Analysis of Lemur Scent Using the zNose - Electronic Sensor ...

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Analysis of Lemur Scent 

Using the zNose ® 

Edward J. Staples, Electronic Sensor Technology 

Electronic Noses 

Conventional electronic noses (eNoses) produce a recognizable response pattern 

using an array of dissimilar but not specific chemical sensors. Electronic noses have interested 

developers of neural networks and artificial intelligence algorithms for some 

time, yet physical sensors have limited performance because of overlapping responses 

and physical instability. eNoses cannot separate or quantify the chemistry of aromas. 

A new type of electronic nose, called the zNose®, is based upon ultra-fast gas 

chromatography, simulates an almost unlimited number of specific virtual chemical sensors, 

and can produce high-resolution two-dimensional olfactory images based upon 

aroma chemistry. The zNose ® is able to perform analytical measurements of volatile 

organic vapors and odors in near real time with part-per-trillion sensitivity. Separation 

and quantification of the individual chemicals within an odor is performed in seconds. 

Using a patented solid-state mass-sensitive detector, picogram sensitivity, universal nonpolar 

selectivity, and electronically variable sensitivity is achieved. An integrated vapor 

preconcentrator coupled with the electronically variable detector, allows the instrument to 

measure vapor concentrations spanning 6+ orders of magnitude. In this paper a portable 

zNose®, shown in Figure 1, was used to assess lemur scent chemistry. 

Figure 1- Portable zNose® technology incorporated into a handheld instrument 

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How the zNose Quantifies the Chemistry of Odors 

A simplified diagram of the zNose system shown in Figure 2 consists of two sections. 

One section uses helium gas, a capillary tube (GC column) and a solid-state detector. 

The other section consists of a heated inlet and pump, which samples ambient air. 

Linking the two sections is a “loop” trap, which acts as a preconcentrator when placed in 

the air section (sample position) and as an injector when placed in the helium section (inject 

position). Operation is a two step 

process. Ambient air (odor) is first sampled 

and organic vapors collected (preconcentrated) 

on the trap. After sampling the 

trap is switched into the helium section 

where the collected organic compounds are 

injected into the helium gas. The organic 

compounds pass through a capillary column 

with different velocities and thus individual 

chemicals exit the column at characteristic 

times. As they exit the column they are 

detected and quantified by a solid state detector. 

An internal high-speed gate array microprocessor 

controls the taking of sensor 

data which is transferred to a user interface 

or computer using an RS-232 or USB connection. 

Odor chemistry, shown in Figure 

3, can be displayed as a sensor spectrum or 

a polar olfactory image of odor intensity vs 

2 

Figure 2- Simplified diagram of the zNose 

showing an air section on the right and a helium 

section on the left. A loop trap preconcentrates 

organics from ambient air in the 

sample position and injects them into the helium 

section when in the inject position. 

retention time. Calibration is accomplished using a single n-alkane vapor standard. A 

library of retention times of known chemicals indexed to the n-alkane response (Kovats 

indices) allows for machine independent measurement and compound identification. 

Figure 3- Sensor response to n-alkane vapor standard, here C6-C14, can be 

displayed as sensor output vs time or its polar equivalent olfactory image.


Chemical Analysis (Chromatography) 

The time derivative of the sensor 

spectrum (Figure 3) yields the 

spectrum of column flux, commonly 

referred to as a chromatogram. The 

chromatogram response (Figure 4) of 

n-alkane vapors (C6 to C14) provides 

a set of reference retention times. 

Graphically defined regions, shown 

as red bands, provide a method 

dependent reference time base against 

which subsequent chemical responses 

can be compared and indexed. As an 

example, a response midway between 

C10 and C11 would have a retention 

time index of 1050. 

Sensitivity 

Figure 4 - Chromatogram of n-alkane vapors C6 to C14). 

Measurement sensitivity is controlled by vapor sample time and SAW detector 

temperature. Using the variable sensitivity of the SAW detector it was possible to 

achieve ppb and even ppt sensitivity by lowering the detector temperature. It is also possible 

to prevent overloading by raising the temperature of the detector. The concentration 

in counts (peak area) of a typical volatile organic compound as a function of detector 

temperature is shown in figure 12. 

Figure 5- The exponential temperature dependence of SAW detector allows electronically variable sensitivity 

to be achieved over a wide range of vapor concentrations. 

