|<< Back to Sampling and Analytical Methods
For problems with accessibility in using figures and illustrations in this method, please contact the SLTC at (801) 233-4900.
These procedures were designed and tested for internal use by OSHA personnel. Mention of any company name or commercial product does not constitute endorsement by OSHA.
||0.05 mg/m3 Uranium, soluble compounds
||A known volume of air is drawn
through a cassette containing an FWS-B (5 µm) filter and a back-up pad.
|Recommended Air Volume:
|Recommended Sampling Rate:
||2.0 liters per minute
||An FWS-B filter is extracted with
electrolyte solution. An aliquot of the sample is then analyzed for
uranium by the technique of Differential Pulse Cathodic Stripping Polarography (DPCSP), or Differential Pulse Stripping
|Qualitative Detection Limit:
||Estimated to be 0.2 µg for a 10 ml
|Precision and Accuracy:
||(CV) 0.036 (Analytical)
| Method Classification:
This method describes the collection and analysis of airborne
particulates containing soluble uranium. The technique used for this
analysis is Differential Pulse Cathodic Stripping
Polarography (DPCSP). This technique involves the reduction of
hexavalent uranium (U6+) on the surface of a static mercury electrode (SME)
drop (7-1). The electrolyte solution used in the analysis contains 0.05
M tartaric acid and 0.05 M triethanolamine; it is weakly acidic, with a
pH = 3.5. The electrolyte solution is used to extract soluble uranium
from the sample filters, because it has been found experimentally to
give better recoveries as compared to extraction using deionized water
(DIW) (7.2). For this reason soluble uranium is defined in the context of
this analytical procedure as that uranium which will dissolve in an
aqueous solution containing 0.05 M tartaric acid and 0.05 M
triethanolamine. Refer to BUD (7.2) for more details.
Uranium samples sent to the OSHA Laboratory have been analyzed by the
method of neutron activation (7.3). Using that technique, samples
prepared at OSHA must be sent to a local University reactor to be bombarded
by neutrons. The uranium can then be quantitated by counting the
number of disintegrations occurring at energy levels specific for uranium.
This method gives good quantitative results, but it is relatively
time-consuming and expensive. Also, samples must be given up for a time to
non-OSHA personnel: For these reasons, a polarographic procedure was
developed at the OSHA Laboratory.
1.3 Toxic Effects (7.4, 7.5)
1.3.1 Toxicity is closely related to solubility, i.e., the more
soluble the uranium compound is, the more toxic it becomes.
1.3.2 Soluble uranium compounds are toxic both when breathed or
ingested. The kidney is the organ most directly affected by uranium,
which causes tubular degeneration and renal failure.
1.3.3 The administration of calcium disodium edetate is useful for
removing uranium from the body.
1.3.4 Of the most important uranium compounds used industrially, UF6 and UO2(NO3)2
ˇ 6H20 are the most toxic, whereas UO3 is only
moderately toxic, and UO2, U308, and UF4 are considered low in
1.4 Physical Properties (7.4, 7.6, 7.7)
1.4.1 Uranium, atomic number 92, has an atomic weight of 238.
It has a density of 19.05 and a melting point of 1132 °C. It is a
silvery, lustrous, malleable, and ductile metal.
It occurs in the earth's crust at a concentration of about 2 ppm.
1.4.2 In the dry state uranium forms compounds having valences of
3+, 4+, 5+, or 6+. In aqueous media only U4+ and U6+ are stable.
Some compounds, such as UCI4, decompose in aqueous media to the U6+
state (see Table 5). In acid solution and in the body, the
oxygen-containing cation UO2+2 , where uranium has a valence of 6+, is
the predominant form. In general, hexavalent uranium compounds are the most soluble.
2. Range and Detection Limit
2.1 The working range is from 0.05 ppm to 2.0 ppm uranium.
2.2 The qualitative detection limit for a 10 mL sample is estimated
to be 0.2 µg, based on the lowest quantity of uranium which produces a
discernable peak. Refer to Figure 1 in the BUD (7.2) for better
3. Precision and Accuracy
3.1 Quantities of soluble uranium were spiked onto FWS-B filters at
levels corresponding to 0.5, 1.0, and 2.0 times the OSHA-PEL,
based upon a 240 L air sample. At each of the three PEL levels, 6
filters were used, giving a total of 18 filters for a complete set. Two
complete sets of filters were analyzed for uranium recovery. Refer to
Back-up Data (BUD) for complete results (7.2).
