Trip blanks

Trip blanks to determine if contaminants are introduced the processes of collecting, shipping, or storing of samples. 

Trip blanks are QC samples associated with the field samples collected for VOC analysis, such as chlorinated and aromatic hydrocarbons and volatile petroleum products. Trip blanks are sometimes called travel blanks. 

To imitate water samples, trip blanks are prepared in volatile organic analysis (VOA) vials with septum caps lined with polytetrafluoroethylene (PTFE). The vials are filled without headspace with analyte-free water. For soil sampled according to the requirements of EPA Method 5035, field blanks may be vials with PTFE-lined septum caps, containing aliquots of methanol or analyte-free water. 

The analytical laboratory prepares the trip blanks and ships them to the project site in a cooler together with empty sample containers. The laboratory is responsible for ensuring that the trip blank and the provided empty sample containers are analyte-free. In the field, the trip blanks are kept together with sample containers and, after the samples have been collected, with the samples. Trip blank vials are never opened in the field. 

The purpose of trip blanks is to assess the collected sample representativeness by determining whether contaminants have been introduced into the samples while they were handled in the field and in transit, i.e. in coolers with ice transported from the site to the analytical laboratory. A possible mechanism of such contamination is the ability of some volatile compounds, such as methylene chloride or chlorofluor-ocarbons (Freons), to penetrate the PTFE-lined septum and dissolve in water. Potential sources of this type of contamination are either ambient volatile contaminants or the VOCs that could be emanating from the samples themselves, causing sample cross-contamination. To eliminate ambient contamination, samples must not be exposed to atmospheres containing organic vapors. Cross-contamination is best controlled by such QA measures as sample segregation and proper packaging. 

One trip blank in each cooler with samples for YOC analysis... 

Most often, trip blank contamination originates in the laboratory, either from common airborne laboratory contaminants (methylene chloride, acetone) or from laboratory water containing VOCs, typically methylene chloride, acetone, and toluene or water disinfection byproducts (chloroform, dichlorobromomethane, chlorodibromomethane, bromoform). Rare, but well documented sources of trip blank and associated field samples contamination are insufficiently clean sample... 

Aqueous trip blanks sometimes accompany soil samples collected into metal liners or glass jars. In this capacity they do not provide any meaningful information. Soil samples do not have the same contamination pathway as water samples because they are not collected in 40-milliliter (ml) VOA vials with PTFE-lined septum caps. In addition, soil does not have the same VOC transport mechanism as water does (adsorption in soil versus dissolution in water). There are other differences that do not permit this comparison different sample handling in the laboratory different analytical techniques used for soil and water analysis and the differences in soil and water MDLs. That is why the comparison of low-level VOC concentrations in water to VOC concentrations in soil is never conclusive. 

The use of clean oven-baked sand for soil trip blanks has also been proposed (USACE 1994 Lewis 1988). This practice does not provide any meaningful information either. The transport mechanism of VOCs in sand is different from the VOC transport mechanism in soils, which, unlike sand, have complex lithological compositions and varying organic carbon content. 

Trip blanks prepared in vials and containing aliquots of methanol or analyte-free water accompany soil samples collected in a similar manner for low concentration VOC analysis according to EPA Method 5035. In this case, field samples and trip blanks have the same contamination pathway when exposed to airborne contaminants and the same VOC transport mechanism. These trip blanks provide important information, which may enable us to recognize the artifacts of improper sample handling, storage, or shipping. 

Justify the need for trip blanks based on the knowledge of existing contaminant concentrations or data use. 

Collect trip blanks for water sample analysis only when low level contamination is a matter of concern. 

To minimize the number of trip blanks and the cost of their analysis, segregate water samples for VOC analysis in one cooler. 

Trip blank a vial with 5 ml of water, preserved or unpreserved... 

The trip blank should correspond to the mode of sampling. 

Was a trip blank included with the samples for VOC analysis ... 

Results of the field QC samples (trip blanks, field duplicates, equipment blanks, etc.) are part of the data packages and, together with field samples, they are evaluated to establish whether they are valid. But what is the significance of these data Like the field samples, these data were collected for a well-defined need, use, and purpose. They provide part of the answer to the question Are the data representative of the sampled matrix ... 

Trip blanks—a clean sample that is sent from the laboratory with the empty sampling bottles and remains with other samples throughout the sampling trip without being opened. This is typically required only for volatiles and assesses contamination during shipping and field handling. 

If a matrix is not represented in a SDG, then no spiked sample is required for that matrix. If the region or samplers have identified a particular sample to be used for the spike, the laboratory must use an aliquot of that sample. If the region or samplers have not identified a specific sample for spiking, then the laboratory may choose a sample from the SDG however, the sample chosen must not be a sample identified by the region as a field or trip blank. 

Aqueous samples should be accompanied by triplicate trip blanks (e.g. reference water samples) to allow cross-contamination in transit to be identified. 

One trip blank (Two 40m vials filled with distilled/deionized water) per cooler of volatile organic samples. Performance evaluation sample (optional)... 

Method blanks, rinsate blanks, trip blanks, as in QA2. 

Trip blanks may be useful in addition to field blanks. These are similar to field blanks but are not uncapped in the field, thus being useful to delineate contamination which occurs from handling and storage from that which occurs from dust or other external sources during containment of real samples. 

Field trip blanks to identify radionuclide contamination in the collection material (e.g.. Alter or sorbent) and container. 

Because many of the constituents of concern were volatile substances, this lengthy timeline and the missing date as to when the samples were actually analyzed are even more important. Also, several trip blank samples were apparently contaminated with volatile compounds, raising a further question on how well the sample blanks were sealed and whether any loss of volatile constituents occurred before analysis. 

---