The Importance of Proper Sample Handling
Jashan Gokal | 3 February 2016
Biological samples are no different from your average emotional teenager or an old stick of dynamite- delicate, temperamental and highly volatile- so HANDLE WITH CARE. In fact, it would not be wrong to think of your biological sample as a really small pet- one that needs to be regularly fed and generally kept happy. In order to keep any downstream findings scientifically accurate and defensible, there are a few parameters that should not be overlooked when taking a biological sample.
- Sampling consistency: Biological samples should be procured at consistent intervals to minimize interference from external factors. Wastewater samples should be obtained at roughly the same time during each sampling period to minimize confounding diurnal flows, water temperature and nutrient variations etc. It is a good practice to take roughly the same amount of sample at each sampling point simply to ensure you have enough left for extra analysis (if there is an interesting observation of course).
- Sampling significantly: The greater the number of samples taken, the lower the overall error of your sampling regime. While that may seem like a lot of work processing these samples, you can always pool your individual samples together into a single representative sample. Pooled samples obtained from many similar locations are almost always better than a single grab sample for truly representing a large system. The key to successfully pooling samples depends on the specific study in question, but as long as the samples were obtained consistently (See point 1) from a zone where all parameters should theoretically be equal, then you’re generally safe to pool.
- Sample integrity: Almost all samples are collected to be analysed off-site. Thus a lot of thought needs to be put into the storage and transportation conditions required by each sample type. Is it an anaerobic or aerobic sample, does it require light or will mixing during transport affect it downstream? For wastewater samples coming from the aerobic zones, a decent headspace should be left in the sampling bottle to maintain aerobic conditions during the journey back to the lab. Conversely anaerobic samples should generally minimize the inclusion of air thus no headspace is required. Wastewater samples should also be chilled for transport or filtered, with the filtrate transported in a separate vessel in order to minimize chemical changes within the sample matrix.
- Sample control: It’s always good practice to immediately jot down your on-site observations, and label your samples with as much detail as you possibly can. For those of us not using fancy RFID tags and barcodes (I’m looking at you pharma-companies), we have no choice but to write out our labels in our legible-only-to me handwriting. As long as you can understand it, make sure your label includes at least the:
- sample name;
- sampling location;
- sampling date;
- purpose of the sample (especially if it’s to be used for a particular study or specific test);
- A reference to any other observations made at the time (sometimes just a star on your sample name reminding you to look at your notes would be enough for that).
These are some basic tips for effective sampling that will soon become second nature to any scientist out in the field, and will allow for far more accurate analysis and far fewer statisticians having fits about non-representative data points. Once you develop the habit for proper sampling procedure, you can dedicate far more brainpower to unravelling the mysteries of the universe rather than trying to remember where this particular sample came from.