II. SAMPLING AND STORAGE
It is important that the sample used for
analysis be representative of the entire contents of the container. Since most materials
encountered by the analyst are homogeneous oils, sampling is not a difficult operation.
However, a few cautions are noted to assure a representative sample. Most essential
oils are obtained by steam distillation with subsequent separation of the oil and
water layers; therefore, shipments of oil frequently contain water. If the oil has
a specific gravity of less than 1.0, the water will be found at the bottom of the
drum. It is a wise precaution to test each drum for water by introducing a
sampling thief made of a long glass tube with one end slightly constricted. With
the other end of the glass tube securely closed (by pressing the thumb over the
opening), the thief is introduced into the drum and lowered until the
constricted end just touches the bottom of the drum; the thumb is removed to permit
the oil and water (if present) to enter the tube; the thumb is replaced and the
tube withdrawn (the thief should be held in a vertical position). The oil within
the tube is permitted to drain into a flint glass bottle or graduate. Any water,
sediment (e.g., dirt and rust) or precipitated waxes are readily discernible. For
oils that have a specific gravity greater than 1.0, any water that is present will
appear as a supernatant layer. Hence, in introducing the thief, the tube is not
closed with the thumb and is lowered into the drum slowly.
The sample in the flint bottle or graduate
should receive a cursory examination color, clarity, viscosity, the presence or
absence of sediments, separated waxes, and water, all should be observed and noted;
finally the odor of the sample should be studied. Oils stored in drums for long
periods will frequently show a slight musty "by-note" which rapidly
disappears; this is a typical "drum-note" and does not reflect adversely
on the quality of the oil. Freshly distilled oils frequently show a slight, sharp
empyreumatic or burned note which disappears as the oil is aged. The "drum-note"
and the "freshly distilled note" should disappear if the oil is permitted
to stand in an open graduate overnight. If such notes do not disappear, the oils
should be examined more carefully; it may be necessary to aerate the oil to remove
persistent "by-notes." A small sample of the oil (about 50 cc.) should
be treated by bubbling air through the oil for a period of several hours. It may
be necessary to warm the air which is bubbled through the oil Diagram 4.1 shows
a convenient apparatus for carrying out such aeration. If this treatment yields
a satisfactory oil, the contents of the Irum may be treated similarly. Citrus oils
frequently deposit large amounts of waxes. These are easily observed by the water
testing technique described above. Another indication is the "feel" of
the tube as it hits the bottom of the drum.
If the drum shows no evidence of water or
insignificant amounts of water and sediment, the sample drawn may be used for analysis.
If water, wax, or sediment is present to a large extent, a fresh sample should
be drawn from the supernatant oil.
When the sample is received by the chemist, it
should be clarified and freed from sediment and separated waxes by decantation
or by filtration if necessary. A small amount of dry sodium chloride placed in the
folded filter will frequently aid in removing traces of water and will remove the
haze from an oil. Treatment with clay or kieselguhr may be necessary to remove a
haze caused by suspended materials. If the oil is very dark in color owing to
the presence of heavy metals or other metallic impurities, the color may be lightened
by shaking with tartaric acid and filtering (see p. 311). The color and appearance
of the oil both before and after treatment should be described in the analytical
report, as well as the treatment used.
Because of possible variation in the oils of a
shipment of more than one drum, it is best to sample each drum of oil. However,
if the oils are to be bulked (e.g., several drums are to be pumped into a tank to
yield a uniform lot), an average or representative sample may be made based on the
weights of the oil in the individual drums. The odor and general appearance of each
drum should be examined before such a sample is made, to prevent the addition of
a drum of poor quality to the tank. If this average sample is found to be of
inferior quality or shows any abnormalities, then each drum must be resampled and
examined individually.
Oils that congeal at temperatures normally
encountered should be given special attention. These drums should be permitted to
stand in a warm place and stirred occasionally (or heated in a steam room if the
congealing point is high) until the last trace of solid material is dissolved. Anise
oil may be taken as a typical example. During the cold weather a drum may be received
in a frozen condition. Upon standing in a warm place, the anethole slowly melts
until the drum is half solid, half liquid. The solid settles to the bottom. If a
sample of the liquid portion is drawn, it will be deficient in anethole and may
fail to meet the official requirements of "The United States Pharmacopoeia"
; such a sample would not be representative of the drum. Synthetics and isolates
such as anethole, benzyl benzoate and diphenyl oxide usually require a steam room
to melt them completely to assure a representative sample. Upon chilling or long
standing, some oils deposit small amounts of crystalline materials such as menthol,
cedrol, or camphor; in these cases, the oil should be gently warmed and stirred
to redissolve the crystalline material before a sample is drawn.
