Near-Real-Time Quantification of Odor Chemistry of Un-derivatized Human Blood

Blood is a highly complicated mixture, and therefore, the number of various blood components that can be determined in the blood’s aroma relies on the separating ability and sensitivity of the technique employed as it does to the samples themselves.

Plasma is one of the components of blood. This is a water matrix composed of constituents such as sugars and carbohydrates, proteins, nucleotides, and lipids and fatty acids.

Blood is composed of a large number of molecular chains containing 20 amino acids, which are highly volatile chemicals and mainly responsible for the odor of blood. Amino acids are linked by a type of covalent bonding called peptide bonds.

Peptides are short chains of amino acids and polypeptides are long chains of amino acids. Amino acids are organic acids with relatively low molecular weight and contain a carboxylic acid group (-COOH) and an amine (-NH2) group.

They are the fundamental building blocks of proteins and always pose a challenge due to significant variations in their chemical structure spanning from highly polar to non-polar. The low vapor pressure and, in some cases, thermal liability of amino acids necessitate synthesis of highly volatile and easily detectable and quantifiable derivatives.

Detectability always poses a challenge to analysts, necessitating the use of special techniques for liquid chromatography, gas chromatography, and in capillary electrophoresis (CE). The advent of sufficiently sensitive GC detectors allows blood odors to be directly chromatographed without derivatization.

New analytical tool for odor measurements

zNose® is a new kind of portable gas chromatograph capable of performing near-real-time analytical measurements of volatile organic odors and vapors with a sensitivity down to part per trillion levels. Thanks to its picogram sensitivity, this device can be used to explore metabolic and bio-chemical processes involving all kinds of volatile organics.

Using the zNose®, the separation and quantification of the organic chemistry of odors can be performed within a minute through ultra-high speed chromatography. The use of a patented solid-state mass-sensitive detector provides the zNose® with electronically variable sensitivity, universal non-polar selectivity, and picogram sensitivity.

The combination of an integrated vapor preconcentrator and the electronically variable detector enables the zNose® to quantify vapor concentrations ranging 12 orders of magnitude. Figure 1 shows the three different commercial instruments equipped with the zNose® technology.

With a high throughput (300 plus measurements per day), the Model 7100 laboratory GC is suitable for auto-samplers. The multi-port Model 7110 zNose® can be used for automated, real-time monitoring of monitor multiple vapor streams of a chemical process. The incorporation of a disposable helium tank allows the portable Model 4200 handheld zNose® to perform onsite ambient air and odor measurements.

Figure 1. zNose® technology incorporated into 3 commercial instruments.

Blood odor chemistry

The odor chemistry of a blood sample can be determined by sorting the amino acids by their molecular weight. An initial estimate of odor intensities can be obtained from the names and concentration range for each acid among three subject age groups. The chemical signature of blood odors can be also be estimated using other physical properties, such as boiling point and vapor pressure.

Based on the properties presented in Table 1, one can anticipate an estimated chromatogram response as shown in Figure 2.

Table 1. Common organic chemicals in human blood

Molecular- Weight

Plasma or Serum µmole/liter

Age in Years

0-2

2-10

>10

Glycine

75.07

178-248

117-223

120-553

Alanine

89.09

239-345

137-305

209-695

Serino

105.09

104-158

79-112

67-193

Proline

115.13

141-245

68-148

100-442

Valine

117.15

123-199

128-283

116-315

Threonine

119.12

141-213

42-95

79-246

Cystine

121.16

16-26

23-39

24-71

Taurine

125.14

101-181

57-115

27-168

Ornithine

132.162

39-61

27-86

29-125

Aspartic Acid

133.1

17-21

<20

<24

Isoleucine

131.17

31-47

28-64

35-97

Lysine

146.19

107-163

71-151

82-236

Glutamic Acid

147.13

27-77

23-250

14-192

Glutamine

146.15

623-895

676

413-690

Methionine

149.21

15-21

11-16

6-39

Histidine

155.16

64-92

24-85

31-106

Phenylalanine

165.19

45-65

26-61

37-115

Tryosine

181.19

33-75

31-71

21-87

Figure 2. Projected response based upon molecular weight and concentration

Odor chemistry

The concentration of the odor chemicals can be directly measured using the zNose® GC, and for each of the odor chemicals detected, their retention times are estimated by identifying peaks in the GC column flux. The time derivative of the detector signal is mathematically performed to compute the column flux in real time.

The result is a chromatogram spanning for less than a minute, denoting the rate of adsorption and desorption of vapors onto the mass-sensitive detector. The chemistry within an odor can be quantitatively measured when the retention times are tabulated together with the total and individual concentration counts (cts).

Within an odor, the retention time of a chemical is referenced to the retention time of a standard odor mixture of linear chain n-alkanes. Figure 3 shows the odor response measured using methanol spiked with C6 through C14 alkanes.

