Spectroscopy Testing

Flame Atomic Absorption (FAA) Spectroscopy

Flame Atomic Absorbance relies on aspirating a digested sample solution, aerosolizing the liquid, and atomizing the aerosol in a flame.  A light beam from a lamp is directed through the flame and into a monochromator which focuses the detector on the wavelength of maximum absorption of the element.  The amount of light absorbed by the flame is inversely proportional to the amount of that element in the sample.  Metal ion concentrations of the sample solution are determined by comparison to standards of known concentration.  The concentration of the metal in the sample can then be calculated using the amount of sample used in digestion, the final volume of the digestion, and any dilutions that were made on the solution.

 

Graphite Furnace Atomic Absorption (GFAA) Spectroscopy

Graphite Furnace Atomic Absorbance is similar to FAA in that it relies on atomic absorption to measure metal concentrations, but it differs in that it uses a furnace to atomize the digested sample solution, not a flame.  This technique offers the advantage of greater atomization of the sample, which affords either a lower detection limit (than conventional FAA) or the use of less sample.  Metal ion concentrations of the sample solution are determined by comparison to standards of known concentration.  The concentration of the metal in the sample can then be calculated using the amount of sample used in digestion, the final volume of the digestion, and any dilutions that were made on the solution.

 

Cold Vapor Atomic Absorption (CVAA) Spectroscopy

Galbraith Laboratories uses Cold Vapor Atomic Absorption to measure mercury content of organic and non-organic samples.  CVAA measures mercury content by reducing it to the elemental state and purging it from solution into a vapor.  The vapor passes through an atomic absorption spectrophotometer where absorption of light at 253.7 nm is measured.  The absorbed light correlates to the mercury content of the sample solution, and the mercury content of the sample can then be calculated using the amount of sample used in digestion, the final volume of the digestion, and any dilutions that were made on the solution.

 

Inductively Coupled Plasma – Atomic Emission Spectroscopy (ICP-AES)

Inductively Coupled Plasma – Atomic Emission Spectroscopy, also known as Inductively Coupled Plasma – Optical Emission Spectroscopy (ICP-OES), measures element-specific spectra emitted from atoms and atomic species in a heated in plasma.  Galbraith Laboratories commonly employs ICP-AES to measure Group I metals, Group II metals, Transition metals, Metalloids (such as boron, silicon, germanium, etc.) and some Non-Metal elements (such as sulfur and iodine) in a wide variety of sample matrices.

Digested sample solutions are introduced into the ICP instrument by way of a peristaltic pump. The solution is nebulized into an aerosol that is transported to a plasma torch.  Metal ions in the sample solution are subjected to intense heat in a radio-frequency inductively coupled argon plasma.  The elements emit characteristic spectra which are separated by optics within the instrument.  The intensity of the emission lines are monitored by a photosensitive device such as a charged couple device or photomultiplier tube.  Metal ion concentrations of the sample solution are determined by comparison to standards of known concentration.  The concentration of the metal in the sample can then be calculated using the amount of sample used in digestion, the final volume of the digestion, and any dilutions that were made on the solution.

 

Inductively Coupled Plasma – Mass Spectroscopy (ICP-MS)

Inductively Coupled Plasma – Mass Spectrometry, measures elements on the basis of their mass to charge ratio. Galbraith Laboratories commonly employs ICP-MS to measure metallic elements, metalloids and some non-metal elements (such as iodine) in a variety of sample matrices.

Digested sample solutions are introduced into the instrument by way of a peristaltic pump.  The solution is nebulized into an aerosol that is transported to a plasma torch.  Metal ions in the sample solution are subjected to intense heat in a radio-frequency inductively coupled argon plasma.  The ions are transported from the plasma through a vacuum interface into a quadrupole where they are separated on the basis of their mass to charge ratio (m/z).  After passing the quadrupole, the ions collide with an electron multiplier detector. Metal ion concentrations of the sample solution are determined by comparison to standards of known concentration.  The concentration of the metal in the sample can then be calculated using the amount of sample used in digestion, the final volume of the digestion, and any dilutions that were made on the solution.

