ARSENIC, organo-
(1) CH3AsO3H2 (2) (CH3)2AsO2H (3) H2NC6H4AsO3H
MW: (1) 139.96 (2) 137.99 (3) 217.07
METHOD: 5022, Issue 2
5022
CAS: (1) 124-58-3 (2) 75-60-5 (3) 98-50-0
RTECS: (1) PA1575000 (2) CH7525000 (3) CF7875000
EVALUATION: FULL
OSHA : 0.5 mg/m 3 (as As) NIOSH: no REL ACGIH: 0.2 mg/m 3 (as As)
PROPERTIES:
Issue 1: 15 May 1985 Issue 2: 15 August 1994
solids; MP (1) 161 °C, (2) 195 °C; (3) 232 °C
SYNONYMS: (1) Methylarsonic acid: methanearsonic acid. (2) Dimethylarsinic acid: cacodylic acid; hydroxydimethyl arsine oxide. (3) p-Aminophenyl arsonic acid: p-arsanilic acid; atoxylic acid. SAMPLING
MEASUREMENT
SAMPLER:
FILTER (1-µm PTFE)
TECHNIQUE:
ION CHROMATOGRAPHY/ HYDRIDE ATOMIC ABSORPTION
FLOW RATE:
1 to 3 L/min
ANALYTE:
anions (IC); AsH 3 (AAS)
VOL-MIN: -MAX:
50 L @ 0.01 mg/m 3 1000 L
EXTRACTION:
borate-carbonate buffer, 25 mL
SHIPMENT:
routine
SAMPLE STABILITY:
stable
BLANKS:
2 to 10 field blanks per set
ION CHROMATOGRAPHY: INJECTION LOOP VOLUME: COLUMNS: ELUENT:
0.8 mL two, 3 x 150-mm anion borate-carbonate buffer; 2.5 mL/min; 3450 kPa (500 psi); ambient temperature
AAS: QUARTZ FURNACE: WAVELENGTH:
800 °C 193.7 nm (no D 2)
CALIBRATION:
organoarsenicals in water
RANGE:
0.5 to 2 µg As per sample
ESTIMATED LOD:
0.2 µg As per sample [1]
PRECISION (Sr):
Table 1
ACCURACY RANGE STUDIED:
0.005 to 0.2 mg/m 3 [1,2]
BIAS:
not significant
ˆ ): 0.047 @ 0.02 mg/m 3 [1]; OVERALL PRECISION (S rT 0.14 @ 0.005 mg/m 3 [1] ACCURACY:
± 20% @ 0.02 mg/m 3
APPLICABILITY: The working range is 0.005 to 10 mg/m 3 (as As) for a 100-L air sample. The method is designed to quantitate particulate organo-arsenic compounds.
INTERFERENCES: Inorganic arsenic (III) co-elutes with dimethylarsenic acid using Eluent A but the two may be separated with Eluent B. Other ions at high concentrations in the sample can interfere with the chromatographic separation of the arsen icals. As 2O 3 is not efficiently sampled by this sampler; for quantitation of that compound see Method 7901.
OTHER METHODS: This is P&CAM 320 in revised format [2]. Method 7200 measures total As by hydride/AAS. Method 7901 measures As 2O 3, which can exist as a vapor and aerosol.
NIOSH Manual of Analytical Methods (NMAM), Fourth Edition, 8/15/94 ARSENIC, organo-: METHOD 5022, Issue 2, dated 15 August 1994 - Page 2 of 6 REAGENTS: 1. 2. 3.
4. 5. 6.
7.
8.
9.
EQUIPMENT:
Deionized water. Hydrochloric acid, conc. Eluent A (2.4 m M HCO -3/1.9 mM CO 32-/1.0 mM B4O 72-). Dissolve 0.8067 g NaHCO 3, 0.8055 g Na 2CO 3, and 1.5257 g Na 2B4O 7 10H 2O in 4 L deionized water. Eluent B (5 m M B4O 72-). Dissolve 7.6284 g Na 2B4O 7 10H 2O in 4 L deionized water. Potassium persulfate solution,* K 2S2O 8, saturated in 15% (v/v) HCl. Sodium borohydride, 1% NaBH 4 (w/v) in 0.2% KOH (w/v). Add 5 g NaBH 4 and 1 g KOH to deionized water; dilute to 500 mL. Prepare fresh weekly. Stock standards, 1000 µg As/mL: a. Methylarsonic acid.* Dissolve 0.9341 g CH 3AsO 3H2 (Ansul Co., Weslaco, TX), in deionized water; dilute to 500 mL. b. Dimethylarsenic acid.* Dissolve 0.9210 g (CH 3)2AsO 2H (Ansul Co.) in deionized water; dilute to 500 mL. c. p-Aminophenylarsonic acid.* Dissolve 1.4485 g p-H2NC 6H4AsO 3H2 in 5 mL 1 N NaOH. Dilute to 500 mL with deionized water. Protect from light. d. Arsenic trioxide.* Dissolve 0.6602 g As 2O 3 in 5 mL 1 N NaOH. Dilute to 500 mL with deionized water. e. Arsenic pentoxide.* Dissolve 0.7669 g As 2O 5 in 5 mL 1 N NaOH. Dilute to 500 mL with deionized water. Calibration stock solution, 1 µg/mL mixed analyte. Dilute 0.1 mL of each stock standard (REAGENTS, 7.) with Eluent A in a 100-mL volumetric flask. Prepare fresh daily. Argon.