Kovats indices are retention times of unknown peaks that are referenced to the n-alkanes. They allow the application of retention time libraries in future identifications. Indices for the n-alkanes show the four-digit notation of Kovates indices, for example, c14=1400.

Figure 3. Retention time calibration using n-alkane response C6 to C14. All relative retention times are called Kovats indices

Kovats indices of amino acids

The Kovats indices and retention times of amino acids were estimated by spiking a septa-sealed vial with a mixture of amino acids of known concentration and quantifying the odor chemistry of the vial headspace using a zNose®.

Here, after injecting 10µL of an amino acid mixture into a 40 milliliter septa sealed vial, it was thermostated at 37°C. In the standard mixture, 1.26 micromoles of cystine and 2.50 micromoles per milliliter of L-phenyl alanine, L-tryosine, L-leucine, L-isoleucine, L-methionine, L-valine, L-alanine, glycine, L-proline, L-glutamic acid, Lserine, L-threonine, Laspartic acid, L-arginine, L-histidine, and Llysine.

Figure 4 shows the odor chemistry obtained through direct sampling of 15mL of headspace vapor. Each peak represents a type of amino acid and the Kovats indices of all peaks identified ranged between 489 and 1653 corresponding to the retention time of the n-alkanes.

A room temperature sample needle was used in this experiment to prevent the collection of higher molecular weight compounds, such as fatty acids. However, the combination of direct sampling and a heated 200°C inlet allows the zNose® to measure even those compounds with Kovats indices up to approximately 2600.

Figure 4. The derivative of odor intensity is a chromatogram used to determine chemical retention times. An analysis of odor from amino acid standards showing Kovats indices and odor concentration in counts.

Blood odor measurements

The solid-state detector measured odor intensity of blood samples directly versus elution time obtained from a GC column, where the temperature was ramped from 40°C to 160°C at a rate of 10°C per second. The detector temperature (20°C) and the sample volume of vapor (15mL) controlled the sensitivity of the instrument.

A 15mL vapor sample from the vial was extracted and preconcentrated, enabling the measurement of chemical vapor concentration from a drop of blood within a minute. At these odor concentrations, background odors obtained from ambient air were not an issue.

Figure 5 shows the comparison of the odor chemistry measurement results in three vertically offset chromatogram traces relative to two blood samples and the headspace vapors obtained from a vial holding the amino acid standards.

Except in a few cases, the odor chemistry of un-derivatized blood agrees well with that of the amino acid standards. The results of this experiment confirmed that amino acids are mainly responsible for the odor of blood.

Figure 5. Odor chemistry of blood compared with odor from amino acid standards

Olfactory images, also known as VaporPrints™, are high-resolution 2D images based on the relative concentrations of the individual chemicals within an odor. A polar display of the odor intensity (radial direction = sensor signal) or odor flux (radial direction = derivative of sensor signal) is formed by these images.

Retention times (volatility) or Kovats indices are denoted by the angular variable with 0 and maximum retention time at the 12 o’clock position of the image. This format allows easy identification of their characteristic shapes based on the unique chemistry of that order.

In summary, the human olfactory response is transformed into a visual response by the olfactory image. Computers and humans can effectively analyze and recognize visual patterns. Individual chemicals can be quantified by computer processing of olfactory images, allowing identification of the aggregate odor response relative to known odors and chemical vapor standards.

Conclusion

The odor chemistry can now be measured in near real time with part per trillion sensitivity, high precision and high accuracy using the combination of a new kind of ultra high-speed gas chromatography-based electronic nose and a new solid state GC detector.

In this article, chromatograms and visual olfactory images based on chemical measurements were used to characterize and compare odors from amino acid standards and blood samples.

The simple amino acids, which are the basic building blocks of proteins present in the blood, were found to be the major volatile chemicals. Thanks to the picogram sensitivity of the instrument, odor chemical concentrations at part per trillion can be made without derivatization.

Since the zNose® works based on the science of gas chromatography, the confirmation and validation of odor measurements can be easily done by independent laboratory measurements performed on quality control samples.

The ability to perform rapid, real-time analytical measurements on biological samples such as blood provides scientists with an economical solution for monitoring VOCs associated with biological samples such as urine and blood.

Acknowledgements

Produced from materials originally authored by Edward J. Staples, Electronic Sensor Technology, CA, USA.

About Electronic Sensor Technology

Electronic Sensor Technology

Electronic Sensor Technology, Inc has developed and patented a breakthrough chemical vapor analysis process. This process applies gas chromatography calculations and technology toward a wide variety of industries, including Homeland Security, Life Sciences, Chemical and Petrochemical, Food & Beverage and Environmental.

How does gas chromatography work? With rapid, accurate analysis of chemical odors and vapors, this patented technology helps to provide real-time analysis for quick response solutions.


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Last updated: May 22, 2017 at 2:41 PM

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