Basic Principles of the MP-AES Technology

There is only one vendor of this technology (Agilent Technologies: 4210 MP). At the heart of this technology is a 2.5 GHz magnetron coupled into nitrogen plasma, which is created using compressed air and a nitrogen generator. By using the magnetic field rather than the electric field for excitation, extremely robust plasma is formed, which is capable of handling much higher dissolved solids than previous MIP designs. The microwave waveguide concentrates both the axial magnetic and radial electrical fields around the torch, which creates a conventional-looking plasma, allowing for a traditional inert concentric nebulizer and double-pass spray chamber to be connected to the torch.

The optical system uses an axial viewing configuration, where the emission from the plasma is directed into a fast-scanning, 600 mm focal length, Czerny-Turner monochromator with a wavelength range 178-780nm. The 2,400 lines/mm holographic grating, blazed at 250nm for optimum UV performance, offers a resolution of 0.050nm. The detection system is a back-lit charge-coupled device (CCD) array detector, which is cooled to 0°C using a thermoelectric Peltier device, and collects the analyte wavelengths and surrounding background spectra, allowing for simultaneous background correction.

Benefits of MP-AES

One of the biggest advantages of this particular design over ICP-OES is that it runs on compressed air, which means that no gaseous or liquid argon is required. This makes it very attractive for laboratories that are on a tight consumables’ budget. However, the benefits over FA A are probably where it will receive the most attention29: These benefits include:

  • • Lower detection limits
  • • Wider linear dynamic range means larger concentration ranges can be determined
  • • Increased sample throughput
  • • Higher productivity, as it can be run unattended overnight
  • • No requirement to purchase or replace multiple hollow cathode lamps
  • • The ability to add other analytes to the suite of elements whenever the demand arises
  • • No safety concerns as neither acetylene nor nitrous oxide is required.

The detection limit improvement over FAA is exemplified in Table 27.3.

TABLE 27.3

Detection Limit Comparison (pg/L) of MP-AES with FAA

Element

FAA

MP-AES

Element

FAA

MP-AES

К

0.8

0.65

As

60

57

Ca

0.4

0.04

Cd

1.5

1.4

Mg

0.3

0.09

Cr

5

0.3

Na

0.3

0.12

Mn

1.0

1.05

An

5

2.1

Pb

14

2.5

Pt

76

6.1

Sb

37

12

Pd

15

1.6

Se

500

77

Ag

1.7

1.2

Zn

1.6

3.1

Rh

4

0.5

Note: 10s integration time, except for As and Se. which were 30s.®

Typical Applications of MP-AES

There is no question, based on the application material in the public domain, that the MP-AES system has been designed to fill the gap between FAA and ICP-AES and particularly to address the many limitations of AA. Some of the most common applications being addressed by this technique include the analysis of geological materials,31 particularly if there is a requirement for remote sampling or w'hen field studies are being carried out; the analysis of petrochemical samples using the addition of air to reduce carbon buildup on the torch; analysis of major, minor, and trace elements in crops and plant materials32; and non-regulated applications, such as the environmental monitoring of industrial waste streams; and the analysis of fruit juices33 and agricultural samples appears to be some of the most common applications that can be readily addressed by using the MP-AES. For a full suite of application literature on this technique, check out the following reference.34

Laser Ablation Laser Ionization Time-of-Flight Mass Spectrometry

LALI-TOFMS is a brand new' development that offers virtually the entire periodic table of the elements at mass spec detection capability directly on solid samples. It has applicability far beyond the cannabis industry but w'ould be w'ell suited for a testing lab that was looking to avoid sample digestion procedures to measure heavy metals in cannabis and hemp. In addition, when the regulatory elemental suite is expanded, as is likely when the FDA gets involved, the technology wfill be ideally positioned to measure other elemental contaminants at sub-ppm levels directly in cannabis and cannabis-related samples. Currently, Exum Instruments is the only manufacturer of this technique with the Massbox™ LALI-TOFMS. So let’s take a closer look at this novel technology.

The Massbox LALI-TOFMS is the first commercial instrument equipped wdth a LALI source. The patented, dual-laser technology extracts and subsequently ionizes material in tw'o discrete steps—first ablation and then ionization. Historically, LALI has been referred to by numerous acronyms in the literature, that is, SALI,35,36 LDI,3Z38L2MS,39 LD-LPI-TOFMS.40 Most of the research regarding LALI was purely academic and performed between the late 1980s and early 1990s. At the time, cost and electronic limitations prohibited commercialization of LALI technology, and other techniques took center stage. However, recent advances in computing technology and miniaturized, high-powered, solid-state lasers make LALI much more commercially viable today.

 
Source
< Prev   CONTENTS   Source   Next >