Water for ICP-OES

The levels of detection in ICP-OES range around 0.1 to 1 µg/L or ppb, depending on the detector utilized. While those levels do not allow for trace analyses, ICP-OES is a very efficient and robust technique for routine analyses, and it finds its place in several types of laboratories, including environmental and chemistry laboratories.

During the analysis, the sample is vaporized and ionized to form ions that are further detected by the optical device. Interferences due to reactions with the argon used for the ICP process are well documented and the technique is fairly simple to use by most personal.

Water is not used during the analysis step, however, sample preparation step, blank, and standard preparation require high purity water. The water selected must meet two basic features:

avoid interferences with the metals being analyzed,
enable the instrument to run in optimum conditions, i.e. reduce contamination of the ICP-OES.

The water quality for ICP, therefore, should meet the following criteria:

Low ionic content, in order to avoid interference with the analytes. A 18.2 MΩ•cm resistivity ensures that no ions will be present in the water at a level that would interfere with the analyses. High resistivity can be achieved via several technologies, including combination of reverse osmosis, electrodeionization and mixed bed ion exchange resins.
Low particle content to avoid spoiling the nebulizer. The particles include hard particles, as well as colloids. Use of a 0.22 µm filter at the final stage of the purification process ensures that no significant particle count will be present in the water.
Low bacterial count, since bacteria behave as particles, and therefore could spoil the nebulizer as well. Use of a 0.22 µm filter at the final stage of the purification process ensures that bacteria levels below 1 cfu/mL.
Moderate to low organic content. Some large organic molecules such as lignin, as well as humic and fulvic acids resulting from natural matter degradation could stick on the nebulizer surface during the atomization step. Those large organic molecules are efficiently removed by combination of reverse osmosis and activated carbon. Other types of organics may also be removed using UV photooxidation process.

Analyses of Type I water (high purity water) using ICP-OES provide results that are below the detection limits for all elements analyzed. Water delivered by purification systems designed to produce Type I water can be used to dilute standards in order to generate calibration curves, as well as for sample rinsing and sample digestion procedures.

Example of data obtained on an Iris Intrepid (Thermo) ICP-OES

Element / λ (Å)	Avg LOQ (mg/L)
Ag3280	<.0015
Al1670	<.0010
Al3961	<.0080
As1890	<.0090
B_2497	<.0010
Ba2335	<.0005
Be3130	<.0005
Bi2230	<.0090
Ca1840	<.0100
Ca3179	<.0100
Cd2144	<.0005
Cd2265	<.0005
Cd2288	<.0005
Co2286	<.0015
Cr2677	<.0012
Cu3247	<.0020
Fe2599	<.0015
K_7664	<.0100
Li6707	<.0010
Mg2852	<.0010
Mn2576	<.0005
Mo2020	<.0015
Na5889	<.0040
Na5895	<.0050
Ni2316	<.0010
P_2136	<.0060
Pb2203	<.0080
S_1820	<.0100
Sb2068	<.0100
Se1960	<.0100
Si2516	<.0010
Sr4077	<.0005
Ti3349	<.0010
V_2924	<.0015
Zn2138	<.0008