Qualitative analysis of drugs and toxic substance in clinical
samples
By Elphas Shikokoti BSC MLS (MMUST)
()
If any tests are to influence immediate clinical management, the results must be available within 2-3
hours of receipt of the specimen.
NB: It is important to maintain high standards of laboratory practice, especially when performing tests on
an emergency basis. It may be better to offer no result rather than misleading data based on an
unreliable test.
The scheme for qualitative analysis of toxic substances
Physical examination
Colour tests
Thin layer chromatography (TLC) Report the preliminary results
If equipment is available
Confirmatory analysis (HPLC, GLC-MS) Confirm the results
A) Physical examination of the specimen
Urine
High concentrations of some drugs or metabolites can impart characteristic colours and smell to
urine. Strong-smelling poisons such as camphor, ethchlorvynol and methyl salicylate can
sometimes be recognized in urine since they are excreted in part unchanged. Acetone may arise
from metabolism of propan-2-ol.
Turbidity may be due to underlying pathology (blood, microorganisms, casts, epithelial cells), or
to carbonates, phosphates or urates in amorphous or microcrystalline forms. Such findings should
not be ignored, even though they may not be related to the poisoning. Chronic therapy with
sulfonamides may give rise to yellow or greenish brown crystals in neutral or alkaline urine.
Phenytoin, primidone, and sultiame form crystals in urine following overdosage, while
characteristic colourless crystals of calcium oxalate form at neutral pH after ingestion of ethylene
glycol.
Stomach contents and scene residues
Many compounds for example, ethchlorvynol, methyl salicylate, paraldehyde, phenelzine) also have
distinctive smells. Very low or very high pH may indicate ingestion of acid or alkali, while a green/blue
, colour suggests the presence of iron or copper salts. Microscopic examination using a polarizing microscope
may reveal the presence of tablet or capsule debris. Starch granules used as a filler in Some tablets and
capsules are best identified using crossed polarizing filters, when they appear as bright grains marked with
a dark Maltese cross.
Undegraded tablets or capsules and any plant remains or specimens of plants thought to have been
ingested should be examined separately. The local poisons services/agencies will normally have
access to publications or other aids to the identification of tablets or capsules by weight, markings,
colour, shape and possibly other physical features.
Take care: specimens containing cyanide may give off hydrogen cyanide, especially if acidified not
everyone can detect hydrogen cyanide by smell. Similarly sulfides evolve hydrogen sulfide the
ability to detect hydrogen sulfide (rotten egg smell) is lost at higher concentrations.
B) Colour tests
Many drugs and other poisons, if present in sufficient concentration and in the absence of
interfering compounds, give characteristic colours with appropriate reagents. Some of these tests
are, specific, but compounds containing similar functional groups will also react, and thus
interference from other poisons, metabolites or contaminants is to be expected.
Many of these tests can be performed satisfactorily in clear glass test-tubes. However, use of a
spotting tile (a white glazed porcelain tile with a number of shallow depressions or wells in its
surface) gives a uniform background against which to assess any colours produced, and also
minimizes the volumes of reagents and sample that need to be used.
samples
By Elphas Shikokoti BSC MLS (MMUST)
()
If any tests are to influence immediate clinical management, the results must be available within 2-3
hours of receipt of the specimen.
NB: It is important to maintain high standards of laboratory practice, especially when performing tests on
an emergency basis. It may be better to offer no result rather than misleading data based on an
unreliable test.
The scheme for qualitative analysis of toxic substances
Physical examination
Colour tests
Thin layer chromatography (TLC) Report the preliminary results
If equipment is available
Confirmatory analysis (HPLC, GLC-MS) Confirm the results
A) Physical examination of the specimen
Urine
High concentrations of some drugs or metabolites can impart characteristic colours and smell to
urine. Strong-smelling poisons such as camphor, ethchlorvynol and methyl salicylate can
sometimes be recognized in urine since they are excreted in part unchanged. Acetone may arise
from metabolism of propan-2-ol.
Turbidity may be due to underlying pathology (blood, microorganisms, casts, epithelial cells), or
to carbonates, phosphates or urates in amorphous or microcrystalline forms. Such findings should
not be ignored, even though they may not be related to the poisoning. Chronic therapy with
sulfonamides may give rise to yellow or greenish brown crystals in neutral or alkaline urine.
Phenytoin, primidone, and sultiame form crystals in urine following overdosage, while
characteristic colourless crystals of calcium oxalate form at neutral pH after ingestion of ethylene
glycol.
Stomach contents and scene residues
Many compounds for example, ethchlorvynol, methyl salicylate, paraldehyde, phenelzine) also have
distinctive smells. Very low or very high pH may indicate ingestion of acid or alkali, while a green/blue
, colour suggests the presence of iron or copper salts. Microscopic examination using a polarizing microscope
may reveal the presence of tablet or capsule debris. Starch granules used as a filler in Some tablets and
capsules are best identified using crossed polarizing filters, when they appear as bright grains marked with
a dark Maltese cross.
Undegraded tablets or capsules and any plant remains or specimens of plants thought to have been
ingested should be examined separately. The local poisons services/agencies will normally have
access to publications or other aids to the identification of tablets or capsules by weight, markings,
colour, shape and possibly other physical features.
Take care: specimens containing cyanide may give off hydrogen cyanide, especially if acidified not
everyone can detect hydrogen cyanide by smell. Similarly sulfides evolve hydrogen sulfide the
ability to detect hydrogen sulfide (rotten egg smell) is lost at higher concentrations.
B) Colour tests
Many drugs and other poisons, if present in sufficient concentration and in the absence of
interfering compounds, give characteristic colours with appropriate reagents. Some of these tests
are, specific, but compounds containing similar functional groups will also react, and thus
interference from other poisons, metabolites or contaminants is to be expected.
Many of these tests can be performed satisfactorily in clear glass test-tubes. However, use of a
spotting tile (a white glazed porcelain tile with a number of shallow depressions or wells in its
surface) gives a uniform background against which to assess any colours produced, and also
minimizes the volumes of reagents and sample that need to be used.
