INDUSTRIAL HYGIENE - ANALYSIS OF GASES AND VAPORS

1. INDUSTRIAL HYGIENE -ANALYSIS OF GASES AND VAPORS UNIVERSITY OF HOUSTON - CLEAR LAKE

2. PURPOSE Address the range of analytical techniques used to quantify gases and vapors in the environment. Quantification of individual contaminants is accomplished either by the selectivity of the analytical method, or by combining a non-selective analytical method with a separation technique. Need a working knowledge and understanding of analytical methods and procedures. Method selection and requirements/limitations as well as interferences should be investigated.

3. LAB ANALYSIS Laboratories have the resources to maintain a high degree of analytical proficiency for a wide variety of substances along with rigorous quality control programs that are simply not economically feasible in a laboratory conducting a small number of analyses. Maintain laboratory communication. Understand limit of detection. Usually combined sampling and analytical method; use validated methods by NIOSH, OSHA, EPA.

4. LIMIT OF DETECTION Given the knowledge of the analytical limit of detection and a defined sampling goal (e.g. to be able to detect a concentration 10% of the TLV or PEL for that substance), a sample volume can be calculated to assure that, although the substance was not detected, the concentration is low and not of concern.

5. STANDARD METHODS Developed to insure analytical reproducibility so that results will be comparable across laboratories. Also, standard methods have been evaluated and tested extensively in terms of measurement range, precision, accuracy, and interferences. Interpret in a statistically meaningful manner. Use of non-standard method can be addressed if documentation is “at least equivalent”.

6. QUALIFIED LABORATORY American Industrial Hygiene Association (AIHA) – IH Laboratory Accreditation Program (IHLAP). Requires evaluation of: • Lab personnel qualifications, • Lab facilities, • Quality control and equipment, • Lab recordkeeping, and • PAT participation.

7. PAT PROGRAM Provides blind reference samples for substances (i.e. asbestos, solvents, metals, silica, etc.) to participating laboratories quarterly/semiannually. Laboratories are considered proficient if their analysis falls within +/- 3 SD of the reference value. Also provide blind external QA samples – e.g. blanks, duplicates, and also spiked samples or samples of known concentration. NIOSH Manual of Analytical Methods!

8. CHROMATOGRAPHY METHODS Powerful tools for separation of gaseous contaminants and their subsequent individual analyses. Chromatography (GC) involves the process of separating the components of a mixture by using a mobile phase and a stationary phase. Mobile phase: GAS or LIQUID based on naming convention. Column has a stationary phase. Figures 12.3.

9. CHROMATOGRAPHY PROCESS Samples introduced onto column containing the stationary phase in solution with the mobile phase. Repeated interactions differentially retard the passage of individual solutes in a mixture, providing separation. Once separated, analytes are detected to quantify the amount present. Output signal plotted against time. Figure 12.4. Baseline, peak, and retention time.

10. CHROMATOGRAPHY RESULTS The size (area) of the chromatographic peak corresponding to a given contaminant is directly proportional to the mass of the contaminant injected. Proper calibration can determine the exact mass of contaminant in an unknown sample. Detectors do not respond identically to all substances.

11. GAS CHROMATOGRAPHY - Used for low concentration of air contaminants. - Applicable to compounds with sufficient vapor pressure and thermal stability to dissolve in the carrier gas and pass through the column in sufficient quantity to be detectable. - Basic components: carrier gas system; sample injector system; column; detector; and, a recording system.

12. THERMAL DESORPTION The contaminant is driven from the sorbent at a high temperature into a carrier gas. Solvent dilution is not involved, so entire mass of contaminant collected is introduced directly into GC. Able to quantify lower concentrations. Limitation is only one chance for successful analysis because the entire sample is used.

13. GAS CHROMATOGRAPHY Each sample component repeatedly sorbs/desorbs from the mobile and stationary phases. Individual compounds elute from the column at different times. Accurate quantification depends on: combined abilities of the chromatographic column; carrier gas flow rate; and temperature conditions to separate or “resolve” analytes from other sample components prior to reaching detector.

