Sampling and Analysis


Published analytical methods address several hundred possible workplace contaminants. However, these methods do not address all chemical hazards. The following references link to resources that provide analysis information on many chemical hazards.

Analytical Methods
Method Modification and Development

Published analytical methods address several hundred possible workplace contaminants. However, these methods do not address all chemical hazards. Some chemicals are so specialized that they are rarely encountered. New chemicals are constantly being developed. Other chemicals are not stable on existing sampling media. In these instances it becomes necessary to modify an existing method to accommodate the contaminant or a new method must be developed.

The procedures for method modification and development vary depending on the properties of the chemical, possible interferences, the desired sampling medium, the desired analytical technique, sensitivity required, and similar factors. Therefore, method modification and development should only be undertaken by an experienced analyst or researcher. However, the following are items which should be considered and answered by any method modification or development.

  • Can the analyte be collected by and removed from the sampling media?
  • What are the collection and recovery factors and are they acceptable?
  • Is the detection limit sufficiently low to provide meaningful data, especially when adjusted for collection and recovery factors?
  • Will expected interferences produce false positive, false negative, or biased results?
  • If possible, can the results be verified by comparison with an accepted procedure?
  • NIOSH Manual of Analytical Methods (NMAM). NMAM is a collection of methods for sampling and analysis of contaminants in workplace air, and in the blood and urine of workers who are occupationally exposed. NMAM also includes chapters on quality assurance, sampling, portable instrumentation, etc.
Laboratory Selection

The selection of a laboratory is influenced by many factors. Among these are:

  • Does the laboratory perform the required analysis?
  • What are my requirements for quality assurance and does the laboratory quality assurance program meet these requirements?
  • Does the laboratory analyze samples and report results within my required turnaround time?
  • Does the analytical report contain the information I need?
  • Are detection limits reported and are they sufficiently low?
  • Are analytical costs acceptable?
  • Does the laboratory provide the client services I desire?
  • Am I confident in the results provided?

Laboratory Accreditation and Certification

Participation in accreditation and certification programs allow laboratories to compare themselves against other laboratories and against accepted standards. Most programs require participation in a performance evaluation testing program where samples of unknown concentration are analyzed and reported to an independent body. Many programs require an on-site assessment by a trained quality assessor. Successful participation in an accreditation or certification program is an indicator that a laboratory operates under a functioning quality assurance program. It does not guarantee that the results produced by the laboratory are beyond question.

Laboratory (Internal)

Laboratories analyzing samples should have a documented quality management system. This system should address topics such as:

  • Organization of the Management System
  • Control of Documents, Data and Records
  • Purchasing
  • Corrective and Preventive Action
  • Internal Audits
  • Selection and Training of Personnel
  • Selection of Analytical Methods
  • Quality Assurance and Estimation of Uncertainty
  • Equipment and Instrumentation
  • Traceability of Standards and Materials
  • Reporting of Results

Laboratory (External)

Laboratories performing industrial hygiene analyses should participate in external performance evaluation programs, and be subject to audit by external assessors. The appropriate accreditation and certification programs discussed above should be part of a laboratory's quality assurance program.

When submitting samples to a laboratory, there are several methods which can be easily used to assess the accuracy and precision of the laboratory's results. In all cases, if a problem is detected, it would be wise to assume that the error is in the external sample, unless other information indicates otherwise. Once a problem has been identified, the laboratory quality assurance manager should be contacted and the problem resolved to the satisfaction of all parties.

  • Collect two samples under the same conditions. Remember, when evaluating these samples, that the two samples are not identical. For instance, a droplet of solvent could be splashed onto one sample but not the second giving a false reading for the first sampler.
  • If the sample is a bulk material, divide it into two portions after thoroughly homogenizing. If the sample is not homogenized, the two portions could contain differing amounts of analyte.
  • Prepare "spiked" samples of known concentration to be submitted blind with field samples. These must be prepared by a skilled individual. Additional spikes should be prepared at the same time so that the spiking can be verified by a second laboratory if questionable results are reported.