3.2 The pooled coefficient of variation (CV) for the two sets (n=36),
a measure of total analytical precision, was calculated to be 0.036.
This value corresponds to a standard deviation of 0.0018 mg/m3 at the
OSHA-PEL standard level.
3.3 The average recovery for the two sets at the three OSHA-PEL
levels (n=36) was 98.4%.
4. Advantages and Disadvantages
4.1.1 This procedure is relatively quick, simple, and exhibits
good reproducibility over the working range.
4.1.2 The method of DPCSP saves on mercury by performing a complete
analysis with one mercury drop.
4.1.3 The chain of evidence stays within OSHA, i.e., samples are not
sent out of the Laboratory for analysis.
4.2.1 Small changes in pH (> O.2 pH) will cause a reduction in signal intensity. This change is minimized by the buffering capacity of the
electrolyte solution. However, it is necessary for the analyst to check
the pH of each sample with pH paper. If the pH of the sample differs by
more than 0.2 pH units from the electrolyte solution, small amounts of
acid or base should be added to the sample until its pH is close to that of the electrolyte.
4.2.2 It has been determined experimentally that the presence of certain ions
(Cr6+, Mo6+, Ti4+, and F¯ at concentrations
one to four times that of the uranium will also result in a reduction
in signal intensity (7.2, 7.8). The three metal cations all have
half-wave potentials more negative than that of hexavalent uranium. High
concentrations of these interfering cations will produce separate peaks from
that of uranium. At concentrations near to that of uranium, however,
varying degrees of shoulder-broadening can be seen on the uranium peak.
5. Sampling Procedure
5.1.1 Personal Sampling Pump: A calibrated pump whose flow rate
an be determined within 5% at the recommended flow rate. Each personal sampling pump must be calibrated with a representative
sampler (filter, sorbent tube, etc.) in
line to minimize errors associated with uncertainties in the volume
5.1.2 Filter holder: A 3-piece polystyrene, 37 mm diameter
5.1.3 Polyvinyl chloride (PVC) membrane filters: 5.0 micron pore
size, 37 mm diameter. FWS-B or equivalent.
5.2.1 Sample at a known flow rate of about 2 L/min. A minimum sample
size of 100 L is recommended.
5.2.2 Include a blank FWS-B filter with each sample set.
5.2-3 After sampling, plug the cassette ports and seal the cassettes
with official seals (OSHA Form 21). Send to the laboratory for analysis.
6. Analytical Procedure
6.1.1 Polarographic analyzer or controller: Princeton Applied
Research (PAR), Model 384-B, or equivalent.
6.1.2 Static mercury drop electrode: PAR Model 303A
6.1.3 Polarographic cells (20-mL). Soak used cells in 6 M HNO3
for one hour and rinse thoroughly with DIW. Air dry on clean absorbent
6.1.4 Digital plotter: Model DMP-40, Houston Instrument, or
6.1.5 Adjustable micropipettes: Gilson P-200 & P-5000, or
6.2 Reagents - All chemicals should be ACS reagent grade or
6.2.1 Uranium stock solution, 1000 ppm: Purchased from Spex, prepared
from HiPure material, in a 2% HNO3
matrix. This solution is good
for one year.
6.2.2 Supporting electrolyte: 0.05 M Tartaric acid + 0.05 M
Triethanolamine. Dissolve 7.50 g Tartaric acid and 7.46 g Triethanolamine in 1
L DIW. Keep closed and prepare fresh when needed. Microorganismic
growth can be observed in the solution after about a week. Although this
growth does not appear to interfere with the analysis, the reagent should
be discarded if growth is noticed.
6.2.3 Mercury, triple-distilled.
6.3.1 Clean all glassware with a 10% HNO3
solution and rinse
several times with DIW. Air dry prior to use.
6.3.2 Wear gloves when handling soluble uranium compounds.
Danger from radioactivity is minimal, but the soluble compounds are
6.3.3 Mercury wastes can be temporarily placed in a beaker
inside a fume hood that is left on. Permanent storage requires that the waste be placed in a securely closed metal container provided for that
6.3.4 Promptly clean up any spill of uranium solution that occurs by
wiping it up with absorbent paper.