14. GC COLUMN TYPES - Packed - solid support provides a large uniform and inert surface areas for distributing the liquid coating with which the contaminants interact; can use a wide variety of solvents. Stationary phase depends on analyte; liquid phase should be chemically similar to the sample being analyzed. - Capillary - better peak resolution due to low resistance to flow; smaller injection volumes must be used.

15. GAS CHROMATOGRAPHY Columns contained in ovens to use temperature control for separation to occur isothermally as well as with programmed changes. Set temp based on time and separation. Rule: retention time doubles for every decrease in temp of 30 degrees C. Temperature programming allows for the separation of analytes with a wide range of boiling points.

16. CHROMATOGRAPHY DETECTORS Separation techniques need detector to quantify the amount of each analyte in the column effluent. Unspecific response and proportional to the amount of analyte present. Need calibration curve for detector response comparisons to standard runs.

17. DETECTOR TYPES Selection of the appropriate detector for the contaminant of interest is essential to realize the full potential of GC analysis: - Flame Ionization (FID) - Nitrogen-Phosphorus (NPD) - Flame Photometric (FPD) - Electron Capture (ECD) - Thermal Conductivity (TCD) - Photoionization (PID) - Discharge Ionization Detector (DID)

18. OTHER DETECTORS/TYPES - Nitrogen & Sulfur Chemiluminescence Detectors (NCD) & (SCD) - GC with Mass Spectrometry (GC/MS) - High Performance Liquid Chromatography (HPLC) - UV-VIS Absorbance (UV-VIS) - Fluorescence Detector - Conductivity Detector (CD) - Electrochemical (ED) - Ion Chromatography (IC)

19. FLAME IONIZATION DETECTOR (FID) - Very sensitive to most organic compounds - One of most widely used GC detectors - High sensitivity and exhibits a linear response over a wide dynamic range (6-7 orders of magnitude). - FID response only to compounds with oxidizable carbon atoms and not to following: water vapor; elemental gases; CO; CO2; HCN; HCOH; formic acid; H20), or most other inorganic compounds. Little response to carbon disulfide.

20. NITROGEN-PHOSPHORUS DETECTOR (NPD) - Thermionic or alkali flame detector - Highly sensitive and selective to nitrogen and phosphorous compounds, including amines and organophosphates. - Similar to FID principle of detection, except that ionization occurs on the surface of an alkali metal salt.

21. FLAME PHOTOMETRIC DETECTOR (FPD) - Used to measure phosphorus- and sulfur- containing compounds - Examples: organophosphate pesticides and mercaptans. - Photomultiplier detects light.

22. ELECTRON CAPTUREDETECTOR (ECD) - Selective and highly sensitive for halogenated hydrocarbons, nitriles, nitrates, ozone, organo- metallics, sulfur compounds, and many other electron-capturing compounds. - Selectivity based on the absorption of electrons by compounds that have an affinity for free electrons because of an electronegative group. - Use radioactive beta-emitting isotopes, (e.g. Ni63/tritium). - Non-chlorinated hydrocarbons have little electron affinity and are not detected. - Limitation is narrow linear range which necessitates careful calibration in the range of interest.

23. THERMAL CONDUCTIVITYDETECTOR (TCD) - Most universal GC detector because measures most gases and vapors. Low sensitivity compared with the other detectors; used primarily for analysis of low MW gases as CO, CO2, N2, and O2. - Measures differences in thermal conductivity between the column effluent and a reference gas (i.e. uncontaminated carrier gas). Most common carrier gas used is helium due to inert and also low MW. - Column effluent and the reference gas pass through separate detector chambers that contain identical electrically heated filaments. - Differences in thermal conductivity between gases is proportional to the rate of diffusion to/from the filament.

24. PHOTOIONIZATION DETECTOR (PID) - Sensitive to compounds with low ionization potentials that can be ionized by ultraviolet light. - Used to selectively detect a wide range of compounds including aromatics, alkenes, ketones, or amines in the presence of aliphatic chromatographic interferences. - Similar to FID, except that, instead of using a flame, it uses ultraviolet light to ionize the analyte molecules. - Different PID lamps are available to provide different photon energy levels. Lamp photon energy is chosen for selectivity of the analyte over the interferences present in sample.

