional glass nebulizer, the X-Flow has similar efficiency. The table below shows ICP-MS data comparing the X-Flow with a 400µl/min uptake line, with a GE Micromist (400µl/min version). Both nebulizers were pumped. Data was acquired on an Agilent 7700x ICP-MS. Sensitivity was generally similar though the X-Flow had a lower random background. Oxides were slightly lower with the X-Flow while doubly charged was slightly higher.

Comparison of an X-Flow (400µl/min uptake line) with a GE Micromist
400µl/min version. Data acquired on an Agilent 7700x ICP-MS.
 7amu89amu205amuBackgroundCeO (%)Ce++ (%)
X-Flow 57104 286374 327241 0.2 0.82 0.92
GE MicroMist 45820 311864 274513 1.3 0.91 0.75


Comparing other properties of the two nebulizers: the X-Flow can be used only with a Scott-type double pass chamber, while the Micromist can be used with both Scott-type and cyclonic. The X-Flow has an integrated end cap for Scott type chambers while the Micromist requires a separate end cap. The X-Flow is unbreakable, is HF resistant, has lower background for boron (the Micromist is made from borosilicate glass), and has better tolerance to very high salt samples and to high levels of suspended particulates. Finally, the X-Flow has lower dead volume and so is capable of higher sample throughput.


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