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Can Sample Size Trends Be Trusted?

Posted by Betsey Seibel on Mon, Oct 24, 2016 @ 03:49 PM

small-smaller.jpgThe euphoric first few hours of a newborn’s life are briefly interrupted when the infant is whisked away, and the nurse informs the parents that staff will be pricking their infant’s foot for blood drops.  This test, that uses dried blood spot (DBS) technology, has been employed for over five decades.  The minimally invasive DBS test requires only a few drops of blood--DBS is the standard newborn screen for developmental, genetic and metabolic disorders.  DBS is also used in a variety of tests for adults; DBS can be employed for gene screening and long-term genetic bio-banking.

The sample preparation methodology used in DBS and other analysis systems has been trending toward using statistically smaller sample amounts.   This movement leaves bioanalysts experts to consider the question, “Is bigger better?”  Does a little sample size shape the exactness of results?  Are there connections linking sampling exactitude and sampling breadth? Do fresh, alternative microsampling approaches provide similar confidence levels? These are questions posed by a recent column in the September 2016 issue of LCGC Asia Pacific, titled “Know Your Sample: Size Matters”

In the column, the author discusses the trend in labs toward using smaller sample sizes.  This approach has shown that extraction and sample-handling techniques can be, in fact, viable at the microscale and smaller level.  This is contrasted with long-standing practices of needing larger sample sizes.  History asserts that the standard deviation of sampling and analysis escalates with the diminishing of analyte concentration.  Departures from this time-honored principle can be triggered because of sample preparation methods and because of the sample matrix.  Studies have illustrated that the anticipated relative standard deviation (RSD) from laboratory subsampling is a role of the maximum particle size in the sample. The lower you go in an analysis, the greater %RSD is possible.

Many of the connections that have been made between sample sizes and homogeneity originated from solid sample inquiry.  Since numerous microsampling techniques are used in bioanalysis, especially those used in blood analysis, considerations must be made for diffusion and turbulent flow.  Therefore, liquid samples can be deemed more homogeneous.

Because of their ease of use and low cost, paper-based and microfluidily techniques are growing in acceptance. Fluid changes are controlled and equalized with hydrophobic and hydrophilic treatments, thus producing reliable results.

SPME has emerged as a viable microsampling preparation approach because it has broad applications.  The biocompatible SPME application accommodates hypodermic needles or pipette tips.  Both SPME and biocompatible SPME are not comprehensive approaches, and they both depend on the balance connecting the analyte in biofluid and the fibre materials.

Biocompatible SPME has the benefit of tolerating several analyses on test animal subjects, consequently producing optimum results for the money. But, bio analysts should take into account that biocompatible SPME can deliver standard deviations close to 30%. 

Bio SPME fibres for mass spectrometry can also deliver straightway ionization of analytes. Spray solvent flow rates and the arrangement of the fibre supply bring measurable data that is analogous to results from bio-SPME.  Additionally, outcomes implementing this approach are five to ten times stronger than by using DBS technologies.

As new tools and technologies continue their marches through laboratories, bioanalytical professionals have a mix of viable analysis opportunities. Nevertheless, the strengths and weaknesses of sample diversity, microsampling techniques, and data integrity requirements all merit appropriate evaluation.

The drive to reduce this %RSD for lower sample concentrations, is what fuels Teledyne Tekmar to strive for continual improvements in their scientific instruments.  For more information on Tekmar's products be sure to contact us visit our website

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Tags: %RSD, SPME

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