Common applications of AA/ICP analyses are listed below:

ICH Q3D Elemental Impurities Analysis

Compendial Monograph Metal Assays (USP, EP, JP)

General Metals Screening

Consumer Product Safety Commission (CPSC) Lead (Pb) Analysis

 

Overview of Metals Preparation Methods

In order to perform an analysis by FAA, GFAA, CVAA, ICP-AES, or ICP-MS, solid samples must first be digested or dissolved. Galbraith Laboratories utilizes a range of techniques to prepare samples for analysis. The following is a representative list of preparation methods available:

 

Hotplate Digestion of Inorganic and Organic Compounds

This method is a hot concentrated acid digestion of both organic and inorganic substances. Acids that are generally used are nitric, hydrochloric, sulfuric, perchloric, and hydrofluoric. Because the digestion is conducted in an open vessel, it is not suitable for volatile metals.

 

Dry Ash of Organic Compounds

This method subjects the sample to high temperatures in a furnace. The high temperature, sometimes in conjunction with an aid such as nitric or sulfuric acids, decomposes the organic components of the sample. The remaining ash is then dissolved in nitric and/or hydrochloric acids. This approach is ideal when larger quantities of sample need to be digested. Because the digestion is conducted in an open vessel, it is not suitable for volatile metals.

 

Microwave Assisted Acid Digestion

This is a closed-vessel digestion technique that relies on a microwave source to heat a high-pressure vessel containing the concentrated acids and a portion of sample. The acids commonly used are nitric and hydrochloric. This technique is widely used by Galbraith for the digestion of organic substances for analysis of volatile metals.

 

Fusions

The following digestion techniques intended for inorganic substances that do not digest using other more conventional means.  These methods are often used for compounds such as aluminum oxide, titanium dioxide, silicon dioxide, barium sulfate, ceramics, ores, etc.

  •  Lithium metaborate fusion
  •  Potassium hydroxide fusion
  •  Potassium persulfate fusion
  •  Sodium carbonate fusion
  •  Sodium hydroxide fusion
  •  Sodium peroxide fusion
  •  Sodium peroxide fusion in a Parr bomb

 

Water Dilution

This method is a water dissolution of water-soluble compounds.  In many cases, the solution is stabilized by the addition of acid.

 

Solvent Dissolution

This method is a solvent dissolution of water-insoluble compounds.  This method is used in FAA analyses, especially for silicone analysis.

Fourier Transform Infrared (FTIR) Spectroscopy

FTIR spectroscopy measures the amount of infrared light absorbed over a range of wavelengths. FTIR is a valuable tool in characterizing functional groups present in organic and inorganic compounds. FTIR is most often used for confirming the identity of pure compounds by comparison to known standards. Galbraith Laboratories performs mid-IR measurements, and the typical wavelength region for measurements is 2.5 µm to 15 µm, or 4,000 to 670 cm-¹.

 

Ultraviolet–Visible (UV-Vis) Spectroscopy

Ultraviolet-visible (UV-Vis) spectroscopy is a very popular analytical technique because it is very versatile and has a wide variety of applications. With UV-Vis spectroscopy, ultraviolet light is passed through a sample and the transmittance of light by a sample is measured. From the transmittance (T), the absorbance can be calculated as A=- log (T).

For each measurement, the wavelength of ultraviolet light is scanned through the spectral range. An absorbance plot is obtained that shows the absorbance of a compound across the spectrum. UV-Vis can be used in a qualitative manner, to identify functional groups or confirm the identity of a compound by matching absorbance spectrums. It can also be used in a quantitatively, as the concentration of the analyte is related to the absorbance using Beer’s Law.

Common applications of UV-Vis analyses are listed below:

Compound Identification by Reference Standard Comparison

Gluten Analysis

Cyanide Analysis

Hexavalent Chromium Analysis

Reducible Sulfur Analysis