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Lemur Scent 

Prosimians, which retain a suite of physical characteristics that have been lost in 

the "higher" primates (monkeys, apes and man), are the closest living analogs to man’s 

ancient primate ancestors who lived during the Eocene epoch (about 55 million years 

ago). Prosimians are often referred to as "lower" 

primates, as they are simply characterized by 

retention of certain body systems that are primitive 

relative to those possessed by higher primates. For 

instance, prosimians tend to rely more heavily on 

the sense of smell. Male ring-tailed lemurs have 

darkly colored scent glands on the inside of their 

wrists with a spur-like fingernail, usually referred 

to as a horny spur, overlay on each. Males also 

have scent glands on their chests, just above the 

collarbone and close to the armpit. Although prosimians 

are greatly olfaction-oriented, little is 

known about the specifics of how they use scent to 

communicate 

Figure 6- Lumur. 

1 . In this preliminary study we 

examine 3 samples of gland secretions from 

lemurs using an ultra-high speed gas 

chromatograph. The results indicate that a portable 

electronic nose based upon gas chromatography 

might be used in the field to study scent marks as a 

way of determining species, sex, and reproductive 

status 

Communication is achieved by both olfactory and vocal means 2 . Olfactory communication 

is extremely important and is made possible by the scent glands located at the 

wrist throat. This type of communication is used for transmitting physical state, location, 

and individual recognition. According to researchers at Duke University 3 when males 

mark, they mark either only with the wrist gland, or they will go through a rubbing motion 

and mix the secretions of the shoulder gland with the secretions of the wrist gland, 

and then deposit that. One of the big questions is whether there's a difference between 

wrist marking and shoulder/wrist marking? What are the different messages encoded? 

Does the shoulder gland have a specific function in terms of message, or is it acting as 

sort of a fixative for the more volatile components of the wrist gland? 

1 R.A. Hayes, T.L. Morelli, P.C. Wright, Anogenital gland secretions of Lemur catta and Propithecus verreauxi coquereli: 

A preliminary chemical examination, Am J Primatol 63:49-62, 2004 

2 Dugmore, S.J. and Evans, C.S. (1990) Discrimination of conspecific chemosignals by female ringtailed 

lemurs, Lemur catta L. In Macdonald, D.W., Muller-Schwarze, D. and Natynczuk, S.E. (eds), Chemical 

Signals in Vertebrates 5. Plenum Press, New York, pp. 360–36 

3 http://www.dukenews.duke.edu/2004/08/DreaLemurscent_0804.html 

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Scent Testing Methods 

Scent samples from lemurs were collected by absorbing approximately 10 µliters of 

scent liquid from the scent gland onto a small cotton ball which was immediately placed 

in a sealed 2 mL vial and stored at 0 o C 

until just before testing. Samples were 

prepared for testing by removing the cap 

of the 2 mL vial and transferring the 

sample into a larger septa-sealed 40 mL 

vial which was then heated to 60 o C using 

the two-zone vial heater shown in Figure 

7. Lemur scents were analyzed using (1) 

direct sampling with the zNose® and (2) 

indirect or remote sampling with a tenax 

filled sorption tube which was then 

desorbed and measured with the zNose ® . 

Direct Sampling 

Figure 7- Direct sampling scent vapors using vial 

heater accessory 

Vapors in the vial (lemur scent) 

were directly sampled using a side-ported 

needle attached to the inlet of the zNose ® as shown in Figure 7. Sample time was typically 

5-10 seconds, which removed approximately 2-4 mL of headspace vapor. Following 

sampling the vapor sample was analyzed in 20 seconds using a dB-5 column ramped 

from 40 o to 140 o C at 5 o C/second. Replicate measurements could be performed every 1.5minute. 

Remote Sampling 

Although requiring an additional step and 

more time, sampling scent vapors with a small 

battery operated pump and preconcentrating in a 

sorbtion tube filled with 250 milligrams of tenax has 

several advantages. First is the convenience of using 

a small 12 oz pump and battery to collect vapors in 

the field from subjects. Second, a higher sample 

flow enables a much larger vapor sample to be 

preconcentrated and measurement sensitivity well 

into the ppt concentration range can be achieved. 

