1.3.1 樣片的制備
將樣品粒度研磨至不大于74μm的分析試樣，稱取分析試樣約10g，加入硼酸墊底，于壓片機上以500MPa壓力條件下壓制30s，壓制成粉末樣片。用洗耳球吹去表面可能存在的顆粒物質(zhì)。制備樣片厚度應不少于3mm。樣片表面需平整，無裂紋、無粉末脫落等缺陷。
1.3.2 試樣分析
將制備的粉末壓片置于單波長激發(fā)能量色散X射線熒光光譜儀中獲取熒光強度信號，采用無標樣全譜擬合-基本參數(shù)法進行無標定量分析，計算得出分析試樣中元素含量。分析試樣進行兩次平行測定取其平均值。
2.結(jié)果與討論
2.1 無標樣全譜擬合算法
基本參數(shù)法分為兩類，一是通過對已知元素和含量的標準物質(zhì)，輸入標準物質(zhì)的元素和含量經(jīng)過一系列計算擬合，確定基本參數(shù)算法；二是對未知樣品定量分析。采用最小二乘擬合算法對未知樣品實測譜擬合全譜[9]。最小二乘法是從誤差擬合的角度對回歸模型進行參數(shù)估計。將樣品實際測量譜線分解為樣品中各個單元素在相同樣品基體情況下，樣品中各個單元素相應含量下的理論譜線的疊加。因?qū)嶋H測量譜線測量結(jié)束后為固定值，如果假定元素初始含量，用假定含量解出該含量的理論譜線，用測量譜線對單元素理論譜線進行全譜匹配，匹配結(jié)果為一個新的含量，不斷重復全譜匹配過程，直到元素含量收斂為樣品中元素的實際含量。本文選擇基于基本參數(shù)法（FP）的全譜擬合無標樣定量算法進行分析。
含鐵物料元素組成復雜，其基體元素成分變化會直接影響待測元素特征X射線強度的測量。低鐵含量樣品（為鐵含量15%以下的含鎳物料）鉻元素檢測情況表明，對于與含鐵物料基體（一般鐵含量在40%以上）相差較大的樣品不宜直接利用含鐵物料的檢測條件進行檢測，說明過大的基體差異會導致結(jié)果的明顯偏差。利用無標樣全譜擬合算法建立相應基體樣品的結(jié)果校正曲線，不改變檢測條件，可以消除明顯的基體差異導致的結(jié)果偏差，保障檢測結(jié)果的準確。選取含有不同含量的各有害元素的含鐵物料，利用基于基本參數(shù)法的無標樣全譜擬合算法進行分析，其檢測結(jié)果與真值的擬合情況見表2。由表2可知，其R2均不小于0.9990。
表2 各元素基本參數(shù)法直接測定結(jié)果與真值的擬合情況
Tab.2 Fitting of Direct Measurement Results of Basic Parameters of Each Element with True Values
| Element |
Number of samples |
Content range |
R2 |
| Cd |
11 |
0.00082-0.112 |
0.9991 |
| As |
15 |
0.0024-0.668 |
0.9990 |
| Pb |
12 |
0.0073-0.795 |
0.9993 |
| Hg |
4 |
0.0014-0.0089 |
0.9991 |
| Cr（High iron content samples） |
10 |
0.015-1.84 |
0.9999 |
| Cr（Low iron content samples） |
7 |
0.060-0.92 |
0.9991 |
2.2 背景及譜線權重優(yōu)化
含鐵物料檢測中，背景來源主要包括入射X射線的康普頓散射和瑞利散射、探測器的康普頓散射逃逸效應、探測器的不完全電荷收集效應、光電子和俄歇電子逃逸效應等。因此，在采用基本參數(shù)法計算過程中需要通過扣背景來消除或降低背景對元素峰擬合的影響，但扣背景不足或過多均會影響元素檢測結(jié)果的準確性。對樣品號為Fe-1的含鐵物料譜圖進行背景優(yōu)化，針對含鐵物料的復雜基體復雜背景問題，為能夠準確提取微量元素信號，建立了分段式多參數(shù)背景補償Snip算法。如圖1為Fe-1含鐵物料背景優(yōu)化譜圖。圖中下曲線為掃描Fe-1含鐵物料原始譜圖，上曲線為優(yōu)化后譜圖。經(jīng)優(yōu)化后的譜圖，可提取出低譜峰信號強度。
圖1 Fe-1樣品背景優(yōu)化譜圖
Fig.1 Optimization spectrum of Fe-1 sample background
2.3 譜線選擇及重疊干擾校正
選擇待測元素特征譜線時應避免基體中共存元素的譜線干擾、和峰干擾、靶材的特征譜線及其康普頓譜逃逸峰干擾。光譜干擾可通過選擇適當?shù)姆治鼍€和采用干擾校正系數(shù)來解決。表3中給出了含鐵物料中砷、鉛、汞、鉻、鎘元素檢測推薦譜線和干擾修正情況。
表3 含鐵物料中微量元素的推薦分析線及干擾情況
Tab.3 Recommended Analysis Lines and Interference Conditions for Trace Elements in Ferrous Materials
| Element |
Recommended spectral lines |
Participate in basic correction elements |
Spectral overlapping interference element lines and typical interference situations |
Interference correction method |
| As |
Kα -line |
Fe、 Ca、Si、Al、Mn、K、O |
The Lα -line of Pb element overlaps with the Kα -line of As element |
Using theLβ -line of Pb element to calculate the content of Pb element, and then re analyzing the Kα -line of As element in overlapping peaks |
| Pb |
Lβ -line |
Fe、 Ca、Si、Al、Mn、K、O |
The double peak of the Kα -line of Fe element overlaps with the Lβ -line of Pb element |
Algorithm of using full spectrum fitting matrix parameters method |
| Hg |