6.3.5 Remove any visible mercury drops that appear by auctioning with
the vacuum hose provided for that purpose.
6.4 Sample preparation
6.4.1 Remove FWS-B filter from cassette and place in 125 mL
Phillips beaker. Add 5 mL aliquot of electrolyte and extract for 30 minutes,
with occasional swirling.
6.4.2 Transfer electrolyte to 25 mL volumetric flask. Rinse beaker
with two more 5 mL aliquots of electrolyte and transfer these to
volumetric flask. Bring flask to volume with electrolyte.
6.5 Standard Preparation
6.5.1 Standards in the range 0.5 - 10.0 µg should normally be
analyzed. For a 10 mL cell volume, this corresponds to a concentration range of
0.05 - 1.0 ppm.
6.5.2 Prepare stock standards of 1.0, 10, and 100 ppm U by
serial dilution of the 1000 ppm stock solution using DIW. Standards
can be kept for six months.
6.5.3 Using calibrated pipettes, add appropriate aliquots of the
stock standards to polarographic cells and bring to 10 ML volume with
electrolyte solution as shown:
|Final U Quantity
in Cell (µg)
6.6.1 Turn on the polarographic analyzer, 384-B, and
allow it to
warm up for about 45 minutes. Prior to analysis, turn on the digital
plotter and prepare it with pen and paper.
6.6.2 The necessary parameters for analyzing soluble uranium by
DPCSP have been entered into the memory of the 384-B. Recall the method
number which analyzes soluble uranium and check the parameters to see that
they correspond to the following conditions:
|| Differential Pulse Stripping (DPS)
|| Approx. -0.050 V
|| Approx. -0.330 V
|| 2 mV/sec
|| 0.1 V
|| 90 sec
|| 5 sec
6.6.3 The half-wave potential for uranium (VI) in this electrolyte
(pH=3.5) is approx. -0.2 V vs. a Saturated Calomel Electrode (SCE). The actual peak voltage may differ a little from this value depending
upon the condition of the reference electrode used.
6.6.4 Analyze the reagent blank and-several standards before
analyzing samples. Analyze a standard after every five or six samples.
6.6.5 Check the pH of each sample with pH paper before analyzing it.
If the pH of the sample differs by > 0.2 pH units from the reagent
blank, add small quantities of acid
(HNO3) or base (NaOH) until the pH of the sample is the same as the
6.6.6 Record the peak current (nA) and voltage of the peak (V) for
each standard and sample. A form is provided for this purpose.
6.6.7 If non-uranium peaks occur or if the uranium peak shows signs
of broadening, interferences should be suspected (4.2.2) and the sample
should be analyzed by ICP or AA to determine the possibility and/or
extent of the interference.
6.6.8 Plot a calibration curve of peak current (nA) vs. amount of
6.7.1 Use the Colorimetric program or equivalent to plot a calibration
6.7.2 Blank correct each air sample and wipe.
6.7.3 The concentration of soluble uranium in the sampled air is expressed as mg/m3.
|U (mg/m3) =
||total µg U (blank corrected)
air volume (L)
7.1 Peterson, W.M., and R.V. Wong: Fundamentals of Stripping Voltammetry.
American Laboratory, pp. 116-128 (Nov., 1981).
7.2 Backup Data Report No. for Soluble Uranium, prepared by
Phil Giles, Inorganic Division, Branch I.
7.3 "Neutron Activation Analysis," OSHA Manual of Analytical
Methods (unpublished), USDOL OSHA, Salt Lake City Analytical Laboratory.
7.4 Patty's Industrial Hygiene and Toxicology Vol. IIA, 3rd
Revised Edition, pp. 1995-2012 (1981).
7.5 Clinical Toxicology of Commercial Products, 4th Edition,
pp.102- 103 (1976).
7.6 Kirk-Othmer Encyclopedia of Chemical Technology, Vol. 23, 3
rd Edition, pp. 512-513 (1983).
7.7 Merck Index, 10th Edition, 1983, P. 9666.
7.8 "Determination of Uranium in Plutoniurw-238 Metal and Oxide by
Differential Pulse Polarography," Analytical Chemistry, Vol. 48, No. 1,
pp. 215-218 (Jan., 1976).