The zNose is equipped with a desorber 

interface which enables it to quickly remove 

preconcentrated vapors from a sample collection 

tube as shown in Figure 8. The collection tube is 

heated to approximately 200 o C and then 

preconcentrated vapors are transferred in 10 seconds 

into the inlet of the zNose ® and chemically analyzed. 

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Figure 8- Remote sampler and desorbtion 

heater.


Direct Sampling Results 

Scent samples were heated 

to 60 o C and sampled directly with 

the zNose®. Vertically offset 

replicate chromatograms using 

different detector sensitivity 

settings (temperature) for the 

three samples are shown in 

Figures 9-11. 

The most notable in all 

samples was a compound with a 

Kovats index of approximately 

1352. Also evident was a very 

volatile compound which had an 

index of 738. Trace amounts of 

other compounds are shown in the 

tabulated results adjacent to each 

chromatogram. 

Increasing sensitivity of 

direct measurements by lowering 

detector temperature was 

sometimes difficult due to the 

large amount of water vapor 

present which tended to overload 

the detector at low temperatures. 

Vertically offset traces 

comparing each sample using a 

10 o C detector are shown in Figure 

12. Samples 1061 and 1097 were 

more alike than sample 1081. 

Figure 9- Direct sampling sample no 1061 

Figure 10- Direct sampling sample no. 1081 

Figure 11- direct sampling sample no. 1097. 

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Figure 12- Comparing samples analyzed using direct sampling and 10 o detector. 

Indirect Sampling 

Chromatograms of scent samples analyzed by first preconcentrating scent vapors 

with a tenax filled collection tube (remote sampler) followed by analysis using the 

zNose® are shown in Figures 13-15. Water vapor in the desorbtion tubes was removed 

by passing 150 ccm of air through the tube at room temperature for 1 minute prior to desorbtion. 

As was seen in the previous direct sampling, the compound with a Kovats index 

of approximately 1352 again appears prominently. Samples 1061 and 1097 both 

show high concentrations of the 

volatile compound with index of 

740, however it is not present in 

sample no 1081. Trace amounts 

of other compounds are shown in 

the tabulated results adjacent to 

each chromatogram. Trace 

amounts of background organics 

from the vial and septa analyzed 

before the lemur scent sample 

was inserted are shown for comparison. 

Figure 13- 15 second sample of scent no 1061using remote 

sampler. 

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Figure 14- 15 second sample of scent no 1081using remote 

sampler 

Figure 15- 15-second sample of scent no 1097 using remote 

sampler. 

Selecting compounds in lemur scent, which are not present in background odors, 

can be used to create a virtual sensor array for lemur scent. The process is shown in Figure 

16 using 5 major compounds from the chromatogram of scent sample no 1061. The 

compounds are selected by placing graphical bands over the selected peaks (top). Although 

the actual chemical names of the compounds are not known it is convenient to 

label them according to their unique Kovats indices e.g. lemur 741. 

The indices of the virtual sensors are defined by a peak file (table), which includes 

user specified response factors, and alarm levels in any convenient units. Once the virtual 

sensor array is defined a simplified user interface showing just a sensor panel is used 

to replace the chromatogram display. 

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Figure 16- Lemur virtual Sensor Array defined by scent no 1061 

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Summary 

Chemical profiles associated with the scent of lemurs can contain a complex cocktail 

of odorous substances. A preliminary analysis of 3 scent samples with the zNose®, 

an ultra-fast portable GC, has indicated high concentrations of a very volatile compound, 

index = 740, and a second much less volatile compound with an index of 1352. Trace 

levels of many other organic compounds were also detected. 

The zNose® is a new quantitative testing tool for in-situ vapor analysis and 

achieves near real time speed. It is particularly useful for many life science applications 

where real time in-situ biochemical measurements are needed. A remote sampler interface 

compliments scent measurements, increases sensitivity, and provides a simple tool 

for collecting scent samples in the field. Future work might be to use the zNose ® to 

quantify lemur scents and relate the findings to factors such as species, sex, and reproductive 

status. Real time measurements might prove useful in understanding lemur olfactory 

communication. It might also be used to measure the difference between wrist marking 

and shoulder/wrist marking, how different messages are encoded, and determine the 

functions associated with specific scent glands. 

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Analysis of Lemur Scent Using the zNose - Electronic Sensor ...

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