30 Part I: Principles
for samples with high fat content (such as meat
products) or for preparation for elemental analysis;
and (3) plasma ashing (low temperature) for when
volatile elemental analysis is conducted.
In dry ashing, samples usually are incinerated in a
muffle furnace at temperatures of 500–600°C. Most
minerals are converted to oxides, phosphates, sul-
fates, chlorides, or silicates. Unfortunately, elements
such as mercury, iron, selenium, and lead may be
partially volatized using this procedure.
Wet ashing utilizes various acids to oxidize or-
ganic materials and minerals that are solubilized
without their volatilization. Nitric and perchloric
acids are often used, and reagent blanks are carried
throughout the procedure and are subtracted from
sample results.
In low-temperature plasma ashing, samples are
treated in a similar way to those in dry ashing, but
under a partial vacuum, with samples being oxidized
by nascent oxygen formed by an electromagnetic
field.
Although the above three methods have been
proven to be appropriate for quantitating the total
amount of mineral within a sample, they do not pos-
sess the ability to either differentiate or quantitate
actual mineral elements within a mixture.
When atomic absorption spectrometers became
widely used in the 1960s and 1970s, they paved the
way for measuring trace amounts of mineral ele-
ments in various biological samples (Miller 1998).
Essentially, atomic absorption spectroscopy is an
analytical technique based on the absorption of
ultraviolet or visible radiation by free atoms in the
gaseous state. The sample must be first ashed and
then diluted in weak acid. The solution is then atom-
ized into a flame. According to Beer’s Law, absorp-
tion is directly related to the concentration of a par-
ticular element in the sample.
Atomic emission spectroscopy differs from atom-
ic absorption spectroscopy in that the source of radi-
ation is, in fact, excited atoms or ions in the sample
rather than from external source, has in part taken
over. Atomic emission spectroscopy does have
advantages with regard to sensitivity, interference,
and multielement analysis (Miller 1998).
Recently, the use of ion-selective electrodes has
made on-line testing of the mineral composition of
samples a reality. In fact, many different electrodes
have been developed for the direct measurement of
various anions and cations such as calcium, bromide,
fluoride, chloride, potassium, sulfide, and sodium
(Hendricks 1998). Typically, levels down to 0.023
ppm can be measured. When working with ion-
selective electrodes it is common procedure to meas-
ure a calibration curve.VITAMIN ANALYSIS
By definition, vitamins are organic compounds of
low molecular weight that must be obtained from
external sources in the diet and are also essential for
normal physiological and metabolic function
(Russell 2000). Since the vast majority of vitamins
cannot be synthesized by humans, they must be
obtained from either food or dietary supplements.
When vitamins are absent or at inadequate levels in
the diet, deficiency disease commonly occurs, (e.g.,
scurvy and pellagra from a lack of ascorbic acid and
niacin, respectively; Eitenmiller et al. 1998).
Analyses of vitamins in foods are performed for
numerous reasons; for example, to check for regula-
tory compliance, to obtain data for nutrient labeling,
or to study the changes in vitamin content attributa-
ble to food processing, packaging, and storage (Ball
2000). Therefore, numerous analytical methods have
been developed to determine vitamin levels during
processing and in the final product.
Vitamins have been divided into two distinct
groups: (1) those that are water soluble (B vitamins,
vitamin C) and (2) those that are fat soluble (vita-
mins A, D, E, and K).
The scientific literature contains numerous ana-
lytical methods for the quantitation of water-soluble
vitamins including several bio-, calorimetric, and
fluorescent assays that have been proven to be accu-
rate, specific, and reproducible for both raw and pro-
cessed food products (Eitenmiller et al. 1998). The
scientific literature also contains an abundance of
HPLC-based methodologies for the quantitation
of water-soluble vitamins (Russell 2000). High per-
formance liquid chromatography (HPLC) has be-
come by far the most popular technique for the
quantitation of these water-soluble vitamins. In gen-
eral, it is the nonvolatile and hydrophilic nature of
these vitamins that make them excellent candidates
for reversed-phase HPLC analysis (Russell 2000).
The ability to automate these analyses using auto-
samplers and robotics makes HPLC an increasingly
popular technique. Since the vast majority of vita-
mins occur in food in trace amounts, detection sensi-