25. DISCHARGE IONIZATION DETECTOR (DID) - High sensitivity to permanent gases and low MW compounds (CO, CO2, N2, O2, argon, hydrogen, methane). - Current is proportional to the amount of analyte in the effluent is amplified and recorded. - Useful in IH labs to analyze gas bag samples for determining the quality of breathing air.

26. NITROGEN AND SULFUR CHEMILUMINESCENCE DETECTORS (NCD & SCD) - Highly sensitive and selective towards nitrogen or sulfur-containing compounds. - NCD – ozone with nitrogen oxide reaction; used for trace-level analysis of nitrosamines and pesticides-containing nitrogen. - SCD – ozone with sulfur oxide, H2S and/or other reactions in an electrical furnace.

27. GC- MASS SPECTROMETRY (GC/MS) If the identify of the contaminant is not known, then GC analysis alone will be insufficient. Therefore, GC column effluent should pass through a detector that will provide a qualitative identification of the numerous peaks exiting the column – use of MS. - GC column effluent is introduced and ionized producing ions that are accelerated and separated by their mass-to-charge ratio. Mass spectrum is the record of the numbers of each kind of ion; and, relative numbers of each ion are characteristic for every compound, including isomers. - MS components: inlet system; ion source; accelerating system; detector system.

28. HIGH PERFORMANCE LIQUID CHROMATOGRAPHY (HPLC) HPLC preferred technique for compounds that have very high boiling points (low vapor pressures) and chemicals that may be unstable at elevated temperatures. - HPLC uses high pressures (500-3000 psi) required to move the mobile phase through a narrow column containing small sorbent particles. - Separation tool that must be combined with a detector (e.g. UV, fluorescence) to provide quantitative results. - PAHs; derivatized airborne organic isocyanates; bulk samples (e.g. oils, tars, resins, etc.)

29. UV-VIS ABSORBANCE DETECTOR - Measures UV or visible light absorbance of the column effluent. - Especially sensitive to aromatic hydrocarbons. - Fixed wavelength and variable wavelength detectors.

30. FLUORESCENCE DETECTOR - Measures emission of light produced by fluorescing eluents and is extremely sensitive to highly conjugated aromatic compounds (e.g. PAHs). - Some analytical methods use derivatization reagents to fluoresce the analyte. - Detectors vary in sensitivity and selectivity.

31. CONDUCTIVITY DETECTOR - Measures conductivity of the total mobile phase. Senses all ions present, from solute or mobile phases. - Detector is used for a large array of analyses which include many of those already described.

32. ELECTROCHEMICAL DETECTOR - Responds to compounds that can be readily oxidized or reduced. Such as phenols, aromatic amines, ketones, aldehydes, and mercaptans. - Electrode systems use working and reference electrodes to quantify analytes over a range of six orders of magnitude.

33. ION CHROMATOGRAPHY (IC) Form of ion exchange chromatography as a method of choice for anion analysis (e.g. sulfate; nitrate; phosphate; chromate; chloride; cyanamide; isocyanate; sulfite; and thiocyanate). - Also suitable for analyses of cationic species as well as used to analyze carcinogens that can be determined as cations (i.e. beta-naphthylamine, benzidene, hydrazines, etc.) - Components: separation column, background ion suppressor column, various eluents, and a detector. - Also use of conductivity detector.

34. VOLUMETRIC METHODS - Wet-chemical methods - Measuring the volume of a solution of a known concentration required to react completely with the substance being determined. - Titrimetric methods – detection of endpoint based on observation of property of the solution that undergoes a characteristic change near the equivalence point (e.g. HCl, H2S, SO2, O3, etc.). - Other examples: color, turbidity, electrical conductivity, electrical potential, refractive index, or temperature of the solution.

35. SPECTROPHOTOMETRIC METHODS - Visible light for “colorimetry”; or “absorption spectrophotometry” for measurement of the absorption of light at a particular wavelength by a solution containing the contaminant or a material that has been quantitatively derived. - Other methods developed involve use of UV or IR radiation. - Extent to which light is absorbed by the solution is related to the concentration of the contaminant in solution and the length of the light beam passing through the absorbing solution. - Described by Beer-Lambert law. - e.g. Saltzman’s reagent for nitrogen dioxide