See SPECIAL PRECAUTIONS
1. Sampler: PTFE polyethylene-backed membrane filter, 1-µm pore size (MilliporeType FA or equivalent), 37-mm diameter with backup pad; in cassette filter holder. 2. Personal sampling pump, 1 to 3 L/min, with flexible connecting tubing. 3. Ion chromatograph with suppressor and detector bypassed. Route column effluent via Microbore PTFE tubing (0.3-mm ID x 0.6-mm OD, Dionex) directly into arsine generator (Figure 1). 4. Syringes, plastic, 10-mL, with male luer fittings. 5. Arsine generator: proportioning pump with flow-rated pump tubes and 1.5-mm ID x 3-mm OD manifold mixing coils, 5-turn and 20-turn (Technicon or equivalent), 1.5-mm ID x 3.5-mm OD glass "T" connectors; gas-liquid separator and expansion chamber (Figure 2); 1 m of 1/4" OD PTFE tubing; three PTFE 1/4" ID Swagelok fittings; and rotometer (100 to 900 mL/min). 6. Atomic absorption spectrophotometer (reciprocal linear UV dispersion 0.65 nm/mm); As electrodeless discharge lamp and power supply; and atomization cell (16-cm x 13-mm ID windowless quartz tube with 18-cm x 4-mm ID inlet tube fused in the center), wound with Nichrome wire (14 Ω/m, spaced 2 to 3 mm between turns and wrapped with heat resistant tape) (Figure 3). Temperature in the cell is measured by a thermocouple (800 °C). Mount the cell on top of a single-slot AAS burner head and align with burner alignment controls. 7. Beakers, 50-mL.* 8. Ultrasonic waterbath. 9. Volumetric flasks, 10-, 100- and 500-mL. 10. Pipets, 25-µL and 0.1- to 1-mL.
Soak all glassware in mild detergent, rinse with deionized water, 10% HNO 3, and deionized water.
SPECIAL PRECAUTIONS: Potassium persulfate is a powerful oxidizing agent. Arsine gas is extremely toxic and can be fatal. The arsenic compounds used in the stock standards are poisonous [3].
NIOSH Manual of Analytical Methods (NMAM), Fourth Edition, 8/15/94 ARSENIC, organo-: METHOD 5022, Issue 2, dated 15 August 1994 - Page 3 of 6 SAMPLING: 1. 2. 3.
Calibrate each personal sampling pump with a representative sampler in line. Sample at an accurately known flow rate between 1 and 3 L/min for a total sample volume of 50 to 1000 L. Cap the cassettes and pack securely for shipment.
SAMPLE PREPARATION: 4. 5. 6.
For each sample, pipet 25 mL Eluent A into a clean 50-mL beaker. Open the cassette, remove the PTFE filter with clean forceps, and transfer it to the beaker. Place the exposed side of the filter in contact with the solution. Cover beaker. Agitate contents of the beaker for 30 min in an ultrasonic water bath. If the extracts will not be analyzed immediately, store at ca. 4 °C until measurement.
CALIBRATION AND QUALITY CONTROL: 7.
Calibrate daily with at least six working standards over the range 0.2 to 2 µg As per sample (0.008 to 0.08 µg As/mL). a. Add known amounts of calibration stock solution to Eluent A in 10-mL volumetric flasks and dilute to the mark. b. Analyze together with the samples and blanks (steps 8 through 12). c. Prepare calibration graph for each arsenic species (peak area or height vs. µg As).
MEASUREMENT: 8.
9.
Set the ion chromatograph to the conditions given on page 5022-1. Allow the columns to equilibrate with eluent ≥1 h before connecting effluent to the arsine generator. NOTE: Eluent A allows the separation of methylarsonic acid (t r = 2 min), p-aminophenylarsonic acid (t r = 4 min), and As(V) (t r = 7.5 min); As(III) and dimethylarsenic acid (t r = 1 min) are not resolved. If a signal is obtained at the approximate retention time of the latter two compounds, or if both compounds are known to be present in the sample, perform a second analysis using Eluent B (lower ionic strength). If either of the two compounds is known not to be present, Eluent A will effectively determine the remaining compounds. With Eluent B the other species have very long retention times and will accumulate on the column, tying up active resin sites. Therefore, flush the column with Eluent A after each 10 to 15 samples and reequilibrate with Eluent B before further analysis. Connect the IC effluent to the arsine generator into which the following flow: Saturated K 2S2O 8 solution: NaBH 4 solution: Ar carrier gas:
10.
