Sample pooling

The three sets of replicate results below were accumulated for the analysis of the same sample. Pool these data to obtain the most efficient estimate of the mean analyte content and the standard deviation. 

MUX, cassette dosing, and sample pooling (parallel chromatography) approaches time-share MS by reducing dwell windows or reducing the number of data points across a chromatographic peak. These approaches in which the data parcels in milliseconds can monitor multiple channels rapidly... 

Sample pooling is also used in a process called cassette assay in which samples are pooled from multiple (typically 5 or 6) dosing experiments.24-83 87-88 Hsieh et al.89 showed that one could pool the plasma from six NCEs into one sample per time point to reduce sample assay time. Kuo et al.88 used a similar sample pooling approach for NCEs dosed into rats. The advantage is that cassette assay requires fewer samples. Two disadvantages are the need to dilute samples and the difficult set-up. 

High-throughput laboratories have turned to assay automation, N-in-one (sample pooling) analysis strategies, and elaborate set-ups for parallel chromatography30 33 to increase capacity and decrease turn-around time. Despite the relatively fast speed of HPLC/MS, this step still creates a bottleneck in ADME work flow. Xu et al.32 reported a fast method for microsomal sample analysis that yields 231 data points per hour using a complex eight-column HPLC/MS set-up. 

Rapid, accurate SNP validation can be carried out using a sample-pooling technique—allele frequency—that rapidly screens and confirms the presence of an SNP and its allelic frequency in patient populations. Conventional technologies typically analyze each SNP in each individual of the population in question, and individual results are then consolidated to yield the overall SNP allele-frequency distribution. MS-based technology is able to determine SNP allele frequencies with high precision in pooled samples, thereby replacing hundreds of individual measurements with one consolidated analysis. To that end, DNA is isolated, purified, and quantitated. A pool of DNA is formed from a high number of different individuals, amplified, and mass measured. 

Finally, sampling with replacement means that in theory, after each portion is selected and measured, it is returned to the total sample pool and thus has the opportunity to be selected again. This is a corollary of the assumption of independence. Violation of this assumption (which is almost always the case in toxicology and all the life sciences) does not have serious consequences if the total pool from which samples are sufficiently large (say 20 or greater) so that the chance of reselecting that portion is small anyway. 

Zhao, Y., Woo, G, Thomas, S., Semin, D., Sandra, P. Rapid method development for chiral separation in drug discovery using sample pooling and supercritical fluid chromatography-mass spectrometry. J. Chromatogr. A 2003, 1003, 157-166. 

A negative and positive control sample (pooled urine, spiked with urobilinogen/ PBG) is run with each batch of patient samples. 

Hexabromobiphenyl was detected (detection limit 6.6 g/kg) at a frequency of 8 57% in human adipose tissue samples from six Canadian Great Lakes municipalities in 1984 (Williams et al. 1988). The concentration of 2,2, 4,4, 5,5 -hexabromobiphenyl in adipose tissue samples pooled from tissues of the general population of the conterminous Unites States ranged from 1 to 2 g/kg (Lewis and Sovocool 1982). PBB levels in the adipose tissues of 15 quarantined dairy farm residents in mid-Michigan (where the mix-up involving FireMaster BP-6 occurred) ranged from 0.104 to 174 mg kg (Humphrey and Hayner 1975). 

Kuo BS et al (1998) Sample pooling to expedite bioanalysis and pharmacokinetic research. J Pharm Biomed Anal 16 837-846... 

The 17 bars represent the 16 individual samples ( ) and the sample pooled HLM(D). 

The subsequent sections will focus on the various elements speciated so far in human milk. Descriptions will be given of the different speciation approaches, reasons for choosing a given element for speciation in human milk, type of samples used (sample pooled or individual, lactation state), separation and detection techniques, identification of species, QC and QA. Lastly, the results available will be briefly overviewed. 

Figure 1 Identification of a linear hexapeptide epitope by Geysen. In the first cycle, all possible hexapeptides are prepared as sample pools where four positions are randomized mixtures of 20 amino acids (X), and Oj and Oj tire defined amino acids, leading to 20x20 = 400 samples. The best sequence, XXLEXX, had an ELISA absorbance of 0.32. In the second cycle, the LE was fixed and two other positions varied, leading to the new best sequences XELEXX and XXLEKX. Eurther cycles of synthesis and screening led to the epitope as a single sequence...

Sixty two serum samples for method comparison were collected from the patient sample pool of Lab A. The S-Li concentrations varied between 0.1 mmol/l and 1.6mmol/l, thus covering both the therapeutic range and the decision making levels of S-Li. All 3 instruments were capable of measuring, quantitatively, 56 samples. Six samples, were beyond the lower measurement ranges of the Microlyte 6 and Chiron 654 instruments. The samples were aliquoted into appropriate tubes and refrigerated until analysed. 

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