Chemical Sampling and Analytical Methods Guide
A practical occupational hygiene reference page for selecting air sampling methods, sampling media, flow rates, analytical techniques and external method references for workplace chemical exposure assessment.
Method selection is one of the most important technical decisions in chemical exposure monitoring.
The sampling method determines what is collected, how much air is sampled, which sampling medium is used, how the sample is preserved, and how the laboratory analyses the contaminant. This page helps users understand the method selection process and links to recognised external resources such as NIOSH and OSHA.
Identify the analyte
Confirm the chemical name, CAS number, physical form, exposure limit, expected concentration range and whether the contaminant is present as gas, vapour, dust, mist, fume or fibre.
Select a validated method
Review recognised sampling and analytical methods such as NIOSH, OSHA, HSE, ASTM, ISO or equivalent validated laboratory procedures.
Match media and laboratory
Confirm the sampling medium, flow rate, sample volume, preservation, holding time, blanks and analytical technique with the laboratory before field sampling.
A practical sequence for selecting chemical sampling and analytical methods.
This workflow can be used when planning workplace air monitoring for solvents, metals, acids, gases, dusts, fumes and other chemical hazards.
Confirm substance
Check chemical identity, CAS number, SDS composition and possible decomposition or reaction products.
Define exposure limit
Identify the relevant Singapore PEL, short-term exposure limit, action level or internal occupational exposure criterion.
Choose method
Review NIOSH, OSHA, HSE or other validated methods and confirm whether the method fits the exposure objective.
Confirm sampling plan
Check medium, pump flow rate, sampling duration, total volume, blanks, preservation and laboratory requirements.
Interpret results
Compare measured concentration with the applicable limit and provide practical exposure control recommendations.
Chemical Sampling Method Finder
Use this starter finder to understand common sampling method categories. For formal monitoring, always verify the current method details with the official method source and the analytical laboratory.
| Chemical / Hazard Group | Typical Method Sources | Common Sampling Media | Common Analysis | Planning Notes | External Reference |
|---|---|---|---|---|---|
| Organic vapours and solvents | NIOSH, OSHA, HSE | Activated charcoal tube, other sorbent tubes, passive samplers where validated | GC-FID, GC-MS or equivalent | Confirm breakthrough volume, desorption efficiency, humidity effects, mixed solvent compatibility and required detection limit. | Search NIOSH NMAM |
| Total dust / inhalable particulate | NIOSH, OSHA, ISO, HSE | Filter cassette or inhalable sampler depending on method | Gravimetric analysis; additional elemental or chemical analysis where required | Confirm particle size fraction, sampler convention, filter type, weighing conditions, blanks and minimum sample mass. | Search NIOSH NMAM |
| Respirable dust | NIOSH, OSHA, ISO, HSE | Cyclone with filter cassette or validated respirable sampler | Gravimetric analysis; silica analysis if required | Use the correct cyclone flow rate and keep the cyclone vertical. Do not invert the cyclone after sampling. | Search NIOSH NMAM |
| Respirable crystalline silica | NIOSH, OSHA, ISO, HSE | Respirable cyclone with PVC filter or method-specified filter | XRD, IR or other validated silica analysis | Confirm quartz, cristobalite and tridymite requirements, expected dust loading and analytical limit of quantitation. | Search OSHA methods |
| Metals, metal fumes and welding fumes | NIOSH, OSHA, HSE | Filter cassette, mixed cellulose ester filter, PVC filter or method-specified media | ICP-AES, ICP-MS, AA or equivalent | Confirm target metals, digestion method, particle fraction, welding task variability and whether hexavalent chromium needs a specific method. | Search NIOSH NMAM |
| Hexavalent chromium | NIOSH, OSHA | Method-specified treated or coated filter where required | IC, UV/VIS or equivalent validated method | Hexavalent chromium can be chemically unstable. Confirm sample preservation, storage, holding time and interference control with the laboratory. | Search OSHA methods |
| Formaldehyde and aldehydes | NIOSH, OSHA, EPA | DNPH-coated media, treated sorbent tube, treated filter or impinger depending on method | HPLC-UV, GC or equivalent | Confirm short-term versus full-shift objective, derivatisation chemistry, humidity, ozone interference and field blank requirements. | Search NIOSH NMAM |
| Acid gases and inorganic gases | NIOSH, OSHA, HSE | Sorbent tube, impregnated filter, impinger or direct-reading method depending on substance | IC, spectrophotometry, specific electrode or equivalent | Confirm gas reactivity, humidity, sampling train compatibility, short-term exposure objective and detection limit. | Search NIOSH NMAM |
| Isocyanates | NIOSH, OSHA, HSE | Impinger, treated filter or derivatising sampler depending on method | HPLC-UV, HPLC-fluorescence or equivalent | Isocyanate sampling is highly method-specific. Confirm derivatisation, sampling stability, aerosol/vapour collection and laboratory capability before monitoring. | Search OSHA methods |
| Screening with direct-reading instruments | Instrument manufacturer methods, OSHA guidance, internal monitoring plan | PID, electrochemical sensor, detector tube or other direct-reading instrument | Real-time reading or colorimetric indication | Useful for screening and process investigation, but may not replace validated sampling for compliance assessment. Confirm selectivity, cross-sensitivity and calibration gas. | Review OSHA resources |
Do not select a method by chemical name alone.
