When most people think about laboratory testing, they picture sophisticated instruments, advanced analytical methods, and detailed reports. While those components are certainly important, there is another factor that often determines the quality of a test result long before a sample ever reaches the laboratory:
The sample itself.
Even the most advanced laboratory equipment cannot compensate for a sample that is poorly collected, contaminated, improperly stored, or unrepresentative of the material being tested. Whether analyzing food, feed, soil, water, urine, or hair, the quality of the sample directly affects the quality of the results.
At Health Research Institute (HRI), we often say that good science begins with good sampling.
The purpose of laboratory testing is to understand the characteristics of a larger system. A soil sample represents an entire garden or field. A water sample represents a well, pond, or municipal source. A grain sample represents a harvest. A urine sample provides insight into compounds that may be passing through the body.
In every case, the laboratory only analyzes the material that arrives in the sample container. If that sample does not accurately represent the larger whole, the resulting data may be misleading.
For this reason, scientists place tremendous emphasis on proper sample collection, handling, and preparation.
One of the most common sampling mistakes is collecting material from a single location and assuming it represents the entire source.
In reality, many substances are not distributed evenly.
For example:
This is why composite sampling is often recommended. Rather than collecting material from a single spot, multiple subsamples are collected from different locations and combined into one representative sample. This approach helps reduce variability and provides a more accurate picture of the whole.
Another important consideration is contamination during collection.
Even trace amounts of foreign material can affect sensitive laboratory analyses. A sample may become contaminated through:
For this reason, HRI recommends using clean collection materials and following the specific instructions provided for each sample type.
A contaminated sample can lead to inaccurate results, unnecessary concern, or the need for repeat testing.
Even the most advanced laboratory instruments depend on the quality and representativeness of the sample they receive.
A contaminated sample can lead to inaccurate results, unnecessary concern, or the need for repeat testing.
While the details vary by sample type, the underlying goal remains the same: collect a sample that accurately represents the material being tested.
Agricultural and food products often exhibit natural variability. One handful of grain, one scoop of feed, or one portion of a food product may not accurately represent the entire batch. Nutrients, pesticide residues, contaminants, and other compounds can be distributed unevenly throughout a product, especially in bulk materials.
To obtain a more representative sample, material should be collected from multiple locations throughout the batch. For example, grains, powders, and feed should be sampled from the top, middle, and bottom rather than from a single location. Packaged products may benefit from sampling multiple units when possible. Thorough mixing prior to submission can further improve sample representativeness.
Proper preparation is also important. Dry materials should be mixed thoroughly to ensure uniformity, while foods that contain multiple ingredients may benefit from chopping or breaking into smaller pieces and creating a composite sample. Care should be taken to avoid introducing moisture, heat, or other changes that could alter the sample before testing.
HRI Tip:
When sampling bulk materials, think "representative, not convenient." A sample collected from multiple locations throughout a batch is often more representative than a single scoop from the top.
Soil may appear uniform on the surface, but pesticide residues, nutrients, and other compounds are often distributed unevenly throughout a garden, pasture, or agricultural field. As a result, a single scoop of soil rarely provides an accurate picture of the entire area.
To obtain a more representative sample, multiple soil cores should be collected from across the area of interest and combined into a composite sample. A soil core is simply a vertical plug or column of soil collected using a soil probe, shovel, or similar tool. For pesticide testing, cores are typically collected to a depth of approximately 6–8 inches to provide a representative profile of the root zone, where many agricultural chemicals and biological processes occur. HRI recommends collecting at least five cores from small areas and approximately ten cores per 100 acres for larger fields. Samples should be collected from within the field rather than along edges, where conditions may differ from the area being evaluated. The image shown illustrates a five-point composite soil sampling pattern commonly used to improve sample representativeness.
Because surface soil can differ significantly from soil just a few inches below, collecting cores to a consistent depth helps ensure more meaningful and comparable results over time.
Proper preparation after collection is equally important. Soil should be air-dried, free of rocks and plant debris, and thoroughly mixed before a sub-sample is selected for laboratory analysis. Homogenization helps ensure that any pesticide residues present are distributed as evenly as possible throughout the sample.
HRI Tip:
A handful of soil rarely tells the whole story. Composite samples created from multiple soil cores generally provide more reliable results. If you prefer not to dry and homogenize the sample yourself, HRI offers a laboratory homogenization service to help ensure a well-mixed, representative sample.
Water and beverages may appear uniform, but important compounds can be distributed unevenly depending on the source, storage conditions, or the presence of suspended solids. As with other sample types, collecting a representative sample is essential for obtaining meaningful results.
For drinking water, it is often recommended to allow the tap to run for one to two minutes before collection unless a first-draw sample is specifically required. For surface water sources such as lakes, ponds, and streams, samples should generally be collected below the surface while avoiding floating debris and disturbed sediment. Similarly, bulk liquids and beverages may benefit from gentle mixing before collection, particularly if separation has occurred.