11.
0.8 mL/min 2.0 mL/min 300 mL/min
NOTE: The gaseous arsines formed in the arsine generator are first separated from liquid solution using the gas-liquid separator (Figure 2) and then transferred by argon carrier gas through PTFE tubing to the heated quartz furnace. Set the AAS according to manufacturer's recommendations and to the conditions given on page 5022-1. Align the quartz cell in the optical path. Heat the quartz cell gradually to 800 °C using a variable transformer and thermocouple. Using a syringe, inject a sample aliquot ( ca. 2 to 3 mL) into the chromatograph, flushing the injection loop to avoid contamination from the previous injection. Rinse the syringe with deionized water and dry it between samples, or use disposable syringes. NIOSH Manual of Analytical Methods (NMAM), Fourth Edition, 8/15/94 ARSENIC, organo-: METHOD 5022, Issue 2, dated 15 August 1994 - Page 4 of 6 12.
Identify the component peaks. Measure peak height or area.
CALCULATIONS: 13. 14.
From the calibration graphs, calculate the amount (µg) of arsenic for each species in the sample (W) and in the average media blank (B). Calculate the arsenic concentrations, C, (mg/m 3) in the air volume sampled, V (L):
EVALUATION OF METHOD: The measurement precision obtained under the conditions recommended in this procedure is presented in Table 1 [1]. The overall precision of the method was tested using filters loaded in a dynamic aerosol generation/sampling system with particulates of the three organoarsenical compounds. The concentration levels tested for each species were 5, 10, and 20 µg As/m 3 of air. Depending on the concentration and species, the relative standard deviation ranged from 14.4% at the lowest level to 4.7% at the highest level. The collection efficiency of the method for organoarsenicals in the range of 5 to 20 µg/m 3 using a 300-L sample was found to be >99%. The collection efficiency of the method for inorganic arsenic was not determined. The accuracy of the overall method was determined by analyzing additional aerosol samples from each set using Neutron Activation (NAA) and X-ray Fluorescence (XRF) analyses. Since NAA and XRF techniques provide only the total elemental arsenic, the total arsenic obtained from the IC-AAS analysis was used for comparison. The accuracy ranged from 90 to 120% of the values obtained by NAA and XRF.
REFERENCES: [1]
[2] [3]
Colovos, G., N. Hester, G. Ricci, and L. Shepard: "Development of a Method for the Determination of Organoarsenicals in Air," NIOSH Contract #210-77-0134, available through National Technical Information Service, Springfield, VA 22161 as Order No. PB83-180794. NIOSH Manual of Analytical Methods, 2nd. ed., V. 6, P&CAM 320, U.S. Department of Health and Human Services, Publ. (NIOSH) 80-125 (1980). The Merck Index, 11th ed., Merck & Co., Rahway, NJ (1989).
METHOD REVISED BY: Mary Ellen Cassinelli, NIOSH/DPSE; P&CAM 320 originally developed under NIOSH Contract 210-77-0134.
NIOSH Manual of Analytical Methods (NMAM), Fourth Edition, 8/15/94 ARSENIC, organo-: METHOD 5022, Issue 2, dated 15 August 1994 - Page 5 of 6 TABLE 1. SENSITIVITY, DETECTION LIMIT AND WORKING RANGE DATA FOR ANALYSIS OF PARTICULATE ARSENICALS [1].
Arsenical Dimethylarsenic acid Arsenic (III) Methylarsonic acid p-Aminophenylarsonic acid Arsenic (V)
Sensitivity (ng/mL/1% Abs)
Detection Limit (as As) 300 L Sample Volume Solution (µg/m 3) ng/mL
Range 1 300 L Measurement Sample Volume Solution Precision (µg/m 3) ng/mL (% Sr)
1.3 2.1
0.62 0.71
7 8
1.7 - 6.7 1.7 - 6.7
20 - 80 20 - 80
11.2 - 1.6 11.2 - 1.3
2.1
0.72
9
1.7 - 6.7
20 - 80
8.1 - 4.4
6.3 13.0
0.64 0.46
8 6
1.7 - 6.7 1.7 - 6.7
20 - 80 20 - 80
6.0 - 3.0 10.8 - 1.0
1
The upper limit of the range can be increased by using higher concentration standards which are injected via loops of smaller volume. Although not tested with air samples, the useful range can be extended from 5 µg/m 3 down to 1.7 µg/m 3 based upon the measurement range.
FIGURE 1. IC/AAS Analytical System. NIOSH Manual of Analytical Methods (NMAM), Fourth Edition, 8/15/94 ARSENIC, organo-: METHOD 5022, Issue 2, dated 15 August 1994 - Page 6 of 6
FIGURE 2. Gas-Liquid Separator and Expansion Chamber.
FIGURE 3. Quartz Furnace Atomization Cell.
NIOSH Manual of Analytical Methods (NMAM), Fourth Edition, 8/15/94