recovered from the sample. The total weight of silicon, divided by the hair sample
weight, gave the concentration of silicon on the hair. The quantity of siloxane polymer
treatment on the hair was determined by multiplying the silicon value by the proper
gravimetric factor for the specific polymer.
A carefully aligned and adjusted atomic absorption spectrometer typically records an
absorbance of 0.050 absorbance units for 10 •xg of silicon per milliliter (10 ppm) in wet
MIBK. For AAS, sensitivity is generally defined as that quantity of analyte per milli-
liter which will produce an absorption signal of one percent, or an absorbance of 0.0044
absorbance units. The sensitivity for organosilicon in wet MIBK is 0.88 •xg of silicone
per milliliter. The instrument should be expected to reproduce an absorbance measure-
ment of 0.050 within _+ 0.002 absorbance units. The absolute detection limit for
silicone for these experiments was 0.002 absorbance units. An absorbance of 0.002
units may not be readily discernible from the normal background noise with instru-
ments equipped only with light-emitting diode array (LED) readouts, but may be seen
on a stripchart recorder. The detection limit for silicon, based on a total solvent volume
of 7 ml, is about 3 •xg, with a precision of -+ 3 }xg. If the spectrometer features scale
expansion capability, moderate scale expansion of 2 X or 3 X may provide some sensi-
tivity improvement. Scale expansion is an aid when one is attempting to discern small
differences in absorbance signals between samples.
RESULTS AND DISCUSSION
METHOD SELECTION
Siloxanes, when placed in contact with porous surfaces such as hair, tend to be adsorbed
into the substrate and can only be partially extracted with organic solvents. Treated hair
must be decomposed prior to extraction. Several reagents were tried for preparing
treated hair samples for AAS assay, including caustic (KOH and NaOH), phosphoric
acid, and tetramethylguanidine. While the hair protein structure could be decomposed
with sodium or potassium hydroxides, those materials were not selected, as they caused
cleavage of the organosiloxane polymer into cyclics, silanols, and silicates. Those reac-
tion products were either volatile or non-extractable in organic solvents. Phosphoric
acid and tetramethylguanidine did not sufficiently decompose the hair at room temper-
ature, even after several weeks, and when heated also caused siloxane polymer degrada-
tion and generation of non-extractable species.
As an alternative, an enzyme digestion method was discovered in a literature search (2)
that employed papain (an enzyme found in papaya). This enzyme is a proteolytic en-
zyme that is active with free sulfhydryl groups. An aqueous solution containing 0.13%
papain and 2% sodium sulfite as a catalyst (with the pH adjusted to 6.8) was heated
with a hair sample at 65øC for three days. Samples prepared by this method were
further extracted with methylisobutyl ketone (MIBK) and a small quantity of hydro-
chloric acid before AAS analysis. The HCI served to precipitate otherwise soluble pro-
teins and aided in phase separation later in the procedure. The extraction was completed
by shaking the vial and contents on a Burrell mechanical shaker, and completing phase
separation in a centrifuge. The top (solvent) layer was drawn off and the silicon content
was assayed by atomic absorption spectroscopy utilizing a nitrous oxide-acetylene flame
recovered from the sample. The total weight of silicon, divided by the hair sample
weight, gave the concentration of silicon on the hair. The quantity of siloxane polymer
treatment on the hair was determined by multiplying the silicon value by the proper
gravimetric factor for the specific polymer.
A carefully aligned and adjusted atomic absorption spectrometer typically records an
absorbance of 0.050 absorbance units for 10 •xg of silicon per milliliter (10 ppm) in wet
MIBK. For AAS, sensitivity is generally defined as that quantity of analyte per milli-
liter which will produce an absorption signal of one percent, or an absorbance of 0.0044
absorbance units. The sensitivity for organosilicon in wet MIBK is 0.88 •xg of silicone
per milliliter. The instrument should be expected to reproduce an absorbance measure-
ment of 0.050 within _+ 0.002 absorbance units. The absolute detection limit for
silicone for these experiments was 0.002 absorbance units. An absorbance of 0.002
units may not be readily discernible from the normal background noise with instru-
ments equipped only with light-emitting diode array (LED) readouts, but may be seen
on a stripchart recorder. The detection limit for silicon, based on a total solvent volume
of 7 ml, is about 3 •xg, with a precision of -+ 3 }xg. If the spectrometer features scale
expansion capability, moderate scale expansion of 2 X or 3 X may provide some sensi-
tivity improvement. Scale expansion is an aid when one is attempting to discern small
differences in absorbance signals between samples.
RESULTS AND DISCUSSION
METHOD SELECTION
Siloxanes, when placed in contact with porous surfaces such as hair, tend to be adsorbed
into the substrate and can only be partially extracted with organic solvents. Treated hair
must be decomposed prior to extraction. Several reagents were tried for preparing
treated hair samples for AAS assay, including caustic (KOH and NaOH), phosphoric
acid, and tetramethylguanidine. While the hair protein structure could be decomposed
with sodium or potassium hydroxides, those materials were not selected, as they caused
cleavage of the organosiloxane polymer into cyclics, silanols, and silicates. Those reac-
tion products were either volatile or non-extractable in organic solvents. Phosphoric
acid and tetramethylguanidine did not sufficiently decompose the hair at room temper-
ature, even after several weeks, and when heated also caused siloxane polymer degrada-
tion and generation of non-extractable species.
As an alternative, an enzyme digestion method was discovered in a literature search (2)
that employed papain (an enzyme found in papaya). This enzyme is a proteolytic en-
zyme that is active with free sulfhydryl groups. An aqueous solution containing 0.13%
papain and 2% sodium sulfite as a catalyst (with the pH adjusted to 6.8) was heated
with a hair sample at 65øC for three days. Samples prepared by this method were
further extracted with methylisobutyl ketone (MIBK) and a small quantity of hydro-
chloric acid before AAS analysis. The HCI served to precipitate otherwise soluble pro-
teins and aided in phase separation later in the procedure. The extraction was completed
by shaking the vial and contents on a Burrell mechanical shaker, and completing phase
separation in a centrifuge. The top (solvent) layer was drawn off and the silicon content
was assayed by atomic absorption spectroscopy utilizing a nitrous oxide-acetylene flame
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