ICP-OES or Flame AAS Q&A

You mentioned the operational costs of FAA versus ICP. But what about the investment costs? So far as I recall the FAA technique is less expensive than ICP and so should be the overall cost.

This has changed. In recent years the prices for entry level ICPs have been reduced to the price level of a quality FAA instrument. E.g. the SPECTRO GENESIS is available starting at under $40,000.

Compared to atomic absorption, emission spectra can be very complex. Isn’t method development more complex to cater for possible interferences?

ICP-OES has developed into a standard laboratory technique. The large variety of application information available makes method development rather simple. Interferences are typically addressed by appropriate line selection, mathematical correction, but also by optic design, which ideally provides a high resolution over the required spectral range.

From an instrumental point of view, what are the prospects for robust “field ” instruments for ICP-OES to compete with spark-emission instruments?

From an instrument construction standpoint an ICP is or can be similarly robust compared with a spark emission spectrometer. But sensitive glassware must be properly stored for transport. The key difference is that an ICP requires a larger infrastructure (e.g. chem lab for sample prep), while spark emission spectroscopy typically requires very little sample preparation.

Can you differentiate between Fe 2+ and total Fe?

FAA and ICP can only determine the total amount. Other methods (e.g. photometry) need to be used to determine Fe (II).

Which applications show more carryover?

Elements which have a tendency to be adsorbed by surfaces (e.g. B and Hg) are most affected.

We just purchased an ARCOS unit. How does the air-cooled unit work over the water-cooled unit?

There is no difference but there is one big advantage: no external cooling system is required.

How do you improve calcium signal in flame AAS?

By the use of an oxidizing acetylene-nitrous oxide flame and the addition of an ionization buffer.

Can titanium be analyzed as a trace element in ICP?

Very much! ICP-OES offers sub ppb level LODs for Titanium. Even with the entry level SPECTRO GENESIS ppb level LODs can be achieved.

Please comment on the development and limits of hydrocarbon-matrix techniques for multi-element detection. We are seeing methods like ASTM D7111 become more common and are interested in differences in results from these and aqueous (digested) matrices.

Middle distillate fuels like diesel can be analyzed very well using the ICP-OES method. The biggest advantage is that no sample preparation is needed, the sample is not diluted for the measurements, and thus good LODs are achieved. The disadvantages are that elements which may be present in the fuel with species of different volatilities (e.g. Si) may not be accurately analyzed and that larger particles (> 10 µm) do not reach the plasma. Here the digestion technique offers advantages.

Why does tungsten need HF to be stable in an ICP OES analysis, instead of Nitric acid like the other elements?

A little HF is added to prevent the precipitation of WO3.

Does the detection accuracy depend on the amount of the element present in the sample?

Among other factors, the achievable accuracy also depends on the amount present in the sample solution as the achievable precision depends on it. While for concentrations at the limit of detection (3 sigma) per definition the precision is 33%, it typically reaches a level of 0.5% for concentrations >BEC and between 0.1-0.5% for concentrations >>BEC. For practical reasons high precision/accuracy analyses (e.g. precious metals) are typically performed at a 100 mg/l level.

What is the best method to analyze La and Ce in Tungsten carbide?

Depends on the concentration of those elements in the tungsten matrix. Principally ICP-OES and MS are usable. To avoid difficulties with the matrix trace element, matrix separation techniques using ion exchangers may be used.

The microwave plasma technique is promoted to use no gas at all. Wouldn’t that be the better option for simple application where analysis costs plays a major role?

That microwave plasmas run on “air” is not completely correct. In fact, such systems use Nitrogen which either needs to be produced using a Nitrogen generator or by using compressed or liquid gas.

Which method is preferred for the determination of iron in an iron supplement medication?

If Iron is the only element to be determined, FAA should be the best option.

Which method is preferred for heavy metals in zinc oxide powder?

ICP-OES is very well suited. Sub ppm LODs in the solid material can be achieved.

Can Boron be analyzed better using atomic absorption?

I don’t think so (the difficulties with contamination and carryover exist with FAA and ICP).

Is there a specific reason the detection limit for Cs on ICP-OES is terrible?

The ICP plasma is extremely hot, Cesium is easily ionizable and therefore to a great extent present in the plasma as ion. Unfortunately the sensitive emission lines of Cesium are atomic lines. Due to that fact emission is not very efficient and so the LODs are high.

What is the recommended approach for fluorine analysis? Would a microwave air plasma overcome the issues associated with the argon plasma?

To use an ion selective electrode is the best approach. Since the sensitive emission line for Fluorine is located at 95 nm and no optical glass has the required transparency in this wavelength region, optical emission spectroscopy is not suitable.

Why is ICP not widely accepted for trace elements for Pb, Bi, Se, Te and Tl and Aerospace still wants it done by AA ? AMS2280 spec particularly for Nickel alloys?

To determine traces of those elements in a line rich Ni matrix using optical emission is not a simple task, but it is feasible using a high-resolution optical system. For the hydride forming elements, hydride generation might be used to separate the matrix and improve the sensitivity. Optical emission spectrometry is in fact widely used for the analyses of Ni matrix material. The fact that AA is still preferred in certain areas is often connected to custom. To achieve comparable results is the paramount task of analytical work and the more people are familiar with the certain technique, the easier this task can be fulfilled.

What would the detection limits be for lead specifically in a clean drinking water matrix in ICP-OES?

Axial view ICP-OES reaches an LOD of about 0.5 to 1 ppb.

Is the use of microwave digestion systems preferred over other methods for digestion of solid samples?

Microwave digestion is more effective, as the energy is delivered directly into the sample and not first through the walls of the digestion vessel.

Could Silica in Brine solutions be done by FAAS?

To run high amounts of totally dissolved solids through an FAA is not recommended. ICP-OES is clearly the better technique as it tolerates TDS concentrations up to 20%.

What is the best technique for the determination of metals in minerals and ores samples particularly for the trace elements?

Since typically many elements need to be determined, clearly ICP, either OES or MS, depending on the required sensitivity, are the preferred techniques.