Lα -line |
Fe、 Ca、Si、Al、Mn、K、O |
The overlapping peaks have no interference, but the Lα -line of Hg element is easily affected by the Kα -line and Kβ -line of Zn element, resulting in background interference |
The content of Zn element greater than 1% affects the determination of low content Hg element |
| Cr |
Kα -line or Kβ -line |
Fe、 Ca、Si、Al、Mn、K、O |
The Kα -line of Cr element overlaps with the escape peak of Fe element's Kβ -line and the Kβ -line of V element, while the Kβ -line of Cr element overlaps with the Kβ -line of Mn element |
By calculating the content of Fe, V, and Mn elements, Cr can be further resolved in overlapping peaks |
| Cd |
Kα -line |
Fe、 Ca、Si、Al、Mn、K、O |
The position where the Lβ1 - line of Pb element accumulates and doubles, and the position where the Lα -line of Pb element accumulates and doubles, will have a combined peak |
Deducting the effect of peak concentration by calculating the Pb element content |
2.4 方法檢測下限及檢出限
選擇SiO2作為空白樣，利用單波長激發(fā)能量色散X射線熒光光譜法對其重復測定11次，以3.14倍測定值的標準偏差（s）計算檢出限（3.14s）[10]。方法的檢測下限可定義為在特定基體某一可信度內(nèi)對分析物能進行可靠確認和定量的最低濃度值，通常取3倍檢出限，結(jié)果保留兩位有效數(shù)字，見表4。
表4 方法檢測下限及檢出限
Tab.4 Method detection lower limit and detection limit
| Sample number |
Determination of elements |
| Hg |
As |
Pb |
Cd |
Cr |
| 1 |
0.00041 |
0.0016 |
-0.0012 |
-0.00015 |
-0.013 |
| 2 |
0.00037 |
0.0015 |
-0.00090 |
-0.00024 |
-0.013 |
| 3 |
0.00013 |
0.0016 |
-0.0010 |
-0.00024 |
-0.014 |
| 4 |
0.00026 |
0.0015 |
-0.0011 |
-0.00014 |
-0.013 |
| 5 |
0.00032 |
0.0015 |
-0.0013 |
-0.00023 |
-0.014 |
| 6 |
0.00015 |
0.0016 |
-0.00098 |
-0.00039 |
-0.013 |
| 7 |
0.00018 |
0.0014 |
-0.0010 |
-0.00023 |
-0.013 |
| 8 |
0.00015 |
0.0013 |
-0.0010 |
-0.00068 |
-0.013 |
| 9 |
0.00014 |
0.0013 |
-0.00093 |
-0.00021 |
-0.013 |
| 10 |
0.00039 |
0.0016 |
-0.0010 |
-0.00049 |
-0.013 |
| 11 |
0.00036 |
0.0013 |
-0.0010 |
-0.00021 |
-0.012 |
| S |
0.00011 |
0.00011 |
0.00012 |
0.00017 |
0.00035 |
| Detection limit |
0.00035 |
0.00036 |
0.00037 |
0.00052 |
0.0011 |
| Method detection lower limit |
0.0011 |
0.0011 |
0.0011 |
0.0016 |
0.0033 |
2.5 方法精密度
選取含有有害元素的含鐵物料樣片，進行精密度試驗。分析結(jié)果見表5。由表5可知，各元素RSD在3.19%~9.00%范圍內(nèi)，RSD均不大于10%，精密度良好。
表5 精密度試
Tab.5 Precision test（n=7） /%
| Sample |
As |
Pb |
Cd |
Cr |
Hg |
| average value |
RSD |
average value |
RSD |
average value |
RSD |
average value |
RSD |
average value |
RSD |
| Fe-1 |
0.048 |
4.9 |
0.76 |
4.8 |
0.00092 |
8.7 |
0.056 |
4.8 |
/ |
/ |
| Fe-2 |
0.0042 |
7.3 |
0.10 |
4.2 |
0.0038 |
7.0 |
0.018 |
3.5 |
|
|
| Hg-3 |
0.022 |
4.0 |
0.21 |
3.2 |
/ |
/ |
0.032 |
4.7 |
0.0037 |
9.0 |
| Hg-4 |
0.0085 |
3.4 |
0.18 |
4.9 |
/ |
/ |
0.0098 |
5.6 |
0.0083 |
4.5 |
2.6 方法正確度