A chemical may have more than one method depending on the exposure objective, expected concentration, physical form, analytical technique, regulatory purpose and sampling duration. The method must be suitable for the actual workplace scenario.
Before sampling
- Confirm the substance name, CAS number and expected exposure level.
- Check whether the sampling objective is TWA, STEL, ceiling, task-based exposure or screening.
- Confirm the applicable Singapore PEL or other occupational exposure criterion.
- Speak with the laboratory before sampling to confirm media, storage, blanks and reporting limits.
During and after sampling
- Calibrate pumps before and after sampling using the complete sampling train where appropriate.
- Record sampling duration, flow rate, temperature, pressure, process conditions and worker activity.
- Submit samples with blanks and chain-of-custody documentation.
- Interpret results against the correct exposure limit and sampling period.
Sampling media must match the contaminant and analytical method.
The examples below are for educational orientation only. The exact medium, flow rate, sample volume and preservation conditions must follow the selected validated method and laboratory instructions.
Sorbent tubes
Commonly used for organic vapours and gases. Selection depends on adsorption capacity, breakthrough risk, desorption efficiency and analytical method.
Filters and cassettes
Commonly used for dusts, fumes, metals and aerosols. Filter material and sampler type affect particle collection and analytical compatibility.
Passive samplers
Useful for selected vapours where validated. They require appropriate environmental conditions and should not be assumed suitable for all chemicals.
Impinger or treated media
Used for selected reactive gases, aldehydes, isocyanates and other chemicals requiring collection into liquid or derivatising media.
GC / GC-MS
Frequently used for volatile and semi-volatile organic compounds, solvents, hydrocarbons and many vapour-phase contaminants.
HPLC
Often used for compounds requiring derivatisation or UV/fluorescence detection, such as some aldehydes and isocyanates.
IC / ICP / AA
Used for inorganic ions, acid gases, metals and metalloids depending on the method and required sensitivity.
Gravimetric
Used for mass-based particulate exposure such as total dust, inhalable dust or respirable dust, with additional analysis where needed.
A sampling guide is not a substitute for competent occupational hygiene judgement.
Method guides are extremely useful, but a competent professional still needs to confirm whether the method is suitable for the workplace, the contaminant, the expected exposure level and the intended interpretation of results.
Method validity
Check whether the method is validated, partially validated, withdrawn, superseded, modified or only suitable for specific concentration ranges.
Detection limits
Confirm that the laboratory reporting limit is low enough for comparison with the relevant PEL, action level or internal exposure criterion.
Interferences
Consider humidity, temperature, co-contaminants, chemical instability, breakthrough, sampler orientation and storage conditions.
Use the current official method source before conducting formal monitoring.
This IEH page is a practical guide for method selection. It should be read together with the current method, laboratory instructions and Singapore regulatory requirements.
NIOSH NMAM: The NIOSH Manual of Analytical Methods is a collection of sampling and analytical methods for workplace exposure monitoring, including workplace air, surface, blood and urine methods. Open NIOSH NMAM.
OSHA Sampling and Analytical Methods: OSHA provides an index of validated or partially validated methods and notes that current media and flow-rate information should be checked through the OSHA Occupational Chemical Database where applicable. Open OSHA Sampling and Analytical Methods.
Professional note: This page does not reproduce proprietary product databases or replace formal method review. It supports preliminary planning and points users to recognised method sources.
Need help selecting methods or planning chemical exposure monitoring?
IEH provides occupational hygiene consultancy, chemical exposure monitoring, air sampling strategy, laboratory coordination and practical exposure control recommendations for workplaces handling hazardous substances.