Proper handling is equally important. Clean, tightly sealed containers help prevent contamination, while appropriate storage and shipping conditions help preserve sample integrity until analysis can be performed. Temperature, transit time, and leakage can all affect sample quality if not properly managed.
HRI Tip:
Water samples should represent the source itself—not floating debris, settled sediment, or contaminants introduced during collection. Clean containers and careful handling go a long way toward improving sample quality.
Urine is commonly used in exposure assessment because it can provide information about compounds that have recently passed through the body.
Proper collection procedures help minimize contamination and ensure that the sample accurately reflects the intended collection period. Following collection instructions carefully is essential for obtaining reliable results.
For many exposure and biomonitoring applications, the first urine of the day (often called the first morning void) is preferred. Overnight, urine becomes more concentrated, which can improve the detection of certain compounds and biomarkers while reducing the influence of recent hydration and dietary patterns.
HRI Tip:
If first morning urine is requested, collect the first urine sample after waking. Consistent collection timing helps improve the quality and comparability of results.
Hair can provide a unique record of environmental exposures over time because compounds may become incorporated into the growing hair shaft. Unlike urine, which often reflects more recent exposures, hair may provide insight into exposures that occurred over months.
Because hair is continually exposed to the environment, proper collection is important. Factors such as collection location, sample quantity, cosmetic treatments, and handling procedures can all influence sample quality and consistency. To obtain a more representative sample, HRI recommends collecting small amounts of hair from several locations at the back of the head rather than taking all of the hair from a single spot. Samples should be cut as close to the scalp as practical, and the 1.5–2 inches of hair nearest the scalp are typically preferred for analysis. Because hair grows gradually over time, this portion generally reflects approximately the previous two to three months of growth and potential exposure. Standardized collection practices help ensure that samples are collected consistently and that results can be interpreted more reliably.
HRI Tip:
Hair can provide a longer-term record of exposure than urine. Collecting hair from several locations at the back of the head and submitting the portion closest to the scalp helps create a more representative and interpretable sample.
Sample quality does not stop at collection.
Even a perfectly collected sample can be compromised during shipping if it is not packaged properly. Improper packaging can result in leaks, contamination, degradation, broken containers, or other issues during transit. Accurate labeling, secure packaging, and timely shipment all help preserve sample integrity from collection through analysis.
One of the most common problems laboratories encounter is leakage during shipment. A container lid that is not fully tightened or properly seated can allow sample material to escape during handling and transportation. In some cases, leaked samples may contaminate accompanying paperwork or other samples within the shipment.
For this reason, many laboratories recommend placing samples in a primary container, sealing them securely, and then placing them inside a second leak-proof bag. Including absorbent material can provide additional protection by containing any accidental leaks before they affect the rest of the package.
When samples arrive damaged, leaking, improperly labeled, or otherwise compromised, laboratories may need to contact the customer, request clarification, delay testing, or in some cases request a replacement sample. These situations can increase turnaround time and may require recollection of the sample.
HRI Tip:
Before shipping, double-check that all lids are tightened securely and squarely, labels are legible, and samples are sealed inside a secondary leak-proof bag. When appropriate, include absorbent material to help contain accidental leaks during transit. A few extra minutes spent packaging a sample properly can help prevent delays and ensure testing can begin as soon as the sample arrives.
In addition to proper packaging, some sample types may be subject to additional shipping, permitting, or regulatory requirements. For example, certain states have restrictions on the testing of human biological samples, while some agricultural and soil samples may require additional documentation when shipped from quarantined areas, U.S. territories, or international locations.
These requirements are intended to protect public health, agriculture, and the environment, and they can vary depending on the sample type and point of origin. Failure to meet these requirements can result in shipment delays, rejected samples, or the need for additional documentation before testing can begin. Before collecting or shipping a sample, it is always a good idea to review the laboratory's current collection instructions and submission requirements.
HRI Tip: If you are submitting biological, soil, agricultural, or international samples, contact HRI before shipping if you are unsure whether additional documentation or approvals may be required.
Advanced instrumentation is an essential part of modern analytical testing, but even the most sophisticated technology depends on the quality of the sample received.
Whether you are testing food, feed, soil, water, beverages, urine, or hair, careful sample collection is one of the most important steps in obtaining meaningful and reliable results.
At HRI, we provide detailed collection instructions for every sample type because accurate science begins long before a sample enters the laboratory. By following proper collection procedures, you help ensure that your sample accurately represents the material being tested—allowing the laboratory to generate the most reliable and meaningful results possible.
Health Research Institute (HRI) is an accredited analytical laboratory providing testing services for environmental samples, food and agricultural products, water, and biological specimens. Our mission is to advance scientific understanding through high-quality analytical testing, research, and education. By helping clients collect representative, high-quality samples and generating reliable analytical data, we strive to support informed decision-making and greater transparency in environmental and biological testing.