選取各元素不同水平含鐵物料樣品，按本試驗方法進行測定，并與ICP-MS法、直接測汞儀法進行結(jié)果比對，檢測結(jié)果見表6~10。由檢測結(jié)果可知，砷元素測定中Fe-2、GSB03-2854-2012及S-4含鐵物料，鉛元素測定中YSBC28786-2015含鐵物料檢測結(jié)果與其他方法或標示值偏差較大，主要原因為接近其方法檢測下限。經(jīng)正確度驗證，該方法滿足分析要求，可開展快速分析檢測。
表6 砷元素檢測比對結(jié)果
Tab.6 Comparison Results of Arsenic Element Detection /%
| Samples |
This method |
ICP-MS measured value |
| Fe-1 |
0.048 |
0.056 |
| Fe-2 |
0.0042 |
0.0024 |
| YSBC14722-98 |
0.11 |
0.10 |
| YSBC28786-2015 |
0.0096 |
0.0095 |
| GSB03-2854-2012 |
0.0064 |
0.0044 |
| GSB03-2855-2012 |
0.22 |
0.22 |
| GSB03-2856-2012 |
0.047 |
0.051 |
| YSBC28785-2015 |
0.013 |
0.011 |
| GSB03-1805-2005 |
0.096 |
0.11 |
| S-4 |
0.0019 |
0.0008 |
| S-1 |
0.094 |
0.097 |
| S-2 |
0.014 |
0.010 |
| S-3 |
0.093 |
0.072 |
| GSB03-2857-2012 |
0.33 |
0.29 |
| Fe-3 |
0.64 |
0.67 |
表7 鉛元素檢測比對結(jié)果
Tab.7 Comparison Results of Lead Element Detection /%
| Samples |
This method |
ICP-MS measured value |
| Fe-2 |
0.10 |
0.11 |
| Fe-1 |
0.73 |
0.79 |
| YSBC14722-98 |
0.099 |
0.120 |
| YSBC28786-2015 |
0.0047 |
0.0073 |
| GSB03-2854-2012 |
0.027 |
0.035 |
| GSB03-2855-2012 |
0.16 |
0.18 |
| GSB03-2856-2012 |
0.031 |
0.034 |
| YSBC28785-2015 |
0.012 |
0.020 |
| GSB03-1805-2005 |
0.085 |
0.11 |
| S-1 |
0.44 |
0.47 |
| S-3 |
0.18 |
0.20 |
| GSB03-2857-2012 |
0.18 |
0.19 |
表8 汞元素檢測比對結(jié)果
Tab.8 Comparison Results of Mercury Element Detection /%
| Samples |
This method |
Direct mercury meter method |
| Hg-1 |
0.0012 |
0.0014 |
| Hg-2 |
0.0025 |
0.0030 |
| Hg-3 |
0.0039 |
0.0045 |
| Hg-4 |
0.0081 |
0.0089 |
表9 鉻元素檢測比對結(jié)果
Tab.9 Comparison Results of Chromium Element Detection /%
| High speed iron containing materials |
Low iron element iron containing materials |
| Samples |
This method |
ICP-MS measured value |
Samples |
This method |
ICP-MS measured value |
| ISO306 |
0.015 |
0.017 |
GBW07146 |
0.13 |
0.12 |
| ISO316 |
0.069 |
0.080 |
GBW07147 |
0.13 |
0.13 |
| ISO315 |
0.031 |
0.036 |
GBW07148 |
0.073 |
0.060 |
| ISO327 |
0.014 |
0.015 |
ZBK413 |
0.80 |
0.76 |
| ZBK459 |
0.055 |
0.047 |
ZBK414 |
0.93 |
0.90 |
| ZBK460 |
0.037 |
0.037 |
ZBK415 |
0.82 |
0.83 |
| ZBK461 |
0.033 |
0.027 |
ZBK416 |
0.76 |
0.76 |
| ZBK418 |
1.31 |
1.38 |
ZBK417 |
0.36 |
0.37 |
| ZBK412 |
1.75 |
1.84 |
/ |
/ |
/ |
| GBW07149 |
0.055 |
0.046 |
/ |
/ |
/ |
表10 鎘元素檢測比對結(jié)果
Tab.10 Comparison Results of Cadmium Element Detection /%
| Sample |
This method |
ICP-MS measured value |
| Fe-1 |
0.00083 |
0.00071 |
| Fe-2 |
0.0036 |
0.0031 |
| Cd-1 |
0.0034 |
0.0035 |
| Cd-2 |
0.0048 |
0.0045 |
| Cd-3 |
0.0063 |
0.0070 |
| Cd-4 |
0.012 |
0.013 |
| S-1 |
0.11 |
0.096 |
| S-2 |
0.0014 |
0.0012 |
| S-3 |
0.011 |
0.011 |
| ZBK410 |
0.050 |
0.047 |
| ZBK417 |
0.029 |
0.028 |
3.結(jié) 論
本文采用壓片制樣-單波長激發(fā)能量色散X射線熒光光譜法測定含鐵物料中多種有害元素，利用基于基本參數(shù)法的無標樣全譜擬合算法對目標元素的基體效應進行校正并進行檢測分析。通過正確度驗證可知，方法滿足快速分析要求。
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