Factors affecting ultrasonic extraction of lead from household paint films:

Abstract

Previous studies at NIST on the use of ultrasonic extraction/anodic stripping voltammetry (UE/ASV) for determining lead in household paint found that the particle size of the ground specimen plays an important role in lead extraction efficiency, particularly when the extraction is performed under the commonly used sonication conditions of 45 °C and 30 min. Consequently, it was proposed that, in conducting an UE/ASV analysis of a paint-film specimen in the field, the specimen particle size should be estimated prior to selecting an appropriate combination of sonication temperature and time. This report presents the results of a follow-up study performed to evaluate the reliability and practicality of the particle size recommendation.In the laboratory phase, specimens from lead-containing paint-film panels were prepared using 16 commercial paints and analyzed using UE/ASV. Experimental variables were: grinding method, sonication temperature, sonication time, paint manufacturer, paint type, gloss level, and binder type. The laboratory-prepared paint-film specimens were difficult to grind manually. The combination of specimen particle size, sonication temperature and sonication time had a highly significant effect on UE/ASV lead extraction efficiency. When particle size was small (passing through a No. 40, 425 μm mesh sieve), and sonication temperature and sonication time were 45 °C and 30 min, respectively, lead recovery was quantitative. When particle size was large (> 425 μm), lead recovery was quantitative only upon 65 °C and 90 min extractions. Paint manufacturer, paint type, gloss level, and binder type generally had little or no effect on UE/ASV lead recovery.In the field phase, NIST research staff and four certified lead inspectors and risk assessors (i.e., operators) trained to perform UE/ASV analyses sampled lead-containing paint from houses and similar buildings. The field samples included older lead-containing paint films that had been recently overcoated. Such samples were taken to determine whether they would be difficult to grind manually into small particles. It was found in the laboratory that manual grinding of the dry ice cooled field specimens readily produced a powder. Appropriate conditions of temperature and time for extracting lead from the field specimens were successfully selected by visually comparing the particle size of the ground specimens against that of a black pepper reference powder (i.e., known to pass through a No. 40, 425 μm mesh sieve). Estimating particle size through sieve analyses of ground field specimens did not result in selecting appropriate extraction temperature and time. It was recommended that, if a ground specimen appears to have adequately small particle size when compared against that of a reference powder, then extraction during a UE/ASV analysis may be performed at 45 °C and 30 min, as is presently carried out in common practice.

Ultrasonic extractionanodic stripping voltammetry for determining lead in dust:

“…The finding that after sonication of the field specimens essentially all the lead was found by NLLAP ICP analysis to be in the UE extract (Section 2.3.2.1) indicated that the sonicator operation conditions were successful in extracting lead from these specimens. Successful sonicator extraction of lead in field-sampled dust, which has generally small particle size (sub-millimeter range), was consistent with the results of previous NIST research on UE/ASV analysis of lead-containing paints [12,17]. In those studies, lead in paint specimens was successfully extracted by sonication at temperatures and times similar to those used in the present study provided that the paint specimens were ground sufficiently small (i.e., generally < 425 µm particle size).…”

Ultrasonic extractionanodic stripping voltammetry for determining lead in dust:

“…Factory calibration of the ASV instrument was checked in the previous NIST UE/ASV paint studies [11][12][13]. A repeat calibration check performed at the beginning of the current study using six standardized lead nitrate solutions (7.5 % volume fraction nitric acid with lead contents ranging from 1 mg/L to 28 mg/L) confirmed that the instrument has remained in calibration.…”

“…One deviation from the apparatus instructions was that the extraction was performed with warm tap water (≈ 45 °C) in the sonicator bath. Use of warm water was based on the results of previous NIST studies showing that lead recovery from laboratory-prepared paint film specimens was enhanced at higher bath temperatures [12,13]. Another deviation was that, for half of the specimens tested by an operator, the extract solutions were filtered using a Millipore PTFE 0.45 mm filter.…”

“…Lead risk assessors and inspectors, who are potential users of field methods (i.e., the operators), may have less skill in conducting lead analyses than chemists and laboratory technicians who participate in evaluation studies. In response to concerns over operator effects on field test reliability, NIST has performed HUD-sponsored studies to examine operator effects on spot test kits and on ASV analyses for detecting and determining lead in paint in the field [10][11][12][13]. Until the present study, operator effect on the reliability of ASV analyses of dust wipe specimens had not been addressed in an experiment in which lead risk assessors or inspectors performed the analyses.…”

Development of an N-methyl pyrrolidone based method of analysis for lead in paint

“…Detailed studies of the sample processing conditions also suggest that particle size, sonication temperature and sonication time can strongly affect the UE/ASV extraction efficiency. 14 In this study, several common solvents (principally N-methylpyrrolidone) were examined as a way to prepare paint samples without the use of mechanical grinding, high-temperature digestion, or sonication. The physical properties of N-methylpyrrolidone (NMP) are well-suited to the eld analysis of paints.…”