In sampling materials other than oils, certain
precautions should be observed. For resinoids, oleoresins and balsams the drum or
can should be stirred well with a flat stick to assure thorough mixing. A sample
should not be drawn before the material is uniform. This is of importance for items
such as styrax, which usually shows a separation of styrene, polystyrene and water.
The sampling of crude drugs offers considerable
difficulties. "The United States Pharmacopoeia"2 gives four
methods for the sampling of vegetable drugs from original containers to obtain an
"official," representative sample.
I. "It is recommended that
gross samples of vegetable or animal drugs in which the component parts are 1 cm.
or less in any dimension, and ail powdered or ground drugs, be taken by means of
a sampler which removes a core from the top to the bottom of the container, not
less than two cores being taken in opposite directions; that when the total weight
of the drug to be sampled is less than 100 kilos (200 pounds) at least 250 g. shall
constitute an official sample. When the total weight of the drug to be sampled is
in excess of 100 kilos, repeated samples shall be taken by the above method, and
according to the schedule given below, mixed and quartered, two of the diagonal
quarters being rejected, the remaining two quarters being combined and carefully
mixed, and again subjected to a quartering process in the same manner until two
of the quarters weigh at least 250 g., which latter quarters shall constitute an
official sample.
II. "It is recommended that
gross samples of vegetable drugs in which the component parts are over 1 cm. in
any dimension be taken by hand. When the total weight of the drug to be sampled
is less than 100 kilos, at least 500 g. shall constitut an official sample, and
this shall be taken from different parts o the container or containers. When the
total weight of th drug to be sampled is in excess of 100 kilos, repeated sample
shall be taken by the above method and according to the schedul below, mixed
and quartered, two of the diagonal quarters bein rejected, and the remaining two
quarters being combined and carefully mixed, and again subjected to a
quartering proces in the same manner until two of the quarters weigh not less tha
500 g., which latter quarters shall constitute an official sample.
When over 100, the total number
sampled should not be less than 10. III. "When the total weight of a drug to
be sampled is less than 10 kilos it is recommended that the above methods be followed
but that somewhat smaller quantities be withdrawn, and in no case should the final
official sample weigh less than 125 g.
IV. "In addition to the withdrawing
of official samples according to methods I, II, and III, the official sample may
consis of the total amount of a direct purchase made by Federal, State, or Municipal
Food and Drug Act enforcement officials."
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2
Thirteenth Revision,
710.
The sampling of a pure chemical which is a solid
(e.g., vanillin) will now be considered. The well-known method of quartering3 will
assure a representative sample. Most manufacturers give an identifying number to
each batch manufactured, and consequently it may be assumed that each batch is uniform
so that a sample taken at random will be representative of the whole batch.
The final sample should be transferred to a bottle
of light-resistant
----------------------------
3 Treadwell and Hall, "Analytical Chemistry," John Wiley & Sons, Inc., New York
Vol. II (1942), 45.
4 "The United States Pharmacopoeia" (Twelfth Revision, 6) defines a light-resistan container as "a container which is opaque, or designed to prevent photochemical deterioratio of the contents beyond the official limits of strength, quality, or purity, under customar conditions of handling,
storage, shipment, or sale.
"Unless otherwise directed, a light-resistant container shall be composed of a substance which in a thickness of 2 mm. shall not transmit more than 10 per cent of the incident radiation of any wave length between 2900 and 4500 angstrom units.
"If the immediate container in its construction is less than 2 mm. in
thickness, the same 10 per cent limit of light transmission shall apply.
"If the immediate container in its construction is not light-resistant, it must be provided with an opaque covering, be enclosed in an opaque covering or in an opaque container." (The definition of the Thirteenth Revision, 5, is essentially the same.)
glass (amber, blue or green). The bottle should
be well filled to prevent adverse action by the air and well stoppered with a sound
cork. Screw caps should be used with caution, since the liners may contaminate the
oil.5 If a screw cap is to be employed it is well to stopper the bottle
with a cork before using the screw cap.
If the shipment of oil is to be stored for any
appreciable length of time, the precautions noted below should be observed :
1. The oils should be clarified and thoroughly
dried.
2. The oils are best stored in glass containers
in a cool6 place protected from light and air. Half filled containers
should be avoided. Storage in glass is frequently impractical; if drums or cans
must be used, heavily galvanized or heavily tinned iron usually will prove satisfactory.
Aluminum7 and stainless steel can be used with some oils, but not universally.
3. Certain oils are much more susceptible to
oxidation and polymerization than others; oils rich in terpenes (e.g., citrus oils)
and oils containing large amounts of aldehydes (e.g., benzaldehyde) are readily
affected. Some oils (e.g., vetiver, sandalwood and patchouly) show very good
keeping qualities and may actually improve upon aging.
4. In general, the use of antioxidants for
essential oils is not necessary if the oils are properly and carefully stored.8
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