When it comes to elemental analysis, inductively coupled plasma-mass spectrometry (ICP-MS) is often considered unparalleled in terms of precision. This method’s detection limits for certain elements may be as low as one part per trillion or quadrillion. Making it the most accurate elemental spectrophotometry approach available.
Several causes may hasten the contamination of ICP MS instruments. Matrix concentrations in the samples need special care. In addition to reducing ionization and affecting how sensitive an analysis is, they may also contribute to deposits on the cone.
Which, over time, induces drift effects by lowering performance. The impact on your ICP-MS may be identified and mitigated via internal standards.
What exactly is ICP-MS?
The world around us is composed of infinite material permutations. Inductively coupled analysts often use plasma mass spectrometry to determine the elemental composition of a sample (ICP-MS, or ICP Mass Spec). In contrast to LC/MS and GC, which measure molecules and compounds, ICP-MS measures individual elements.
With ICP-MS, a sample is first ionized in an argon (Ar) plasma (the ICP) before being analyzed in a mass spectrometer (the MS). Inductively coupled plasma optical emission spectroscopy (ICP-OES) and inductively coupled plasma mass spectrometry (ICP-MS) are very similar techniques. Still, ICP-OES controls the light transmitted from elements as they cross through some plasma using an optical spectrometer.
While ICP-MS quantifies the elements (ions) directly, both methods can quickly analyze many elements in a sample. ICP-MS is superior for analyzing trace elements due to its substantially lower detection limits. The ion source (the ICP), the mass spectrometer (MS) — often a scanner quadrupole filter — and the sensor make up an ICP-MS system.
An ICP-MS also needs vacuum filtration and a suction interface. And also, electrostatic ion “lenses” concentrate the ions from the ICP to the MS and detector, which work in a vacuum chamber. As a result, the most up-to-date ICP-MS systems also have a method to deal with spectrum interferences.
Major Components of an ICP-MS Instrument
Four basic components comprise the ICP-MS instrument. High-temperature ions are produced by the inductively-coupled argon plasma (ICP). The ICP employed in mass spectrometers is almost identical to that utilized in ICP atomic absorption instruments. The plasma in optical components is an atom source.
The interface and ion optics pull the ions out of the low-pressure plasma and direct them into the high-pressure mass analyzer. The mass spectrometer sends ions with different mass-to-charge ratios (m/z) to the detector in a controlled, sequential manner. The electron-multiplying detector transmits an electrical signal to the measuring circuitry for every ion that hits it.
In addition to the interface and analytical quadrupole, most modern quadrupole ICP-MS equipment also has a collision-reaction cell. This cell filters out molecular interferences from mass spectrometry before the actual mass measurement is performed. This cell may exhibit signal attenuation due to analyte ion–gas collisions.
Factors that Influence ICP-MS Sensitivity
ICP-MS systems are excellent for analyzing traces. Users must take precautions to avoid contamination for the best results. The sample preparation process must be well thought out, and chemicals and ultrapure water must be handled with the utmost care. Both the ionization level of an isotope and its quantity in the plasma affect the sensitivity with which it may be detected.
For instance, 232Th has a natural abundance of 100% and is almost completely ionized in a conventional ICP system. While 32.9% of its atoms are naturally occurring, and 194Pt is only around 62% ionized. If everything else is equal, this indicates that 194Pt is only approximately 20% as sensitive as 232Th.
Thousands and thousands of count data per sec per every million parts is a common unit of normalization for isotope sensitivity in ICP-MS. In this mass range, the sensitivity of state-of-the-art ICP-MS equipment varies from around 10 Mcps/(mg/L) up to 1000 Mcps/(mg/L). These two isotopes’ sensitivities are dissimilar because of their dissimilar abundances in nature in the plasma.
Benefits of Inductively Coupled Plasma Mass Spectrometry
Toxicology assessments in environmental scanning, medical analysis, and water quality management. And the beverage and food industries rely on the precise and accurate measurement of elemental composition, chemistry bonding, and oxidation states.
Monitoring the surroundings for dangerous chemicals and demanding greater quality assurance and control systems are becoming more vital to preserve the foundation of our survival. Ion chromatography and inductively coupled plasma mass spectrometry (IC/ICP/MS) hybridized online are powerful tools for this quality control. Even the most challenging analyses are no match for this powerful instrumental tool.
The ICP/MS method has high detection limits and can determine the entire quantity of an element in a sample (element selectivity). The ability to separate ionic analytes according to their chemical composition is a key function of IC, which is why it can manage species selectivity.
Furthermore, the molecular sensitivity of IC is combined with the element selectivity and sensitivity of ICP/MS via the online hyphenation of the two techniques. The molecule’s chemical bonding and oxidation states impact the bioavailability, affecting the toxicity. These characteristics may be determined with high precision and reliability using IC-ICP/MS.
How does ICP-MS function?
The first step involves introducing the samples as aerosol droplets into an argon plasma. The plasma dries aerosol, molecules are dissociated, and electrons are removed to create singly charged ions, which are then sucked into a mass spectrometer to be analyzed. Quadrupole mass spectrometers, used in most commercial ICP-MS systems, quickly scan the mass range.
Mass spectrometers only enable one mass-to-charge ratio to flow through the instrument from the inlet to the outlet at any moment. Ions leaving the mass spectrometer crash into the detector at the first dynode of an electron multiplier. When ions collide, they create a chain reaction of free electrons that may be amplified into a detectable pulse.
The program calculates the element concentration by comparing the observed pulse intensities to those of standards that make up the calibration curve. As the ratio of isotopes, or abundance in nature, is constant, a single isotope of each element must be tested in most cases.
Labs focused on one isotope of a component or in the proportion of two isotopes may benefit from using ICP-MS since it can test both simultaneously.
An ICP-MS’s high sensitivity is a helpful instrument for identifying ultra-trace quantities of isotopes without ultra-trace considerable spectrum interference. This makes ICP-MS a beneficial tool. Increasing sensitivity results in lower detection limits for certain isotopes. It is also important to minimize the presence of any continuous background that might affect the results of the analyte.